Phase transformations of icosahedral AlCuFe quasicrystals

Abstract

Phase transformations with alloy compositions in the vicinity of the AlCuFe icosahedral quasicrystalline phase (i-phase) were studied. This phase forms via a ternary peritectic reaction at 882°C from liquid and two primary solid phases termed λ and β. With decreasing temperature, the icosahedral phase is a reaction partner with liquid, λ, β and tetragonal ω in two different transition reactions. Furthermore, two solid-state phase transformations, involving the i-phase (a quasi-binary eutectoid β → i + φ at 640°C and a ternary transition-type reaction i + β → ω + φ at 616°C), are reported. The conclusions are based on differential thermal analysis combined with powder X-ray diffraction investigations. A three-dimensional sketch of a wire model for the icosahedral phase was constructed, which demonstrates the shrinkage of the phase field of icosahedral phase with a decreasing temperature.

Acknowledgements

Support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged. Many thanks are to Dr. J. Schneider for helpful support with powder X-ray diffraction and structure refinement, to Prof. P. Gille and Mr. T. Gödecke for fruitful discussions.