RESISTOMETRIC STUDY OF NANOCRYSTALLIZATION KINETICS IN FE-BASED METALLIC GLASSES

This paper is devoted to the kinetics of nanocrystallization occurring in the FeCuNbSiB metallic glasses at the time of their annealing abov e the primary crystallization temperature. This process has been studi ed by means of the resistometric method, and the results obtained were analyzed in terms of the so-called Johnson-Mehl-Avrami equation. It s hows that the nanocrystallization proceeds in two steps. The first, oc curring within the initial range of the annealing time, is characteriz ed by the Avrami exponent n congruent-to 1.5, a value which correspond s to three-dimensional diffusion-controlled growth in the bulk with th e pre-existing nuclei. Whereas the second, which takes place for longe r annealing time, shows n congruent-to 0.8, a value reflecting a slowi ng down of the kinetics. The origin of this reduction is not clear. Th e activation energy of the first process has also been estimated givin g E almost-equal-to 1.5 eV, a value much smaller than those hitherto r eported.