THERMODYNAMIC AND KINETIC FACTORS CONTROLLING THE FORMATION OF NANOCRYSTALLINE FECUNBSIB MATERIALS

A detailed study of nanocrystallization by thermal annealing of amorph ous Fe73.5Cu1Nb3Si17.5B5 is presented. Experimental technique s includ e X-ray diffraction, transmission electron microscopy, Mossbauer spect roscopy and differential scanning calorimetry. Isothermal annealing in the temperature range 450-515 degrees C results in a sharp increase o f the transformation rate and a subsequent slowing down of the process at long times (typically up to 4h). The evolution of the nanocrystall ine phase has bee followed as a function of annealing time at 490 degr ees C. The results show that a quasi DO3 structure emerges directly fr om the amorphous matrix and the faster changes correspond to an increa se of the amount crystalline phase. the first stages of the crystalliz ation process (up to 10% of crystalline phase achievement) under both isothermal and continuous heating regimes are controlled by homogeneou s nucleation and three dimensional growth whose rates, and the viscosi ty, are calculated as a function of temperature. The further nanocryst allization is controlled by diffusion limited growth.