Effect of welding on impact toughness of butt-joints in a titanium alloy

Impact toughness of a gas tungsten arc welded Ti–6Al–4V alloy butt-joint was evaluated at room temperature using standard Charpy V-notch specimens. The Charpy specimens were prepared with notch roots located either in the parent metal, in the heat-affected zone (HAZ), or in the weld metal. Optical metallography and Vickers microhardness test showed that the weld metal has the coarsest grains and highest microhardness compared with the HAZs and parent metal. However, Charpy impact toughness of the weld was found to be more than 50% higher than that of the parent metal or HAZ. The significant improvement in impact toughness was shown to be due to the much reduced amount of primary α grains in the weld metal. Boundaries of primary α grains were observed to be preferential sites for microcrack nucleation and provide relatively easy path for fracture propagation.