Crystalline and quasicrystalline phases in rapidly solidified Al-Ni alloys

The formation and structures of stable and metastable phases in splat-cooled Al-Ni alloys with 10-35 at.% Ni have been investigated by transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. The splats show a three-layer microstructure, the formation of which can be qualitatively explained by the assumption of a high undercooling of the melt prior to solidification. Two metastable phases-monoclonic Al9Ni3 and a decagonal phase-were found in the as-quenched alloys. Heat treatment leads to the decomposition of these phases, starting at the surface layer of the splat and continuing into the adjacent layers. In the alloy Al85Ni15, the Al9Ni2 crystals form during the recrystallization of the fine-grained surface layer. The electron diffraction patterns of partly transformed quasicrystals show strong diffuse intensities both perpendicular and parallel to the periodic direction. Structural relationships between the Various phases are discussed. (C) 1997 Acta Metallurgica Inc.