Nanoindentation studies of Zr-based bulk metallic glasses

Hardness (H) and Young modulus (E) of three different chemical compositions of Zr-based bulk metallic glasses were investigated through the use of nanoindentation. The effects of the chemical composition and microstructure of bulk metallic glasses on mechanical properties were examined. Additionally, plastic deformation of studied alloys during nanoindentation's measurements, with different indentation-loading rates was carried out. The increase in hardness with the increase of crystalline volume fraction (Vcr) for all alloys was observed. Increasing Vcr, Young modulus of studied alloys increases almost linearly in the range up to about 75%. For fully crystalline alloys small decrease of Young modulus is observed. Alloy C, containing the highest Al amount, exhibits the highest values of H and E among all studied alloys. It was noticed that plastic deformation of amorphous alloys is punctuated by many discrete bursts of rapid displacement. This behaviour showed to be strongly depended on the indentation-loading rate. As the loading rate is increased, the nature of serrated flow observed on load-displacement (P-h) curves, changes significantly. Low rates P-h curves exhibit characteristic serrations, while curves obtained at higher rates are smoother. The character of plastic deformation of partially crystallised alloys was analysed, as well. For those materials, the change in the nature of the plastic deformation, from serrated to non-serrated flow, is observed at lower indentation rates, as compared to results obtained for amorphous alloys.