Effect of ceramic particles on microstructure and properties of CoCrMoNbTi high-entropy alloy coating fabricated by laser cladding

In this study, CoCrMoNbTi, CoCrMoNbTi(B4C)0.2 and CoCrMoNbTi(SiC)0.2 high-entropy alloy coatings are prepared by laser cladding. These three coatings show significant differences in terms of microstructure and mechanical properties. In terms of microstructure, the Pure-HEA exhibits a uniform microstructure distribution, and the coating consists of two BCC phase-solid solution structures (BCC1 and BCC2) with different lattice constants. SiC-HEA exhibits a denser microstructure than Pure-HEA, and both coatings exhibit a typical dendritic structure. In contrast, the microstructure of B4C-HEA transformed from dendritic crystals to fully equiaxed crystals, and the grain refining effect can even up to two orders of magnitude. Both B4C-HEA and SiC-HEA are composed of BCC1, BCC2 and TiC phases, where TiC is obtained by the in-situ reaction. The effects of B4C and SiC on the mechanical properties of the high-entropy alloy are evaluated in terms of microhardness and wear resistance. The results show that B4C has the best strengthening effect on the alloy properties, the microhardness of the coating increases from 666.2 HV0.5 to 886.9 HV0.5. The room temperature wear resistance of the alloy is enhanced, and the frictional coefficient and wear rate are significantly reduced. Moreover, the wear mechanism is transformed from adhesive wear to abrasive wear due to the addition of B4C. This work provides insight into the application of ceramic particle-reinforced high-entropy alloys.