Concentration and temperature dependence of titanium self-diffusion and interdiffusion in the intermetallic phase Ti3Al

Abstract

Abstract Tracer diffusion of 44 Ti was measured between 1373 and 1126 K in four alloys in the composition range from 25 to 35 at% Al in ordered Ti 3 Al using the standard precision grinding sectioning technique and polycrystalline samples. The self-diffusion coefficient D ∗ Ti was found to be lower than self-diffusion in pure α-Ti and to increase very little with Al concentration. D ∗ Ti reveals Arrhenius behaviour which is described by the frequency factor D 0 = (2.44 −1.04 +1.81 ) · 10 −5 m 2 /s and the activation enthalpy Q Ti = (288.2 ± 5.7) kJ mol . Especially, the stoichiometric composition shows no distinguished diffusion behaviour. Interdiffusion was measured in single phase conditions by combining samples of 25 and 35 at% Al. The interdiffusion coefficient D was evaluated by Boltzmann-Matano analysis between 26 and 34 at% Al at different temperatures. Again, only a weak concentration dependence of D and an Arrhenius behaviour were detected. Applying Darken's equation, the self-diffusion coefficient of aluminium D ∗ Ti was calculated by combining D ∗ Ti (X Al , T) and D (X Al , T) with the thermodynamic factor Φ ( X Al, T ) in Ti 3 Al. D ∗ Al turned out to be smaller than D ∗ Ti , e.g. by a factor of 6 at 1170 K. The Arrhenius relation is characterized by D 0 = (2.32 −1.20 +2.48 ) · 10 −1 m 2 / s and Q Al = (394.5 ± 7.5) kJ mol . Different jump possibilities of the Al atoms are discussed. From the overall diffusion behaviour in the Ti 3 Al-phase it is concluded that atomic migration proceeds via thermal vacancies. There is no indication regarding the formation of constitutional vacancies. Diffusion behaviour of the components Al and Ti in Ti 3 Al is compared with our recent results of Al impurity diffusion (SIMS analysis) and self-diffusion in pure α-Ti.