Crystallization Behavior and Phase Formation in Zr–Al–Cu–Ni Metallic Glass Containing Oxygen

Abstract

Differential scanning calorimetry, X-ray diffraction and transmission electron microscopy were used to study the thermal stability and the phase formation during annealing of (Zr_0.65Al_0.075Cu_0.175Ni_0.10)_100−xO_x metallic glasses (0.2≤x≤0.8) prepared by melt spinning. Increasing oxygen content changes the crystallization mode from a single to a double step process. The glass transition temperature T_g increases slightly with increasing oxygen content whereas the crystallization temperature T_x decreases, causing a reduction of the undercooled liquid region. The deterioration of the thermal stability is related to oxygen-induced formation of metastable quasicrystalline and fcc NiZr₂-type phases which coexist with tetragonal Cu(Al, Ni)Zr₂ and hexagonal Zr₆NiAl₂ for x=0.2 and 0.4. For x=0.8 only the quasicrystalline phase is observed in the first step of crystallization. The details of phase formation and transformation during crystallization depend strongly on the annealing conditions. At elevated temperatures the quasicrystals transform into Cu(Al, Ni)Zr₂ and the fcc phase transforms into the stable Zr₆NiAl₂ compound. Increasing oxygen content leads to more pronounced metastable phase formation in the first step of crystallization at lower temperatures, and extends the stability regime of these phases to higher temperatures. For annealing temperatures ≥873 K the samples exhibit the same crystallization products regardless of the oxygen content of the material.