Two-Tier Compatibility of Superelastic Bicrystal Micropillar at Grain Boundary
- Mostafa KaramiMostafa KaramiDepartment of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong KongMore by Mostafa Karami,
- Zeyuan ZhuZeyuan ZhuDepartment of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong KongMore by Zeyuan Zhu,
- Zhuohui ZengZhuohui ZengDepartment of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong KongMore by Zhuohui Zeng,
- Nobumichi TamuraNobumichi TamuraAdvanced Light Source, Lawrence Berkeley National Lab, Berkeley, California 94720, United StatesMore by Nobumichi Tamura,
- Yong Yang , and
- Xian Chen*Xian Chen*Email: [email protected]Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong KongMore by Xian Chen
Abstract
Both crystallographic compatibility and grain engineering are super critical to the functionality of shape memory alloys, especially at micro- and nanoscales. Here, we report a bicrystal CuAl24Mn9 micropillar engraved at a high-angle grain boundary (GB) that exhibits enhanced reversibility under very demanding driving stress (about 600 MPa) over 10 000 transformation cycles despite its lattice parameters are far from satisfying any crystallographic compatibility conditions. We propose a new compatibility criterion regarding the GB for textured shape memory alloys, which suggests that the formation of GB compatible twin laminates in neighboring textured grains activates an interlock mechanism, which prevents dislocations from slipping across GB.
The magnificent self-expanding and mechanical damping features of shape memory alloys (SMAs) make them the primary metals for biomedical and microelectronic applications.(1−6) In tandem with the rapid growth of nanofabrication technologies,(7,8) more complicated functional devices can be made at smaller scales, which promotes the development of shape memory alloys for the tiny neural stents for brains.(9,10) These small and precise micro- and nanodevices demand a more reliable superelastic response upon numerous superelastic cycles.
A well-accepted theory that intrinsically improves the transformability and lowers the functional fatigue is to make the material satisfy the compatibility conditions.(11) These conditions are the geometric measures of lattice mismatch for symmetry-breaking structural transformation through a coherent transformation stretch tensor.(12) Such a stretch tensor depends only on the lattice parameters of parent and product phases and can be determined algorithmically.(13) The satisfaction of all compatibility conditions by special lattice parameters guarantees a stress-free interface configuration between the parent and product phases. In this scenario, the bulk elastic energy dissipation is minimized during the phase transformation; as a result, the material shows low hysteresis and high reversibility. Experimentally, the lattice parameters can be systematically tuned to fulfill the compatibility conditions by slight chemical doping, which underlies a design strategy for alloy development. Guided by this design strategy, people have successfully demonstrated the lowered thermal-hysteresis and the improved functional fatigue life in both NiTi- and Cu-based shape memory alloys.(14−16) At small scales, some very special alloys can reach millions of nondegradable superelastic cycles in thin-films(17) and micropillars.(18) Similar experimental evidence are also reported in phase transforming ceramics at small scales.(19,20)
Engineering grain morphology is an alternative way to improve the fatigue life for SMAs independent of tuning lattice parameters. Through the repeated cold rolling processes, the grains can be reduced to nanometer scales constrained by numerous nontransforming grain boundaries. This has been successfully demonstrated in Nitinol, that is, binary Ni50Ti50 alloy.(21) Although the B2 (cubic) to B19′ (monoclinic) phase transformation of NiTi is very incompatible(22) without additional chemical doping, the engineered NiTi micropillar with ultrafine grains exhibits prominent superelasticity even after 1 million demanding stress-induced transformation cycles.(23,24) It strongly suggests that the grain boundaries are crucial to the functional fatigue of the superelastic alloy. In nanocrystalline superelastic micropillar, it was conjectured that the grain boundary can mediate the discontinuities between neighboring grains, thus suppressing the fatigue caused by plastic deformations and microcrack propagation.(21) This grain boundary mediated mechanism implies another level of compatibility, however the quantitative measures for such a mediation are not thoroughly rationalized. So far, there has not been much experimental work directly characterizing the mechanical properties of a single grain boundary with textures.
Can the phase transformation of a shape memory polycrystal be still highly reversible without fulfilling the compatibility conditions by lattice parameters? What role does the grain boundary (GB) play in a textured polycrystal under stress-induced phase transformation? In this paper, we study these emerging problems using a phase-transforming bicrystal micropillar with a single GB under the nanomechanical experiments. The studied alloy is CuAl24Mn9 whose lattice parameters are far from satisfying any intrinsic compatibility conditions. This alloy family suffers greatly from the functional degradation problems, especially for those polycrystalline alloys under the cyclic stress-induced transformations.(25,26) Similar to its sibling ternary and quarternary alloys,(26−28) the single crystal CuAl24Mn9 micropillars show anisotropic superelastic strains corresponding to different critical driving stresses.
Unlike the common Cu-based shape memory alloys undergoing cubic to monoclinic transformation, the chosen CuAl24Mn9 alloy transforms between cubic austenite and orthorhombic martensite. The martensite crystal structure was carefully characterized by synchrotron X-ray microdiffraction at the Advanced Light Source Beamline 12.3.2, Lawrence Berkeley National Lab. The symmetry of martensite is determined to be Pmmn by the newly established crystallographic theory of derived crystal structure.(29) Using a monochromator energy scan,(30) we collected more than 20 peaks diffracted by distinct crystallographic planes from which we obtained the refined lattice parameters for the orthorhombic martensite as a = 4.43196 Å, b = 5.34533 Å, c = 4.26307 Å. The symmetry of austenite phase is confirmed to be Fm3̅m by synchrotron X-ray Laue microdiffraction with the refined lattice parameter a0 = 5.87897 Å. On the basis of the lattice parameters, we used the StrucTrans algorithm(13) to calculate the transformation stretch tensor
(1)with ordered eigenvalues 
in which λ2 = 1.0255. According to crystallographic compatibility theory,(11,12) the closeness of λ2 to 1 strongly affects the reversibility of the phase transformation for shape memory alloys.(11,14,16−18) This material is far from satisfying the compatibility condition compared to other Cu-based SMAs shown in Table 1. To minimize the lattice mismatch across the austenite/martensite interface, the alloy has to form twin laminates that are finely branched to austenite through an elastic transition layer in which the nontransforming defects would nucleate and propagate, thus the functionality of the material degrades over transformation cycles.
A very large thermal hysteresis of 38 °C is observed in such an incompatible material, as characterized by differential scanning calorimetry (DSC) in Figure S1A (Supporting Information). Under the stress-free condition, we conducted a total of 573 thermal cycles for the CuAl24Mn9 alloy. After the thermal cycling, about 50 °C thermal hysteresis is accumulated, corresponding to more than 20 °C migration of transformation temperature. The same piece of CuAl24Mn9 alloy was taken for surface morphology observation under optical microscopy, as seen in Figure S1B (Supporting Information) after the 10th, 100th, 300th, and 500th cycles. The microstructure of the triple junction at the grain boundaries exhibits a clear trace of nonrecoverable deformations and cracking.
Under both optical microscope and scanning electron microscope (SEM), we identified a grain boundary across which the neighboring grains show sufficient contrast. By focused-ion beam (FIB) milling, several cylindrical pillars of 4 μm diameter were fabricated in the neighboring grains and at the grain boundary in Figure 1a. The inset SEM images show the trace of a grain boundary in a pillar. It indicates that the pillar is a bicrystal comprised of two different orientations. In order to quantitatively map the orientations of the neighboring grains and the GB, we conducted synchrotron X-ray Laue microdiffraction scan over several austenite grains, as in Figure 1b,c. By the intensity map obtained by averaging the pixalated intensity of each of the Laue patterns, we located the grain boundary and obtained its geometric normal as gb = cos θX + sin θY relative to the sample basis X (rolling) – Y (transverse) – Z (normal). The GB normal angle θ = 20° as seen from Figure 1b. Here we assume GB’s Z component vanishes because we observed a cliff along the trace of GB, which is almost aligned with the longitudinal direction of the pillar during the FIB milling process. The neighboring grains are labeled as gr1 and gr2 in Figure 1b, whose orientations are characterized in Figure 1c. The sample axes are written in gr1 basis as
(2)Note that Z-direction is the end-surface direction of pillars along the compressive direction under nanoindentation. The end-surface normal of grain gr2 is written as Z = [Z]gr2 ≈ [4 5 12]gr2, which differs from [Z]gr1 by 33.73°. The orientations of grains gr1 and gr2 are related by a misorientation matrix Q determined in Supporting Information.
Figure 1
Figure 1. Morphology of grain boundary and the corresponding micropillar in austenite phase. (a) Optical micrograph of CuAl24Mn9 grain boundary structure with the inset of SEM image for the morphology of the bicrystal pillar at GB ab initio FIB milling. (b) Intensity map of the surface by scanning white-beam synchrotron X-ray. (c) Orientation map of the surface normal by synchrotron Laue microdiffraction.
The nanocompression cycling tests were conducted at a fixed loading rate of 200 μN/s at room temperature by Hysitron TI 980 TriboIndenter. In each of the stress-induced transformation cycles, the pillar was loaded until the phase transformation from austenite to martensite completes, then fully unloaded to recover the superelastic deformation. The details are included in Materials and Methods in Supporting Information.
Figure 2a–c shows the stress–strain curves of pillars at various numbers of cycles from grain gr1, grain boundary, and grain gr2. The superelasticity is captured in all three micropillars, but their functionalities and corresponding degradations vary drastically. For single crystal pillar in [101]gr1 grain and bicrystal pillar at GB in Figure 2a,b, the stress for inducing phase transformation is about 600 MPa, which is much higher than that for the single crystal pillar in [4 5 12]gr2 grain in Figure 2c. In fact, this critical stress is one of the highest reported driving stresses in Cu-based shape memory alloys.(4,18,26−28,33,34) Among the ternary CuAlMn alloys, the usual value of critical stress is below 300 MPa,(26,27,34) and their superelasticity behaviors exhibit large degradations in the first few tens of cycles. In CuAl24Mn9 case, it is spectacular to see the stability of superelastic strain over 10 000 demanding mechanical cycles for the micropillars in [101]gr1 grain and at the GB. For the single crystal micropillar in [4 5 12]gr2 grain, significant degradation occurs after 600 cycles under much lower driving stress. From the post-mortem images of these pillars at the first and the last cycles, we can clearly see the longitudinal shortening in [4 5 12]gr2 pillar but not in the other two pillars even under a higher number of mechanical cycles. In contrast to the thermal fatigue behavior of this alloy, the functional fatigue under stress-induced transformations in micropillars is much reduced for the special orientation. Note that the pillar size in our experiment is small but not sufficiently small to trigger a size effect of sudden strengthening.(35)
Figure 2
Figure 2. Nanomechanical behaviors and post-mortem images of CuAl24Mn9 4 μm-diameter pillars under cycling microcompression tests. (a) The single crystal pillar oriented along [101]gr1. (b) The bicrystal pillar at the GB. (c) The single crystal pillar oriented along [45 12]gr2. Their superelastic behaviors and the dissipation behaviors over stress-induced transformation cycles for CuAl24Mn9 [101]gr1, GB, and [4 5 12]gr2 pillars. Particularly, they are cyclic degradation of (d) superelastic strain. (e) Critical stress inducing phase transformation. (f) Area of hysteresis loop. (g) Recoverable strains.
