Effect of laser shock peening on boring hole surface integrity and conformal contact fretting fatigue life of Ti-6Al-4 V alloy

The service performance of hole surface is directly tied to its machining-induced surface integrity which is usually produced by sequential operations. Due to its conformal geometry, the assembly hole has a high risk of fretting damage when connecting parts. This paper investigated the effect of laser shock peening on the surface integrity of boring hole and fretting fatigue life of Ti-6Al-4 V alloy. The results showed that the fretting fatigue life of the specimens was dramatically improved at various fatigue stress levels after LSP. The fretting fatigue life was respectively increased by 14 %, 2.27, and 9.35 folds at fatigue stress levels of high (800 MPa), intermediate (500 MPa), and low (300 MPa). In addition, the fatigue stress limit was increased by 70.4 % at the fatigue cycle of 1.0 × 10⁷. The improvement was resulted from the beneficial surface integrity which inhibited fretting wear, and decreased short crack growth rate. Besides, the LSP could not necessarily introduce a greater compressive residual stress (CRS) but should certainly increase the penetration depth of the CRS. The LSP process partially relaxed the CRS depending on whether the existed surface residual stress reached a certain threshold, which was – 450 MPa under the selected conditions in this study. This research helps understand the surface integrity evolution in successive processing, which may contribute to planning appropriate processes for desirable surface integrity.