Investigation of Surface Integrity on TC17 Titanium Alloy Treated by Square-spot Laser Shock Peening

Laser shock peening (LSP) is an innovative surface treatment method, which has been shown to greatly improve the fatigue life of many metallic components. This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot. Nd: glass laser with duration of 30 ns and spot size of 4 mmx4 mm is applied. The surface morphology and surface residual stress of the TC17 titanium alloy, treated with varying peening parameters such as laser power density and overlapping ratio, have been studied in detail. The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas, and compressive residual stresses are saturated as laser pulse energy is over 55 J. There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios. A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8%. The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz. The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.