Investigation of phases on a Zr-based bulk glass alloy

Zr52.5Ni14.6Al10Cu17.9Ti5 alloy with oxygen content of 0.08 wt.% is cast into bulk sheet samples with different thicknesses. Fully glass and glass with quenched-in crystallites are obtained. With increasing the sheet thickness, the quenched-in crystallites increase in volumetric fraction and tend to form a net-shape phase. Transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis indicates that the quenched-in crystallites, which are enriched in aluminum, have a well-faceted morphology with average size of about 500 nm, and have a fee structure with cell size a = 1.197 nm. In subsequent thermal treatment, the quenched-in crystallites are stable and do not act as nucleation and growth sites. For fully glass samples, different volumetric fraction of nanoscale crystals, with grain size of about 50 nm, form when annealed for 10 min at temperatures from 673 K up to 823 K. The crystallized phases are determined by selected-area diffraction to be ZrAl, Zr2Cu as well as Zr-2(Ni0.67O0.33). High-temperatures (200 K above crystallization temperature) and short-time (30 s) annealing induce a nickel and aluminum-enriched fine nanoscale crystalline to form with grain size less than 20 nm. (C) 2000 Elsevier Science S.A. All rights reserved.