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Energy Technology Division Tribology | |
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Coating Process DevelopmentProjects in this area are aimed at exploring the factors that control the tribological properties of surfaces given surface-modifying treatments such as ion-beam-assisted deposition (IBAD), ion beam deposition, microwave and plasma-assisted chemical vapor deposition, and plasma-sputter deposition. The major emphasis is on developing low-friction, highly wear-resistant surfaces that can endure extreme tribological conditions due to high loads, speeds, and temperatures. We have developed a variety of low-friction, wear-resistant coatings and deposited them on metals, ceramics, and polymers intended for utilization in components for low-heat-rejection diesels and other high-temperature advanced engines and engine power trains. Specific examples include the development and testing of diamondlike carbon coatings (DLCs) on polymers and ceramic parts under conditions of high loads, speeds, and temperatures; development of smooth, nanocrystalline diamond films on ceramics for machining and sliding wear applications; development of naturally occurring lubricious-oxide layers on superalloys for gas turbine applications at temperatures to 1000ºC; development of wear-resistant boride layers on steels and other alloys. We are continuing efforts on the development of DLC films (which we now call NFC) that exhibit extremely low friction coefficients (<0.001) under dry sliding conditions. Response from industry on the NFC coatings continues, and we currently have collaborations with CemeCon to commercialize the process. More recently, we have initiated efforts to develop superhard nanocomposite coatings in collaboration with the Istanbul Technical University. These coatings have chemical and mechanical properties that make them extremely attractive for engine applications. Our coating processing research focuses on two broad deposition techniques: development of low-friction and low-wear surfaces by a variety of surface-modification methods, including physical-vapor-deposition (PVD) techniques, and development of ultrahard, low-friction diamond, diamondlike, and other similar coatings by plasma-assisted chemical vapor deposition (PACVD). Chemical Vapor Deposition CoatingsOver the past 36 months, the Section’s coating development effort has focused primarily on the use of PACVD to deposit NFC coatings. The Section has two facilities for deposition of these coatings: a PACVD unit and a microwave PACVD unit. The microwave PACVD system was procured for the study and development of polycrystalline diamond films. While the microwave plasma deposition source allows production of diamond, NFC, and similar ultrahard coatings on ceramics and other high-temperature materials, the main thrust of the R&D on this system is production of smooth, adherent crystalline diamond films that serve as lubricious, wear-resistant coatings without causing severe wear of mating components. The plasma-sputtering system was designed as a PVD system, but is now being used in a PACVD mode using an RF-etch capability. This system consists of a 0.6-m-diameter vacuum vessel set up for diode (RF-diode, RF-magnetron, or DC-magnetron) sputter deposition from three target locations. This system is being utilized because, in general, PACVD can be scaled up much more readily to handle large quantities of parts than can IBAD or microwave-assisted CVD, where the technology is not as mature. Recent R&D efforts on this system have shown that very high-quality NFC films can be achieved, and that the tribological properties can be effectively tuned and optimized for particular conditions by controlling the gas chemistry. Physical Vapor Deposition CoatingsWhen the Tribology Section was established almost 20 years ago, its primary focus was on generic long-term research on advanced surface modification processes to improve the friction and wear performance of materials used in energy-intensive sectors such as transportation. The coating research originally focused on PVD processes with major emphasis on IBAD. This facility consists of a large, ultrahigh-vacuum chamber with two individually controlled electron-beam evaporation sources and simultaneous or sequential ion sources that produce ions with energies from a few eV up to 1500 eV. Materials that can be evaporated include Ag, Al, B, Ba, Ca, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Pt, Sn, Ti, and Zn, either singly or in combination. Various types of specimen holders enable rotational motion, ensuring uniformity in the coating. Parts as large as engine pistons can be coated. In addition, the Section has a three-target sputtering apparatus for the deposition of multilayer coatings comprising Si, Au, B, C, Al, Ti, Cr, Fe, Ni, Cu, Mo, Ag, W, Pt, or Al2O3. An ultrahigh-vacuum apparatus for depositing fullerene compounds as tribological coatings has been built, as has an apparatus for exposing test specimens to fuels and solvents.
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