Metallic glass formation in the NiBGe system

Abstract

Metallic glasses may be formed at transition metal/metalloid ratios substantially removed from the usual 80/20 atom fraction for binary systems such as NiB and CoB. The present investigation is of the NiBGe ternary systems in which the Ge is used as a substitutional probe atom for B in a subsequent EXAFS study. Ribbon samples have been fabricated for a wide range of compositions with metalloid content up to 45 at.%, the glass-forming region of which has been determined by bend ductility, XRD, DSC, SEM, and TEM measurements. Samples found to have relatively low thermal stability also tend to crystallize during ion-milling sample preparation for TEM, or during electron irradiation during TEM observation. Some of the ternary ribbon samples are ductile but are partially crystalline on XRD and TEM investigation. Other samples are brittle but show no crystallites, even after careful TEM study. Most ribbon samples made were fully glassy, as determined by XRD and TEM. The dual glass-forming composition range found in the NiB binary system is alternatively interpreted as a single continuous glass-forming regime, interrupted by an Ni 3B intermetallic region which is of such character as to make metallic glass formation very difficult by melt-spinning.