The diffusivity of Sn in -Ti was determined, at temperatures ranging from 1173 to 1773K, under pressures of between 0.1MPa and 2.8GPa, by using Ti/Ti-4.9at%Sn diffusion couples. It was found that the diffusion coefficients at each pressure level exhibited an upwards curvature of the Arrhenius plot. The degree of curvature became greater with increasing pressure. The activation volume, V, was deduced (from the isothermal pressure dependences) to be between 0.27Vo and 0.41Vo, where Vo was the molar volume of Ti at room temperature and atmospheric pressure. The magnitude of V/Vo was equal to about half of the V/Vo value which was expected for body-centered cubic systems and a simple monovacancy diffusion mechanism. However, it was very close to a published value (0.33) for self-diffusion in -Ti, and to the values (0.28 to 0.41) which had been reported for W diffusion in -Ti. The increase in curvature of the Arrhenius plots, due to pressure, and the small values of V/Vo were attributed to the softening of phonons by pressure.

H.Araki, T.Yamane, Y.Minamino, S.Saji, Y.Fujiishi, Y.Miyamoto: Materials Transactions, 1993, 34[9], 763-70

Table 248

Diffusivity of Sn in -Ti