The composition of the decagonal quasicrystalline phase in the Al–Cu–Co alloy system

A part of the Al–Cu–Co alloy system, including the region of the decagonal phase, was studied by scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffractometry. The decagonal phase in the Al–Cu–Co system was found to behave as a stable phase in the temperature range 550–1000°C. Its compositional region depended strongly on temperature. In a wide range of alloy compositions the decagonal phase produced at higher temperatures became supersaturated at lower temperatures. The formation of (Al, Cu)13Co4 in an aged supersaturated single-decagonal-phase sample was observed.