There has been substantial and growing interest in high-entropy alloys (HEAs), which were originally defined as multicomponent alloys containing a minimum of five metallic elements with amounts in the range 5-35 at. %. Because some HEAs have shown excellent mechanical properties, there have been a number of wear studies performed on either bulk HEAs or HEA coatings at room temperature at fixed sliding velocities and fixed load to determine their wear resistance, and in a few instances HEAs with outstanding wear resistance have been identified. However, there have been no studies of the cryogenic wear behavior of HEAs - and few of metallic materials in general. This project will determine the cryogenic wear behavior of two HEAs that that have recently been shown to have excellent mechanical properties at 77 K, viz., equi-atomic CoCrFeMnNi and carbon-doped Fe40.4Ni11.3Mn34.8Al7.5Cr6 (at. %).
The work will involve extensive microstructural characterization of the pre- and post-wear specimens by transmission electron microscopy, including X-ray dispersive spectroscopy; computed-assisted profilometry; X-ray diffraction; nanoindentation; cross-sectional scanning electron microscopy, atom probe tomography; X-ray mapping in a scanning transmission electron microscope; and X-ray photoelectron spectroscopy.
The aim to examine the hypotheses that equi-atomic CoCrFeMnNi and carbon-doped Fe40.4Ni11.3Mn34.8Al7.5Cr6 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.