ON THE SOLIDIFICATION OF AL62CU20CO15SI3 AND AL61CU19.5CO14.5SI5 ALLOYS

The solidification behavior of Al62Cu20Co15Si3 and Al61Cu19.5Co14.5Si5 alloys was studied by means of optical metallography, scanning and transmission electron microscopy, energy-dispersive x-ray analysis, powder x-ray diffraction, and differential thermal analysis. Slowly as well as rapidly cooled ingots of both alloys contained a decagonal quasicrystalline phase as the dominant phase with, additionally, several minor crystalline phases. The structure of the rapidly solidified Si-containing alloys was similar to that of the ternary Al65Cu20Co15 alloy. In the slowly solidified alloys the substitution of 3 at. % Al by Si did not change the basic phase constitution. Si was only partially incorporated in the decagonal phase and a significant quantity of Si was found in elemental form. The increase of Si concentration to 5 at. % resulted in the appearance of new minor phases.