Conditions for quasicrystal formation from mechanically alloyed Zr-based glassy powders

The absence of quasicrystalline phase formation in mechanically alloyed Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy powders with respect to melt-spun ribbon having the same composition has been investigated by analyzing the influence of mechanical deformation, oxygen contamination and chemical composition on quasicrystal (QC) formation. The results suggest that oxygen affects the formation of QCs by selectively reacting with zirconium thus driving the chemical composition of the glassy phase out of the range suitable for QC formation. This hypothesis has been verified by appropriately adjusting the composition of the powders. The addition of an adequate amount of zirconium changes the crystallization behavior inducing the formation of the quasicrystalline phase as the first crystallization product. This implies that if a particular short-range order is necessary for the formation of QCs, it can be achieved also by solid-state processing and therefore the presence of a specific quenched-in short-range order is not a mandatory prerequisite for QC formation.