Effect of Ni/Cr ratio on phase, microstructure and mechanical properties of Ni_xCoCuFeCr_2-x (x = 1.0, 1.2, 1.5, 1.8 mol) high entropy alloys

Ni_xCoCuFeCr_2-x (x = 1.0, 1.2, 1.5, 1.8 mol) high entropy alloys (HEAs) were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The effect of the increase of Ni/Cr ratio in NiCoCuFeCr alloy system on the phase, microstructure, and mechanical properties was investigated. Results show that with increase in Ni/Cr ratio, FCC phase increased while BCC phase reduced in the MA powders, and after SPS Cu segregation gradually disappeared and σ phase transformed from BCC phase evidently decreased. When Ni/Cr ratio =1.5/0.5, relatively homogeneous microstructure was observed in the consolidated alloys. However, mechanical properties of the bulk HEAs did not change monotonously with the increase of Ni/Cr ratio. Among the four studied alloys, Ni_1.5CoCuFeCr_0.5 alloy, which had yield strength of 1009 MPa, compressive strength of 1985 MPa and plasticity of up to 29.5%, exhibited the optimal comprehensive mechanical properties.