钛合金薄壁构件激光冲击残余应力稳定性研究

Study on Stability of Residual Stress Induced by Laser Shock Processing in Titanium Alloy Thin-Components

针对航空发动机压气机薄叶片激光冲击后残余压应力的严重松弛问题,对TC11钛合金薄壁试件激光冲击后进行轴向拉-拉疲劳实验和真空保温处理,通过X射线衍射测试获得疲劳载荷和热应力载荷作用下的应力松弛规律,并分析松弛机理。实验结果表明:疲劳载荷(最大应力σ_(max)=500 MPa,应力比R=0.1)作用下表面残余压应力松弛了53%,前5次循环占了95%,且表面松弛程度和严重松弛深度都随疲劳载荷增大而增大,其松弛机理是局部材料发生塑性变形而引起的应力场重新分布。在200、300和400℃下恒定保温120 min后,表面残余压应力分别松弛了3%、29%和48%,而在200℃+400℃和300℃+400℃交替保温120 min后分别松弛了18%和58%,松弛均发生在前60 min内,且严重松弛深度随温度呈现相同变化规律,其松弛机理是热应力激活位错、晶界等进行运动和消亡而导致塑性回复。由于松弛机理不同,疲劳载荷与热应力载荷复合作用下应力松弛呈现出叠加效应。

Because the compressor thin-blades of aero-engine often fractured in service, laser shock processing was suggested to be applied as a surface strengthening technology. Aim at the problem of compressive residual stress relaxation in laser-peened compressor thin-blades, TC11 titanium alloy thin- components were treated by laser shock processing and then conducted in axial tensile-tensile fatigue test and thermal insulation in vacuum. X-ray diffraction tests were carried out to obtain the relaxation rules of residual stress under fatigue loading and thermal stress loading. In addition, the relaxation mech- anisms of residual stress were indicated. Experiment results demonstrate that surface compressive resid-ual stress relaxes by 53%, and 95% of stress relaxation occurs in the previous 5 fatigue cycles under the fatigue loading （maximum stress ~max=500 MPa, stress ratio R=0.1）. The surface relaxation degree and severely-relaxed depth increase with fatigue loading, and the relaxation mechanism is that plastic defor- mation of local area material results in residual stress redistribution. Surface compressive residual stress relaxes by 3%, 29% and 48% respectively after thermal insulation for 120 min under the constant temper- ature of 200 ℃, 300 ℃ and 400 ℃. Surface compressive residual stress relaxes by 18% and 58% respec- tively after thermal insulation for 120 min under the altering temperature of 200 ℃＋400 ℃ and 300 ℃＋ 400 ℃. The relaxation all occurs in the previous 60 min. There is a similar trend with temperature in the aspect of severely-relaxed depth. The relaxation mechanism under thermal stress loading is that disloca- tions and grain-boundaries are activated to move and annihilated, and then plastic deformation recovery occurs. Due to the distinction of relaxation mechanisms, there is an obvious superimposed effect under the combined action of fatigue loading and thermal stress loading.