Fracture Behaviour of Ti-6Al-4V Weldments and its Relation to Microstructural Features.

Tensile fracture of a-(5 titanium alloy weldments is sensitive to microstructure. Thus, though it occurs macroscopically at low ductility, it follows a void coalescence mechanism. The paper describes work in which the alloy Ti-6AI- 4V has been welded and heat-treated under different conditions. The role of the morphology and distribution of the a and p phases on the mode of tensile fracture has been discussed. Fracture toughness measurements of the fusion zone have shown that (i) the as-welded structure resists crack growth better than the base material; and (ii) post-weld treatment high in the (x-p field (say at 900°C) confers a further improvement over the as-welded level, while treatment at intermediate temperatures like 700°C could actually be detrimental. The paper explains the reasons for this behaviour in terms of microstructural features and scanning-electron fractographic observations.