Why do cracks occur in the weld joint of Ti-22Al-25Nb alloy during post-weld heat treatment?
Ling Shao, Xinyu Zhang, Yingwei Chen, Zhu Liu, Sujun Wu, Qijie Liu, Weiwei Li, Na Xue, Zhibiao Tu, Tianle Wang, Jitang Zhang, Sheng Dai, Xinxing Shi, Mengliang Chen
Abstract
Ultrasonic pulse frequency tungsten inert gas welding technology was adopted to join Ti-22Al-25Nb alloy. There were some cracks in the Ti-22Al-25Nb alloy weld joint after post-weld heat treatment. The hardness and Young’s modulus of α 2 , O, and β /B2 phases in Ti-22Al-25Nb alloy were examined with an in situ nanoindentation technique. The phase transition stresses of three different phases in the weld joint of Ti-22Al-25Nb alloy were analyzed to explain why cracks occur in the weld joint of Ti-22Al-25Nb alloy during post-weld heat treatment. The results show that mean hardness is highest for the α 2 phase, second-highest for the O phase, and lowest for the β /B2 phase; the mean Young’s modulus has the same trend in Ti-22Al-25Nb alloy. Phase transition stress results in cracks in the weld joint of Ti-22Al-25Nb alloy during post-weld heat treatment. By improving post-weld heat treatment, the ultimate strength of the Ti-22Al-25Nb alloy weld joints reaches 750 MPa, which is 72.5% that of the base material.