Weldability and microstructure of laser-surface-remelted TiAl intermetallic alloy

Through the combination of superplastic forming/diffusion bonding (SPF/DB) with laser surface processing, a new approach to join TiAl workpieces is proposed. In situ observations of the transformation of laser-surface-remelted TiAl intermetallic alloy (LSMTIA) were carried out during heating. The effect of different temperatures on the rate of dendritic structure refinement and the mechanism of refinement were discussed. The results show that the metastable microstructure of TiAl alloy obtained by laser surface remelting can be transformed into fine, equiaxed grains at certain elevated temperatures, and the structural transformation rate accelerates with the elevation of heating temperature. During continuous heating with a heating rate of 10 °C min−1, the dendritic structure is transformed into fine-grained structure at about 860 °C; the hardness of LSMTIA varies correspondingly. The fine-grained structure and the property variation of LSMTIA offer a good basis to SPF/DB. With significant microstructural refinement achieved by laser treatment of the surface and subsequent heat treatment, SPF/DB at a lower temperature and in a shorter time than conventional SPF/DB was achieved, and the bonding effects brought by temperature, pressure and time were discussed, respectively. The results show that, at the condition of 900 °C and 60 MPa, sound bonds could be obtained in 1 h.