Abstract
Differential scanning calorimetry was used to investigate the thermal behavior and non-isothermal crystallization kinetics of Fe80P13C7 glassy alloy in the forms of both bulk rod and the melt-spun ribbon. The apparent activation energy E of the first crystallization event for the ribbon and bulk samples are determined to be 432±17kJ/mol and 529±26kJ/mol, respectively, by Kissinger method, and 421±17kJ/mol and 514±26kJ/mol, respectively, by Ozawa method. It is proposed that larger the apparent activation energy E in the bulk sample may be ascribed to less amount of free volume in the supercooled liquid state of the bulk sample. The crystallization kinetics of the first crystallization event in the bulk and ribbon samples has been studied by non-isothermal approach and the local Avrami exponent for the first crystallization peak is evolved to reveal the crystallization mechanism. The local Avrami exponent of the bulk sample is less than 1.5 in the whole process for the first crystallization event, which means the crystallization mechanism of diffusion-controlled growth of pre-existing nuclei. While the local Avrami exponent for the ribbon sample is in the range of 1.5–2.5 in most cases, which means the crystallization mechanism is diffusion-controlled growth of the initial crystal type, at the same time, along with the nucleation rate decreases with time. The difference in the local Avrami exponent for the first crystallization event between the bulk and ribbon sample indicates that there are higher degree of short-range order in the bulk sample than that in the ribbon sample in the supercooled liquid state. These results distinctly indicate that the difference of crystallization behavior for the first crystallization event between the bulk and ribbon samples of Fe80P13C7 glassy alloy results from the difference nature in their supercooled liquid states which is related to the as-prepared state of samples.
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