Quantitative mechanics analysis over microcompressive cycles reveals that the bicrystal pillar at GB exhibits the lowest degradation for all functionalities plotted in Figure 2d–g. We use the plateau strain to represent the superelastic strain and use the onset stress of the plateau to represent the critical stress for inducing phase transformation. As in Figure 2d,e, the single crystal micropillar in [4 5 12]gr2 grain delivers a large superelastic strain (i.e., 0.048) under stress of 400 MPa in its first few cycles, but the value sharply drops to near zero after 600 cycles. The single crystal micropillar in [101]gr1 grain exhibits 0.029 superelastic strain under the stress of 610 MPa in the first cycle. Both superelastic strain and the driving stress gradually degrade to half of their original values after 10 000 cycles. The bicrystal pillar at GB shows 0.02 superelastic strain under the stress of 580 MPa in the first cycle, which sustains for 10 000 cycles with very subtle degradation. The energy dissipation is represented by the area of the hysteresis loop upon loading and unloading, and the recoverability was expressed by the recoverable strain per cycle. The cyclic behaviors of these two functionalities were plotted in Figure 2f,g, with similar trends seen among the tested micropillars. Conventionally, a nontransforming GB would make the mechanical properties of polycrystalline solids worse upon large deformations, especially in Cu-based shape memory alloys.(25,26) At a high-angle GB (about 34° angular misorientation), the mechanism that confines the recoverable strain and enhances the reversibility of the bicrystal pillar is unclear according to our nanomechanics experiments.
For a cubic to orthorhombic transformation, there exist six distinct martensite variants expressed by the symmetry-related stretch tensors in the set 
where U is given in eq 1, the symbols 
and 
denote the point group of cubic and orthorhombic lattices, respectively.(12,22) The matrix forms and corresponding labels of these variants are given in Supporting Information. By symmetry, any pair of distinct variants 
can form a twin as RUj = Ui + a(i,j) ⊗ n(i,j) for twinning plane normal 
and twinning shear 
subjected to some rotation R ∈ SO(3) . (The symbol SO(3) denotes the group of 3 × 3 orthogonal matrices with determinant 1.) In Supporting Information, we examined the twin relation for all pairwise variants summarized in the twin Table S1. Restricted by the crystallographic compatibility(22)
(3)for some orthogonal matrix R̂ ∈ SO(3), vectors 
and the volume fraction f ∈ [0, 1]. All 12 pairs of variants can form 96 compatible twin laminates with austenite through a habit plane m(i,j) by a shear vector b(i,j). Here, we use F(i,j) = I + b(i,j) ⊗ m(i,j) to express the averaged deformation gradient of the compatible twin laminates (i, j) that solve eq 3. Supposing that the pillar completely transforms from austenite to twinned martensite, the averaged axial strain of the pillar under uniaxial loading is defined as
(4)where 
is a unimodular vector along the loading axis. In our nanocompression experiment, it is required that ϵ(i,j) < 0. According to energy minimization,(12,22,36) the pair of martensite variants that would appear upon the uniaxial compressive stress-induced phase transformation should be the maximizer of the strain function along compressing direction, that is
(5)
For single crystal micropillars, the axial loading direction is aligned with [101]gr1 for grain gr1 and [4 5 12]gr2 for grain gr2. We calculated the maximum compressive strains for each of the orientations among all compatible twin laminates, summarized in Table 2. For the single crystal micropillar in grain gr1, two crystallographically equivalent pairs of variants (U3, U6) and (U4, U5) offer the same superelastic strain, ϵ(3,6) = ϵ(4,5) = −0.02805 that agree with the superelastic plateau strain in the nanomechanics experiment (Figure 2a). For the single crystal micropillar in grain gr2, there is only one pair of variants (U2, U5) corresponding to −0.04414 superelastic strain, which also matches the superelastic plateau strain in experiment. However, the measured superelastic strain of bicrystal pillar at GB does not agree with the linear mixtures of the axial strains contributed by the orientations [101]gr1 and [4 5 12]gr2.
| orientation | pair of variants | habit plane | shear vector | axial strain | Schmid factor m(i,j) |
|---|---|---|---|---|---|
| [101]gr1 | (3, 6) | (−0.7535, −0.6327, 0.1787)gr1 | [0.0735, −0.0709, 0.0259]gr1 | –0.02805 | 0.2712 |
| (3, 6) | (−0.2556, −0.7072, −0.6592)gr1 | [−0.0174, −0.0626, 0.0829]gr1 | –0.02805 | 0.2845 | |
| (4, 5) | (−0.6592, −0.7072, −0.2556)gr1 | [0.0829, −0.0626, −0.01738]gr1 | –0.02805 | 0.2845 | |
| (4, 5) | (0.1787, −0.6327, −0.7535)gr1 | [0.02590, −0.07088, 0.07353]gr1 | –0.02805 | 0.2712 | |
| [4 5 12]gr2 | (2, 5) | (0.6321, −0.2549, −0.7318)gr2 | [0.0705, −0.0122, 0.0733]gr2 | –0.04414 | 0.4371 |
Beyond the energetic constraint on axial compression, the compatible twin laminates tend to minimize the lateral shear deformation.(18) Among the crystallographically compatible twin laminates, the resolved shear, that is, Schmid factor for twinning(37) along the austenite/martensite interface, should be minimized. For the unimodular vector c along the loading direction, the twinning Schmid factor is defined as
(6)
For the single crystal oriented in [101]gr1, the minimum twinning Schmid factor is 0.2712, corresponding to the habit planes
and
For the single crystal oriented in [4 5 12]gr2, the twinning Schmid factor is 0.4371 that almost reaches the maximum possible Schmid factor for an fcc crystal. These results imply that the slip by dislocations along m(2,5) in [4 5 12]gr2 pillar is much easier than that in [101]gr1 pillar, therefore the accumulated residual plastic deformations are much larger in grain gr2 over mechanical-induced transformation cycles.
The normal of grain boundary written in grain gr1 basis is gb = [0.574, 0.585, – 0.574]gr1, almost parallel to [111̅]gr1. If we use the twin laminates as the building blocks to derive the microstructure for the bicrystal pillar at GB, as shown in Figure 3a,b, the deformed configurations of either (3,6) or (4,5) twin laminates in grain gr1 are subjected to a very large discontinuity from the (2,5) twin laminates in grain gr2 at the grain boundary. To mediate such a spatial cracking at the GB, the pairs of variants in neighboring grains need to minimize both the areal and directional differences of the GB deformed from two sides. For two orthonormal vectors r1 and r2 such that r1·gb = r2·gb = 0, the pairs of twin variants in neighboring grains should satisfy
(7)where 
denotes the set of all pairs of variants of CuAl24Mn9 that solve the crystallographic eq 3. The function D(i,j,k,l) is defined as the GB-compatibility metric
(8)where b̃(k,l) = Qb(k,l), and m̃(k,l) = Qm(k,l) for the misorientation matrix Q characterized by synchrotron Laue microdiffraction. In eq 8, the first term calculates the areal jump, and the second term calculates the sum of the directional differences from one side of GB to the other.
Figure 3
Figure 3. Theoretical calculation of twinning microstructure in the bicrystal pillar at GB for (a) (3,6) variants of grain gr1 and (2,5) variants of grain gr2, (b) (4,5) variants of grain gr1 and (2,5) variants of grain gr2 and (c) (4,6) variants of grain gr1 and (4,5) variants of grain gr2. The light green color refers to the domain of austenite phase.
We examined all compatible twin laminates and identified the type II twin formed by a pair of variants (4,6) in grain gr1 and the type I twin formed by pair of variants (4,5) in grain gr2 are the minimizers of eq 7. The GB-compatibility metric of (4,6) and (4,5) laminates is calculated as D(4,6,4,5) = 0.000407. Note that the GB-compatibility metric is an area measure, while the crystallographic compatibility metric λ2 is an axial length measure along the middle eigenvector of the transformation stretch tensor. In this material, the square of the crystallographic compatibility, |λ2 – 1|2 = 0.00065 is comparable to the GB-compatibility metric. It implies that two-tier compatibility coexists in this polycrystalline alloy to make it highly reversible. The deformed configuration of these GB-compatible twin laminates are drawn in Figure 3c, which fit together nicely from opposite sides. The GB-compatibility metric given by eq 8 offers a new kinematic constraint on microstructure formation, which guarantees the spatial continuity at the high-angle grain boundary. In other words, the crystallographically compatible twins accommodate themselves to mediate the discontinuity at GB.
Moreover, the GB-compatible twin laminates (4,6) and (4,5) act as the interlock that prevents the shear deformation crossing over the grain boundary. The habit planes and corresponding shear vectors are expressed as
with twinning Schmid factor m(4,6) = 0.29403, and
with twinning Schmid factor m(4,5) = 0.37445. Compared to m(2,5) = 0.4371 in single crystal micropillar in axial direction [4 5 12]gr2, the twinning Schmid factor of the bicrystal micropillar in grain [4 5 12]gr2 is very reduced and is associated with a low risk of plastic deformations.
Figure 4a,b shows the orientation-dependent twinning Schmid factors for the type II twin (4,6) and type I twin (4,5) respectively. In the bicrystal micropillar, the twin (4,6) has a higher twinning Schmid factor in the grain gr1, while the twin (4,5) has a higher twinning Schmid factor in the grain gr2. When gliding dislocations travel from one grain to the other through the GB, a sudden decrease of the Schmid factor will prevent them from proceeding. As a consequence, the dislocations are trapped at the GB and the accumulation of plastic deformations over cycles could be much lessened. The axial strains given by the GB-compatible twin laminates are both lower than the values given by the twins developed in the single crystal micropillars. It provides a reasonable explanation for the reduced plateau strain in Figure 2c under stress-induced phase transformation.
Figure 4
Figure 4. Contours of the Schmid factors for the twin laminates of (a) type II twin (4,6) variants in [101]gr1 orientation and (b) type I twin (4,5) variants in [4 5 12]gr2 orientation.
To summarize, this paper combines the crystallographic compatibility and grain boundary morphology to derive a two-tier compatibility mechanism for polycrystalline shape memory alloys. Through a rational measurement of the cyclic superelastic behaviors in a phase-transforming bicrystal micropillar, we showed that both the crystallography and kinematics properties of GB play an important role in formation of microstructure in adjacent grains. For specific neighboring textures, the GB-compatibility ensures that the twins near the boundary minimize the spatial crack and act as an interlock to prevent dislocations from slipping from one grain to the other, thus enhancing the reversibility of the transforming metals over mechanical cycles. This work provides an important insight for the development of superelastic microdevices and may foster the applications of Cu-based SMAs for precise microstents and other biomedical applications.
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03486.
Supplementary text, Figures S1 and S2, Table S1, additional references (PDF)
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Author Information
- Xian Chen - Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong;
http://orcid.org/0000-0002-0114-4642;
Email: [email protected]
The authors declare no competing financial interest.
Acknowledgments
M.K., Z. Zhu, Z. Zeng, and X.C. thank the HK Research Grants Council for financial support under Grants 16207017 and 16201019. Beamline 12.3.2 and the Advanced Light Source were supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
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- 10Chen, Y.; Howe, C.; Lee, Y.; Cheon, S.; Yeo, W.-H.; Chun, Y. Microstructured thin film nitinol for a neurovascular flow-diverter. Sci. Rep. 2016, 6, 23698, DOI: 10.1038/srep23698[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvVCnsr0%253D&md5=c25bee92262b4a1e187f4aee9b9f3c11Microstructured Thin Film Nitinol for a Neurovascular Flow-DiverterChen, Yanfei; Howe, Connor; Lee, Yongkuk; Cheon, Seongsik; Yeo, Woon-Hong; Chun, YoungjaeScientific Reports (2016), 6 (), 23698CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)A cerebral aneurysm occurs as a result of a weakened blood vessel, which allows blood to flow into a sac or a ballooned section. Recent advancement shows that a new device, 'flow-diverter', can divert blood flow away from the aneurysm sac. People found that a flow-diverter based on thin film nitinol (TFN), works very effectively, however there are no studies proving the mech. safety in irregular, curved blood vessels. Here, we study the mech. behaviors and structural safety of a novel microstructured TFN membrane through the computational and exptl. studies, which establish the fundamental aspects of stretching and bending mechanics of the structure. The result shows a hyper-elastic behavior of the TFN with a negligible strain change up to 180° in bending and over 500% in radial stretching, which is ideal in the use in neurovascular curved arteries. The simulation dets. the optimal joint locations between the TFN and stent frame. In vitro exptl. test qual. demonstrates the mech. flexibility of the flow-diverter with multi-modal bending. In vivo micro X-ray and histopathol. study demonstrate that the TFN can be conformally deployed in the curved blood vessel of a swine model without any significant complications or abnormalities.
