Dissimilar diffusion bonding behavior of hydrogenated Ti2AlNb-based and Ti-6Al-4V alloys

Highlights: • Hydrogen enhances diffusion bonding abilities of Ti₂AlNb-based and Ti-6Al-4V alloys. • Dissimilar joint shear strength of 711 MPa is obtained by proper hydrogen addition. • Joint shear strength depends on diffusion zone width. • Hydrogen can increase plasticity & diffusion ability and tailor microstructure. The effects of hydrogen concentration, heating rate and bonding temperature on dissimilar diffusion bonding of Ti₂AlNb-based and Ti-6Al-4V alloys were investigated. The microstructural evolutions of bonded joints and substrates during the diffusion bonding were observed using SEM and EDS while the mechanical properties of the joints were evaluated by shear tests. The average joint shear strength was found dependent on the diffusion zone width determined from EDS line scan. The typical joint interface shows a layered microstructure, comprising Ti₂AlNb substrate, continuous β layer, discontinuous α layer, equiaxed β layer and Ti-6Al-4V substrate. If both substrates are hydrogenated with 0.2 wt% hydrogen before diffusion bonding, a sound joint can be formed at 850 °C with a fast heating rate. This sound joint has a shear strength of 711 MPa, and its Ti-6Al-4V substrate favors a non-damaged bimodal microstructure. The fast heating rate also causes less hydrogen desorption and oxidation during the heating stage, which facilitates the subsequent diffusion bonding process. The hydrogen addition influences the diffusion bonding process through three main routes including plasticity improvement, diffusion ability enhancement and microstructure tailoring.