The influence of powder size on the microstructure and properties of Mo₂FeB₂ coating fabricated via laser cladding with pre-placed powder

Mo₂FeB₂ coatings were fabricated by laser cladding with different pre-placed powder sizes. In the present research, a coaxial nozzle head coupled with a continuous fiber laser with a maximum power of 3 kW was used. The influence of powder size (~ 6 μm, ~ 13 μm, ~ 65 μm) on the morphology, microstructure, microhardness, wear resistance, and fracture toughness of the coating were discussed in this research. The morphology showed that coating obtained with ~ 6-μm powder size had excellent wettability and avoided obvious defects; microstructure revealed that the coating appeared particle agglomeration phenomenon with the increase of powder size. The coating obtained with ~ 6 μm had herringbone and feature structures to improve the density, and the bonding zone had typical columnar crystal and no cracks. The microhardness, wear resistance, and fracture toughness decreased as the increase of powder size. The optimal microhardness, COF, and fracture toughness of coating reached 1138.56 HV_0.5, 0.59, 14.65 MPa·m^1/2, respectively, when powder size was ~ 6 μm. The wear form of coatings was typical abrasive wear and adhesive wear; the fracture mechanism was transgranular fracture. The research can provide a reference for the preparation of Mo₂FeB₂ ternary boride coating.