Analysis of the interfacial microstructure, phase transformation, and diffusion mechanism of Ti2AlNb/TA2 joint diffusion-bonded at low temperature

Ti2AlNb-based alloys are mostly diffusion-bonded with conventional titanium alloy at a high temperature of above 920 degrees C. However, the high temperature could reduce the mechanical properties of the matrix alloy, especially the significant decrease in ductility. Therefore, trying to lower the temperature of the hot process of Ti2AlNb-based alloy is a work worth exploring. The microstructure evolution of the Ti2AlNb-based alloy and the conventional titanium during the bonding process at low temperatures has not been analyzed in detail. In this work, Ti2AlNb-based alloy is diffusion-bonded with TA2 titanium at a low temperature of 800 degrees C under the pressure of 10 MPa for 1 h. The detailed microstructure and phase transformation of the dissimilar joint are analyzed to reveal the interface reaction during the diffusion process. The ternary interdiffusion coefficients of the TA2/Ti2AlNb alloys diffusion couple are calculated to detect the diffusion behavior and mechanism of different elements at the low temperature of 800 degrees C. The result shows that the interfacial reaction phases are Al-rich alpha phase / Nb-rich beta + omega phase / tiny alpha phase / striped alpha(2) phase / beta/B2 + O + alpha(2) phase respectively from the TA2 titanium (alpha phase) matrix to the Ti2AlNb-based alloy (beta/B2 + O phase). The interdiffusion coefficients obtained suggest that the diffusion rate of Al is higher than that of Ti, while Ti diffuses faster than Nb. Additionally, it was observed that Ti facilitates the diffusion of Al and hinders the diffusion of Nb. On the other hand, both Al and Nb impede the diffusion of Ti in the TA2/Ti2AlNb alloy diffusion couple during the 800 degrees C diffusion process.