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Kinetics of fcc-Al nanocrystallization in Al90Tb10 metallic glass

Kalay, Yunus Eren
The crystallization kinetics of Al90Tb10 amorphous alloy were investigated by a combined study of differential scanning calorimetry (DSC), transmission electron microscopy (TEM), Cu-K alpha X-ray diffraction (XRD) analyses and microhardness measurements. Amorphous to fcc-Al transformation kinetics were descried through Johnson-Mehl-Avrami OMA) approach based on the isothermal DSC hold at 220 degrees C. XRD and TEM revealed the formation of highly populated (similar to 10(21) m(-3)) fcc-Al nanocrystals after the first crystallization event. JMA indicated a three dimensional diffusional growth with constant nucleation rate. TEM and XRD analyses agree well with the three dimensional diffusional growth of fcc-Al within the amorphous matrix. Nucleation of fcc-Al nanocrystals was attributed to already existing Al rich clusters embedded in the amorphous matrix. The deviation in cooling rate at the free and the wheel sides caused variations in Al rich cluster size and population through the thickness of the ribbon specimen. Microhardness tests captured this discrepancy which results in anomalous Avrami exponent, n(x). (C) 2013 Elsevier B.V. All rights reserved.