Impurity-diffusion investigations in amorphousTi60Ni40

Tracer-diffusion coefficients D of the impurities B, Be, Fe, and Si in the amorphous alloy ${\mathrm{Ti}}_{60}$ ${\mathrm{Ni}}_{40}$ have been measured in the temperature range 598–690 K using the technique of secondary-ion-mass spectrometry for concentration depth profiling. The temperature dependence of the measured diffusion coefficients in each case exhibited an Arrhenius behavior and yielded the values of the activation energy Q in units of eV as (2.05±0.14), (2.20±0.15), (2.33±0.14), and (2.35±0.15) for the diffusion of B, Be, Fe, and Si, respectively. The corresponding values of the preexponential factor of the diffusion coefficient ${\mathit{D}}_0$ in units of ${\mathrm{m}}^2$ ${\mathrm{s}}^{\mathrm{-}1}$ were obtained as 7.4×${10}^{(\mathrm{-}4.0\pm 1.1)}$, 1.7×${10}^{(\mathrm{-}3.0\pm 1.2)}$, 2.5×${10}^{(\mathrm{-}3.0\pm 1.1)}$, and 5.8×${10}^{(\mathrm{-}4.0\pm 1.8)}$. The results show the size dependence of D in this alloy according to which the small boron atoms diffuse about 2 orders of magnitude faster than the big silicon atoms while the diffusivities of Be and Fe had intermediate values following the trend ${\mathit{D}}_{\mathrm{B}}$>${\mathit{D}}_{\mathrm{Be}}$>${\mathit{D}}_{\mathrm{Fe}}$>${\mathit{D}}_{\mathrm{Si}}$ which is opposite to that of atomic radii r of the diffusing species, i.e., ${\mathit{r}}_{\mathrm{Si}}$>${\mathit{r}}_{\mathrm{Fe}}$>${\mathit{r}}_{\mathrm{Be}}$>${\mathit{r}}_{\mathrm{B}}$. The present data have been compared with those available in other amorphous alloys and in crystalline α-Zr and α-Ti. The notable distinct differences in the diffusion behavior in the amorphous and the crystalline cases are highlighted. On the basis of an observed correlation between the activation energy Q and the prefactor ${\mathit{D}}_0$ the possible diffusion mechanism in amorphous alloys is discussed.