Nanocrystallisation mechanisms in FeCuNbSiB-type alloys from comparative HREM, STM, TGM and calorimetric studies

The process of nanocrystallisation in two alloys (Fe73.5Cu1Nb3S13.5B9 and Fe77.5Cu1Nb3Si9.5B9) as a function of their annealing treatments was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TGM) under magnetic field, conventional transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HREM), electron diffraction (ED) and scanning tunneling microscopy (STM). In addition to information about nucleation and growth of the grains, the two microscopic methods reveal amorphous interfaces between α-Fe(Si) nanoprecipitates. It was shown by means of HREM that during annealing an overlapping of the diffusion fields between neighboring α-Fe(Si) nanoparticles causes their coalescence into grains, which saturate with the annealing time. Scanning tunneling microscopy reveals atomic resolution in the nanocrystals as well as in their grain boundaries. On the basis of these experiments we established annealing conditions which yield the best soft magnetic properties.