Al and Mo synergistic enhancement of CoCrFeNi high-entropy alloy laser cladding layer

A CoCrFeNi high-entropy alloy (HEA) coating, enhanced with Al and Mo, was fabricated on Q235 steel using laser cladding technology. The synergistic enhancement effect of Al and Mo on the coatings was studied. The findings revealed that the CoCrFeNi coating mainly comprised the single-phase FCC. In contrast, the BCC and σ phases were observed when Al and Mo were individually doped. The simultaneous doping of both these elements resulted in a coating consisting of the BCC and σ phases. Mo addition led to grain refinement and increased the kernel average misorientation value; similarly, Al addition further enhanced these effects. The separate additions of Al and Mo significantly refined the microhardness and wear resistance of the coating. When both elements were added simultaneously, the microhardness and wear resistance of the coating were further enhanced, demonstrating the synergistic effects of Al and Mo on these characteristics. Moreover, the individual doping of Al and Mo decreased the Kp value and the oxide layer's thickness. Meanwhile, their combined addition reduced the Kp value by approximately 82.5 % and 89.8 %, respectively. During the initial oxidation stage, rapid oxidation of Al occurred, thereby decreasing the oxidation rate. In contrast, Mo facilitated the formation of Al2O3.