Morphological and structural study of gas atomized Zr–Cu-based glass-forming alloys

Zr–Cu-based glass-forming alloys were processed in a laboratory scale gas atomizer, operated in sonic conditions with nitrogen or helium as the atomizing medium. Powders of rather wide size distributions were obtained, in the under 212 μm range, which afforded to carry out comparative phase analyses on particles which underwent quite different cooling conditions. X-ray diffraction examinations as well as light microscopy, transmission electron microscopy, differential thermal analysis (DTA) and microhardness determinations were used to investigate the powders belonging to different size ranges. Amorphous, partially crystalline and fully crystalline powders were obtained from each atomization batch. Light microscopy afforded to evaluate the morphometric details such as the secondary dendrite arm spacing in the crystalline particles, which were correlated with the estimated cooling rates computed by means of a simplified computer code. X-ray diffraction, TEM examinations and electron diffraction confirmed that conditions were established for the development of amorphous or nanocrystalline particles, in particular in the “under 38 μm” and in the 38–45 μm size ranges. Microhardness determinations showed an extremely high hardness, of the order of 1000–1100 HV0.05 in the case of fully amorphous particles, which could be encountered mainly in the smaller size ranges, while in the case of crystalline powders the hardness was around a half of such value mainly in the larger, fully crystalline ones.