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.
Highlights
Advanced aero-engines pursue a higher thrust-weight ratio, promoting the development of compressor blades toward integration and light weight
The thermal stability of the compressive residual stress (CRS) relaxation, microstructures, and fatigue property of the LSPed TC11 titanium alloy was investigated by the residual stress test, TEM observation, and vibration fatigue test
The following conclusions can be drawn from this work: (1) After Laser shock peening (LSP) treatment of technology B, the relaxation rate and relaxation depth of the TC11 titanium alloy were greater than those after technology A, indicating that the thermal stability of residual stress is better under high-power density and multiple impact LSP
Summary
Advanced aero-engines pursue a higher thrust-weight ratio, promoting the development of compressor blades toward integration and light weight. Scitation.org/journal/adv research results have found that LSP can prefabricate CRS and can refine microstructure on the surface or form crystal defects like high-density dislocations and twins, thereby improving the strength of materials, retarding fatigue crack initiation, and reducing crack growth rate.. The previously reported researches mainly demonstrated that the CRS and nanostructure induced by LSP can improve the fatigue performance, and the fatigue performance was weakened by residual stress relaxation or grain growth under thermal loads. There are few discussions about combining the evolution of residual stress relaxation and microstructures under annealing to analyze the effects on fatigue performance. In this investigation, the microstructure was observed by the methods of TEM and μXRD. The effect of the thermal stability of nanostructure on fatigue performance was verified
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