Tracer diffusion and thermal stability in amorphous Co-Zr and their relevance for solid-state amorphization

Measurements have been made of tracer diffusion, thermal relaxation, and crystallization in amorphous ${\mathrm{Co}}_{89}$ ${\mathrm{Zr}}_{11}$ samples prepared by melt spinning in vacuum. The diffusivity in as-quenched material is enhanced due to the presence of quasivacancies (excess free volume). During an annealing treatment, the quasivacancies are eliminated and the diffusivity approaches a constant value that depends on temperature only and pertains to a metastable equilibrium state. Tracer self-diffusion of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ measured over the temperature range 513–693 K in relaxed amorphous material can be described by D${(}^{57}$Co)=8.03×${10}^{\mathrm{-}7}$ exp(- 147 kJ ${\mathrm{mol}}^{\mathrm{-}1}$ / RT ) ${\mathrm{m}}^2$ ${\mathrm{s}}^{\mathrm{-}1}$. Tracer diffusion of Au in the temperature range 633–684 K is represented by D${(}^{195}$Au)=7.90×${10}^{\mathrm{-}1}$ exp(- 274 kJ ${\mathrm{mol}}^{\mathrm{-}1}$ / RT ) ${\mathrm{m}}^2$ ${\mathrm{s}}^{\mathrm{-}1}$.