Effect of Mo Addition on The Microstructure and Mechanical Properties of CoCuFeNi High Entropy Alloy

In order to reveal the effect of Mo addition on the microstructure and mechanical properties, (CoCuFeNi)(100-x)Mo-x (x= 0, 10, 15, 19, and 25,xvalues in atomic ratio) high entropy alloys were prepared by vacuum arc-melting. The results showed that with Mo addition, the mu phase formed and serious separation occurred in the high entropy alloys. The content of mu phase increased with the increase in Mo content. The microstructure of the alloys changed from an initial single-phase face-center-cubic (FCC) solid solution structure (x= 0) to a hypoeutectic microstructure (x= 15), then to a full eutectic microstructure (x= 19), and finally to a hypereutectic microstructure (x= 25). Coherent interface between mu phase and FCC phase was observed. The (CoCuFeNi)(81)Mo-19 alloy with fully eutectic microstructures exhibited the highest yield strength of 557 MPa and fracture strength of 767 MPa in tensile tests at room temperature. The fracture surface revealed that the formation of great amounts of the mu phase resulted in the loss of ductility of (CoCuFeNi)(100-x)Mo-x alloys.