Effect of cooling rate on the formation of metastable icosahedral quasicrystal phase in rapidly solidified Al-8.2 at % Mn alloy

Abstract

The microstructure of rapidly solidified Al-8.2 at % Mn alloy was analysed by X-ray diffraction, transmission electron microscopy and energy-dispersive analysis of X-rays and the effect of cooling rate on the formation of the metastable icosahedral quasicrystal phase (IQP) was investigated. The formation of IQP was found to be sensitive to the cooling rate in a rapidly solidified alloy of a certain composition. A lower critical cooling rate at which metastable IQP starts to appear and an upper critical cooling rate at which IQP suppresses completely the stable crystalline phase exist. The fact that the amount and the manganese concentration of IQP change non-linearly with the cooling rate suggests that there is an optimum cooling rate at which both the amount of IQP and its solute concentration reach maximum values in an alloy of a certain composition.