Nucleation and growth of TiAl3 intermetallic phase in diffusion bonded Ti/Al Metal Intermetallic Laminate

Abstract

A novel nucleation and growth phenomenon for TiAl3 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/TiAl3 interface. With such dominant diffusion of Al towards Ti, the nucleation and growth of TiAl3 intermetallic phase in Ti/Al couple happens mainly at the Ti/TiAl3 interface rather than Al/TiAl3 interface which is evident by the presence of very fine nearly nano-sized TiAl3 nuclei/grains near the Ti/TiAl3 interface. Even though the intermetallic phase is expected to nucleate at Al/TiAl3 interface, the relatively larger TiAl3 grains near that interface depicts grain growth with minimal nucleation. The theoretical calculations on diffusion parameters are in accordance with experimental observations of TiAl3 intermetallic growth phenomenon in Ti/Al system.

Reactivity of the Ti–Al system: Experimental study and molecular dynamics simulations

“…Moreover, TiAl 3 was a major phase formed dur-ing the diffusion welding 24 . Recent works confirmed the leading role of TiAl 3 in the interface reaction between Ti and Al below melting point of Al 25,26 . Measurements of the linear growth rate of TiAl 3 layer in the temperature range 823 -923 K gave activation energy 128.7 kJ/mol 26 .…”

“…Measurements of the linear growth rate of TiAl 3 layer in the temperature range 823 -923 K gave activation energy 128.7 kJ/mol 26 . Since the forming has polycrystalline structure with well-developed grain boundaries network 25 , the grain boundary diffusion must be also taken into account. Basing on to the normal parabolic growth of the TiAl 3 layer (which was the only phase appeared on the Ti/Al boundary at 823-923 K), activation energy of 33.1 kJ/mol was obtained for the low temperature grain boundary diffusion controlled growth, and 296.2 kJ/mol -for the high temperature bulk diffusion controlled growth 27 .…”

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“…Work [25] is a study of the process of initiation and growth of Al 3 Ti intermetallic phase between Al and Ti layers in diffusion welding with further annealing. Used for this purpose were aluminium and titanium sheets of 0.5 mm thickness.…”

A Review on Laser-Assisted Joining of Aluminium Alloys to Other Metals

“…The growth is promoted by an increase in heat input, providing a slower cooling rate. It was determined that the Al diffusion coefficient is 20 times higher than that of Ti, which makes the Ti diffusion rate controlling [172]. Some researchers [173] observed only the presence of the TiAl 3 phase in the reaction layer at low heat input, with possible low fraction of Ti-rich phases.…”