Hideki Araki, Toshimi Yamane, Tetsuya Nakatuka, Yoritoshi Minamino
May 2, 2013
It is shown that Arrhenius plots of diffusion coefficients of Cr in β-Ti can be represented under each pressure by two straight lines which are fitted in the temperature regions above and below about 1390 K. The activation enthalpies for high temperature are 167 kJ/mol under 0.1 MPa and 191 kJ/mol under 2.1 GPa, and those for low temperature are 147 kJ/mol under 0.1 MPa and 153 kJ/mol under 2.1 GPa. The ratios of activation volumes for impurity diffusion to the molar matrix volume are in the range of 0.38 to 0.45. When the phonon-softening model is applied, the activation enthalpy for the impurity diffusion in the absence of any phonon-induced lattice instabilities is 226 kJ/mol under 0.1 MPa and increases with pressure. Its pressure dependence indicates that the activation volume for the diffusion with no assistance from phonons is 66% of the molar matrix volume, and this result agrees with the activation volume for the diffusion in “normal” bcc metals.