Improvements Of The Phase Transformation Kinetic Models And Their Application To The Crystallization Of Amorphous Alloy

Phase transformation kinetics describing the variation of transformation features along with time or temperature has been widely adopted to investigate the microstructural evolution and the optimization of the actual process parameters. Though much contribution has been made, it is still not enough, especially in fields of multi-phase transformation, diffusion-controlled transformation and the isochronal transformation. Therefore, it's meaningful to focus our attention on such a classical and modern topic. In this paper, the isothermal mixed nucleation kinetics, the multi-peak transformation kinetics and the improved isochronal kinetics were proposed with similar considerations of the classical Johnson-Mehl-Avrami-Kolmogorov model (JMAK), and the models have been adopted to investigate the crystallization process of the amorphous Mg₆₅Cu₂₅Y₁₀ alloy.The isothermal mixed nucleation kinetics indicates that the parameters of its JMAK-like formal are no longer constant simultaneously as the classical JMAK model but vary with time determined by the choosing of parameters. The multi-peak transformation kinetics which is consistent with the classical JMAK model in single peak case indicates that during multi-peak transformation each peak can be treated with a JMAK case. A common asymptotic expansion for the so-called temperature integral has been proved unreasonable, and an improved approximation has been adopted. Upon this, an analytical model for isochronal transformation has been built, from which the general model can be approached with a wide transformation temperature interval. The improved approximation and analytical model have been proved more effective than the general approximation and the general analytical model by numerical calculations.Finally, the crystallization of amorphous Mg₆₅Cu₂₅Y₁₀ alloy has been investigated by incorporating XRD, DSC and the improved analytical model, which indicates that the corresponding crystallization process is composed of three continuous nucleation plus interface-controlled growth processes. The results of the isothermal kinetics and the isochronal kinetics are consistent well with each other, which in some tendency certified the validation and the consistency of those improved analytical models.