- 11Chen, X.; Srivastava, V.; Dabade, V.; James, R. D. Study of the cofactor conditions: conditions of supercompatibility between phases. J. Mech. Phys. Solids 2013, 61, 2566– 2587, DOI: 10.1016/j.jmps.2013.08.004[Crossref], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVClsb3F&md5=a6118f891b7e5ef4be6c80d7ed7d66deStudy of the cofactor conditions: Conditions of supercompatibility between phasesChen, Xian; Srivastava, Vijay; Dabade, Vivekanand; James, Richard D.Journal of the Mechanics and Physics of Solids (2013), 61 (12), 2566-2587CODEN: JMPSA8; ISSN:0022-5096. (Elsevier Ltd.)The cofactor conditions, are conditions of compatibility between phases in martensitic materials. They consist of three subconditions: (i) the condition that the middle principal stretch of the transformation stretch tensor U is unity (λ2 = 1), (ii) the condition a·Ucof(U2-I)n = 0, where the vectors a and n are certain vectors arising in the specification of the twin system, and (iii) the inequality trU2+detU2-(1/4)|a|2|n|2≥2. Together, these conditions are necessary and sufficient for the equations of the crystallog. theory of martensite to be satisfied for the given twin system but for any vol. fraction f of the twins, 0≤f≤1. This contrasts sharply with the generic solns. of the crystallog. theory which have at most two such vol. fractions for a given twin system of the form f* and 1-f*. In this paper we simplify the form of the cofactor conditions, we give their specific forms for various symmetries and twin types, we clarify the extent to which the satisfaction of the cofactor conditions for one twin system implies its satisfaction for other twin systems. In particular, we prove that the satisfaction of the cofactor conditions for either Type I or Type II twins implies that there are solns. of the crystallog. theory using these twins that have no elastic transition layer. We show that the latter further implies macroscopically curved, transition-layer-free austenite/martensite interfaces for Type I twins, and planar transition-layer-free interfaces for Type II twins which nevertheless permit significant flexibility (many deformations) of the martensite. We identify some real material systems nearly satisfying the cofactor conditions. Overall, the cofactor conditions are shown to dramatically increase the no. of deformations possible in austenite/martensite mixts. without the presence of elastic energy needed for coexistence. In the context of earlier work that links the special case λ2 = 1 to reversibility, it is expected that satisfaction of the cofactor conditions for Type I or Type II twins will lead to further lowered hysteresis and improved resistance to transformational fatigue in alloys whose compn. has been tuned to satisfy these conditions.
- 12Ball, J.; James, R. Fine phase mixtures as minimizers of energy. Arch. Ration. Mech. Anal. 1987, 100, 13– 52, DOI: 10.1007/BF00281246
- 13Chen, X.; Song, Y.; Tamura, N.; James, R. D. Determination of the stretch tensor for structural transformations. J. Mech. Phys. Solids 2016, 93, 34– 43, DOI: 10.1016/j.jmps.2016.02.009
- 14Cui, J.; Chu, Y. S.; Famodu, O. O.; Furuya, Y.; Hattrick-Simpers, J.; James, R. D.; Ludwig, A.; Thienhaus, S.; Wuttig, M.; Zhang, Z. Combinatorial search of thermoelastic shape-memory alloys with extremely small hysteresis width. Nat. Mater. 2006, 5, 286– 290, DOI: 10.1038/nmat1593[Crossref], [PubMed], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XjtVKmtbY%253D&md5=febf6cfd0125f27f07953e0dba6bb105Combinatorial search of thermoelastic shape-memory alloys with extremely small hysteresis widthCui, Jun; Chu, Yong S.; Famodu, Olugbenga O.; Furuya, Yasubumi; Hattrick-Simpers, Jae.; James, Richard D.; Ludwig, Alfred; Thienhaus, Sigurd; Wuttig, Manfred; Zhang, Zhiyong; Takeuchi, IchiroNature Materials (2006), 5 (4), 286-290CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Reversibility of structural phase transformations has profound technol. implications in a wide range of applications from fatigue life in shape-memory alloys to magnetism in multiferroic oxides. The geometric nonlinear theory of martensite universally applicable to all structural transitions has been developed. It predicts the reversibility of the transitions as manifested in the hysteresis behavior based solely on crystal symmetry and geometric compatibility between phases. Verification of the theory was done by using the high-throughput approach. The thin-film compn.-spread technique was devised to map the lattice parameters and thermal hysteresis of ternary alloy systems rapidly. A clear relationship between the hysteresis and middle eigenvalue of the transformation stretch tensor as predicted by the theory was obsd. A compn. region for titanium-rich Ti-Ni-Cu and Ti-Ni-Pd shape-memory alloys with potential for improved control of their properties was identified.
- 15Zhang, Z.; James, R. D.; Müller, S. Energy barriers and hysteresis in martensitic phase transformations. Acta Mater. 2009, 57, 4332– 4352, DOI: 10.1016/j.actamat.2009.05.034[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXpt1Cgsrs%253D&md5=88c2ca02f40f6012e371e66fe643d92aEnergy barriers and hysteresis in martensitic phase transformationsZhang, Zhiyong; James, Richard D.; Mueller, StefanActa Materialia (2009), 57 (15), 4332-4352CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Ltd.)The results from a systematic program of alloy development in the system Ti-Ni-X with X being Cu, Pt, Pd, Au, to pursue certain special lattice parameters that have been identified previously with low hysteresis. λ2 = 1 Was obsd. with λ2 being the middle eigenvalue of the transformation stretch matrix for alloys with X = Pt, Pd, Au. In all cases there is a sharp drop in the graph of hysteresis vs. compn. at the compn. where λ2 = 1 . When the size of the hysteresis is replotted vs. λ2, a universal graph for these alloys is obtained. Motivated by these exptl. results, a new theory is presented for the size of the hysteresis based on the growth from a small scale of fully developed austenite martensite needles. The energy of the transition layer plays a crit. role in this theory. Overall, the results point to a simple systematic method of achieving low hysteresis and high degree of reversibility in transforming alloys.
- 16Song, Y.; Chen, X.; Dabade, V.; Shield, T. W.; James, R. D. Enhanced reversibility and unusual microstructure of a phase-transforming material. Nature 2013, 502, 85– 88, DOI: 10.1038/nature12532[Crossref], [PubMed], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFGru73P&md5=3da0e7b4e1f9d8eb93907b092c9b79faEnhanced reversibility and unusual microstructure of a phase-transforming materialSong, Yintao; Chen, Xian; Dabade, Vivekanand; Shield, Thomas W.; James, Richard D.Nature (London, United Kingdom) (2013), 502 (7469), 85-88CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Materials undergoing reversible solid-to-solid martensitic phase transformations are desirable for applications in medical sensors and actuators, eco-friendly refrigerators, and energy conversion devices. The ability to pass back and forth through the phase transformation many times without degrdn. of properties (termed 'reversibility') is crit. for these applications. Materials tuned to satisfy a certain geometric compatibility condition were shown to exhibit high reversibility, measured by low hysteresis and small migration of transformation temp. under cycling. Recently, stronger compatibility conditions called the 'cofactor conditions' were proposed theor. to achieve even better reversibility. Here we report the enhanced reversibility and unusual microstructure of the first martensitic material, Zn45Au30Cu25, that closely satisfies the cofactor conditions. We observe four striking properties of this material. (1) Despite a transformation strain of 8%, the transformation temp. shifts <0.5° after >16,000 thermal cycles. For comparison, the transformation temp. of the ubiquitous NiTi alloy shifts up to 20° in the first 20 cycles. (2) The hysteresis remains approx. 2° during this cycling. For comparison, the hysteresis of the NiTi alloy is up to 70°. (3) The alloy exhibits an unusual riverine microstructure of martensite not seen in other martensites. (4) Unlike that of typical polycrystal martensites, its microstructure changes drastically in consecutive transformation cycles, whereas macroscopic properties such as transformation temp. and latent heat are nearly reproducible. These results promise a concrete strategy for seeking ultra-reliable martensitic materials.
- 17Chluba, C.; Ge, W.; Lima de Miranda, R.; Strobel, J.; Kienle, L.; Quandt, E.; Wuttig, M. Ultralow-fatigue shape memory alloy films. Science 2015, 348, 1004– 1007, DOI: 10.1126/science.1261164[Crossref], [PubMed], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXovVKltL8%253D&md5=2b360dcc562f5254f7499888ffa72b31Ultralow-fatigue shape memory alloy filmsChluba, Christoph; Ge, Wenwei; Lima de Miranda, Rodrigo; Strobel, Julian; Kienle, Lorenz; Quandt, Eckhard; Wuttig, ManfredScience (Washington, DC, United States) (2015), 348 (6238), 1004-1007CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Functional shape memory alloys need to operate reversibly and repeatedly. Quant. measures of reversibility include the relative vol. change of the participating phases and compatibility matrixes for twinning. But no similar argument is known for repeatability. This is esp. crucial for many future applications, such as artificial heart valves or elastocaloric cooling, in which \>10 million transformation cycles will be required. We report on the discovery of an ultralow-fatigue shape memory alloy film system based on TiNiCu that allows at least 10 million transformation cycles. We found that these films contain Ti2Cu ppts. embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle.
- 18Ni, X.; Greer, J. R.; Bhattacharya, K.; James, R. D.; Chen, X. Exceptional resilience of small-scale Au30Cu25Zn45 under cyclic stress-induced phase transformation. Nano Lett. 2016, 16, 7621– 7625, DOI: 10.1021/acs.nanolett.6b03555[ACS Full Text
], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVSju7bL&md5=cfe6c2865c6d6b305b5089f997de7551Exceptional Resilience of Small-Scale Au30Cu25Zn45 under Cyclic Stress-Induced Phase TransformationNi, Xiaoyue; Greer, Julia R.; Bhattacharya, Kaushik; James, Richard D.; Chen, XianNano Letters (2016), 16 (12), 7621-7625CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Shape memory alloys that produce and recover from large deformation driven by martensitic transformation are widely exploited in biomedical devices and microactuators. Generally their actuation work degrades significantly within first a few cycles and is reduced at smaller dimensions. Further, alloys exhibiting unprecedented reversibility have relatively small superelastic strain, 0.7%. These raise the questions of whether high reversibility is necessarily accompanied by small work and strain and whether high work and strain is necessarily diminished at small scale. Here we conclusively demonstrate that these are not true by showing that Au30Cu25Zn45 pillars exhibit 12 MJ m-3 work and 3.5% superelastic strain even after 100000 phase transformation cycles. Our findings confirm that the lattice compatibility dominates the mech. behavior of phase-changing materials at nano to micron scales and points a way for smart microactuators design having the mutual benefits of high actuation work and long lifetime. - 19Jetter, J.; Gu, H.; Zhang, H.; Wuttig, M.; Chen, X.; Greer, J. R.; James, R. D.; Quandt, E. Tuning crystallographic compatibility to enhance shape memory in ceramics. Phys. Rev. Mater. 2019, 3, 093603 DOI: 10.1103/PhysRevMaterials.3.093603[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXit1WjtL%252FF&md5=91d204e3e375b2d5e306c0da86bd6743Tuning crystallographic compatibility to enhance shape memory in ceramicsJetter, Justin; Gu, Hanlin; Zhang, Haolu; Wuttig, Manfred; Chen, Xian; Greer, Julia R.; James, Richard D.; Quandt, EckhardPhysical Review Materials (2019), 3 (9), 093603CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)The extraordinary ability of shape-memory alloys to recover after large imposed deformation motivates efforts to transpose these properties onto ceramics, which would enable practical shape-memory properties at high temps. and in harsh environments. The theory of mech. compatibility was utilized to predict promising ceramic candidates in the system (Y0.5Ta0.5O2)1-x-(Zr0.5Hf0.5O2)x, 0.6<x<0.85. When these compatibility conditions are met, a redn. in thermal hysteresis by a factor of 2.5, a tripling of deformability, and a 75% enhancement in strain recovery within the shape-memory effect was found. These findings reveal that predicting and optimizing the chem. compn. of ceramics to attain improved crystallog. compatibility is a powerful tool for enabling and enhancing their deformability that could ultimately lead to a highly reversible oxide ceramic shape-memory material.
