Influence of laser power on microstructure and properties of laser clad Co-based amorphous composite coatings

Co-based amorphous composite coatings were produced by laser cladding on the 45# medium steel substrate. The influences of laser power on the microstructure and properties of the coatings were investigated. Results show that the coatings exhibit layered structure, which can be generally divided into three different zones: surface zone consisting of the Co2B equiaxed dendrite dispersed in the amorphous matrix, transition zone containing dendritic/columnar Co2B intermetallic compound plus intergranular Co3B intermetallic compound, and interface bonding zone composed of α'-(Co, Fe) solid solution distributed in the α-(Co, Fe) solid solution. The layered structure results from the dilution and stir influence from the substrate. With the increase of laser power, the volume fraction of the amorphous phase in surface zone significantly increases, with the highest fraction (92%) obtained at laser power of 4.0 kW. As a result, the average hardness of the coatings decreases, while the wear resistance and anti-friction properties increase.