Technology and properties of Ti₃Al/Ti/Ti₂AlNb diffusion welding

Ti₃Al and Ti₂AlNb alloy were connected by diffusion bonding with Ti foil as interlayer. Through a number of analysis methods such as SEM, EDS and XRD, it was discovered that the typical interface structure of Ti₃Al/Ti/Ti₂AlNb joint was Ti₃Al/α-phase +β-phase/B₂-rich phase/Ti₂AlNb. The effect of process parameters, including thickness of interface layer, bonding temperature and holding time, on the interface morphology and property of the joint was investigated. The results show that when the thickness of Ti foil was 10μm, bonding temperature was 900℃ and holding time was 120 min, the resultant Ti₃Al/Ti/Ti₂AlNb joint had the optimized microstructure and properties. Increasing the foil thickness caused uneven diffusion of Ti, Al and Nb. The direct bonding temperature of Ti₃Al/Ti₂AlNb was 1000℃, the addition of Ti foil interlayer could reduce the bonding temperature to 900℃. So the damage of high temperature thermal cycling to Ti₃Al alloy was decreased. The tensile strength of the joint increased from 795 MPa to 906 MPa. The holding time from 90 min to 120 min could ensure sufficient diffusion and reliable connection.