Wear resistance of FeCoCrNiMnAlx high-entropy alloy coatings at high temperature

The FeCoCrNiMnAlx high-entropy alloy (HEA) coatings were produced on 4Cr5MoSiV steel by laser cladding, which can improve the high temperature oxidation resistance and wear resistance of the substrate steel in its service environment. The effects of Al addition on the microstructure and properties of the coatings were systematically investigated. The addition of Al element promoted the transition of FCC to FCC + BCC (B2) phases in the cladding layer and also refined the grains. Thereby, with the Al addition from 0 to 0.75, the micro-hardness and room-temperature wear weight loss of the HEA coatings increased and decreased, respectively, i.e. from 224.4 HV0.5 and to 344.2 HV0.5 and from 6.0 mg to 1.1 mg, compared with those of the base metal (227.1 HV0.5 and 10.5 mg). In the high-temperature oxidation process, fine and dense α-Al2O3 was preferentially generated because of its lowest absolute Gibbs free energy compared to the other oxides. The generation of α-Fe2O3 and Cr2O3 also promoted the heterogeneous nucleation of α-Al2O3. The high-temperature oxidation weight gain and wear weight loss of the FeCoCrNiMnAl0.75 cladding layer was approximately 58% and 17% of those of the base metal, respectively, and the wear mechanism was mainly abrasive wear.