Effect of Cu and Co addition on non-isothermal crystallization kinetics of rapidly quenched Fe-Sn-B based alloys

Crystallization kinetics of rapidly quenched Fe-Sn-B alloys under non-isothermal conditions were studied using differential scanning calorimetry. Formation of crystalline phases was analyzed by X-ray diffraction. Nominal chemical compositions were Fe ₈₁Sn ₇B ₁₂, (Fe ₃Co ₁) ₈₁Sn ₇B ₁₂ and (Fe ₈₁Sn ₇B ₁₂) ₉₉Cu ₁. Alloys were prepared by planar flow casting in the form of ribbons approximately 20 µm thick and 6 mm wide. Mechanism of crystallization was studied under framework of the Johnson-Mehl-Avrami-Kolmogorov model. Alloys exhibit two stages of crystallization. Results show decrease in activation energy of the first stage of crystallization with addition of Cu and increase with addition of Co. Crystallization mechanism of the first stage of crystallization for Fe ₈₁Sn ₇B ₁₂ and (Fe ₈₁Sn ₇B ₁₂) ₉₉Cu ₁ alloy starts as growth with increasing nucleation rate and continues as growth with decreasing nucleation rate. Addition of Co changes mechanism of crystallization. Which in case of (Fe ₃Co ₁) ₈₁Sn ₇B ₁₂ alloy starts as a growth with increasing nucleation rate. Then changes to growth with decreasing nucleation rate. After which nucleation rate decreases to zero. Rest of crystallization stage is governed by growth of pre-existing nuclei. In the first stage of crystallization α-Fe phase with bcc structure crystallizes from amorphous matrix. In the second stage of crystallization the remaining amorphous matrix crystalizes into tetragonal Fe ₂B phase and hexagonal FeSn phase. After the first stage of crystallization, 50 % to 55 % volume of studied alloys were crystalized. Addition of Cu decreases crystalline size of α-Fe crystallites by 60 % and decreases concentration of Sn in α-Fe phase by 0.8 at. %. Addition of Co doesn`t affect the size of α-Fe crystallites and decreases the concentration of Sn in α-Fe phase by 1.7 at. %.