Microstructure evolution of laser cladded NiCrBSi coating assisted by an in-situ laser shock wave

Laser cladding assisted by an in-situ laser shock wave was proposed in this study to obtain a refined grain structure, and NiCrBSi coatings -with and without laser shock waves, (LSW) -were prepared on the surface of a 16Mn steel sample. The phases, microstructure, grain size, texture orientation, and microhardness of coatings were investigated. The results showed that the phases for both coatings were γ-Ni, M7C3 and that CrB is formed in the coating with LSW, while the content of the ceramic phases was increased after applying the LSW. The grain size of the γ-Ni in the coating with LSW was significantly refined and tended to be equiaxed. The texture orientation of γ-Ni was also weakened and the microhardness of the coating increased by 14.45% after the application of in-situ laser shock wave because the LSW propagates to the bottom of the molten pool, breaking the growing dendrites and resulting in grain refinement. The refined grains shortened the distance between the atoms and grain boundaries, promoting the formation of ceramic phases. Thus, this technique can successfully control microstructure in metallic materials during laser cladding.