Influence of oxygen impurities on the crystallization mechanism of NiZr2 metallic glasses

The influence of oxygen impurities on the crystallization mechanism of NiZr 2 metallic glasses was studied. For this glass system, the first crystalliz ation product is the metastable E9(3)(cF96) cubic structure instead of the equilibrium C16(tI12) tetragonal structure. A possible mechanism for the fo rmation of this metastable phase has previously been put forth. The hypothe sis is that oxygen forms a semipermanent bond with Zr resulting in the oxyg en atom being surrounded by six Zr atoms in octahedral configuration which act as nucleation sites for the E9(3) cubic phase. Hydrogenation of the amo rphous composition eliminates the nucleation sites required for the formati on of this metastable cubic phase, thereby allowing the glass to crystalliz e directly into the stable tetragonal C16 phase, and thus providing strong evidence in support of the proposed crystallization mechanism. (C) 2001 Ame rican Institute of Physics.