The effect of minor addition of insoluble elements on transformation kinetics in amorphous Al alloys

Highlights: • By doping Pb or In in AlYFe alloys, the primary crystallization of Al is promoted. • The catalytic effect is based on the good wetting behavior between Al and Pb. • Pb promotes crystallization by providing heterogeneous nucleation sites. • Through doping 0.5–2 at.% of In, T_x decreases by 35–47 °C. • The coherent interface shows a good contacting behavior between Al and In. - Abstract: Nanocrystalline metallic materials based on partial devitrification of amorphous aluminum alloys show an attractive combination of high strength and low density. A key feature concerning the improved mechanical properties is the high number density of Al nanocrystals (10²²–10²³ m⁻³) that precipitate within the amorphous precursor structure upon low temperature annealing. For Al₈₇Y₇Fe₅Pb, the melt-spun ribbons consisted of an amorphous matrix with a dispersion of Pb nanoparticles (10 nm diameter). HRTEM images of the Pb–Al interface revealed a good wetting behavior between the Al and the Pb nanoparticles. Isothermal annealing for Al₈₇Y₇Fe₅Pb showed no transient stage even though the crystallization onset, T_x, was at a much lower temperature (247 °C) compared with Al₈₈Y₇Fe₅ (267 °C). For Al_(88−x)Y₇Fe₅In_x (x = 0.5, 1.0, 1.5, 2.0), the DSC results indicated that T_x continuously decreased from 232 °C to 220 °C as the indium level increases from 0.5 at.% to 2.0 at.%. Under STEM, the image showed a coherent interface between Al and In particles. In the analysis of the transformation kinetics, the addition of minor elements can effectively promote additional nucleation of Al nanocrystals by providing heterogeneous nucleation sites. These developments offer new opportunities for the control of nanoscale microstructures