In this study, the effect of ultrasonic impact treatment (UIT) on the fatigue crack growth (FCG) rate of titanium alloy laser-welded joints was investigated to determine the FCG. Accordingly, the surface roughness, surface topography, microstructure, microhardness, and residual stress of specimens treated with two distinct UIT amplitudes (18 and 25 μm) were investigated as a result. A scanning electron microscope was used to examine the specimens’ fatigue fracture. The surface roughness of the UIT-treated specimens was 4.3 times that of the untreated specimens, but the surface scratches were eliminated. Surface grains were refined to form an approximately 100-µm-thick plastic deformation layer, and compressive residual stress (− 506.4 MPa) was introduced to the surface layer of the specimens. Compared with the untreated specimens, the fatigue life and hardness of UIT-treated specimens increased by 60.6 and 11.5%, respectively, and the hardness influence depth was ~ 0.07 mm. The fracture morphology revealed narrow and thick fatigue cracks, indicating that the FCG rate considerably reduced. Finally, the crack growth process was thoroughly investigated, and the FCG rate and trend were predicted.

在本研究中，研究了超声冲击处理 (UIT) 对钛合金激光焊接接头疲劳裂纹扩展 (FCG) 速率的影响，以确定 FCG。因此，研究了用两种不同的 UIT 振幅（18 和 25 μm）处理过的试样的表面粗糙度、表面形貌、微观结构、显微硬度和残余应力。使用扫描电子显微镜检查试样的疲劳断裂。UIT处理后的试样表面粗糙度是未处理试样的4.3倍，但表面划痕消失。细化表面晶粒以形成约 100 µm 厚的塑性变形层，并将压缩残余应力 (− 506.4 MPa) 引入试样的表层。与未处理的标本相比，UIT处理后试样的疲劳寿命和硬度分别提高了60.6%和11.5%，硬度影响深度为~0.07 mm。断口形貌显示出窄而粗的疲劳裂纹，表明 FCG 率大大降低。最后，对裂纹扩展过程进行了深入研究，并预测了 FCG 速率和趋势。