β-Ti中のCuおよびAgの拡散

Abstract

Interdiffusion coefficients in the β-phase Ti-Cu and Ti-Ag alloys have been determined by Matano’s method in the temperature range between 1173 and 1773 K with (pure Ti)-(Ti-2.28 at%Cu alloy) and (pure Ti)-(Ti-2.76 at%Ag alloy) couples. In both alloys the interdiffusion coefficients have been shown to be independent of concentration of solutes, and then the impurity diffusion coefficients of Cu and Ag in β-Ti have been estimated by extrapolating the interdiffusion coefficient to infinite dilution of the solute in each alloy. The diffusion coefficient of Ag, \ ildeDAg(0), in β-Ti is of nearly the same magnitude as the self-diffusion coefficient of β-Ti, DTi∗, and the Arrhenius plot of \ ildeDAg(0) shows a significant curvature, as in the case of the self-diffusion in β-Ti. On the other hand, the diffusion coefficient of Cu, \ ildeDCu(0), in β-Ti is larger than DTi∗ by about one order of magnitude, and the Arrhenius plot of \ ildeDCu(0) shows also a curved line but the curvature of it is slightly looser than that in the case of \ ildeDAg(0). The curved Arrhenius plots can be explained by a monovacancy mechanism with a temperature dependent migration energy due to the softening of the LA 2/3 〈111〉 phonon mode in β-Ti. It has been noted that the activation energy for the impurity diffusion of Cu and Ag and self-diffusion in β-Ti is proportional to the square of radius of the diffusing atom.