Microstructural Evolution and Deformation Behavior of Ni-Si- and Co-Si-Containing Metastable High Entropy Alloys

Two high entropy alloy (HEA) compositions were compared to explore the individual effects of Co and Ni on phase stability and resultant deformation response in Fe-Mn-Cr-Si-containing HEAs. It was observed that Co-Si-containing HEA depicted responsive phase evolution upon friction stir processing owing to decreased γ (f.c.c.) matrix stability as against Ni-Si-containing HEA. As a result, the Co-Si HEA showed the presence of dual-phase microstructure with the dominance of ε (h.c.p.) phase (52 pct), whereas the Ni-Si HEA showed single-phase γ microstructure under similar processing condition. Also, the dominant deformation mechanisms were different in the two alloys. Co-Si HEA showed uniform strain partitioning between the f.c.c. and h.c.p. phases. Conversely, single-phase f.c.c. microstructure in Ni-Si HEA accommodated strain by twinning-induced plasticity.