A comparison of the dry sliding wear of single-phase f.c.c. carbon-doped Fe40.4Ni11.3Mn34.8Al7.5Cr6 and CoCrFeMnNi high entropy alloys with 316 stainless steel

The dry sliding wear behaviors of the face-centred cubic (f.c.c.) high entropy alloys carbon-doped Fe40.4Ni11.3Mn34.8Al7.5Cr6 and equiatomic CoCrFeMnNi were determined under ambient conditions and compared with that of 316 stainless steel at two sliding velocities and in argon at a slow sliding velocity. Scanning electron microscopy, energy dispersive X-ray spectrometry, electron backscattered diffraction, X-ray photoelectron spectroscopy, and atom probe tomography analyses were employed to characterize the worn microstructures. It was found that in air at the slow sliding velocity of 0.1 m/s C-doped FeNiMnAlCr exhibited a much lower wear rate of 3.0 x 10(-5) mm(3)/N/m compared to either 316 stainless steel (2.9 x 10(-4) mm(3)/N/m) or CoCrFeMnNi (3.4 x 10(-4) mm(3)/N/m). In contrast, both in argon at this slow sliding velocity and in air at the high sliding velocity of 1.0 m/s, all three material showed similar wear rates of similar to (2.4 +/- 0.6) x 10(-5) mm(3)/N/m and similar to (1.2 +/- 0.3) x 10(-5) mm(3)/N/m, respectively, indicating the strong effect of the environment and pin tip temperature on the wear rates. The oxide that formed on the C-doped FeNiMnAlCr alloy was found to be more stable and durable than that on either the CoCrFeMnNi or on the 316 stainless steel, and the wear debris from C-doped FeNiMnAlCr had the smallest diameter (3 mu m) and the lowest oxygen content of 39 at. %. Greater Al2O3 and less Fe2O3, MnOx or Cr2O3 on the worn surface of C-doped FeNiMnAlCr contributed to a peeled-off or delaminated morphology with a higher oxygen content of 46 at. % compared to the worn surfaces of the 316 stainless steel and the CoCrFeMnNi, which both exhibited grooved worn surfaces with lateral cracks and lower oxygen contents of 7.5 at. % and 31 at. %, respectively. The harder Al2O3 oxide film was stable and adherent during wear testing and helped protect the worn pin's tip, which was the reason for the increased wear resistance of the C-doped FeNiMnAlCr. The wear protection mechanism of 316 stainless steel was attributed to a hard mechanically deformed layer, while the CoCrFeMnNi lacked protection from either the oxide film or a hard deformed layer.