Interdiffusion between the ordered intermetallic compound TiAl and Mo

Abstract

Abstract Diffusion experiments on Mo/γ-TiAl couples were conducted at 900, 1000 and 1100 °C for annealing times varying from 121 to 553 h. Two intermediate phases, δ-(Mo,Ti)3Al and β′-(Mo,Al)Ti, were found to develop between the Mo and γ-TiAl phases. The diffusion path was found to be Mo/δ-(Mo,Ti)3Al/β′-(Mo,Al)Ti/γ-TiAl. The growth of both the δ and β′ phases can be described by parabolic relationships. All diffusion couples were examined by electron probe microanalysis (EPMA). The Boltzmann-Matano analysis was applied to the δ and β′ phases. The interdiffusion coefficients obtained at 1000 °C are: D MoMo δ = 3.0 × 10 −12 , D AlAl δ = 2.9 × 10 −12 , D MoMo β′ = 3.2 × 10 −12 and D AlAl β′ = 4.0 × 10 −12 cm 2 /Sec . Using the Darken-type relationship between interdiffusivities and intrinsic diffusivities, the intrinsic diffusion coefficients of the β′-phase were also obtained. The intrinsic diffusion coefficients obtained at 1000 °C are: DMoβ′ = 2.0 × 10−12, DAlβ′ = 8.7 × 10−12 and DTiβ′ = 4.7 × 10−12 cm2 sec Analysis of the data for the Mo/γ-TiAl couple annealed at 1100 °C for 308 h shows that the high interdiffusion fluxes of Mo are a consequence of the lattice movements toward γ-TiAl with respect to the Matano plane. The existence of planar interfaces in this diffusion couple was also discussed. By determining the dominant diffusing species in each intermediate phase and the velocities of all three interfaces, it was shown that planar interfaces should be stable during the growth of the δ and β intermediate phases.