ABSTRACT
Bulk metallic glasses are of critical interest for a wide range of applications, including their use in spacecraft gearboxes and mechanisms due to their excellent low-temperature, unlubricated wear resistance. Also of interest, is the potential for in-space manufacturing of metal alloys and the use of microgravity to determine fundamental thermophysical properties to inform ground-based modeling and experimentation. In this work, a Zr-based bulk metallic glass was processed in the electromagnetic levitator ISS-EML to determine undercooling, electrical resistivity, specific heat capacity, surface tension, and viscosity. A 6.5 mm sphere was vitrified during the processing, resulting in the first bulk metallic glass manufactured on board the international space station (ISS).
ABSTRACT
The mechanism of the increase in ductility in bulk metallic glass matrix composites over monolithic bulk metallic glasses is to date little understood, primarily because the interplay between dislocations in the crystalline phase and shear bands in the glass could neither be imaged nor modelled in a validated way. To overcome this roadblock, we show that shear bands can be imaged in three dimensions by atom probe tomography from density variations in the reconstructed atomic density, which density-functional theory suggests being a local-work function effect. Imaging of near-interface shear bands in Ti48 Zr20 V12 Cu5 Be15 bulk metallic glass matrix composite permits measurement of their composition, thickness, branching and interactions with the dendrite interface. These results confirm that shear bands here nucleate from stress concentrations in the glass due to intense, localized plastic deformation in the dendrites rather than intrinsic structural inhomogeneities.