The sliding wear behaviour of CoCrFeMnNi and AlxCoCrFeNi high entropy alloys at elevated temperatures

High entropy alloys (HEAs) show promise as materials for structural applications, even at elevated temperatures. However, their wear behaviour over a wide range of temperatures has not been extensively studied. CoCrFeMnNi and AlxCoCrFeNi HEAs were subjected to pin-on-disc dry sliding wear at temperatures between 25 degrees C and 900 degrees C against an alumina ball, and the tribological performance benchmarked against AISI 304 and Inconel 718. A detailed characterisation of the wear tracks using electron microscopy and surface profilometry revealed a transition in wear mechanism from abrasive wear at room-temperature to oxidative and delamination wear above 600 degrees C. The wear performance of the HEAs, AlCoCrFeNi in particular, is substantially enhanced with increasing temperature, surpassing that of Inconel 718 at 900 degrees C. The enhanced wear performance of the HEAs above 600 degrees C is attributed to the formation of a compact oxide scale in the contact region, and relative subsurface strengthening in the form of a fine-grained recrystallised structure containing precipitation hardening phases.