Fracture toughness and fatigue crack growth in Ti-6Al-4V friction stir welds

摘要

Friction stir welding of titanium holds the promise for producing joints with microstruc-tures and mechanical properties that are more comparable to wrought material than traditional fusion welding processes. Extensive data exist on the microstructure and static mechanical properties of titanium friction stir welds, but very little are available on the durability (fatigue) and even less on the damage tolerance (fracture toughness and fatigue crack growth). This paper presents the results of an investigation into the damage tolerance of friction stir welds made in 6 mm thick Ti-6Al-4V after a post-weld heat treatment. It was found that the apparent fracture toughness was lower than the wrought base material, 7-25% depending on the crack orientation relative to the weld, but the crack growth performance (ΔK vs. da/dN) of the weld in the absence of weld-induced residual stresses was identical to the base material.