The "big-cube" phase found in Zr-Cu-Al-Ni easy glass forming alloys

The glass forming ability of Zr-based easy glass forming alloys is strongly affected by small amounts of oxygen. The discrepancy of results found in this family of alloys processed by different research groups is now attributed to different oxygen contents. In such a way the presence of a Zr2Ni metastable CFC phase also called "big-cube" phase reported by the literature is reviewed. This phase were reported to be present in non-fully amorphous samples and even in crystallized from amorphous state. Although this phase is reported as a metastable structure of Zr2Ni our recent research show that it is in fact an oxide of the filled-Ti2Ni type structure. In the present work Zr55Cu30Al10Ni5 bulk partial amorphous samples are investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show the presence of crystals with Zr4Cu2O structure. Further, the crystals were found to have Al enrichment thus making the phase near the matrix composition and so leading to almost polimorphic crystallization. Finally the formation of a such complex structure (112 atoms per unit cell) during quenching is discussed based on the near polimorphic transformation, the short range ordering caused by the strong bond of O with Zr and the usual non-stoichiometry of the phase with respect to oxygen.