Thermal stability study of TC11 titanium alloy thin component after surface nanocrystallization induced by laser shock processing

Abstract

Laser shock peening (LSP) can induce the compressive residual stress (CRS) on the surface of the material, and surface nanocrystallization can be realized with a nanocrystal layer, thereby significantly improving the high-cycle fatigue performance. However, due to weak material constrain and the high working temperature of thin aero-engine compressor blades, CRS and refined grain structure are more likely to result in stress relaxation and microstructural recovery under thermal stress load, resulting in reducing the anti-fatigue effect of LSP. In this paper, on the basis of the surface nanocrystallization induced by LSP, residual stress and microstructure of TC11 titanium alloy thin components were measured and observed. The residual stress relaxation was characterized and the microstructure evolution was discussed. Also, the thermal stability mechanism of CRS and the nanostructure on the surface were analyzed. The experimental results show that after thermal loads, the CRS was decreased, and the stress relaxation amplitude was increased with an increase in temperature. After annealing at 400 °C, the dislocation density was significantly reduced, but the grain sizes of surface nanostructure did not greatly increase. After annealing at 400 °C for 2 h, the fatigue strength of the LSPed specimen was reduced compared with that before annealing, but it was still increased compared with the original state without LSP, especially under high-power density for multiple LSP treatment. It can be concluded that the surface nanostructure has good stability and effectively retards the initiation of fatigue cracks on the surface, which ensures the effectiveness of LSP under thermal loads.

Picosecond Laser Shock Micro-Forming of Stainless Steel: Influence of High-Repetition Pulses on Thermal Effects

“…Figure 9 shows that for a wider range of f, the simulation predicts a linear relation between the maximum cool-down temperature of the surface and the repetition rate. The thermal relaxation of the residual stresses induced by LSP has been reported previously [19,20] in annealing processes with temperatures in the range of 200-650 • C, although this effect is more important for longer times. In this case, the annealing time is short, but the affected volume is also smaller than in previous studies.…”