Devitrification process of FeSiBCuBbX nanocrystalline alloys:: Mossbauer study of the intergranular phase

Mossbauer experiments were performed at room temperature using different experimental configurations on several series of nanocrystalline FeSiBCuNbX alloys (X = Zr, Nb, Mo and V) obtained after annealing treatments of melt-spun ribbons. The refinement of Mossbauer spectra allows the kinetics and the local structural rearrangement mechanisms associated with the nanocrystallization process to be compared. The hyperfine field distributions of the intergranular phase show the emergence of a bimodal behaviour that becomes significantly more pronounced from volumetric crystalline fractions estimated at similar to 20-25%, regardless of the nature of the substituting element. The hyperfine field distribution can be described by means of two Gaussian components, consistent with of a two-cluster-like model. Such a behaviour can be attributed to the presence of iron-rich and iron-poor zones within the intergranular phase, resulting from the diffusion process. These mechanisms are found to be independent of the nature of X. In addition, strong in-plane magnetic structures are evidenced for Nb-, Mo-, and V-based systems while the magnetic domains tend to be randomly distributed in Zr-based nanocrystalline alloys.