Growth of intermetallic layer in multi-laminated Ti/Al diffusion couples

Solid-state reactive diffusion between Ti and Al was investigated in the temperature range of 520–650 °C by employing multi-laminated Ti/Al diffusion couples. In samples annealed up to 150 h intermetallic TiAl3 is the only phase observed in the diffusion zone and the preferential formation of this compound in Ti/Al diffusion couples was predicted using an effective heat of formation model. The present work indicated that both Ti and Al diffused into each other and the growth of the TiAl3 layers occurred mainly towards the Al side. The TiAl3 growth changes from parabolic to linear kinetics between 575 and 600 °C, characterized by activation energy of 33.2 and 295.8 kJ mol−1, respectively. It is suggested that the low-temperature kinetics is dominated by the diffusion of Ti atoms along the grain boundaries of the TiAl3 layers, while the reaction at the TiAl3/Al interfaces in the high-temperature regime is limited by the diffusion of Ti atoms in the Al foils as a result of increased solubility of Ti in Al with increasing temperature.