Influence of the preparation cooling rate on crystallization kinetics of Fe74Mo6P13C7 amorphous alloys

Fe ₇₄Mo ₆P ₁₃C ₇ amorphous alloys have been prepared by three techniques with different preparation cooling rates, namely the melt-spinning, copper-mold casting, and J-quenching techniques. Differential scanning calorimetry (DSC) was used to investigate the thermal behavior and non-isothermal crystallization kinetics of the amorphous alloy samples. Through this, the effect of the preparation cooling rate on the amorphous alloy thermal parameters, apparent activation energy ( E _app ), and first crystallization event kinetics were investigated. The DSC tests show that there are no significant differences in the glass transition temperature ( T _g ) and the initial crystallization temperature ( T _x) among the Fe ₇₄Mo ₆P ₁₃C ₇ amorphous alloy samples prepared by the different techniques, but the total crystallization heat increases with the preparation cooling rate. The E _app values corresponding to the first crystallization events of the three amorphous alloy samples are determined by the Kissinger and Ozawa methods, and the results show that E _app increases with a decreasing preparation cooling rate. This indicates that the amorphous alloy sample prepared at the lower cooling rate has a larger crystallization resistance, which may be ascribed to the lesser free volume. The non-isothermal kinetics analyses of the first crystallization events show that the local Avrami exponents ( n) of the three amorphous alloy samples are < 1.5 during the initial stages, implying a crystallization mechanism based on the direct growth of pre-existing nuclei with a zero nucleation rate. This is then < 2.5 for the two bulk samples and in the range of 2.5–3.0 for the melt-spun ribbon sample in the intermediate crystallization stages. These values indicate the diffusion-controlled three-dimensional growth of small particles with decreasing ( n < 2.5) and increasing ( n > 2.5) nucleation rates. Meanwhile, the n values increase with the preparation cooling rate, indicating more short-range order in the amorphous alloy sample prepared at the lowest cooling rate.