Interfacial microstructure and mechanical properties of diffusion bonding of Ti₃Al and Ti₂AlNb alloys

Ti₃Al and Ti₂AlNb alloys were joined by direct diffusion welding. The influence of bonding pressure, bonding temperature and holding time on the interface morphology and property of the joint was studied. The interface structure was analyzed by SEM, EDS and XRD, and the mechanical properties of joints were tested. The results show that typical interface structure of direct diffusion bonding joints is Ti₃Al/O-phase and α₂-phase/B₂-rich phase/Ti₂AlNb. When bonding temperature is 1000℃, holding time is 60min, bonding pressure is 5MPa, the shear strength could reach 635MPa and the tensile strength could reach 795MPa. Both joints fracture at the Ti₃Al-base alloy. After thermal cycling (1000℃/60 min), the tensile strength of Ti₃Al decreases to 76% of the original strength. Welding defects occur when bonding temperature is below 950℃ or holding time is less than 60min. The bonding temperature higher than 1050℃ or holding time more than 120min will lead to phase transition of Ti₃Al.