Effects of annealing on the mechanical and wear resistance properties of a designed novel eutectic high-entropy alloy

In this work, a eutectic high-entropy alloy, CoCrFeNi(TiNb)0.325, was successfully prepared via vacuum arc melting. In this investigation, the microstructures, mechanical properties, and wear behaviors of the samples in the as-cast state and after annealing at temperatures of 850 °C and 1160 °C were systematically examined. The results demonstrated that annealing significantly influenced the microstructures, mechanical properties and wear behaviors of CoCrFeNi(TiNb)0.325 EHEAs. After annealing at 850 °C, a substantial number of nanoscale L12 phases and needle-like phases precipitated within the alloy microstructure, remarkably increasing alloy hardness and yield strength from 635.34 HV and 1552.3 MPa in the as-cast state to 742.34 HV and 2537.7 MPa, respectively. Annealing at 1160 °C resulted in the disappearance of the eutectic structure within the alloy microstructure, causing a spherical transformation that enhanced the ductility of the alloy. The wear mechanisms for all three alloys were found to involve a combination of oxidative wear and delamination wear, although their severity varied. For the EHEA annealed at 850 °C, the combined effect of high hardness and the precipitation of needle-like phases with a noncoherent interface played a significant role in slowing delamination wear. As a result, this alloy exhibited the lowest wear rate at 3.41 × 10−5 (mm3/Nm).