Phase stability and microstructure in devitrified Al-rich Al–Y–Ni alloys

A transmission electron microscopy study has been performed on the phase distribution and morphology in a series of four Al-rich Al–Ni–Y alloys. The alloys were produced from amorphous gas-atomized powder precursors by hot compaction and extrusion. They had fine fully devitrified microstructures and in each case these were three-phase consisting of: α-Al, binary Al3Ni or Al3Y (depending on alloy composition), and a ternary phase. The same ternary phase was present in each alloy and this was found to correspond to Al19Ni5Y3. This phase has the orthorhombic Al19Ni5Gd3-type crystal structure but has not been reported previously in the Al–Ni–Y system. The presence of thin embedded slabs of the equilibrium Al23Ni6Y4 compound within the Al19Ni5Y3 particles indicated that this structure may be metastable, although it did not decompose even after extended annealing.