Nanocrystallization mechanisms of a Al-rich glass-forming alloys

The partial devitrification of Al(88)y(7)Fe(5) upon controlled thermal treatments results in a microstructure consisting of fine dispersions of Al-nanocrystals (>10(21) m(-3)) in a residual Al-Y-Fe matrix. These nanostructures offer improved performance and exceptional properties. While the origin of the nanocrystals is still uncertain, experiments coupled with kinetics analyses indicate that the nanocrystals originate from quenched-in nuclei. In this respect, the increase of the nanocrystal number density requires the control of the nucleation site density in the molten material. For this purpose, Al-Y-Fe glasses containing 1 at.% Pb or 1 at.% In, respectively, have been produced by rapid melt quenching. Calorimetry experiments show for both alloys a decreased onset temperature of the primary crystallization reaction compared to Al(88)y(7)Fe(5). While possible mechanisms have been proposed, careful microstructure analyses by TEM of the as-spun and the thermally-treated In-containing sample give new evidence that the inclusions generate a modification of the local structural arrangements of the amorphous matrix by promoting the retention of precursor nuclei during rapid quenching. (c) 2007 Elsevier B.V. All rights reserved.