Diffusion of ⁵⁷Co in amorphous Fe-RE (RE = Dy, Tb, and Ce) and Fe-Si-B alloys

Abstract

Tracer diffusion of ⁵⁷Co in amorphous Fe_100−xDy_x (x = 20–40), Fe₇₅Tb₂₅, Fe₆₇Ce₃₃, and Fe₈₀Si₆B₁₄ alloys prepared by dc sputtering has been studied at temperatures of 523 and 573 K. In the Fe-Dy alloys the diffusion coefficient of ⁵⁷Co shows a maximum at 33 at.% Dy. The magnitude of the diffusion coefficient of ⁵⁷Co in Fe₇₅Tb₂₅ is nearly equal to that in Fe₇₅Dy₂₅, while those in Fe₆₇Ce₃₃ and Fe₈₀Si₆B₁₄ are about one order of magnitude less than the values in Fe₆₇Dy₃₃ and Fe₈₀Dy₂₀. This suggests that the atomic size of the diffusant and the density of the matrix are dominant in the diffusion. Temperature dependence of the diffusion coefficient D of ⁵⁷Co in the amorphous Fe₇₅Dy₂₅ alloy has been determined in the range from 493–673 K. It shows a linear Arrhenius relationship expressed by D = 5.7 × 10⁻² exp(−199 kJ mol⁻¹/RT) m² s⁻¹. The magnitudes of the pre-exponential factor and the activation energy suggest that the cobalt tracer atoms in the amorphous Fe₇₅Dy₂₅ alloy diffuse by an interstitial-like mechanism.