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 Kα 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.