Dr. Xun-Li Wang

Group Leader, Powder Diffraction Group
Lead Instrument Scientists
Engineering Materials Diffreactometer (VULCAN), SNS
http://neutrons.ornl.gov/instrument_systems/beamline_07_vulcan/contact.shtml

Education

• PhD in Solid State Physics, Iowa State University

Description of Research

Dr. Wang’s research encompasses mechanical properties, phase transformation, and magnetism in advanced materials. Although neutron scattering is his primary research tool, he also uses other characterization techniques through collaborations.

In the area of mechanical properties, Dr. Wang has extensive experience in residual stress determination in engineering materials [1]. His early work on welding residual stresses was awarded the A. F. David Medal from the American Welding Society. Recently, in collaboration with Dr. Zhili Feng of ORNL’s Welding Group, he has been experimenting with in situ measurements of transient behaviors during welding. They demonstrated an in situ neutron diffraction experiment with a specially built portable friction stir welding machine [2]. For the first time, the transient thermal stress, temperature, and dynamic recrystallization were experimentally determined in situ during friction stir welding, a solid state joining and material processing technology based on a very high-strain rate and extreme material flow/deformation. 

In addition to residual stress determination, Dr. Wang is also interested in a fundamental understanding of deformation behaviors. In his early career, he carried out an extensive study of residual stresses and their effect on phase transformation in Al²O³-ZrO² ceramic composites [3]. Dr. Wang’s group was one of the first to report the development of intergranular stress due to cyclic loading [4]. Recently his group has been conducting research on deformation at small length scales [5].

The structure and phase transformation in metallic glasses is another area of research. The atomic structure of metallic glasses has been a long-standing scientific mystery. A recent contribution from Dr. Wang’s group shows that in metallic glasses, the fundamental building blocks¾solute centered clusters¾are connected in a fractal network [6]. Upon annealing, crystallization takes place, leading to a novel microstructure with an unusually high density of nanoscale crystalline particles. By employing simultaneous measurements of diffraction and small angle scattering, Wang et al. demonstrated that crystallization in metallic glasses proceeds by nanoscale phase separation [7]. Furthermore, Dr. Wang and his collaborators showed that the nanoscale crystalline particles have a characteristic core-shell structure [8].

In the area of magnetism, Dr. Wang’s work has included high-Tc superconductors [9] and a molecular magnet [10]. He also contributed to fundamental understanding of softening in intermetallic alloys due to magnetic interaction [11].

In neutron instrumentation, Dr. Wang has made a major contribution to understanding the source of errors and potential pitfalls in strain measurements [12-13]. As lead instrument scientist for VULCAN, a state-of-the-art engineering diffractometer at the SNS [14], he is responsible for the overall design and construction efforts. The instrument features an innovative focusing neutron guide system [15]. He is also a co-author of IDEAS – Instrument Development and Experimental Design Suite – a general computer program for simulation of neutron scattering instruments [16].

Selected Publications

Residual Stress and Deformation Behaviors

1. X.-L. Wang, “Application of neutron diffraction to engineering problems,” JOM, March, 53-58, 2006.
   
   
2. W. Woo, Z. Feng, X-L. Wang, D. W. Brown, B. Calusen, K. An, H. Choo, C. Hubbard, and S. A. David, “In-situ neutron diffraction measurements of temperature and stresses during friction stir welding of 6061-T6 aluminum alloy,” Sci. Tech. Welding & Joining, 12, 298-303 (2007).
   
   
3. X.-L. Wang, C. R. Hubbard, K. B. Alexander, P. F. Becher, J. A. Fernandez-Baca, and S. Spooner, "Neutron Diffraction Measurements of the Residual Stresses in Al₂O₃-ZrO₂ Ceramic Composites," J. Amer. Ceram. Soc., 77, 1569-1575 (1994).
   
   
4. Y.D. Wang, H. Tian, A. D. Stoica, X.-L. Wang, P. K. Liaw, and J.W. Richardson, “Development of Large Grain-Orientation-Dependent Residual Stresses in a Cyclically-Deformed Alloy,” Nature Materials, 2, 103-106 (2003).
   
