MILLIMETER-SIZE SINGLE QUASI-CRYSTALS IN AL-CU-FE ALLOY

Millimetre-sized grains of F-type icosahedral phase are formed in ingots of Al-Cu-Fe alloy, for which the nominal composition is Al-20-41 at.% Cu-13-27 at.% Fe. These grains are located in the upper half part of the ingots. The lower half does not include the icosahedral phase but ordinary crystalline phases. In order to form these grains, the following heat treatment was applied: The specimens were kept at 1143 K for 12 h and slowly cooled to 1095 K with the cooling rate 2 or 4 Kh-1. They were successively annealed at this temperature for several tens of hours and then quenched in water and subsequently in liquid nitrogen. This quenching is essential in order to prevent structural transformation from the icosahedral phase to non- icosahedral approximate structure. Electron diffraction experiments as well as X- ray Laue diffraction confirmed that the millimetre-size grains correspond to ‘single quasicrystals’, and that deviations from the perfect icosahedral symmetry are small. © 1990 Taylor & Francis Group, LLC.