The effect of phase constituents on the low and high stress abrasive wear behaviour of high entropy alloys

The tribological properties of high-entropy alloys (HEAs) have been extensively studied in recent times but majority of the investigations have been limited to sliding wear behaviour and 2-body abrasive wear. There has been limited research on the three-body abrasive wear behaviour across different stress regimes. In this study, HEAs with different microstructures (FCC, FCC + secondary phases and BCC) were fabricated by systematic addition of Al, Ti and Mo to an FCC phase CoCrFeNi HEA and subjected to three-body abrasion. The abrasion resistance of different HEAs under low and high stress abrasion were measured using ASTM G65 and B611 methods, respectively. Under low stress, abrasion resistance increased with hardness for dual phase HEAs and BCC HEAs. Interestingly, the abrasion resistance of single phase FCC HEAs was comparable to the much harder dual phase HEAs. This was attributed to the formation of work-hardened sub-surface layer in the FCC alloys and a ploughing dominated wear mechanism on the surface. Further, the severe plastic deformation under high stress abrasion in the FCC HEAs resulted in the formation of a sub-surface layer with a nano-crystalline structure with high hardness. However, the dual phase HEA with 13 at.% Al showed the lowest wear loss under high stress abrasion due to the combined effect of hardness provided by the BCC phase and the ability of FCC phase to undergo work-hardening and accommodate plastic deformation.