Novel, Equimolar, Multiphase CoCuNiTiV High-Entropy Alloy: Phase Component, Microstructure, and Compressive Properties

Abstract

The phase component, microstructure, and compressive properties of a novel 3d transition metal high entropy alloy, CoCuNiTiV, derived from Fe replaced by V in CoCuNiTiFe alloy, were evaluated in as-cast and annealed conditions. The experiments showed that the as-cast alloy possessed a typical BCC + FCC dual-phases, which distinctly varied from the single FCC phase of an adjacent CoCuNiTiFe alloy. The BCC phase takes up the majority acting as the matrix, in which Cu was depleted, and the other elements (i.e., Co, Ni, Ti, and V) were distributed homogenously. Meanwhile, the FCC phase was Cu-rich, and sandwiched in the interval space between the BCC phases forming a net-like framework. After annealing, the matrix bifurcated into two parts: (i) one that remained as the primary BCC phase and (ii) another that decomposed into a Co2Ti-type laves phase and a new BCC phase. Meanwhile, the Cu-rich net-like framework is deteriorated forming a series of evenly distributed particles. The yield strength and the fracture strength of the as-cast and annealed alloy are highly similar— about 1674 and 2400 MPa, respectively. The hardness of the annealed alloy (572.9 ± 10.6 HV) was slightly higher than that of the as-cast alloy (530.3 ± 12.2 HV).