HIGH-TEMPERATURE PHASE-TRANSFORMATION KINETICS AND THEIR EFFECTS ON DIFFUSION BONDING OF TI-48AL-2MN-2NB

Diffusion bonding of the intermetallic compound Ti-48Al-2Mn-2Nb has be en carried out in order to determine what effect temperature, time and starting base microstructure have on the bond line microstructure, in particular the extent of grain growth that occurs at the interface. T he results showed that the non-equilibrium lamellar and duplex microst ructures gave more grain growth at the interface compared with the equ ilibrium fully gamma microstructure for bonding upto 45 minutes in the temperature range 1200 degrees C-1350 degrees C. It was also observed that the base microstructure in the duplex and fully gamma samples wa s little changed during bonding, whereas in the lamellar samples decom position of the lamellar (alpha(2) + gamma) regions to allotriomorphic gamma occurred, particularly at 1250 degrees C.