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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 AlCoCrFeNi 2.1 eutectic high entropy alloy consisting of BCC (B2), and FCC (L1 2) lamellae. A transition from adhesive to oxidative wear was observed in reciprocating wear analysis. The L1 2 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 L1 2. 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 L1 2 , supporting the selective corrosion and higher coefficient of friction of B2.

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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 wellknown 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 Alcocrfeni 2.1 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 ~18% and ultimate compressive strength was 1863 MPa with a total compressive fracture strain of ~34%. Dual mode fracture was observed with ductile failure for L1 2 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. Multi-principal element alloys (MPEAs), also known as high entropy alloys (HEAs), offer a new paradigm in structural alloy design and development owing to their appealing physical and mechanical properties such as high fracture toughness, good wear and fatigue resistance, high strength and good elevated temperature properties 1-3. Several HEA systems have been reported with a single-phase face center cubic (FCC) or body center cubic (BCC) structure 4-6. To concurrently achieve good ductility of FCC HEAs along with high strength of BCC HEAs, eutectic high entropy alloys (EHEAs) have recently been developed to overcome the limitations of single-phase HEAs 7. EHEAs typically consist of a mixture of two solid-solution phases in the form of lamellae or rod-like dispersions in a matrix. To date, several EHEAs have been reported with excellent combination of high strength and ductility including CoFeNi 1.