Influence of thermal treatment upon the diffusion characteristics of Mo in Fe76Mo8Cu1B15 alloy

Mo tracer diffusion in Fe76Mo8Cu1B15 alloy was studied using serial sectioning method in the temperature range 548-648 K. Sputtering by Ar+ ions was applied as a sectioning technique. The measurement was carried out with the ribbon-like samples in as quenched state (q) and in two states after pre-anneals 683 K/1 h (a1) and 743 K/1 h (a2). The volume fraction of crystalline phase was checked by the Mössbauer spectroscopy. Measured concentration profiles consist of two distinct branches suggesting that two diffusion paths are operating. Diffusion coefficients Dv calculated from the near-surface branch were attributed to Mo volume diffusion in amorphous phase. Their values obtained for (a1) are lower than those obtained for (q) which is due to relaxation of free volume. The higher values, on the other hand, obtained for (a2) are influenced by faster short-circuit diffusion, which was attributed to diffusion in interfacial amorphous phase. Short-circuit diffusivity, P, of Mo was evaluated from concentration tails using both LeClaire's analysis and Divinski's theory derived for transition type-A/B regime.