Crystallization kinetics of Mg 65Cu 25Nd 10 amorphous alloy

Abstract

Amorphous Mg-based alloy Mg 65Cu 25Nd 10 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 α was given by an isoconversional method, and the average value of E a 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 Mg 65Cu 25Nd 10 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 × 10 14. It was found that the crystallization process of melt-spun Mg 65Cu 25Nd 10 ribbons consists of three steps. The first crystallization reaction at about 453 K is connected with the formation of Mg 2Cu nanocrystalline phase, followed by formation of a coarser grained α-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 Mg 2Cu, α-Mg and Cu 5Nd phases are present.