Hole surface texture reconstructed with laser shock peening and effect on fretting behavior

Laser Shock Peening (LSP) has been widely employed as a post-processing surface treatment technique in improving fatigue resistance of various titanium alloy parts. However, most of the concerns on the LSP application are focused on the alteration in the subsurface layer, rather than the texture properties of the surface layer, which are crucial sensitive factors of the nucleation of fretting induced micro-crack. In this paper, the feasibility and ability of LSP treatment on the reconstruction of surface texture properties in four groups of sequentially milled hole surfaces were investigated. Two different impact routes were set to perform the LSP treatment. The produced surface texture properties, microstructure alteration, surface roughness, residual stress, as well as the fretting fatigue life and fretting behaviors were compared. The results showed that the LSP process could be regarded as a potential technique in constructing the surface texture to introduce beneficial resistance to fretting wear, by which the positive surface skewness value could be altered to negative, and the high surface kurtosis could be changed from leptokurtic to platykurtic or mesokurtic distribution. Moreover, the symmetrical strengthening method (SSM) in LSP treatment (LSPb route) tended to generate surface layer with a more negative skewness, better texture flow trend, numerous low angle grain boundaries (LAGBs), grains with high kernel average misorientation (KAM), and more refined grains, resulted in a lower crack growth rate and approximately doubling the fretting fatigue life. This work provides a method for reconstructing surface texture properties by LSP treatment to meet the performance requirement of components, as well as to expand the application field and ability of the LSP technique.