Enhanced thermal stability of a quasicrystalline phase in rapidly solidified Al-Mn-Fe-X alloys

Abstract

A series of rapidly solidified Al-Mn-Fe-X alloys, where X is one of Mo, W or V, were prepared using a melt spinning technique. Microstructures of obtained ribbons comprised of an aluminium solid solution matrix containing metastable quasicrystalline particles of icosahedral type (I-phase). Micro-analytical studies by X-ray diffraction, transmission and scanning transmission electron microscopy after various heat treatments, including in situ TEM heating experiments, have been performed to elucidate details of the I-phase decomposition mechanisms. Results of these investigations and values of activation energies of the transition calculated based on differential scanning calorimeter measurements indicated that V-modified alloys exhibit significantly increased thermal stability of the I-phase relative to Mo- and W-modified alloys and the un-modified ternary Al-Mn-Fe benchmark. In V-modified alloys the quasicrystalline particle transformations resulted in formation of the Al45(Mn, Fe, V)7 intermetallic phase, while the Al12(Mn, Fe, X = Mo, W) crystalline product formed during annealing of Mo- and W-modified alloys. Notably, the Al45(Mn, Fe, V)7 intermetallic phase shows considerable structural similarity to the quasicrystalline I-phase. This correlates with a small value of measured heat release during the I-phase decomposition and implies the stabilization of icosahedral structural ordering by V addition.