Plastic strain partitioning in dual phase Al₁₃CoCrFeNi high entropy alloy

High entropy alloys present opportunities to develop new materials with unique mechanical properties. Through careful selection of constituent elements and thermal processing, different microstructures with varying properties can be achieved. This study is focused on an interesting class of high entropy alloys with dual phase microstructure, a soft FCC and a hard BCC phase. Specifically, the local material response of Al₁₃CoCrFeNi (atomic %), at the microscale and in the vicinity of phase boundaries, is analyzed using high resolution strain and grain orientation measurements. Different heat treatments resulting in varying phase volume fractions and deformation temperatures were considered. The local response of this high entropy alloy displayed significant heterogeneity in plastic strain accumulation with preferential accumulation in the FCC grains and localizations at phase boundaries. The preferential accumulation of plastic strains in FCC grains (33–85% higher than BCC) was further enhanced with very high temperature heat treatments conducted at 1300 °C. These changes in plastic strain partitioning were associated with the increase in BCC phase volume fraction which was altered during heat treatment. At the macro-scale, the unloading response of Al₁₃CoCrFeNi revealed a nonlinear unloading behavior with large magnitudes of recoverable strains (0.9–1.4%). Deformation at cryogenic temperatures revealed slip dominated plasticity and no changes in the underlying deformation mechanism due to temperate reduction. However, the plastic strain partitioning between the FCC and BCC phases is shown to be affected with larger magnitudes of plastic strains accumulating in the FCC phase, and less in the BCC phase, compared to the room temperature deformation response.