- 20Pang, E. L.; McCandler, C. A.; Schuh, C. A. Reduced cracking in polycrystalline ZrO2-CeO2 shape-memory ceramics by meeting the cofactor conditions. Acta Mater. 2019, 177, 230– 239, DOI: 10.1016/j.actamat.2019.07.028[Crossref], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsFWitrzI&md5=3ad41b1d3f8309cf863d66bd96365b61Reduced cracking in polycrystalline ZrO2-CeO2 shape-memory ceramics by meeting the cofactor conditionsPang, Edward L.; McCandler, Caitlin A.; Schuh, Christopher A.Acta Materialia (2019), 177 (), 230-239CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Ltd.)Cracking is generally regarded as an unavoidable consequence of martensitic transformation in polycryst. ZrO2-based ceramics. This shortcoming has limited ZrO2-based shape-memory ceramics (SMCs) to micron-sized single- or oligo-crystals to reduce bulk transformation stresses. In this paper we explore an alternate approach to reduce transformation-induced cracking by manipulating the crystallog. phase compatibility in polycryst. ZrO2-CeO2 ceramics. For a range of compns. 12.5-15 mol% CeO2, we present lattice parameter measurements for the tetragonal and monoclinic phases from in situ X-ray diffraction, direct observation of lattice correspondences by electron backscatter diffraction, and calcns. of interface and bulk compatibility. We identify ZrO2-13.5 mol% CeO2 as having preferred interface compatibility in that it closely meets the crystallog. cofactor conditions. This compn. resists cracking through 10 thermal cycles, whereas other compns. all crack. These results suggest that interface compatibility may contribute more strongly to transformation-induced cracking in ZrO2-based SMCs than previously believed and opens a strategy for designing crack-resistant polycryst. SMCs.
- 21Yin, H.; He, Y.; Moumni, Z.; Sun, Q. Effects of grain size on tensile fatigue life of nanostructured NiTi shape memory alloy. Int. J. Fatigue 2016, 88, 166– 177, DOI: 10.1016/j.ijfatigue.2016.03.023[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xltlagt7k%253D&md5=6d7089819903968360addd8e2087ba25Effects of grain size on tensile fatigue life of nanostructured NiTi shape memory alloyYin, Hao; He, Yongjun; Moumni, Ziad; Sun, QingpingInternational Journal of Fatigue (2016), 88 (), 166-177CODEN: IJFADB; ISSN:0142-1123. (Elsevier Ltd.)The effects of grain size (GS) on tensile fatigue life of nanostructured NiTi superelastic shape memory alloys (SMAs) with GS = 10 nm, 42 nm and 80 nm are investigated. Macroscopic stress-controlled tensile fatigue tests, acoustic energy measurements and fracture surface observations were performed. It is shown that low-cycle fatigue life (under σmax = 450MPa) of nanostructured NiTi polycryst. SMA increases significantly when GS decreases from 80 nm to 10 nm. However, there is no significant effect of GS on the intermediate-cycle fatigue life (under σmax = 300MPa). It is found that accumulated acoustic energy can be used to distinguish the three stages of fatigue: slow crack propagation, fast crack propagation and final fracture. Micro cracks were found on fracture surfaces of all GS specimens under intermediate-cycle fatigue and on fracture surfaces of 10 nm GS specimen under low-cycle fatigue, while micro voids were found in 42 nm and 80 nm GS specimens under low-cycle fatigue. The results of the paper indicate that grain refinement down to nanoscale has potential in developing high fatigue resistance SMAs.
- 22Bhattacharya, K. In Microstructure of martensite: why it forms and how it gives rise to the shape-memory effect; Sutton, A. P., Rudd, R. E., Eds.; Oxford University Press, 2003; Vol. 2.
- 23Kabirifar, P.; Chu, K.; Ren, F.; Sun, Q. Effects of grain size on compressive behavior of NiTi polycrystalline superelastic macro-and micropillars. Mater. Lett. 2018, 214, 53– 55, DOI: 10.1016/j.matlet.2017.11.069[Crossref], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvV2qs73K&md5=5d8812d58acab3b6bc4c4f9555a6a3deEffects of grain size on compressive behavior of NiTi polycrystalline superelastic macro- and micropillarsKabirifar, Parham; Chu, Kangjie; Ren, Fuzeng; Sun, QingpingMaterials Letters (2018), 214 (), 53-55CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)Polycryst. NiTi pillars of 0.5 μm diam. and 1.5 μm height with av. grain sizes from 10 to 421 nm are fabricated by focused ion beam and compressed by nanoindentation. It is found that stress-strain hysteresis loop area, transformation stress and transformation strain vary non-monotonically with grain size. Anal. of the results reveals that increasing the grain size from 10 nm enhances the transformation by promoting the nucleation and growth of martensite domains. When the grain size approaches the pillar size, the transformation is suppressed by an increase in granular constraints and heterogeneity of internal stress-strain state among large grains.
- 24Hua, P.; Chu, K.; Ren, F.; Sun, Q. Cyclic phase transformation behavior of nanocrystalline NiTi at microscale. Acta Mater. 2020, 185, 507– 517, DOI: 10.1016/j.actamat.2019.12.019[Crossref], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjtlyjsw%253D%253D&md5=55a9da1e7c05a5a52931936d8871bdc2Cyclic phase transformation behavior of nanocrystalline NiTi at microscaleHua, Peng; Chu, Kangjie; Ren, Fuzeng; Sun, QingpingActa Materialia (2020), 185 (), 507-517CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Ltd.)Cuboidal micropillars of nanocryst. superelastic NiTi shape memory alloys with an av. grain size of 65 nm were fabricated by focused ion beam and then subjected to cyclic compression. It is found that the micropillars have maintained superelasticity for over 106 full-transformation cycles under a max. compressive stress of 1.2 GPa. Functional degrdn. of the micropillars mainly occurs in the first 104 cycles where hysteresis loop area and forward transformation stress rapidly decrease from initial 11 MPa (MJ/m3) and 586 MPa to 6 MPa and 271 MPa. In the 104 ∼ 106 cycles, stress-strain responses of the micropillars show asymptotic stabilization. Residual strain is accumulated to 3.3% and multiple ∼50 nm wide extrusions are found at the surface of the micropillars after 106 cycles. SEM and TEM studies indicate that cyclic phase transformation results in formation and glide of transformation-induced dislocations that create surface steps and the extrusions. The dislocations inhibit reverse transformation and result in residual martensite and residual stresses. The dislocations and the residual martensite lead to the functional degrdn. The role of the residual martensite in the functional degrdn. is further verified by 21% recovery of the residual strain and an increase of 278 MPa in the forward transformation stress after heating up the cyclically deformed micropillars to 100°C. The recorded over 106 phase transformation cycles under a max. stress of 1.2 GPa of the NiTi shape memory alloys at microscale open up new avenues for applications of the material in microscale devices and engineering.
- 25Funakubo, H.; Kennedy, J. Shape memory alloys; Gordon and Breach, 1987; xii– 275.
- 26Zárubová, N.; Novák, V. Phase stability of CuAlMn shape memory alloy. Mater. Sci. Eng., A 2004, 378, 216– 221, DOI: 10.1016/j.msea.2003.10.346[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXlsVeisbY%253D&md5=af7c94f945b19853bcc0f84dd854edddPhase stability of CuAlMn shape memory alloysZarubova, N.; Novak, V.Materials Science & Engineering, A: Structural Materials: Properties, Microstructure and Processing (2004), A378 (1-2), 216-221CODEN: MSAPE3; ISSN:0921-5093. (Elsevier Science B.V.)Thermoelastic martensitic transformations in single crystals of two CuAlMn shape memory alloys were investigated using tension/compression stress-strain tests, thermal cycling tests, stress recovery tests and calorimetric measurements. Pseudoelastic behavior was obsd. in the as-quenched samples stressed above the Af temp. Near the Ms temp., the stress-strain response changed and became pseudoplastic. A pronounced dependence of the thermoplastic behavior on the transformation history was found. The samples once subjected to tension/compression cycling at a temp. near or below Ms remained pseudoplastic during subsequent stress-strain expts. at higher temps., and a large increase of the Af temp. was obsd. This stabilization of martensite is similar to that obsd. on CuAlNi, and can be ascribed to the de-twinning of the martensitic phase and formation of a single variant of the γ1'-martensite.
- 27Sutou, Y.; Omori, T.; Kainuma, R.; Ishida, K.; Ono, N. Enhancement of superelasticity in Cu-Al-Mn-Ni shape-memory alloys by texture control. Metall. Mater. Trans. A 2002, 33, 2817– 2824, DOI: 10.1007/s11661-002-0267-2[Crossref], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xnt1emtbc%253D&md5=c6c5443b9410637ba687fd57de160f64Enhancement of superelasticity in Cu-Al-Mn-Ni shape-memory alloys by texture controlSutou, Y.; Omori, T.; Kainuma, R.; Ono, N.; Ishida, K.Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science (2002), 33A (9), 2817-2824CODEN: MMTAEB; ISSN:1073-5623. (Minerals, Metals & Materials Society)A significant improvement in the degree of superelasticity in Cu-Al-Mn ductile polycryst. alloys has been achieved through the addn. of Ni and control of the recrystn. texture by thermomech. processing, which contain annealing in the fcc (α) + bcc (β) two-phase region, followed by heavy cold redns. of over 60%. The addn. of Ni to the Cu-Al-Mn alloys shows a drastic effect on the formation of the strong {112}<110> recrystn. texture. Superelastic strains on the order of 7%, 3 times larger than those in other Cu-based shape-memory alloys, have been realized in the textured Cu-Al-Mn-Ni alloys. The superelastic strains obtainable in the textured Cu-based SMAs are on a par with those attainable in NiTi-based alloys.
