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Cryogenic wear of novel high-entropy alloys

This project explores the complex interactions between materials (two novel high entropy alloys CoCrFeMnNi and carbon-doped FeNiMnAlCr, and stainless steel), temperature, sliding velocity and testing environment during dry sliding wear at room and cryogenic temperatures. Wear is the major determinant of durability of mechanical components, and therefore it has significant economic ramifications throughout industry, particularly in the energy, manufacturing, medical and transportation sectors. The task of designing tribological components to resist wear is becoming even more difficult as the components have to face higher operating speeds and more difficult operating environments. The information gained by the proposed research will assist engineers in this important task. The results will be published in refereed journals and presented at conferences. The projectwill lead totraining of a Ph.D. student and several undergraduates. 

The aim of this project is to examine the hypotheses that the high entropy alloys (HEAs) CoCrFeMnNi and carbon-doped Fe40.4Ni11.3Mn34.8Al7.5Cr6, because of their superior yield strengths compared to stainless steel, will show better wear resistance than stainless steel at 77 K, that that the contacting surfaces of the two alloys will be resistant to phase transformations during dry sliding wear at either room temperature or 77 K, and that the worn surfaces will not exhibit ferromagnetism, whereas austenitic stainless steel AISI 316 will exhibit both of these problems. Dry sliding pin-on-disk wear tests will be performed at both 77 K and 293 K at different sliding velocities and in different environments, i.e. dry air, argon, on these two HEAs and compared to the behavior of 316 stainless steel. We will determine the relationship between the microstructure, deformation processes (including material transfer), phase transformations, friction and wear behavior, including the role played by third bodies (wear debris) on the wear process. A key issue is the role of sliding velocity. Dry sliding friction at higher sliding velocities results in higher temperatures that can soften the material being worn, enabling compaction of wear debris onto the worn surface to form a protective tribolayer, thus reducing wear rates. Higher sliding velocities also produce plastic deformation at higher shear rates that can work harden the material or induce a phase transformation. We will determine which of these effects will dominate. Microstructural characterization of the pre- and post-wear specimens will include transmission electron microscopy, including X-ray dispersive spectroscopy; computed-assisted profilometry; X-ray diffraction; nanoindentation; cross-sectional scanning electron microscopy, atom probe tomography; and X-ray photoelectron spectroscopy.

Funded by the U.S. National Science Foundation.

Faculty contact: Ian Baker