激光冲击/机械喷丸复合强化对TC4钛合金外物损伤疲劳性能的影响

Effect of co-strengthening of laser impact/mechanical shot peening on fatigue performance of TC4 titanium alloy damaged by foreign objects

针对航空发动机叶片前缘外物损伤(foregin object damage,FOD)后疲劳性能严重下降的问题,采用激光冲击/机械喷丸复合强化对TC4钛合金薄壁试样进行表面处理。采用X射线衍射测量复合强化前后试样表面残余应力梯度分布;通过硬度计预制不同形状的凹坑在试样表面引入FOD,利用电磁振动台测试处理前后TC4钛合金薄壁试样的高周一阶振动疲劳寿命;通过扫描电镜分析疲劳断口形貌;采用有限元动力学数值仿真模拟FOD前后试样表面残余应力分布演化规律,揭示了复合强化层对FOD缺口疲劳性能的影响机制。结果表明:相比未强化的FOD和无FOD试样,复合强化FOD试样的平均疲劳寿命分别提高了370%和60%;复合强化后试样表层形成的深层残余压应力场(厚度500μm)是提高FOD试样疲劳寿命的重要原因。

Aiming at the problem that the fatigue performance of aeroengine blade leading edge was seriously degraded after foreign object damage(FOD),the surface of TC4 titanium alloy thin wall specimen was treated by laser shock/mechanical shot peening,and the residual stress gradient distribution on the specimen surface before and after the composite strengthening was measured by X-ray diffraction method;The high order vibration fatigue life of TC4 titanium alloy thin wall specimens before and after treatment was tested by electromagnetic vibration table,and FOD was introduced into the specimen surface by fabricating pits of different shapes with a hardness tester;The fatigue fracture surface was analyzed by SEM;The evolution of residual stress distribution on the specimen surface before and after FOD was simulated by finite element dynamic numerical simulation,and the mechanism of the influence of the composite strengthening layer on the notch fatigue performance of FOD was revealed.The results show that the average fatigue life of the composite strengthened FOD specimen is 370%and 60%higher than that of the non strengthened FOD specimen and the non strengthened FOD specimen,respectively.The deep residual compressive stress field(thickness 500μm)formed on the surface layer of the specimen after composite strengthening is an important reason for increasing the fatigue life of FOD specimen.