- 28Fornell, J.; Tuncer, N.; Schuh, C. Orientation dependence in superelastic Cu-Al-Mn-Ni micropillars. J. Alloys Compd. 2017, 693, 1205– 1213, DOI: 10.1016/j.jallcom.2016.10.090[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCru7vL&md5=789540320b8ac605785348e8a27b7030Orientation dependence in superelastic Cu-Al-Mn-Ni micropillarsFornell, J.; Tuncer, N.; Schuh, C. A.Journal of Alloys and Compounds (2017), 693 (), 1205-1213CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)The superelastic behavior of single crystal Cu-Al-Mn-Ni shape memory alloy micro-pillars was studied under compression as a function of crystallog. orientation. Cylindrical pillars of about 2 μm diam. were micro-machined from targeted crystal orientations. While pillars oriented close to the [001] direction showed the largest total transformation strain (∼7%), plastic deformation dominated the compressive response in the pillars milled close to the [111] direction due to their high elastic anisotropy combined with the large stresses required to induce the transformation. Shape strain contour plots were constructed for γ' and β' martensites, and the martensite start stress was calcd. using the Clausius-Clapeyron equation. The same general trends are obsd. in both the exptl. and calcd. results, with some exceptions: larger transformation stresses and lower transformation strains are obsd. in the microsized pillars.
- 29Karami, M.; Tamura, N.; Yang, Y.; Chen, X. Derived crystal structure of martensitic materials by solid–solid phase transformation. Acta Crystallogr., Sect. A: Found. Adv. 2020, 76, 521– 533, DOI: 10.1107/S2053273320006087[Crossref], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht12itbfL&md5=2abff5ac82cd07bc80ba5c9e92d4ff7bDerived crystal structure of martensitic materials by solid-solid phase transformationKarami, Mostafa; Tamura, Nobumichi; Yang, Yong; Chen, XianActa Crystallographica, Section A: Foundations and Advances (2020), 76 (4), 521-533CODEN: ACSAD7; ISSN:2053-2733. (International Union of Crystallography)A math. description of crystal structure is proposed consisting of two parts: the underlying translational periodicity and the distinct at. positions up to the symmetry operations in the unit cell, consistent with the International Tables for Crystallog. By the Cauchy-Born hypothesis, such a description can be integrated with the theory of continuum mechanics to calc. a derived crystal structure produced by solid-solid phase transformation. In addn., the expressions for the orientation relationship between the parent lattice and the derived lattice are generalized. The derived structure rationalizes the lattice parameters and the general equiv. at. positions that assist the indexing process of X-ray diffraction anal. for low-symmetry martensitic materials undergoing phase transformation. The anal. is demonstrated in a CuAlMn shape memory alloy. From its austenite phase (L21 face-centered cubic structure), it is identified that the derived martensitic structure has orthorhombic symmetry Pmmn with the derived lattice parameters ad = 4.36491, bd = 5.40865 and cd = 4.2402 Å, by which the complicated X-ray Laue diffraction pattern can be well indexed, and the orientation relationship can be verified.
- 30Chen, X.; Dejoie, C.; Jiang, T.; Ku, C.-S.; Tamura, N. Quantitative microstructural imaging by scanning Laue x-ray micro-and nanodiffraction. MRS Bull. 2016, 41, 445– 453, DOI: 10.1557/mrs.2016.97[Crossref], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XptlOns7o%253D&md5=3c9e42504fe78eb9c560dbf74119e128Quantitative microstructural imaging by scanning Laue x-ray micro- and nanodiffractionChen, Xian; Dejoie, Catherine; Jiang, Tengfei; Ku, Ching-Shun; Tamura, NobumichiMRS Bulletin (2016), 41 (6), 445-453CODEN: MRSBEA; ISSN:0883-7694. (Cambridge University Press)Local crystal structure, crystal orientation, and crystal deformation can all be probed by Laue diffraction using a submicron x-ray beam. This technique, employed at a synchrotron facility, is particularly suitable for fast mapping the mech. and microstructural properties of inhomogeneous multiphase polycryst. samples, as well as imperfect epitaxial films or crystals. As synchrotron Laue x-ray microdiffraction enters its 20th year of existence and new synchrotron nanoprobe facilities are being built and commissioned around the world, we take the opportunity to overview current capabilities as well as the latest tech. developments. Fast data collection provided by state-of-the-art area detectors and fully automated pattern indexing algorithms optimized for speed make it possible to map large portions of a sample with fine step size and obtain quant. images of its microstructure in near real time. We extrapolate how the technique is anticipated to evolve in the near future and its potential emerging applications at a free-electron laser facility.
- 31Otsuka, K.; Ohba, T.; Tokonami, M.; Wayman, C.M. New description of long period stacking order structures of martenites in β-phase alloys. Scr. Metall. Mater. 1993, 29, 1359– 1364, DOI: 10.1016/0956-716X(93)90139-J[Crossref], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXmtlWmsbc%253D&md5=4184bde19e240f653e06dc6850411a8aNew description of long period stacking order structures of martensites in β-phase alloysOtsuka, K.; Ohba, T.; Tokonami, M.; Wayman, C. M.Scripta Metallurgica et Materialia (1993), 29 (10), 1359-64CODEN: SCRMEX; ISSN:0956-716X.New unit cells and nomenclature are proposed to describe the long-period stacking order structures of martensites in β-phase alloys. The use of the new unit cells eliminates the long period.
- 32Chakravorty, S.; Wayman, C. Electron microscopy of internally faulted Cu-Zn-Al martensite. Acta Metall. 1977, 25, 989– 1000, DOI: 10.1016/0001-6160(77)90127-4[Crossref], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1cXktFSgsbc%253D&md5=5bc405b7394eb436a79d72f455956e5aElectron microscopy of internally faulted copper-zinc-aluminum martensiteChakravorty, S.; Wayman, C. M.Acta Metallurgica (1977), 25 (9), 989-1000CODEN: AMETAR; ISSN:0001-6160.A large no. of alloys show the shape memory effect. There is evidence that internally faulted (untwinned) martensites (e.g. CuAl and CuZnAl) show this effect. A Cu68Zn15Al17 alloy [66704-23-2] was studied, whose stoichiometry is between that of the DO3 (Fe3Al) structure and the Heusler (Cu2MnAl) structure. Ingots were betatized 2 h at 875° and quenched into iced 10% NaOH soln. A microscopic examn. was made to det. the crystal structure of the matrix (β' parent) and β'1 martensite phases. A dislocation model for the parent-martensite interface was examd. exptl. to explain the thermoelastic (glissile) nature of the transformation from a DO3 parent to an 18R martensite. The matrix phase structure of the alloy was DO3 with a = 5.996Å. The matensite structure was M1,R (modified 1,R, monoclinic) with β = 87.5°, a = 4.553Å, b = 5.452Å, and c = 3,.977Å. The 18 layer martensite structure forms as a result of periodic shifts on the martensite basal plane in the [100]18R direction. Ordered dislocations on every 3rd (001) plane were not obsd., but random dislocations caused by extra faults were obsd. having a Burgers vector of [100]βh1.
- 33Liu, J.-L.; Huang, H.-Y.; Xie, J.-X. The roles of grain orientation and grain boundary characteristics in the enhanced superelasticity of Cu71.8Al17.8Mn10.4 shape memory alloys. Mater. Eng. 2014, 64, 427– 433, DOI: 10.1016/j.matdes.2014.07.070
- 34Dutkiewicz, J.; Kato, H.; Miura, S.; Messerschmidt, U.; Bartsch, M. Structure changes during pseudoelastic deformation of CuAlMn single crystals. Acta Mater. 1996, 44, 4597– 4609, DOI: 10.1016/1359-6454(96)00086-9[Crossref], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsFeksbo%253D&md5=8cf6f1f9fc053d400b9d5860120bd98eStructure changes during pseudoelastic deformation of CuAlMn single crystalsDutkiewicz, J.; Kato, H.; Miura, S.; Messerschmidt, U.; Bartsch, M.Acta Materialia (1996), 44 (11), 4597-4609CODEN: ACMAFD; ISSN:1359-6454. (Elsevier)Structure changes during pseudoelastic deformation of CuAlMn single crystals were investigated using in situ optical and high-voltage electron microscopy (HVEM). Several crystal orientations were investigated, from an irrational to 〈100〉 and 〈100〉 tensile axis and plane orientations in the case of thin foils. The compn. of the alloy was chosen such as to obtain superelastic behavior at room temp. Optical microstructures allowed to identify parallel plates at the beginning of the stress plateau, the no. of which increased with strain. The stress/temp. phase diagram was established within the range of existence of γ'1 and β"1. During in situ HVEM deformation in the 〈100〉 direction of γ'1 plates nucleated on pre-existing ones. At later deformation stages 18R martensite was formed in stacks of narrow needles. The following crystallog. relationship was obsd.: [001]β1||[010]β'1, γ'1 and [110]β1||[001]β'1, γ'1. A small permanent deformation obsd. after stress release was connected with the presence of residual martensite of a high random stacking fault d. and consisting often of α'1, γ'1 and β'1 martensite layers. During deformation in the 〈100〉 direction a larger permanent deformation and a d. of dislocation was obsd.
- 35Gómez-Cortés, J. F.; Nó, M. L.; López-Ferreño, I. n.; Hernández-Saz, J.; Molina, S. I.; Chuvilin, A.; San Juan, J. M. Size effect and scaling power-law for superelasticity in shape-memory alloys at the nanoscale. Nat. Nanotechnol. 2017, 12, 790– 797, DOI: 10.1038/nnano.2017.91[Crossref], [PubMed], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXovVGru7Y%253D&md5=8561576c4c541aa1f87ab510b6994428Size effect and scaling power-law for superelasticity in shape-memory alloys at the nanoscaleGomez-Cortes, Jose F.; No, Maria L.; Lopez-Ferreno, Inaki; Hernandez-Saz, Jesus; Molina, Sergio I.; Chuvilin, Andrey; San Juan, Jose M.Nature Nanotechnology (2017), 12 (8), 790-796CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Shape-memory alloys capable of a superelastic stress-induced phase transformation and a high displacement actuation have promise for applications in micro-electromech. systems for wearable health care and flexible electronic technologies. However, some of the fundamental aspects of their nanoscale behavior remain unclear, including the question of whether the crit. stress for the stress-induced martensitic transformation exhibits a size effect similar to that obsd. in confined plasticity. Here we provide evidence of a strong size effect on the crit. stress that induces such a transformation with a threefold increase in the trigger stress in pillars milled on [001] L21 single crystals from a Cu-Al-Ni shape-memory alloy from 2 μm to 260 nm in diam. A power-law size dependence of n = -2 is obsd. for the nanoscale superelasticity. Our observation is supported by the at. lattice shearing and an elastic model for homogeneous martensite nucleation.
- 36Bhattacharya, K.; Kohn, R. V. Symmetry, texture and the recoverable strain of shape-memory polycrystals. Acta Mater. 1996, 44, 529– 542, DOI: 10.1016/1359-6454(95)00198-0[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xls1Shtw%253D%253D&md5=c01b990b87164d5ce20a6d4022139fc7Symmetry, texture and the recoverable strain of shape-memory polycrystalsBhattacharya, K.; Kohn, R. V.Acta Materialia (1996), 44 (2), 529-42CODEN: ACMAFD; ISSN:1359-6454. (Elsevier)Shape-memory behavior is the ability of certain materials to recover, on heating, apparently plastic deformation sustained below a crit. temp. Some materials have good shape-memory behavior as single crystals but little or none as polycrystals, while others display good shape-memory behavior even as polycrystals. In this paper, we propose a theor. explanation for this difference: we show that the recoverable strain in a polycrystal depends on the texture of the polycrystal, the transformation strain of the underlying martensitic transformation and esp. critically on the change of symmetry during the underlying transformation. Roughly, we find that the greater the change in symmetry during transformation, the greater the recoverable strain. We include an extensive survey of the exptl. literature and show that our results agree with these observations. We make recommendations for improved shape-memory effect in polycrystals.
