| A series of Al-Cu-Fe alloys with chemical composition of Al48-6oCu33.5oFeo-io was prepared and the phase constituents in these alloys quenched from various temperatures were identified by using optical microscopy (OM), X-ray diffraction (XRD), differential thermal analyses (DTA), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDXS) and electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM) including high resolution TEM (HRTEM). The present investigation revealed that the stable ternary Al-Cu-Fe O phase has two variants. The high temperature variant (designated as 甶 phase) is stable when temperature is higher than 873 K and has a structure of t3(Al3Cu2) phase, which is a 3 times modulation structure along a <111>2 direction. The low temperature variant (designated as ? phase) is stable when temperature is lower than 763 K and has a 10 times modulation structure along a <011>2 direction. EDXS revealed that the chemical composition of co + q (revised fromU?: L+ 3 ?co + n.).A thermodynamic model and the calculation method of the change of Gibbs free energy during the primary solidification of the IQC and its approximant crystal phase have been proposed. The thermodynamic analyses show that the IQC is stable at high temperature and solidifies as a primary stable phase when temperature is greater than 938 K. Under which, its approximant crystal phase emerges.By using a proposed thermodynamic model for the calculation of the change of Gibbs free energy during the primary solidification of the IQC and its approximant crystal phase, the nucleation energies and nucleation rates for the IQC and its approximant crystal phase were calculated according to the classic theory. Calculation reveals that the nucleation energy for IQC is below lOev, and for its approximant cryatal phase, the nucleation energy reaches to infinity when the undercooling is in the range of 0-150 K. As a result, the IQC will nucleate primarily when the temperature of the undercooled liquid alloy is in the range of 1130 K to 980 K.A simplified heat transfer model was used to calculate the volume fraction of the primary IQC, and calculation results were compared with the experimental measurements. While the maximum volume fraction of the primary IQC in the equilibrium state can be determined by the chemical composition of the alloy and the data of the phase diagram, the slow cooling and solidification of the alloy in a mould retained at certain temperature followed by subsequent quenching into water can provide a relatively large volume fraction of the primary IQC.This project were supported by the Foundation of the Key Laboratory for Special Functional Materials of Henan Province (Grant No.9926) and National Natural Science Foundation of China (Grant No. 19974030).
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