激光冲击强化对Ti6Al4V合金表面完整性和四点弯曲疲劳性能的影响

Effect of Laser Shock Peening on Surface Integrity and Fatigue Property of Ti6Al4V Alloy

摘要:

采用扫描电镜、显微硬度仪、X射线应力测量仪及透射电镜等对激光冲击强化Ti6Al4V合金的表面完整性进行了分析,采用MTS疲劳试验机测试了疲劳性能,并采用扫描电镜分析了疲劳断口,探讨了激光冲击强化机制。结果表明:经功率密度为15. 9 GW/cm~2的激光处理后,其四点弯曲中值疲劳寿命较未处理试样提高了4. 2～23. 5倍;激光功率密度越大,试样的中值疲劳寿命越长。激光冲击强化表现出比喷丸强化更优的疲劳寿命增益效果。经激光冲击强化后,Ti6Al4V合金表面形成了深度为600～1 400μm的残余压应力场,表面硬度比未强化区域提高了约10%,且亚表层内部的位错密度也有显著提高。

Abstract:

The effect of laser shock peening( LSP) on the surface integrity and four-point bending fatigue life of Ti6Al4V alloy was investigated. The surface integrity including residual stress,micro-hardness and micro-structure of LSP region was characterized by scanning electron microscopy( SEM),micro-hardness tester,X-ray diffraction( XRD)instrument and transmission electron microscope( TEM). The fatigue property was tested by MTS fatigue tester.And the fatigue fracture was observed with SEM. The enhancement mechanism of the LSP was also investigated. The results show that the predicted median value of the four-point bending fatigue life of the LSP specimens with the laser power density of 15. 9 GW/cm~2 is about 4. 2～23. 5 times larger than that of the non-treated specimens. The fatigue performance of the specimens increases with the increase of laser power density. The LSP shows higher fatigue life improvement than shock peening( SP). Besides,it is found that a residual compressive stress field with the depth of about 600～1 400 μm is formed after LSP. The micro-hardness of LSP region is increased by about 10% compared with un-treated region. And the density of dislocation in the LSP treated sub-surface layer is also larger than that of un-treated specimen.