- 37Shu, Y.; Bhattacharya, K. The influence of texture on the shape-memory effect in polycrystals. Acta Mater. 1998, 46, 5457– 5473, DOI: 10.1016/S1359-6454(98)00184-0[Crossref], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXmsFWqtL4%253D&md5=7c7095d05ce5598f74d1092f870f3b58The influence of texture on the shape-memory effect in polycrystalsShu, Y. C.; Bhattacharya, K.Acta Materialia (1998), 46 (15), 5457-5473CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Science Ltd.)A model is developed to show that texture is a crucial factor in detg. the shape-memory effect in polycrystals. Texture is the reason why the strains recoverable in Ti-Ni are so much larger than those in Cu-based shape-memory alloys in rolled, extruded and drawn specimens. Both these materials recover relatively small strains in sputter-deposited thin films due to unfavorable texture. Even the qual. behavior of combined tension-torsion can critically depend on the texture. The results are in good agreement with exptl. observations. Finally, textures are suggested for improved shape-memory effect.
Cited By
Abstract
Figure 1
Figure 1. Morphology of grain boundary and the corresponding micropillar in austenite phase. (a) Optical micrograph of CuAl24Mn9 grain boundary structure with the inset of SEM image for the morphology of the bicrystal pillar at GB ab initio FIB milling. (b) Intensity map of the surface by scanning white-beam synchrotron X-ray. (c) Orientation map of the surface normal by synchrotron Laue microdiffraction.
Figure 2
Figure 2. Nanomechanical behaviors and post-mortem images of CuAl24Mn9 4 μm-diameter pillars under cycling microcompression tests. (a) The single crystal pillar oriented along [101]gr1. (b) The bicrystal pillar at the GB. (c) The single crystal pillar oriented along [45 12]gr2. Their superelastic behaviors and the dissipation behaviors over stress-induced transformation cycles for CuAl24Mn9 [101]gr1, GB, and [4 5 12]gr2 pillars. Particularly, they are cyclic degradation of (d) superelastic strain. (e) Critical stress inducing phase transformation. (f) Area of hysteresis loop. (g) Recoverable strains.
Figure 3
Figure 3. Theoretical calculation of twinning microstructure in the bicrystal pillar at GB for (a) (3,6) variants of grain gr1 and (2,5) variants of grain gr2, (b) (4,5) variants of grain gr1 and (2,5) variants of grain gr2 and (c) (4,6) variants of grain gr1 and (4,5) variants of grain gr2. The light green color refers to the domain of austenite phase.
Figure 4
Figure 4. Contours of the Schmid factors for the twin laminates of (a) type II twin (4,6) variants in [101]gr1 orientation and (b) type I twin (4,5) variants in [4 5 12]gr2 orientation.
References
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- 13Chen, X.; Song, Y.; Tamura, N.; James, R. D. Determination of the stretch tensor for structural transformations. J. Mech. Phys. Solids 2016, 93, 34– 43, DOI: 10.1016/j.jmps.2016.02.009
- 14Cui, J.; Chu, Y. S.; Famodu, O. O.; Furuya, Y.; Hattrick-Simpers, J.; James, R. D.; Ludwig, A.; Thienhaus, S.; Wuttig, M.; Zhang, Z. Combinatorial search of thermoelastic shape-memory alloys with extremely small hysteresis width. Nat. Mater. 2006, 5, 286– 290, DOI: 10.1038/nmat1593[Crossref], [PubMed], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XjtVKmtbY%253D&md5=febf6cfd0125f27f07953e0dba6bb105Combinatorial search of thermoelastic shape-memory alloys with extremely small hysteresis widthCui, Jun; Chu, Yong S.; Famodu, Olugbenga O.; Furuya, Yasubumi; Hattrick-Simpers, Jae.; James, Richard D.; Ludwig, Alfred; Thienhaus, Sigurd; Wuttig, Manfred; Zhang, Zhiyong; Takeuchi, IchiroNature Materials (2006), 5 (4), 286-290CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Reversibility of structural phase transformations has profound technol. implications in a wide range of applications from fatigue life in shape-memory alloys to magnetism in multiferroic oxides. The geometric nonlinear theory of martensite universally applicable to all structural transitions has been developed. It predicts the reversibility of the transitions as manifested in the hysteresis behavior based solely on crystal symmetry and geometric compatibility between phases. Verification of the theory was done by using the high-throughput approach. The thin-film compn.-spread technique was devised to map the lattice parameters and thermal hysteresis of ternary alloy systems rapidly. A clear relationship between the hysteresis and middle eigenvalue of the transformation stretch tensor as predicted by the theory was obsd. A compn. region for titanium-rich Ti-Ni-Cu and Ti-Ni-Pd shape-memory alloys with potential for improved control of their properties was identified.
- 15Zhang, Z.; James, R. D.; Müller, S. Energy barriers and hysteresis in martensitic phase transformations. Acta Mater. 2009, 57, 4332– 4352, DOI: 10.1016/j.actamat.2009.05.034[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXpt1Cgsrs%253D&md5=88c2ca02f40f6012e371e66fe643d92aEnergy barriers and hysteresis in martensitic phase transformationsZhang, Zhiyong; James, Richard D.; Mueller, StefanActa Materialia (2009), 57 (15), 4332-4352CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Ltd.)The results from a systematic program of alloy development in the system Ti-Ni-X with X being Cu, Pt, Pd, Au, to pursue certain special lattice parameters that have been identified previously with low hysteresis. λ2 = 1 Was obsd. with λ2 being the middle eigenvalue of the transformation stretch matrix for alloys with X = Pt, Pd, Au. In all cases there is a sharp drop in the graph of hysteresis vs. compn. at the compn. where λ2 = 1 . When the size of the hysteresis is replotted vs. λ2, a universal graph for these alloys is obtained. Motivated by these exptl. results, a new theory is presented for the size of the hysteresis based on the growth from a small scale of fully developed austenite martensite needles. The energy of the transition layer plays a crit. role in this theory. Overall, the results point to a simple systematic method of achieving low hysteresis and high degree of reversibility in transforming alloys.
- 16Song, Y.; Chen, X.; Dabade, V.; Shield, T. W.; James, R. D. Enhanced reversibility and unusual microstructure of a phase-transforming material. Nature 2013, 502, 85– 88, DOI: 10.1038/nature12532[Crossref], [PubMed], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFGru73P&md5=3da0e7b4e1f9d8eb93907b092c9b79faEnhanced reversibility and unusual microstructure of a phase-transforming materialSong, Yintao; Chen, Xian; Dabade, Vivekanand; Shield, Thomas W.; James, Richard D.Nature (London, United Kingdom) (2013), 502 (7469), 85-88CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Materials undergoing reversible solid-to-solid martensitic phase transformations are desirable for applications in medical sensors and actuators, eco-friendly refrigerators, and energy conversion devices. The ability to pass back and forth through the phase transformation many times without degrdn. of properties (termed 'reversibility') is crit. for these applications. Materials tuned to satisfy a certain geometric compatibility condition were shown to exhibit high reversibility, measured by low hysteresis and small migration of transformation temp. under cycling. Recently, stronger compatibility conditions called the 'cofactor conditions' were proposed theor. to achieve even better reversibility. Here we report the enhanced reversibility and unusual microstructure of the first martensitic material, Zn45Au30Cu25, that closely satisfies the cofactor conditions. We observe four striking properties of this material. (1) Despite a transformation strain of 8%, the transformation temp. shifts <0.5° after >16,000 thermal cycles. For comparison, the transformation temp. of the ubiquitous NiTi alloy shifts up to 20° in the first 20 cycles. (2) The hysteresis remains approx. 2° during this cycling. For comparison, the hysteresis of the NiTi alloy is up to 70°. (3) The alloy exhibits an unusual riverine microstructure of martensite not seen in other martensites. (4) Unlike that of typical polycrystal martensites, its microstructure changes drastically in consecutive transformation cycles, whereas macroscopic properties such as transformation temp. and latent heat are nearly reproducible. These results promise a concrete strategy for seeking ultra-reliable martensitic materials.
- 17Chluba, C.; Ge, W.; Lima de Miranda, R.; Strobel, J.; Kienle, L.; Quandt, E.; Wuttig, M. Ultralow-fatigue shape memory alloy films. Science 2015, 348, 1004– 1007, DOI: 10.1126/science.1261164[Crossref], [PubMed], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXovVKltL8%253D&md5=2b360dcc562f5254f7499888ffa72b31Ultralow-fatigue shape memory alloy filmsChluba, Christoph; Ge, Wenwei; Lima de Miranda, Rodrigo; Strobel, Julian; Kienle, Lorenz; Quandt, Eckhard; Wuttig, ManfredScience (Washington, DC, United States) (2015), 348 (6238), 1004-1007CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Functional shape memory alloys need to operate reversibly and repeatedly. Quant. measures of reversibility include the relative vol. change of the participating phases and compatibility matrixes for twinning. But no similar argument is known for repeatability. This is esp. crucial for many future applications, such as artificial heart valves or elastocaloric cooling, in which \>10 million transformation cycles will be required. We report on the discovery of an ultralow-fatigue shape memory alloy film system based on TiNiCu that allows at least 10 million transformation cycles. We found that these films contain Ti2Cu ppts. embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle.
- 18Ni, X.; Greer, J. R.; Bhattacharya, K.; James, R. D.; Chen, X. Exceptional resilience of small-scale Au30Cu25Zn45 under cyclic stress-induced phase transformation. Nano Lett. 2016, 16, 7621– 7625, DOI: 10.1021/acs.nanolett.6b03555[ACS Full Text], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVSju7bL&md5=cfe6c2865c6d6b305b5089f997de7551Exceptional Resilience of Small-Scale Au30Cu25Zn45 under Cyclic Stress-Induced Phase TransformationNi, Xiaoyue; Greer, Julia R.; Bhattacharya, Kaushik; James, Richard D.; Chen, XianNano Letters (2016), 16 (12), 7621-7625CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Shape memory alloys that produce and recover from large deformation driven by martensitic transformation are widely exploited in biomedical devices and microactuators. Generally their actuation work degrades significantly within first a few cycles and is reduced at smaller dimensions. Further, alloys exhibiting unprecedented reversibility have relatively small superelastic strain, 0.7%. These raise the questions of whether high reversibility is necessarily accompanied by small work and strain and whether high work and strain is necessarily diminished at small scale. Here we conclusively demonstrate that these are not true by showing that Au30Cu25Zn45 pillars exhibit 12 MJ m-3 work and 3.5% superelastic strain even after 100000 phase transformation cycles. Our findings confirm that the lattice compatibility dominates the mech. behavior of phase-changing materials at nano to micron scales and points a way for smart microactuators design having the mutual benefits of high actuation work and long lifetime.
- 19Jetter, J.; Gu, H.; Zhang, H.; Wuttig, M.; Chen, X.; Greer, J. R.; James, R. D.; Quandt, E. Tuning crystallographic compatibility to enhance shape memory in ceramics. Phys. Rev. Mater. 2019, 3, 093603 DOI: 10.1103/PhysRevMaterials.3.093603[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXit1WjtL%252FF&md5=91d204e3e375b2d5e306c0da86bd6743Tuning crystallographic compatibility to enhance shape memory in ceramicsJetter, Justin; Gu, Hanlin; Zhang, Haolu; Wuttig, Manfred; Chen, Xian; Greer, Julia R.; James, Richard D.; Quandt, EckhardPhysical Review Materials (2019), 3 (9), 093603CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)The extraordinary ability of shape-memory alloys to recover after large imposed deformation motivates efforts to transpose these properties onto ceramics, which would enable practical shape-memory properties at high temps. and in harsh environments. The theory of mech. compatibility was utilized to predict promising ceramic candidates in the system (Y0.5Ta0.5O2)1-x-(Zr0.5Hf0.5O2)x, 0.6<x<0.85. When these compatibility conditions are met, a redn. in thermal hysteresis by a factor of 2.5, a tripling of deformability, and a 75% enhancement in strain recovery within the shape-memory effect was found. These findings reveal that predicting and optimizing the chem. compn. of ceramics to attain improved crystallog. compatibility is a powerful tool for enabling and enhancing their deformability that could ultimately lead to a highly reversible oxide ceramic shape-memory material.
