Pressure dependence of anomalous diffusion of zirconium in β-Titanium

Abstract

The impurity diffusion coefficients of Zr in β-Ti have been determined at temperatures from 1173 to 1773 K under pressures of 0.1 MPa and 1.0, 2.1, and 3.0 GPa using Ti/Ti-3.06 at. pct Zr diffusion couples. The Arrhenius plots of the diffusion coefficients exhibit strong curvature, and their degree becomes larger with increasing pressure. The activation volumes, ΔV, evaluated from the isothermal pressure dependence of the diffusion coefficient are 0.22 to 0.36 Ω, where Ω is the atomic volume of the host metal. The values of ΔV/Ω are very close to the ratio of 0.33 for self-diffusion in β-Ti reported by Jeffery and the ratios of 0.28 to 0.41 for W and Sn diffusion in β Ti reported by Arakiet al., whereas they are considerably smaller than that normally expected for diffusion in bcc metalsvia “simple” monovacancy mechanism. The increase in degree of curvature in the Arrhenius plot by pressure and the small values of ΔV/Ω can be interpreted in terms of the model of phonon-assisted diffusion jumpsvia monovacancies.