Effect of laser shock peening on the properties of Cr coatings on Zr alloy surfaces

Abstract

The coating prepared by physical vapor deposition technology will inevitably have some defects, such as pinholes, pores and so on. In this study, a low-energy laser shock peening (LE-LSP) technique was employed to post-treat Cr coatings with varying laser energies, both in absence and presence of an absorbing layer. The surface morphology, cross-sectional microstructure, crystal structure, and corrosion resistance of the Cr coatings were investigated before and after LE-LSP. The results show that the presence of the absorbing layer can avoid the ablation of the Cr coating surface and the generation of a large number of cracks. Compared with the untreated Cr coating, the number of droplet particles on the surface was reduced. The surface hardness increases with the increase of laser energy. The thickness of the coating decreases as the laser energy increases. After LE-LSP treatment, the crystal structure of the coating was significantly deformed, and the strength direction of the texture was also changed. The zirconium alloy substrate was also affected by LE-LSP. In the absence of an absorbing layer, the corrosion current density (i_corr) increases and the polarization resistance (R_p) decreases due to the formation of cracks on the surface and section of the coating after LE-LSP treatment. When an absorbing layer is present, the Cr coating becomes denser, the i_corr decreases and the R_p increases after LE-LSP treatment.