Diffusion Bonding of Dissimilar Intermetallic Alloys Based on Ti2AlNb and TiAl

Direct diffusion bonding of an orthorhombic Ti2AlNb base alloy to a TiAl base alloy, Ti-22Al-23Nb-2Ta and Ti-46.2Al-2Cr-2Nb-0.15B (at. pct), was carried out and the interface microstructure, formation of new phase at the interface and joint strength were characterized. At low temperature, a new phase with AlNb2-structure, Al(Nb, Ti)(2), was formed in the interface region adjacent to the 0 base alloy. The alpha(2) was found to be the major reaction product and developed in the interface region adjacent to the TiAl alloy as well as in the region adjacent to the O base alloy accompanying the formation of Al(Nb, Ti)(2). The occurrence of Al(Nb, Ti)(2) has been attributed to the different diffusivity of Nb and Al, leading to a eutectoid-like reaction. At relatively high temperature, Al(Nb, Ti)(2) did not form due to enhanced diffusion of Nb but a B2-enriched zone formed on the O alloy side instead after long holding time. Only when an appropriate interface microstructure was achieved by optimizing the bonding parameters, could the shear strength of the joint reach 80% of that of the TiAl base alloy.