This study investigated fatigue crack propagation rates in the base metal (BM), heat affected zone (HAZ) and weld metal (WM) of a double-sided electron beam welded (EBW) joint of Ti alloy with a thickness of 140 mm in different layers. Firstly, this research measured fatigue crack propagation rates at different zones in each layer of the joint and drew curves thereof. The results demonstrate that the WM in the second layer of the double-sided EBW joint shows poor resistance to fatigue crack propagation. Secondly, the metallographic microstructures of different zones in different layers of the joint were observed. It is found that there are a lot of needle-shaped martensites growing in a specific direction at the HAZs in different layers of the joint. Finally, precipitates in different zones in each layer of the joint were studied by using a high-resolution scanning electron microscope (SEM). The results show that needle-shaped martensites in the WM of the joint are interlaced and present basketweave microstructures, while there are needle-shaped, lamellar martensites at the HAZs in each layer of the joint.

本研究研究了厚度为140 mm的钛合金双面电子束焊接（EBW）接头在母材（BM），热影响区（HAZ）和焊接金属（WM）中的疲劳裂纹扩展速率，层。首先，这项研究测量了接头每一层不同区域的疲劳裂纹扩展速率，并绘制了曲线。结果表明，双面EBW接头第二层的WM对疲劳裂纹扩展的抵抗力较差。其次，观察了接头不同层不同区域的金相组织。发现在关节不同层的热影响区有许多沿特定方向生长的针状马氏体。最后，使用高分辨率扫描电子显微镜（SEM）研究了关节各层不同区域的沉淀物。结果表明，接头WM中的针状马氏体是交织的，并具有篮状微结构，而接头的每一层中的热影响区都有针状的层状马氏体。