Highly deformable Laves phase in a high entropy alloy

Abstract

By replacing Nb with (Hf+Nb+Ta) in CoCrFeNi2.1(Nb)0.2 high entropy alloy (HEA), which contained hard and brittle hexagonal C14 Laves phase, a novel CoCrFeNi2.1(HfNbTa)0.2 HEA was designed. Heavy cold-rolling complemented by microstructural and nanoindentation studies produced evidence of the surprisingly soft and ductile attributes of the Laves phase in the CoCrFeNi2.1(HfNbTa)0.2 HEA, in striking contrast to the almost universal brittle behavior of the Laves phases. Crystallographic and chemical analyses of the Laves phase in the CoCrFeNi2.1(HfNbTa)0.2 HEA confirmed the cubic C15 structure, realized by the site occupancy preferences of the constituent elements. The unusual deformability of the Laves phase was attributed to the spectacular propensity for nano-twin formation on the {111}<112> system, presumably resulting from its increased compositional complexity. Meanwhile, the results should open a pathway for designing highly deformable Laves phases in HEAs.