The diffusion coefficient of W in -Ti was determined at temperatures ranging from 1323 to 1673K, under pressures of between 90kPa and 2.8GPa, by using diffusion couples. The value of the activation volume, V, which was deduced from the pressure dependence of the diffusion coefficient at various temperatures, was between 0.28Vo and 0.41Vo, where Vo was the molar volume of Ti at room temperature and atmospheric pressure. These values were considerably smaller than those found for body-centered cubic systems with a simple monovacancy diffusion mechanism. A model for phonon-controlled diffusion was applied to diffusion in Ti under high pressures, and V was evaluated for self-diffusion and W diffusion in Ti as functions of temperature and To/P, where P was the pressure and To was the hypothetical temperature at which the body-centered cubic lattice became unstable to atomic displacements in the <111> direction. The V value which was estimated for To/P = 11K/GPa agreed with experimental results for W diffusion and self-diffusion in Ti. This agreement suggested that diffusion in -Ti involved phonon-assisted diffusion jumps via monovacancies, and was characterized by a positive temperature-dependent migration enthalpy and a positive temperature-dependent migration volume.

H.Araki, Y.Minamino, T.Yamane, S.Saji, S.Ogino, Y.Miyamoto: Journal of the Japan Institute of Metals, 1993, 57[5], 501-8