IMPURITY-DIFFUSION INVESTIGATIONS IN AMORPHOUS TI60NI40

Tracer-diffusion coefficients D of the impurities B, Be, Fe, and Si in the amorphous alloy Ti60Ni40 have been measured in the temperature ra nge 598-690 K using the technique of secondary-ion-mass spectrometry f or concentration depth profiling. The temperature dependence of the me asured diffusion coefficients in each caw exhibited an Arrhenius behav ior and yielded the values of the activation energy Q in units of eV a s (2.05+/-0.14), (2.20+/-0.15), (2.33+/-0.14), and (2.35+/-0.15) for t he diffusion of B, Be, Fe, and Si, respectively. The corresponding val ues of the preexponential factor of the diffusion coefficient D0 in un its of m2 s-1 were obtained as 7.4 X 10(-4.0+/-1.1), 1.7 X 10(-3.0+/-1 .2), 2.5 X 10(-3.0+/-1.1), and 5.8 X 10(-4.0+/-1.8). The results show the size dependence of D in this alloy according to which the small bo ron atoms diffuse about 2 orders of magnitude faster than the big sili con atoms while the diffusivities of Be and Fe had intermediate values following the trend DB > D(Be) > D(Fe) > D(Si) which is opposite to t hat of atomic radii r of the diffusing species, i.e., r(Si) > r(Fe) > r(Be) > r(B). The present data have been compared with those available in other amorphous alloys and in crystalline alpha-Zr and alpha-Ti. T he notable distinct differences in the diffusion behavior in the amorp hous and the crystalline cases are highlighted. On the basis of an obs erved correlation between the activation energy Q and the prefactor D0 the possible diffusion mechanism in amorphous alloys is discussed.