Effects of in-situ synthesized carbides on microstructure and properties of FeCoCrNiMo0.2 / graphene composite coatings via laser cladding

Abstract

The FeCoCrNiMo_0.2 high-entropy alloy exhibits excellent corrosion resistance due to its ability to suppress the precipitation of σ phase, thus possessing enormous application potential in the field of corrosion-resistant coatings. However, its insufficient mechanical properties limit its application scope. This study reports a method to reinforce FeCoCrNiMo_0.2 high-entropy alloy coatings by in-situ synthesizing M₂C-type carbides through the addition of graphene via laser cladding technology. As the graphene content increases, the microhardness of the composite coating gradually rises. At 0.8 wt% graphene content, the coating achieved a peak microhardness of 254.6 HV_0.5, representing a 21.1 % improvement over the HEA coating without graphene addition. Additionally, the wear resistance of the coating initially enhances, then decreases, and subsequently improves again with increasing graphene content. The optimal wear resistance occurred at 0.2 wt% graphene content, where wear volume decreased by 34.17 % compared with the HEA coating without graphene. However, the introduction of in-situ synthesized carbides compromises the integrity of the passive film and induces galvanic corrosion, leading to a gradual decline in corrosion resistance as graphene content increases. Notably, the coating with 0.2 wt% graphene maintained passive film integrity through repairable secondary passivation due to its fine carbide size. This work provides crucial insights into the mechanisms governing the influence of graphene-induced in-situ carbide synthesis on the microstructure and properties of HEA coatings.