Influence of laser shock peening on microstructure and property of Ni60 cladding layer and the combined area of 20CrNiMo alloy

The effects of laser shock peening (LSP) on the microhardness, residual stress, and microstructure of the Ni60 cladding layer and the combined area of the 20CrNiMo alloy for high-speed rail brake disks are investigated to address the problem of coarse columnar crystals and residual tensile stress, which affect the coating-substrate bonding performance and the application development of the laser cladding repair process. The results indicate that LSP can improve the microhardness, prefabricate residual compressive stress field, and refine the microstructure of the cladding layer and the combined area. The surface hardness of the cladding layer increased by 14.55%, 34.92%, and 40.21% after the energy impact of 6, 9, and 12 J, with an impact depth of about 1.2, 2.2, and 2.5 mm, respectively. The roughness result showed that the effect is more satisfactory under the 9 J energy impact. The grain refinement is significant compared to the Clad specimen, with the average grain area at the molten layer's top, middle, and bottom reduced by 35.5%, 79.6%, and 85.8%, respectively. A residual compressive stress of -538 MPa is introduced on the surface of the clad layer, with a compressive stress value of -30 MPa at a depth of 2 mm. After the LSP, the microstructure and properties of the clad layer and the combined area are significantly improved. Still, no new phases appear and do not significantly affect the diffusion of elements between the dendrites and the dendrites.