Effect of laser shock processing on the surface morphology and microstructure of metal material

Laser shock processing (LSP) is a surface hardening technology by using plasma shock waves, which can improve the mechanical properties of material and extend the service life significantly. This work introduced the mechanism of LSP briefly, the analysis of the effect of LSP on the surface morphology, microstructure of material and its related laws are summarized with the aspect from aluminum alloy, titanium alloy and superalloy. The results show that the strong plastic deformation would be appeared in the near-surface of material due to the laser-generated stress effect, resulting the change of surface roughness and the microstructure evolution. At the same time, high-density dislocation walls, dislocation tangles and mechanical twins are generated on the surface, which are accompanied by changes in grain refinement and increased grain boundaries, thereby significantly improve the mechanical properties of material. The convex structure can be found on different material surfaces after LSP, which is micro-scale reverse deformation caused by the free plastic flow of materials under laser shock. And the high pressure of shock waves can lead to destructive dimples on the material surface, and affect its service performance. Aiming at the characteristics of different material, this work comprehensively compares the differences in the surface morphology and microstructure changes of the alloys caused by LSP, and makes a detailed analysis and discussion. This work is helpful for researchers to further understand the high strain rate dynamic plastic deformation mechanism of material treated by LSP, and promote the development of LSP.