Comparative analysis of fracture toughness of EBW and TIG welded joints of TC4 titanium alloy

For TC4 titanium alloy joints prepared by electron beam welding (EBW) and tungsten inert-gas arc welding (TIG), the fracture toughness of the weld, heat -affected zone and base metal were tested at four temperatures. Furthermore, the fracture toughness test results were analyzed by comparing the fracture morphologies, hardness distributions and microstructures. It is found that the fracture toughness of TC4 titanium alloy TIG joint weld or heat- affected zone is better than that of titanium alloy base metal, and the CTOD value decreases with the reduction of test temperature. In contrast, the fracture toughness for EBW joint seam is lower than that of the base metal, and the CTOD value for HAZ is close to that for base metal. Meanwhile, the change of temperature has no significant effect on the corresponding CTOD values. The weld in the titanium alloy TIG joint has a relatively lower hardness value, which is basket-shaped α Phase and lower proportion of martensite distribution. Those are the basic reasons for its higher fracture toughness. The acicular martensite distribution in titanium alloy EBW joint leads to the higher local hardness and lower fracture toughness.