Crystallization kinetics of Mg65Cu25Nd10 amorphous alloy

Amorphous Mg-based alloy Mg65Cu15Nd10 was prepared by melt-spinning. The kinetics of crystallization of the alloy was investigated by DSC using various heating rates, and its crystallization process and microstructure were confirmed by TEM, X-ray and electron diffraction. The changeable activation enthalpy E-a with crystalline fraction alpha was given by an isoconversional method, and the average value of Ea was 150 +/- 10 kJ/mol. What is more important, it is shown that this process cannot be described by the JMA model but the two-parameter empirical Sestak-Berggren equation gives a more quantitative description. It was established that the crystallization of Mg65Cu25Nd10 alloy is a multi-step mechanism and can be described by the Sestak-Berggren model with the kinetic parameters as follows: m = 0.59, n = 1.42, A = 6.35 x 10(14). It was found that the crystallization process of melt-spun Mg65Cu25Nd10 ribbons consists of three steps. The first crystallization reaction at about 453 K is connected with the formation of Mg2Cu nanocrystalline phase, followed by formation of a coarser grained alpha-Mg crystalline phase (483-500 K) corresponding to a second crystallization reaction. At higher temperatures a third exothermic effect (at about 593 K) can be detected and the stable Mg2Cu, alpha-Mg and Cu5Nd phases are present. (C) 2007 Elsevier B.V. All rights reserved.