Kinetics study on non-isothermal crystallization of the metallic Co 43Fe 20Ta 5.5B 31.5 glass

Abstract

The crystallization kinetics of metallic Co 43Fe 20Ta 5.5B 31.5 glass has been studied by continuous heating differential scanning calorimetry. The DSC traces have been analyzed in terms of activation energy and kinetic model. It is found that all the DSC traces have a single exothermic peak which is asymmetrical, with a steeper leading edge and a long high temperature tail. The heating rate has a significant influence on the shape of the DSC curve, activation energy and transformation mechanism. The existence of a critical heating rate, β crit = 20 K min −1, is evident. The activation energy for crystallization are determined as 594.8 and 581.4 KJ mol −1 for the heating rates β = 5–20 K min −1, and 437.7 and 432 KJ mol −1 for the heating rates β = 25–65 K min −1, when using the Kissinger equation and the Ozawa equation, respectively. For the volume fraction crystallized, α, E c dependence was obtained by the general Ozawa's isoconversional method. Using the Suriñach curve fitting procedure, the kinetics was specified. Namely, the crystallization begins with the Johnson–Mehl–Avrami nucleation-and-growth mode and the mode which has been well described by the normal grain growth kinetic law. These two modes are mutually independent. The proportion between the JMA-like and the NGG-like modes is related to the heating rate. The JMA kinetics is manifested as a rule in the early stages of the crystallization. The JMA exponent, n, initially being larger than 4 and continuously decreases to 1.5 along with the development of crystallization. The NGG-like mode dominates in the advanced stages of the transformation with the NGG exponent, m = 0.5 and is the major and principal kinetic characteristics for heating rate, β > 25 K min −1.