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2017_JNCS_Hurakova_1Influence of loading rate on the mechanical performance of metallic glass

M. Huráková⁠,  K. Csach, ... V. Ocelík, J.Th.M. De Hosson, Journa of Non-crystalline solids, accepted


2017_JNCS_Hurakova_22017_JNCS_Hurakova_3Amorphous metallic glass Cu⁠47Ti⁠35Zr⁠11Ni⁠6Si⁠1 was investigated by load-control nanoindentation experiments using the cube corner indenter tip over a wide range of loading rates. The indentation hardness was calculated using different methods either from the loading curves or indent area. Pop-in events were observed on the loading part of the indentation curves mainly at lower rates of loading. Instantaneous plastic deformation decreases with increasing loading rate according to a power law. At high loading rate the instantaneous deformation is suppressed by continuous plastic deformation and no well-developed pop-ins are observed. The morphology of shear bands in the pile-up area of indents showed no correlation with the pop-in event population of the nanoindentation
curves and the loading rate.

Nanoindentation experiments have revealed the presence of many pop-in events in the loading part of indentation curves at loading rates up to 10 mN/s. It has been found that the pop-ins are influenced by the indentation depth and the loading rate. With decreasing the loading rates the pop-in events are more developed. It is importantto note that no simple correlation between the presence of pop-ins and the shear band morphology of the indent region was observed. At low loading rates the plate-like morphology of pile up areas is created by one or small numbers of events with higher deformations, whereas at higher deformation rates the plate-like structure is created via successive small shearing along properly oriented shear bands. Hardness estimated by several methods takes similar values for all loading rates. It has been revealed that the instantaneous deformation corresponding
to a pop-in event during nanoindentation depends on the loadwhereas the continuous plastic deformation reaches the values of 5 to 40 nm without a simple dependence on either the load or loading rate. We have found that the minimal value of instantaneous displacement
of 18 nm exists and does not depend on the loading rate. As the loading rate increases, the sensitivity of instantaneous deformation to the load decreases according to a power law behaviour. By extrapolation of this dependence the expected values for instantaneous deformation at the loading rate of 100 mN/s were estimated in the range of 18 to 38 nm. At this loading rate the values of instantaneous and continuous deformation steps are comparable and therefore almost no well-developed pop-ins are observed at high loading rates.