Effect of postweld heat treatment on microstructure of electron beam welded joints of Ti₃Al

The postweld heat treatment of the electron beam welded joints of Ti₃Al-Nb was carried out at 650°C and 1000°C for 2 hours, respectively. Its effect on the microstructure of electron beam welded joints of Ti₃Al was investigated. Experimental results show that the microstructure of the weld under welding conditions is predominantly metastable, the columnar crystal metastructure of B2 phase. The microstructure of the weld is significantly influenced by the method of the heat treatment. The microstructure of the weld for postweld heat treatment at 1 000°C for 2 hours is the laminar structure (Widmanstaten structure) consisted of interphase α₂ and B2.After postweld heat treatment at 650°C for 2 hours, the small α₂ phase is precipitated in grain boundary and intragranular of B2 phase in the weld. After postweld heat treatment, whether 650°C/2 h or 1000°C/2 h, the microhardness distribution of the joints are both more uniform than that of the weld without heat treatment. However, The whole joint is softened after the postweld heat treatment at 1000° for 2 hours and the microhardness of the whole joint is not higher than that of postweld heat treatment at 650°C for 2 hours.