Titanium alloy welded structures are often subjected to cyclic loading with composite waveform and variable amplitude during actual service, exacerbating the damage to the joints and leading to low fatigue life. Therefore, a three-stage heat treatment was adopted in this work to enhance the fatigue life of TC4 titanium alloy pulsed laser-arc hybrid welded joints, and its microstructure evolution and fracture mechanism were investigated. The results show that the high-density phase boundary formed by the finely dispersed secondary α phase precipitated after heat treatment was the main reason for the increase of life by 3 times. The crack initiation was mainly due to the accumulation of Pyramidal < c + a > dislocations and base < a > dislocations. The difference was that, combined with molecular dynamics calculations and characterization by TEM and EBSD, it was found that the heat-treated cracks underwent dislocation accumulation, deformation twinning, and low-angle grain boundaries before the initiation of the lamellar α-concave position.

中文翻译：

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三阶段热处理对TC4钛合金脉冲激光电弧混合焊接接头复合波形和变幅疲劳性能的影响


钛合金焊接结构在实际使用过程中经常受到复合波形和可变振幅的循环载荷，加剧了对接头的损伤，导致疲劳寿命短。因此，本工作采用三阶段热处理来提高 TC4 钛合金脉冲激光电弧混合焊接接头的疲劳寿命，并研究了其微观组织演变和断裂机理。结果表明，热处理后细分散的二次α相析出形成的高密度相界是寿命增加 3 倍的主要原因。裂纹的萌生主要是由于锥体 < c + a > 位错和基底 < a > 位错的积累。区别在于，结合分子动力学计算以及 TEM 和 EBSD 的表征，发现热处理裂纹在层状α凹位置开始之前经历了位错积累、变形孪生和低角度晶界。