Effect of μ phase on mechanical properties and wear behavior of CoCrFeNiMox high-entropy alloy coating

The CoCrFeNiMox (x = 5,10,15,20,25) high-entropy alloy (HEA) coatings have been designed and prepared by laser cladding, which controls the precipitation of the μ phase by adjusting Mo content. The microstructure evolution, mechanical properties and tribological properties of the coatings have been thoroughly examined. Results show excessive lattice distortion affects the stability of FCC single-phase as Mo content increases, resulting in the precipitation of the μ phase. Moreover, the intergranular precipitated phase associated with higher Mo content exhibits a ffner microstructure. High-density dislocations can greatly enhance the hardening ability of the HEA coating. The synergistic mechanisms of solid solution strengthening, ffne grain strengthening and precipitation strengthening improves the hardness of the 25 at% Mo-doped FeCoCrNi coating (Mo25 coating: 675 HV0.2). The higher H/E and H3/E2 values of the Mo25 coating exhibit superior ability to resist plastic deformation. At medium and low temperatures, fatigue spalling of Mo-doped CoCrFeNi HEAs is alleviated. At high temperatures, multiple oxides generated in situ form a glaze layer that enhances tribological performance. As a result, the Mo25 coating exhibits good wear resistance at different temperatures. This study not only provides ideas for the μphase strengthening of FCC HEAs, but also further broadens the application of HEAs in the friction environments.