Investigation into the microstructure and mechanical properties of diffusion bonded TiAl alloys

TiAl alloys are potential candidates for replacing conventional Ti-alloys in gas turbine applications in the relatively lower temperature sections, owing to their low density and excellent high temperature properties. However, their intolerable ambient temperature brittleness hinders their use in such applications. Recently, TiAl alloys with some room temperature ductility were developed through alloy development programmes using special production routes such as powder metallurgy. However, the room temperature brittleness of these alloys could not be overcome. Sound joining of these alloys is a fundamental prerequisite for their successful integration into high temperature aerospace applications. It has been well demonstrated that diffusion bonding, a commonly used joining technology in conventional Ti-alloys, can successfully be used in joining of TiAl alloys both in as-cast or special-rolled conditions. In this study, diffusion bondability of a recently developed C containing TiAl alloy with a duplex microstructure using bonding parameters in the range of commercially available equipments was studied. Microstructural investigations in the joint area of the bonds were conducted to observe the presence of any weld defect. Additionally, the mechanical behaviour of the bonds was determined by shear testing to find out the optimum bonding parameters. Furthermore, the effect of post-bond heat treatment on the mechanical properties was investigated.