Correlation between thermal, kinetic, magnetic and electric effects in the crystallization process of amorphous magnetic alloys

By use of differential scanning calorimetry the mechanism of crystallization (devitrification) was investigated for magnetic amorphous alloys of compositions Fe 82B 13Si 5 (A) and Fe 75B 10Si 15 (B) in the temperature range between ambient and 600 °C. It was shown that both alloys crystallize in two stages between 480° and 520 °C. The energies of activation of the process, E 1 = 435.2 kJ/ mol and E 2 = 909.5 kJ/ mol for alloy A were derived, with corresponding frequency factors Z 1 = 1.1×10 30 min −1 and Z 2 = 8.1 × 10 60 min −1, where subscripts 1 and 2 denote the first and second stage of crystallization respectively. With alloy B the corresponding figures are E 1= 660.2 kJ/ mol, E 2 = 870.3 kJ/ mol, Z 1 = 4.9 × 10 45 min −1 and Z 2 = 7.6 × 10 58 min 1̄. The temperature dependence of the crystallization rate constants was followed with values at exo maxima of k 1 = 1.73 min −1 and k 2 = 4.17 min −1 for alloy A and k 1 = 3.1 min −1 and k 2 = 6.6 min −1 for alloy B. Parallel to the thermal and kinetic investigations, measurements of changes of the relative electric resistance and the relative magnetic permeability were followed. A clear correlation was observed between the changes in crystal structure (X-ray diffractograms) with the changes in electron and magnetic structures, particularly in the temperature range of the principal processes of alloy devitrification. The enthalpies of crystallization are rather close and are − ΔH =128 J/g for alloy A and 125 J/g for alloy B.