Surface degradation mechanisms in a eutectic high entropy alloy at microstructural length-scales and correlation with phase-specific work function

High entropy alloys represent a new paradigm of structural alloy design consisting of (near) equal proportions of constituent elements resulting in a number of attractive properties. In particular, eutectic high entropy alloys offer a remarkable combination of high strength and good ductility from the synergistic contribution of each phase in the eutectic, thereby circumventing the strength-ductility trade-off in conventional structural materials. In the present study, wear and corrosion behavior were evaluated for the AlCoCrFeNi2.1 eutectic high entropy alloy consisting of BCC (B2), and FCC (L12) lamellae. A transition from adhesive to oxidative wear was observed in reciprocating wear analysis. The L12 phase with lower hardness preferentially deformed during the wear test. The ratio of hardness to modulus was almost two times higher for the B2 phase as compared to L12. The overall corrosion resistance of the eutectic high entropy alloy was comparable to 304 stainless steel in 3.5 wt% NaCl solution. However, detailed microscopy revealed preferential dissolution of the B2 phase. Phase-specific scanning kelvin probe analysis showed relatively higher electropositivity for the B2 phase as compared with L12, supporting the selective corrosion and higher coefficient of friction of B2.