Initial crystallization in a nanostructured Al-Sm rare earth alloy

The transformation kinetics and microstructural evolution during initial crystallization in highly driven Al90Sm10 were investigated using transmission electron microscopy (TEM). conventional Cu K-alpha and high-energy synchrotron X-ray diffraction (HEXRD) and differential scanning calorimetry (DSC). The highest cooling rate obtained in this study yielded a high number density of fcc-Al nanocrystals, with sizes on the order of 2-5 nm, embedded in a disordered matrix rich in an Al-Sm medium range order (MRO) structure. Isothermal in-situ HEXRD results indicated a single crystallization of a large primitive cubic phase from the disordered state. Further analysis using DSC showed two crystallization events; a small peak overlapping the peak from the main crystallization event. TEM analysis performed at different stages of crystallization resolved pre-existing fcc-Al crystals, further crystallization of fcc-Al, (corresponding to the first small peak) and evolution of the cubic phase, corresponding to the main crystallization event. Fcc-Al nanocrystals showed a restricted growth and stayed at an average size of 16 nm after full crystallization was established. Transformation kinetics was described using Johnson-Mehl-Avrami approach after deconvolution of the overlapping crystallization peaks using a Gaussian approximation. (C) 2010 Elsevier B.V. All rights reserved.