Glass Forming And Crystallization Analysis Of Co-Based Amorphous Alloys

The kinetic effects of glass transition on Co₄₃Fe₁₈Ta_5.5Sn₂B₃₀Si_1.5 and Co₄₁Fe₂₀Ta_5.5Sn₂B₃₀Si_1.5 amorphous alloys at different heating rates and the crystallization process with continuously heating were investigated in this study. The effects of solidification cooling rates and the compositions on glass forming ability were analyzed.Co-Fe-Ta-B-Si-Sn bulk amorphous alloy rods with different diameters were prepared with copper mold casting based on Co-Fe-Ta-B alloy by elements substitution. The amorphous ribbons were also made by melt-spinning. Thermal analysis shows that glass transition temperatures are decreased after substitution and the supercooled regionΔT is 69K for Co₄₃Fe₁₈Ta_5.5Sn₂B₃₀Si_1.5 bulk amorphous alloys with diameter of 3mm, showing a good thermal stability and a three-step process crystallization.The Gibbs free energy differences between the supercooled liquid and the crystal for Co₄₃Fe₁₈Ta_5.5Sn₂B₃₀Si_1.5 bulk amorphous alloys with different diameters and the amorphous ribbon indicate the increase in solidification cooling rates leads to the easiness of glass forming and a decrease in free energy, which is close to that of the crystal.The characteristic temperatures of Co₄₃Fe₁₈Ta_5.5Sn₂B₃₀Si_1.5 amorphous alloys show significant kinetic effects on the heating rates change and the glass transition effect becomes stronger with the increasing of solidification cooling rate. The crystallization active energy of amorphous ribbon calculated by Ozawa function is lest, while the bulk amorphous with the diameter of 1 mm is the largest. The crystallization active energies of amorphous ribbon increase at the initial stage and then drop with the augment of crystallized volume fraction. However, the crystallization active energies of bulk amorphous alloys decline linearly with the crystallized volume fraction increasing.The crystallization process of Co₄₃Fe₁₈Ta_5.5Sn₂B₃₀Si_1.5 and Co₄₁Fe₂₀Ta_5.5Sn₂B₃₀Si_1.5 bulk amorphous alloys with the same diameter of 2 mm were investigated. The active energies at different characteristic temperatures were calculated by Kissinger function. The Co₄₃Fe₁₈Ta_5.5Sn₂B₃₀Si_1.5 bulk amorphous alloy...