Effect of NiAl content on microstructure and properties of (NiAl)x(CoCrFeNi)94-xTa6 alloy

The triphase composite eutectic high-entropy alloys, (NiAl)_x(CoCrFeNi)_94-xTa₆ (x = 12, 15, 17, 23, 28, 34), were designed and prepared using the pseudo-ternary method, and the microstructures and mechanical properties were investigated. The vertical section phase diagram of the pseudo-ternary eutectic at Ta = 6 at. % was plotted on the basis of the principle of solid-state immiscibility. The theoretical solidification paths are likely to be different from the actual solidification paths due to the finite solid solution in the solid state, the nonequilibrium solidification, and the sluggish diffusion effect of high-entropy alloys. In this study, all developed alloys consist of the primary phase, biphase, and triphase eutectics. The primary phase of NiAl-12, NiAl-15, NiAl-17, and NiAl-23 alloys is FCC phase, while that of NiAl-28 and NiAl-34 alloys is the B2 phase. When the primary phase is B2, it is rich in nanoprecipitates with BCC structure. The synergistic effects of the B2 and Laves phases reinforce the overall mechanical properties of the CoCrFeNi high-entropy alloy. In particular, the NiAl-15 alloy displays superior overall mechanical properties, with high yield strength, fracture strength, and maximum compressive strain values of 859.1 MPa, 2559.5 MPa, and 41.6 %, respectively. The yield strength of NiAl-15 alloy is calculated based on the mixing rule, and the results show that the strength is mainly contributed by the Laves phase.