2003 Volume 44 Issue 1 Pages 2-13
Impurity diffusion in α-Ti and α-Zr is characterized by fast interstitial diffusion of small atoms and slow substitutional diffusion of large atoms. The mechanism of the fast diffusion is discussed on the basis of the several features: the effect of α-β phase transformation, the diffusion anisotropy, the atomic size effect and the correlation between solubility and diffusivity. The temperature dependence of the diffusion coefficients of all the solutes and solvent Ti studied in α-Ti follows the Arrhenius law, whereas in α-Zr, all the elements studied with exception of Ti show downward curvatures that follow the self-diffusion behaviour in α-Zr. The influence of ultra-fast diffusion impurities on the diffusion process in these matrices, as well as the possibility that different mechanism acts in each matrix is analyzed.