The effect of annealing on microstructure and tensile properties of Ti-22Al-25Nb electron beam weld joint

This study investigated the microstructure evolution and tensile properties of Ti-22Al-25Nb EBW joints. The fusion zone of the as-welded joint exhibited a fully B2 microstructure. Widmanstätten O particles precipitated out of B2 matrix after annealing and their size increased within a temperature range from 750 °C to 900 °C. In the heat affected zone, there was a transition of microstructure moving away from the fusion zone towards the base material. Strength and elongation of the as-welded sample were significantly improved after annealing, which was attributed to the strengthening effect of O precipitates and the slip transmission between O and B2 phases. Samples tensile tested at 650 °C all failed within the fusion zone and exhibited intergranular failure instead of transgranular failure at room temperature. The room temperature strength and hardness of the joints decreased with annealing temperature due to the coarsening of O precipitates. At 650 °C, failure occurred by intergranular fracture in the fusion zone and the joint strength of all annealed samples was similar due to similar B2 grain boundary strength.