Microstructure evolution and mechanical properties of diffusion bonding high Nb containing TiAl alloy to Ti ₂ AlNb alloy

A serious of diffusion bonding (DB) tests between high Nb containing TiAl alloy and Ti ₂ AlNb alloy were conducted and the bonded joints were post-bonded heat treated (PBHT) at 1000 °C for 10h. The microstructure observation showed that the thickness and microstructure of the bonding interface were changed with the bonding parameters. The optimized parameter for direct solid-state DB high Nb containing TiAl to Ti ₂ AlNb alloy was obtained as 1000°C-20MPa-90min. PBHT at 1000 °C/10h can significantly promote elements diffusion, phase transformation and microstructure evolution in bonding interface. The tensile results showed that PBHT can remarkably improve the tensile strength of TiAl/Ti ₂ AlNb joints. After PBHT, the tensile strength can be increased from 80% to 146% compared with TiAl alloy by changing the failure mode. However, the Al(Nb,Ti) ₂ phase in the bonding interface can't eliminated by PBHT in this study. This work provides a strategy not only contributing to control the structure of bonding interface during DB and after PBHT but also improving the properties of TiAl/Ti ₂ AlNb joints.