- 20Pang, E. L.; McCandler, C. A.; Schuh, C. A. Reduced cracking in polycrystalline ZrO2-CeO2 shape-memory ceramics by meeting the cofactor conditions. Acta Mater. 2019, 177, 230– 239, DOI: 10.1016/j.actamat.2019.07.028[Crossref], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsFWitrzI&md5=3ad41b1d3f8309cf863d66bd96365b61Reduced cracking in polycrystalline ZrO2-CeO2 shape-memory ceramics by meeting the cofactor conditionsPang, Edward L.; McCandler, Caitlin A.; Schuh, Christopher A.Acta Materialia (2019), 177 (), 230-239CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Ltd.)Cracking is generally regarded as an unavoidable consequence of martensitic transformation in polycryst. ZrO2-based ceramics. This shortcoming has limited ZrO2-based shape-memory ceramics (SMCs) to micron-sized single- or oligo-crystals to reduce bulk transformation stresses. In this paper we explore an alternate approach to reduce transformation-induced cracking by manipulating the crystallog. phase compatibility in polycryst. ZrO2-CeO2 ceramics. For a range of compns. 12.5-15 mol% CeO2, we present lattice parameter measurements for the tetragonal and monoclinic phases from in situ X-ray diffraction, direct observation of lattice correspondences by electron backscatter diffraction, and calcns. of interface and bulk compatibility. We identify ZrO2-13.5 mol% CeO2 as having preferred interface compatibility in that it closely meets the crystallog. cofactor conditions. This compn. resists cracking through 10 thermal cycles, whereas other compns. all crack. These results suggest that interface compatibility may contribute more strongly to transformation-induced cracking in ZrO2-based SMCs than previously believed and opens a strategy for designing crack-resistant polycryst. SMCs.
- 21Yin, H.; He, Y.; Moumni, Z.; Sun, Q. Effects of grain size on tensile fatigue life of nanostructured NiTi shape memory alloy. Int. J. Fatigue 2016, 88, 166– 177, DOI: 10.1016/j.ijfatigue.2016.03.023[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xltlagt7k%253D&md5=6d7089819903968360addd8e2087ba25Effects of grain size on tensile fatigue life of nanostructured NiTi shape memory alloyYin, Hao; He, Yongjun; Moumni, Ziad; Sun, QingpingInternational Journal of Fatigue (2016), 88 (), 166-177CODEN: IJFADB; ISSN:0142-1123. (Elsevier Ltd.)The effects of grain size (GS) on tensile fatigue life of nanostructured NiTi superelastic shape memory alloys (SMAs) with GS = 10 nm, 42 nm and 80 nm are investigated. Macroscopic stress-controlled tensile fatigue tests, acoustic energy measurements and fracture surface observations were performed. It is shown that low-cycle fatigue life (under σmax = 450MPa) of nanostructured NiTi polycryst. SMA increases significantly when GS decreases from 80 nm to 10 nm. However, there is no significant effect of GS on the intermediate-cycle fatigue life (under σmax = 300MPa). It is found that accumulated acoustic energy can be used to distinguish the three stages of fatigue: slow crack propagation, fast crack propagation and final fracture. Micro cracks were found on fracture surfaces of all GS specimens under intermediate-cycle fatigue and on fracture surfaces of 10 nm GS specimen under low-cycle fatigue, while micro voids were found in 42 nm and 80 nm GS specimens under low-cycle fatigue. The results of the paper indicate that grain refinement down to nanoscale has potential in developing high fatigue resistance SMAs.
- 22Bhattacharya, K. In Microstructure of martensite: why it forms and how it gives rise to the shape-memory effect; Sutton, A. P., Rudd, R. E., Eds.; Oxford University Press, 2003; Vol. 2.
- 23Kabirifar, P.; Chu, K.; Ren, F.; Sun, Q. Effects of grain size on compressive behavior of NiTi polycrystalline superelastic macro-and micropillars. Mater. Lett. 2018, 214, 53– 55, DOI: 10.1016/j.matlet.2017.11.069[Crossref], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvV2qs73K&md5=5d8812d58acab3b6bc4c4f9555a6a3deEffects of grain size on compressive behavior of NiTi polycrystalline superelastic macro- and micropillarsKabirifar, Parham; Chu, Kangjie; Ren, Fuzeng; Sun, QingpingMaterials Letters (2018), 214 (), 53-55CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)Polycryst. NiTi pillars of 0.5 μm diam. and 1.5 μm height with av. grain sizes from 10 to 421 nm are fabricated by focused ion beam and compressed by nanoindentation. It is found that stress-strain hysteresis loop area, transformation stress and transformation strain vary non-monotonically with grain size. Anal. of the results reveals that increasing the grain size from 10 nm enhances the transformation by promoting the nucleation and growth of martensite domains. When the grain size approaches the pillar size, the transformation is suppressed by an increase in granular constraints and heterogeneity of internal stress-strain state among large grains.
- 24Hua, P.; Chu, K.; Ren, F.; Sun, Q. Cyclic phase transformation behavior of nanocrystalline NiTi at microscale. Acta Mater. 2020, 185, 507– 517, DOI: 10.1016/j.actamat.2019.12.019[Crossref], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjtlyjsw%253D%253D&md5=55a9da1e7c05a5a52931936d8871bdc2Cyclic phase transformation behavior of nanocrystalline NiTi at microscaleHua, Peng; Chu, Kangjie; Ren, Fuzeng; Sun, QingpingActa Materialia (2020), 185 (), 507-517CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Ltd.)Cuboidal micropillars of nanocryst. superelastic NiTi shape memory alloys with an av. grain size of 65 nm were fabricated by focused ion beam and then subjected to cyclic compression. It is found that the micropillars have maintained superelasticity for over 106 full-transformation cycles under a max. compressive stress of 1.2 GPa. Functional degrdn. of the micropillars mainly occurs in the first 104 cycles where hysteresis loop area and forward transformation stress rapidly decrease from initial 11 MPa (MJ/m3) and 586 MPa to 6 MPa and 271 MPa. In the 104 ∼ 106 cycles, stress-strain responses of the micropillars show asymptotic stabilization. Residual strain is accumulated to 3.3% and multiple ∼50 nm wide extrusions are found at the surface of the micropillars after 106 cycles. SEM and TEM studies indicate that cyclic phase transformation results in formation and glide of transformation-induced dislocations that create surface steps and the extrusions. The dislocations inhibit reverse transformation and result in residual martensite and residual stresses. The dislocations and the residual martensite lead to the functional degrdn. The role of the residual martensite in the functional degrdn. is further verified by 21% recovery of the residual strain and an increase of 278 MPa in the forward transformation stress after heating up the cyclically deformed micropillars to 100°C. The recorded over 106 phase transformation cycles under a max. stress of 1.2 GPa of the NiTi shape memory alloys at microscale open up new avenues for applications of the material in microscale devices and engineering.
- 25Funakubo, H.; Kennedy, J. Shape memory alloys; Gordon and Breach, 1987; xii– 275.
- 26Zárubová, N.; Novák, V. Phase stability of CuAlMn shape memory alloy. Mater. Sci. Eng., A 2004, 378, 216– 221, DOI: 10.1016/j.msea.2003.10.346[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXlsVeisbY%253D&md5=af7c94f945b19853bcc0f84dd854edddPhase stability of CuAlMn shape memory alloysZarubova, N.; Novak, V.Materials Science & Engineering, A: Structural Materials: Properties, Microstructure and Processing (2004), A378 (1-2), 216-221CODEN: MSAPE3; ISSN:0921-5093. (Elsevier Science B.V.)Thermoelastic martensitic transformations in single crystals of two CuAlMn shape memory alloys were investigated using tension/compression stress-strain tests, thermal cycling tests, stress recovery tests and calorimetric measurements. Pseudoelastic behavior was obsd. in the as-quenched samples stressed above the Af temp. Near the Ms temp., the stress-strain response changed and became pseudoplastic. A pronounced dependence of the thermoplastic behavior on the transformation history was found. The samples once subjected to tension/compression cycling at a temp. near or below Ms remained pseudoplastic during subsequent stress-strain expts. at higher temps., and a large increase of the Af temp. was obsd. This stabilization of martensite is similar to that obsd. on CuAlNi, and can be ascribed to the de-twinning of the martensitic phase and formation of a single variant of the γ1'-martensite.
- 27Sutou, Y.; Omori, T.; Kainuma, R.; Ishida, K.; Ono, N. Enhancement of superelasticity in Cu-Al-Mn-Ni shape-memory alloys by texture control. Metall. Mater. Trans. A 2002, 33, 2817– 2824, DOI: 10.1007/s11661-002-0267-2[Crossref], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xnt1emtbc%253D&md5=c6c5443b9410637ba687fd57de160f64Enhancement of superelasticity in Cu-Al-Mn-Ni shape-memory alloys by texture controlSutou, Y.; Omori, T.; Kainuma, R.; Ono, N.; Ishida, K.Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science (2002), 33A (9), 2817-2824CODEN: MMTAEB; ISSN:1073-5623. (Minerals, Metals & Materials Society)A significant improvement in the degree of superelasticity in Cu-Al-Mn ductile polycryst. alloys has been achieved through the addn. of Ni and control of the recrystn. texture by thermomech. processing, which contain annealing in the fcc (α) + bcc (β) two-phase region, followed by heavy cold redns. of over 60%. The addn. of Ni to the Cu-Al-Mn alloys shows a drastic effect on the formation of the strong {112}<110> recrystn. texture. Superelastic strains on the order of 7%, 3 times larger than those in other Cu-based shape-memory alloys, have been realized in the textured Cu-Al-Mn-Ni alloys. The superelastic strains obtainable in the textured Cu-based SMAs are on a par with those attainable in NiTi-based alloys.
- 28Fornell, J.; Tuncer, N.; Schuh, C. Orientation dependence in superelastic Cu-Al-Mn-Ni micropillars. J. Alloys Compd. 2017, 693, 1205– 1213, DOI: 10.1016/j.jallcom.2016.10.090[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCru7vL&md5=789540320b8ac605785348e8a27b7030Orientation dependence in superelastic Cu-Al-Mn-Ni micropillarsFornell, J.; Tuncer, N.; Schuh, C. A.Journal of Alloys and Compounds (2017), 693 (), 1205-1213CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)The superelastic behavior of single crystal Cu-Al-Mn-Ni shape memory alloy micro-pillars was studied under compression as a function of crystallog. orientation. Cylindrical pillars of about 2 μm diam. were micro-machined from targeted crystal orientations. While pillars oriented close to the [001] direction showed the largest total transformation strain (∼7%), plastic deformation dominated the compressive response in the pillars milled close to the [111] direction due to their high elastic anisotropy combined with the large stresses required to induce the transformation. Shape strain contour plots were constructed for γ' and β' martensites, and the martensite start stress was calcd. using the Clausius-Clapeyron equation. The same general trends are obsd. in both the exptl. and calcd. results, with some exceptions: larger transformation stresses and lower transformation strains are obsd. in the microsized pillars.
