Microstructure evolution and diffusion mechanism of Nb/TiAl alloy diffusion-bonded joints

The interdiffusion behavior in Nb/TiAl alloy diffusion couples was studied. The process was carried out in the temperature range of 950-1400 degrees C for 8 h in the vacuum hot-pressure sintering furnace. The microstructural evolution was observed by optical microscopy (OM), electron backscattered diffraction (EBSD), X-ray diffraction (XRD) technique and transmission electron microscopy (TEM). The element concentration distribution at the bonded interface was obtained by scanning electron microscopy with an energy-dispersive X-ray spectroscopy (EDS) apparatus. The thickness of reaction interface increases with bonding temperature increasing. The formed phases in diffusion interface are found to be O-Ti2AlNb, sigma-Nb2Al, delta-Nb3Al and Nb solid solution (Nbss) at 1350 degrees C. The average interdiffusion coefficient of the interface elements was calculated by the theory of Dayananda. The results indicate that Al diffuses faster than Nb and Nb diffuses faster than Ti in the Ti-Al-Nb system. Meanwhile, it is found that Ti promotes the diffusion of Al and Nb and Nb inhibits the diffusion of Ti and Al in the process of diffusion.