激光冲击强化对TC4钛合金单面修饰激光焊接接头疲劳性能的影响

对TC4钛合金单面修饰激光焊接接头进行激光冲击强化，对比强化前后焊接接头的疲劳寿命，在光学显微镜和扫描电镜下观察断口疲劳断裂特征，并从焊接接头的显微硬度、微观组织、残余应力分布等方面综合分析激光冲击强化对TC4钛合金单面修饰激光焊接接头的强化机理。试验结果表明：未强化和强化试样均在焊缝咬边处萌生疲劳裂纹，强化试样疲劳寿命是未强化试样疲劳寿命的3.77~9.15倍，强化试样焊缝咬边处马氏体细化，显微硬度提高，焊缝表面呈残余压应力分布，焊缝咬边处残余压应力达-564.37±9.85MPa。晶粒细化和高幅值残余压应力综合作用下抑制了焊缝咬边处疲劳裂纹的萌生，且增大了裂纹扩展阻力，从而提高了焊接接头疲劳性能。

Effects of Laser Shock Processing on Fatigue Performances of TC4 Titanium Alloy Single-side Laser Modification Welding Joints

The standard fatigue specimens made of TC4 titanium alloy single-side laser modification welding joints were treated by laser shock processing. The tension fatigue tests were conducted to verify the reinforcement effects, and the fracture analyses were utilized to analyze the fatigue mechanism of the treated specimens. The strengthening mechanism of fatigue performances was explained by the experiments of micro-hardness, microstructure and residual stress. The results show that the fatigue cracks of all specimens are initiated in the welding undercut, while the fatigue life of the treated specimens is increased to 3.77~9.15 times by LSP. Coarse martensite refinement is generated in the welding undercut of the treated specimens, and LSP introduces a great compressive residual stress in the surfaces of the welding joints. The residual stress in the welding undercut may reach -564.37±9.85MPa, while the surface hardnesses are increased. The combined actions of high structure refinement and high compressive residual stress are the main causes of the fatigue performance improvements, which blocks fatigue crack initiations and reduces crack growth rates.