Correlation between isothermal expansion and functional properties change of the Fe81B13Si4C2 amorphous alloy

The structural changes effect on functional properties of ribbon shaped samples of the Fe81B13Si4C2 amorphous alloy during annealing process was investigated in this paper. Differential scanning calorimetry method has shown that this alloy crystallizes in one stage, in temperature range from room temperature up to 700?C. Structural relaxation process was investigated by sensitive dilatation method in nonisothermal and isothermal conditions. It has been shown that structural relaxation process occurs in two stages by measuring thermal expansion at constant temperatures of t1=420?C, t2 = 440?C and t3 = 460?C. The first stage is characterized by linear logarithmic dependence of thermal expansion upon time at constant temperature. The second stage of structural relaxation process is characterized by linear dependence of isothermal expansion upon the square root of process time. These results imply that the first stage of structural relaxation process is a rapid kinetic process, while the second stage of structural relaxation process is a slow diffusion process. The rate constants k11 = 2,27?10- 3 s-1, k12 = 2,79?10-3 s-1, k13 = 3,6?10-3 s-1, k21 = 0,67?10-4 s-1, k22 = 3,72?10-4 s-1, k23 = 21,53?10-4 s-1 and activation energies E1 = 48,64 kJ/mol and E2 = 366, 23 kJ/mol were determined for both stages of structural relaxation process. The distinct correlation between structural relaxation process and magnetic susceptibility relative change was determined by thermomagnetic measurements. It has been shown that magnetic susceptibility can be increased by up to 80%, by convenient annealings after structural relaxation process, at magnetic field intensity of 8 kA/m.