- 29Karami, M.; Tamura, N.; Yang, Y.; Chen, X. Derived crystal structure of martensitic materials by solid–solid phase transformation. Acta Crystallogr., Sect. A: Found. Adv. 2020, 76, 521– 533, DOI: 10.1107/S2053273320006087[Crossref], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht12itbfL&md5=2abff5ac82cd07bc80ba5c9e92d4ff7bDerived crystal structure of martensitic materials by solid-solid phase transformationKarami, Mostafa; Tamura, Nobumichi; Yang, Yong; Chen, XianActa Crystallographica, Section A: Foundations and Advances (2020), 76 (4), 521-533CODEN: ACSAD7; ISSN:2053-2733. (International Union of Crystallography)A math. description of crystal structure is proposed consisting of two parts: the underlying translational periodicity and the distinct at. positions up to the symmetry operations in the unit cell, consistent with the International Tables for Crystallog. By the Cauchy-Born hypothesis, such a description can be integrated with the theory of continuum mechanics to calc. a derived crystal structure produced by solid-solid phase transformation. In addn., the expressions for the orientation relationship between the parent lattice and the derived lattice are generalized. The derived structure rationalizes the lattice parameters and the general equiv. at. positions that assist the indexing process of X-ray diffraction anal. for low-symmetry martensitic materials undergoing phase transformation. The anal. is demonstrated in a CuAlMn shape memory alloy. From its austenite phase (L21 face-centered cubic structure), it is identified that the derived martensitic structure has orthorhombic symmetry Pmmn with the derived lattice parameters ad = 4.36491, bd = 5.40865 and cd = 4.2402 Å, by which the complicated X-ray Laue diffraction pattern can be well indexed, and the orientation relationship can be verified.
- 30Chen, X.; Dejoie, C.; Jiang, T.; Ku, C.-S.; Tamura, N. Quantitative microstructural imaging by scanning Laue x-ray micro-and nanodiffraction. MRS Bull. 2016, 41, 445– 453, DOI: 10.1557/mrs.2016.97[Crossref], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XptlOns7o%253D&md5=3c9e42504fe78eb9c560dbf74119e128Quantitative microstructural imaging by scanning Laue x-ray micro- and nanodiffractionChen, Xian; Dejoie, Catherine; Jiang, Tengfei; Ku, Ching-Shun; Tamura, NobumichiMRS Bulletin (2016), 41 (6), 445-453CODEN: MRSBEA; ISSN:0883-7694. (Cambridge University Press)Local crystal structure, crystal orientation, and crystal deformation can all be probed by Laue diffraction using a submicron x-ray beam. This technique, employed at a synchrotron facility, is particularly suitable for fast mapping the mech. and microstructural properties of inhomogeneous multiphase polycryst. samples, as well as imperfect epitaxial films or crystals. As synchrotron Laue x-ray microdiffraction enters its 20th year of existence and new synchrotron nanoprobe facilities are being built and commissioned around the world, we take the opportunity to overview current capabilities as well as the latest tech. developments. Fast data collection provided by state-of-the-art area detectors and fully automated pattern indexing algorithms optimized for speed make it possible to map large portions of a sample with fine step size and obtain quant. images of its microstructure in near real time. We extrapolate how the technique is anticipated to evolve in the near future and its potential emerging applications at a free-electron laser facility.
- 31Otsuka, K.; Ohba, T.; Tokonami, M.; Wayman, C.M. New description of long period stacking order structures of martenites in β-phase alloys. Scr. Metall. Mater. 1993, 29, 1359– 1364, DOI: 10.1016/0956-716X(93)90139-J[Crossref], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXmtlWmsbc%253D&md5=4184bde19e240f653e06dc6850411a8aNew description of long period stacking order structures of martensites in β-phase alloysOtsuka, K.; Ohba, T.; Tokonami, M.; Wayman, C. M.Scripta Metallurgica et Materialia (1993), 29 (10), 1359-64CODEN: SCRMEX; ISSN:0956-716X.New unit cells and nomenclature are proposed to describe the long-period stacking order structures of martensites in β-phase alloys. The use of the new unit cells eliminates the long period.
- 32Chakravorty, S.; Wayman, C. Electron microscopy of internally faulted Cu-Zn-Al martensite. Acta Metall. 1977, 25, 989– 1000, DOI: 10.1016/0001-6160(77)90127-4[Crossref], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1cXktFSgsbc%253D&md5=5bc405b7394eb436a79d72f455956e5aElectron microscopy of internally faulted copper-zinc-aluminum martensiteChakravorty, S.; Wayman, C. M.Acta Metallurgica (1977), 25 (9), 989-1000CODEN: AMETAR; ISSN:0001-6160.A large no. of alloys show the shape memory effect. There is evidence that internally faulted (untwinned) martensites (e.g. CuAl and CuZnAl) show this effect. A Cu68Zn15Al17 alloy [66704-23-2] was studied, whose stoichiometry is between that of the DO3 (Fe3Al) structure and the Heusler (Cu2MnAl) structure. Ingots were betatized 2 h at 875° and quenched into iced 10% NaOH soln. A microscopic examn. was made to det. the crystal structure of the matrix (β' parent) and β'1 martensite phases. A dislocation model for the parent-martensite interface was examd. exptl. to explain the thermoelastic (glissile) nature of the transformation from a DO3 parent to an 18R martensite. The matrix phase structure of the alloy was DO3 with a = 5.996Å. The matensite structure was M1,R (modified 1,R, monoclinic) with β = 87.5°, a = 4.553Å, b = 5.452Å, and c = 3,.977Å. The 18 layer martensite structure forms as a result of periodic shifts on the martensite basal plane in the [100]18R direction. Ordered dislocations on every 3rd (001) plane were not obsd., but random dislocations caused by extra faults were obsd. having a Burgers vector of [100]βh1.
- 33Liu, J.-L.; Huang, H.-Y.; Xie, J.-X. The roles of grain orientation and grain boundary characteristics in the enhanced superelasticity of Cu71.8Al17.8Mn10.4 shape memory alloys. Mater. Eng. 2014, 64, 427– 433, DOI: 10.1016/j.matdes.2014.07.070
- 34Dutkiewicz, J.; Kato, H.; Miura, S.; Messerschmidt, U.; Bartsch, M. Structure changes during pseudoelastic deformation of CuAlMn single crystals. Acta Mater. 1996, 44, 4597– 4609, DOI: 10.1016/1359-6454(96)00086-9[Crossref], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsFeksbo%253D&md5=8cf6f1f9fc053d400b9d5860120bd98eStructure changes during pseudoelastic deformation of CuAlMn single crystalsDutkiewicz, J.; Kato, H.; Miura, S.; Messerschmidt, U.; Bartsch, M.Acta Materialia (1996), 44 (11), 4597-4609CODEN: ACMAFD; ISSN:1359-6454. (Elsevier)Structure changes during pseudoelastic deformation of CuAlMn single crystals were investigated using in situ optical and high-voltage electron microscopy (HVEM). Several crystal orientations were investigated, from an irrational to 〈100〉 and 〈100〉 tensile axis and plane orientations in the case of thin foils. The compn. of the alloy was chosen such as to obtain superelastic behavior at room temp. Optical microstructures allowed to identify parallel plates at the beginning of the stress plateau, the no. of which increased with strain. The stress/temp. phase diagram was established within the range of existence of γ'1 and β"1. During in situ HVEM deformation in the 〈100〉 direction of γ'1 plates nucleated on pre-existing ones. At later deformation stages 18R martensite was formed in stacks of narrow needles. The following crystallog. relationship was obsd.: [001]β1||[010]β'1, γ'1 and [110]β1||[001]β'1, γ'1. A small permanent deformation obsd. after stress release was connected with the presence of residual martensite of a high random stacking fault d. and consisting often of α'1, γ'1 and β'1 martensite layers. During deformation in the 〈100〉 direction a larger permanent deformation and a d. of dislocation was obsd.
- 35Gómez-Cortés, J. F.; Nó, M. L.; López-Ferreño, I. n.; Hernández-Saz, J.; Molina, S. I.; Chuvilin, A.; San Juan, J. M. Size effect and scaling power-law for superelasticity in shape-memory alloys at the nanoscale. Nat. Nanotechnol. 2017, 12, 790– 797, DOI: 10.1038/nnano.2017.91[Crossref], [PubMed], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXovVGru7Y%253D&md5=8561576c4c541aa1f87ab510b6994428Size effect and scaling power-law for superelasticity in shape-memory alloys at the nanoscaleGomez-Cortes, Jose F.; No, Maria L.; Lopez-Ferreno, Inaki; Hernandez-Saz, Jesus; Molina, Sergio I.; Chuvilin, Andrey; San Juan, Jose M.Nature Nanotechnology (2017), 12 (8), 790-796CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Shape-memory alloys capable of a superelastic stress-induced phase transformation and a high displacement actuation have promise for applications in micro-electromech. systems for wearable health care and flexible electronic technologies. However, some of the fundamental aspects of their nanoscale behavior remain unclear, including the question of whether the crit. stress for the stress-induced martensitic transformation exhibits a size effect similar to that obsd. in confined plasticity. Here we provide evidence of a strong size effect on the crit. stress that induces such a transformation with a threefold increase in the trigger stress in pillars milled on [001] L21 single crystals from a Cu-Al-Ni shape-memory alloy from 2 μm to 260 nm in diam. A power-law size dependence of n = -2 is obsd. for the nanoscale superelasticity. Our observation is supported by the at. lattice shearing and an elastic model for homogeneous martensite nucleation.
- 36Bhattacharya, K.; Kohn, R. V. Symmetry, texture and the recoverable strain of shape-memory polycrystals. Acta Mater. 1996, 44, 529– 542, DOI: 10.1016/1359-6454(95)00198-0[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xls1Shtw%253D%253D&md5=c01b990b87164d5ce20a6d4022139fc7Symmetry, texture and the recoverable strain of shape-memory polycrystalsBhattacharya, K.; Kohn, R. V.Acta Materialia (1996), 44 (2), 529-42CODEN: ACMAFD; ISSN:1359-6454. (Elsevier)Shape-memory behavior is the ability of certain materials to recover, on heating, apparently plastic deformation sustained below a crit. temp. Some materials have good shape-memory behavior as single crystals but little or none as polycrystals, while others display good shape-memory behavior even as polycrystals. In this paper, we propose a theor. explanation for this difference: we show that the recoverable strain in a polycrystal depends on the texture of the polycrystal, the transformation strain of the underlying martensitic transformation and esp. critically on the change of symmetry during the underlying transformation. Roughly, we find that the greater the change in symmetry during transformation, the greater the recoverable strain. We include an extensive survey of the exptl. literature and show that our results agree with these observations. We make recommendations for improved shape-memory effect in polycrystals.
- 37Shu, Y.; Bhattacharya, K. The influence of texture on the shape-memory effect in polycrystals. Acta Mater. 1998, 46, 5457– 5473, DOI: 10.1016/S1359-6454(98)00184-0[Crossref], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXmsFWqtL4%253D&md5=7c7095d05ce5598f74d1092f870f3b58The influence of texture on the shape-memory effect in polycrystalsShu, Y. C.; Bhattacharya, K.Acta Materialia (1998), 46 (15), 5457-5473CODEN: ACMAFD; ISSN:1359-6454. (Elsevier Science Ltd.)A model is developed to show that texture is a crucial factor in detg. the shape-memory effect in polycrystals. Texture is the reason why the strains recoverable in Ti-Ni are so much larger than those in Cu-based shape-memory alloys in rolled, extruded and drawn specimens. Both these materials recover relatively small strains in sputter-deposited thin films due to unfavorable texture. Even the qual. behavior of combined tension-torsion can critically depend on the texture. The results are in good agreement with exptl. observations. Finally, textures are suggested for improved shape-memory effect.
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