Phase selection in undercooled quasicrystal-forming Al-Mn alloy melts

Small droplets in size of 20-1000 mu m of Al--Mn alloys (i.e. Al sub 88 Mn sub 12 ) have been undercooled by containerless solidification during free fall in a drop tube or by melt atomization. The as-solidified droplets were analyzed with respect to the phases formed from the undercooled melt by electron microscopy, X-ray diffraction, and differential thermal analysis. Depending on the droplet size, various phases have been identified ranging from supersaturated Al sub SS , intermetallic Al sub 6 Mn, to quasicrystalline phases. The observed phase formation was interpreted in terms of nucleation, crystal growth, and transformation kinetics on the basis of current theories. This analysis gives a comprehensive description of phase formation in undercooled Al--Mn alloys in agreement with the experimental findings.