   
5. S. Cheng, A.D. Stoica, X.-L. Wang, G.Y. Wang, H. Choo, and P.K. Liaw, “Fracture of Ni with Grain Size from Nanocrystalline to Ultrafine Scale under Cyclic Loading,” Scripta Mat. 57, 217-220 (2007).

   Metallic Glasses

6. D. Ma, A. D. Stoica, and X.-L. Wang, “Power-law scaling and fractal nature of the medium range order in metallic glasses,” Nature Mat. (accepted)
   
   
7. L. Yang, M. K. Miller, X.-L. Wang, C. T. Liu, A. D. Stoica, D. Ma, J. Almer, and D. Shi, “Nanoscale solute partitioning in devitrified bulk metallic glass,” Adv. Mat. (in press)
   
   
8. X.-L. Wang, J. Almer, Y. D. Wang, J. K. Zhao, C. T. Liu, A. D. Stoica, D R. Haeffner, and W. H. Wang, “In-situ Synchrotron Study of Phase Transformation Behaviors in Bulk Metallic Glass Using Simultaneous X-ray Diffraction and Small Angle Scattering,” Phys. Rev. Lett. 91, 265501 (2003).

   Magnetism

9. X. L. Wang, C. Stassis, D. C. Johnston, T. C. Leung, J. Ye, B. N. Harmon, G. H. Lander, A. J. Schultz, C.-K. Loong, and J. M. Honig, "Neutron Diffraction Study of the Antiferromagnetic Form Factor of La₂NiO₄," Phys. Rev. B 45, 5645 (1992).
   
   
10. Z. Wang, X.-L. Wang, J. A. Fernandez-Baca, D. C. Johnston, and D. Vaknin, "Antiferromagnetic Ordering and Paramagnetic Behavior of Ferromagnetic Clusters in BaCuO_2+x," Science, 264, 402-404 (1994)
    
    
11. C. T. Liu, C. L. Fu, M. F. Chrisholm, and J. R. Thompson, Krcmar, and X.-L. Wang, “Magnetism and solid solution effects in NiAl (40%Al) alloys,” Prog. Mat. Sci. 52, 352-370, 2007.

    Neutron Instrumentation

12. S. Spooner and X.-L. Wang, “Diffraction Peak Displacement in Residual Stress Samples due to Partial Burial of the Sampling Volume,” J. Appl. Cryst., 30, 449-455 (1997).
    
    
13. X.-L. Wang, Y. D. Wang, and J. W. Richardson, "Experimental Error due to Displacement of Sample in Time-of-flight Diffractometry," J. Appl. Cryst., 35, 533-537 (2002)
    
    
14. X.-L. Wang, T. M. Holden, G. Q. Rennich, A. D. Stoica, P. K. Liaw, H. Choo, and C. R. Hubbard, “VULCAN – The Engineering Diffractometer at the SNS,” Physica B, 385-386, 673-675 (2006).
    
    
15. X.-L. Wang and A. D. Stoica, “Focusing neutron guides for VULCAN – Design Aspects, Estimated Performance, and Detector Deployment,” submitted to Nuc. Inst. Meth. (in press).
    
    
16. W.-T. Lee and X.-L. Wang, "IDEAS, a General-purpose Computer Program for Simulation of Neutron Scattering Instruments," Neutron News, 13 (No. 4), 30-34 (2002).

Contact Information

Dr. Xun-Li Wang
Neutron Scattering Science Division
Building 8600
Oak Ridge National Laboratory
P.O. Box 2008 MS-6475
Oak Ridge, TN 37831-6475

Telephone: 865.574.9164
Fax: 865.574.6080
E-mail: wangxl@ornl.gov

Dr. Xun-Li Wang is a senior scientist and group leader of the Powder Diffraction Group in the Neutron Scattering Science Division, Oak Ridge National Laboratory. He received his PhD from Iowa State University and B.S. from Beijing University, both in Physics. The Powder Diffraction Group has six instruments at the Spallation Neutron Source and the High Flux Isotope Reactor, two facilities which are world leaders in neutron science.

As an individual scientist, Dr. Wang uses neutron scattering as a primary research tool and his research topics encompass mechanical properties, phase transformation, and magnetism in advanced materials. He has published more than 100 papers, some of which have appeared in such prestigious journals as Science, Nature Materials, Advanced Materials, and Physical Review Letters.