Effect of Strain Rate on Microstructure and Mechanical Properties of TC18 Thick Plate by Electron Beam Welding

Influence of the strain rate on microstructures, tensile properties and strain hardening behavior of the electron beam welded joint of TC18 titanium alloy under optimized welding parameters was investigated with three slices (top, middle and bottom). The results show that the welding leads to significant microstructural changes across the joint. The microstructure of fusion zone is composed of coarsened β phase and secondary α-phase. Compared with the base metal, the joint slices along the thickness exhibits a lower strength and plasticity but a further higher hardening capacity. The strength and ductility of the bottom slices are higher than those of the middle and top slices. The maximum yield strength and ultimate tensile strength of the welding slices reach 83% of those of the base metal at the strain rate of 1×10⁻² s⁻¹ . The hardening capacity of welding slices decreases with increasing of the strain rate. Tensile fracture occurs in the weld zone. The fracture process of the top slice is cleavage fracture. However, the middle and bottom slices are quasi-cleavage crack.