Influence of oxygen on the viscosity of Zr-Al-Cu-Ni metallic glasses in the undercooled liquid region

The viscosity of Zr-Al-Cu-Ni metallic glasses prepared as melt-spun ribbons, slowly cooled bulk samples, and mechanically alloyed powder exhibiting different oxygen contents was measured above the glass transition temperature Tg using parallel-plate rheometry. For rapidly quenched ribbons, oxygen contents less than or equal to 0.8 at. % do not drastically affect the viscosity of the glassy phase, but changes in the composition of the metallic constituents are more significant. For slowly cast samples, oxygen levels above 0.3 at. % lead to an increase in viscosity due to formation of crystalline phases. In contrast, mechanical alloying provides completely amorphous powders even for oxygen contents above 2 at. %. This allows measurement of the influence of oxygen on the viscosity of single-phase glassy alloys for high oxygen levels, revealing a significant increase in viscosity with increasing oxygen content. The viscosity in the undercooled liquid can be fitted well by a Vogel-Fulcher-Tammann (VFT) relation. Independent of their oxygen content, the samples exhibit a small VFT temperature To and a high melt viscosity which are characteristic of a strong glass. (C) 1998 American Institute of Physics.