Small-scale mechanical behavior of a eutectic high entropy alloy

Eutectic high entropy alloys, with lamellar arrangement of solid solution phases, represent a new paradigm for simultaneously achieving high strength and ductility, thereby circumventing this well-known trade-off in conventional alloys. However, dynamic strengthening mechanisms and phaseboundary interactions during external loading remain unclear for these eutectic systems. In this study, small-scale mechanical behavior was evaluated for AlCoCrFeNi2.1 eutectic high entropy alloy, consisting of a lamellar arrangement of L1(2) and B2 solid-solution phases. The ultimate tensile strength was 1165 MPa with ductility of similar to 18% and ultimate compressive strength was 1863 MPa with a total compressive fracture strain of similar to 34%. Dual mode fracture was observed with ductile failure for L12 phase and brittle mode for B2 phase. Phase-specific mechanical tests using nano-indentation and micro-pillar compression showed higher hardness and strength and larger strain rate sensitivity for B2 compared with L1(2). Micro-pillars on B2 phase deformed by plastic barreling while L1(2) micro-pillars showed high density of slip steps due to activation of more slip systems and homogenous plastic flow. Mixed micropillars containing both the phases exhibited dual yielding behavior while the interface between L1(2) and B2 was well preserved without any sign of separation or cracking. Phase-specific friction analysis revealed higher coefficient of friction for B2 compared to L1(2). These results will pave the way for fundamental understanding of phase-specific contribution to bulk mechanical response of concentrated alloys and help in designing structural materials with high fracture toughness.