Abstract
A novel nucleation and growth phenomenon for TiAl(3) intermetallic phase in Ti/Al diffusion couple is proposed based on diffusion kinetics. The interdiffusion and intrinsic diffusion co-efficients are calculated to make evident of dominant diffusion of Al towards Ti in Ti/Al diffusion couple obtained by solid state diffusion bonding. It was surprising to observe that the diffusion rate of Al was around 20 times higher than Ti with the formation of Kirkendall pores near the Al/TiAl(3) interface. With such dominant diffusion of Al towards Ti, the nucleation and growth of TiAl(3) intermetallic phase in Ti/Al couple happens mainly at the Ti/TiAl(3) interface rather than Al/TiAl(3) interface which is evident by the presence of very fine nearly nano-sized TiAl(3) nuclei/grains near the Ti/TiAl(3) interface. Even though the intermetallic phase is expected to nucleate at Al/TiAl(3) interface, the relatively larger TiAl(3) grains near that interface depicts grain growth with minimal nucleation. The theoretical calculations on diffusion parameters are in accordance with experimental observations of TiAl(3) intermetallic growth phenomenon in Ti/Al system.