Effects of post-weld heat treatment on fracture toughness of linear friction welded joint for dissimilar titanium alloys

The effect of post-weld heat treatment processing parameters on the microstructure, fracture morphology, fracture toughness and crack propagation direction of the linear friction welded joint for dissimilar titanium alloys was investigated. Results show that weld zone and one side of thermo-mechanically affected zone are weak zones for fracture toughness of linear friction welded joint for dissimilar titanium alloys after welding; post-weld heat treatment can effectively improve the fracture toughness of the weak zones, but has less effect on that of the other side. During the heat treatment process, the fine acicular and equiaxed microstructures in the weak weld zones grow and partly transform into lamellar microstructure which can increase the total length of the crack along with energy consumption and relieve the residual stress, resulting in enhancing the fracture toughness of the joint. Meanwhile, the fracture morphology gradually transforms from intergranular fracture to ductile-brittle mixed fracture and dimple fracture.