Size Effect in Plastic Deformation and Failure of Metallic Glasses

Depending on the composition and structure of metallic glasses cells with the dimensions in the range from tenths nanometers to tenths micrometers were observed on the ductile fracture surface. The variation in dimple size was compared with the serrations presented on the loading curve at the nanoindentation of the metallic glasses with different compositions. Higher instantaneous deformation can be connected with simultaneous shearing at more suitable shear band configurations. The cell morphology with the various cell sizes is observed at the failure of the metallic glasses. At the failure of high strength metallic glasses, the cells are formed in short time due to the release of high amount of stored elastic energy. In this case the uniform cell morphology with the cell size of about 20 nm is observed

Nanoindentation in Metallic Glasses with Different Plasticity

Nanoindentation and thermomechanical experiments on three types of metallic glasses with different glass forming ability were carried out. The nanoindentation behaviour at room temperature was associated with the creep at elevated temperatures. Different discontinuity populations and their shape observed on the nanoindentation loading curves were compared with morphology of plastic deformed indent regions. The influence of the differences in thermal stability of studied alloys on the nanoindentation in these alloys were studied as well

Crack propagation in metallic glass ribbon as a function of the position of stress concentrators

An amorphous metallic ribbon of Fe40Ni40B20 was used for in-situ observation of the crack propagation and shear band formation during tensile tests. Prior to the tensile tests, two holes (with different positions with respect to the tensile axis) were made by laser ablation as stress concentrators. The nucleation and propagation of shear bands on the ribbon surface during tensile tests were analysed with scanning electron microscopy (SEM). At room temperature inhomogeneous plastic deformation of amorphous alloy occurs via the development of primary and secondary shear bands. The influence of the different loading geometry on the topology of shear bands and crack propagation was studied

Shear band morphology of indented region in Cu-based metallic glass

Plastic deformation after indentation of the metallic glass Cu47Ti35Zr11Ni6Si1 at different loading conditions was examined. Discontinuities on the loading curves were observed, the magnitude of which depends on the loading rate. The presence of these discontinuities is influenced by the precise shape of the indentation tip. At lower loading rates and using a cube corner indenter tip the discontinuities on the loading curves are more pronounced. An increase of the loading rate tends to diminish instantaneous plastic deformation as appear by pop-ins. Using a Berkovich type indenter tip the plastic deformation is more steady. It is concluded that the final morphology of the pile-up area strongly depends on the geometry of the indenter tip, whereas no correlation between discontinuities in the loading part of the indentation curve and the formation of shear band patterns was observed

Serrated Plastic Flow of Various Metallic Glasses during Nanoindentation

Nanoindentation experiments were executed on amorphous metallic ribbons made of Fe40Ni40B20, Cu47Ti35Zr11Ni6Si1 and Zr65Cu17.5Ni10Al7.5 that differ in microhardness and glass forming ability. The individual serrated plastic flow events were analyzed in a wide range of the loading rates. In the individual pop-in events of the load-displacement (P-h) curve the contributions of plastic deformation (Δhpl) were calculated depending on the loading rate and the alloy composition. It is concluded that the contribution of the serrated plastic deformation flow varies with the composition of the alloy. The highest plastic deformation for the individual pop-ins was observed for Zr-based metallic glasses

Influence of loading rate on the mechanical performance of metallic glass

Amorphous 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

Basil seeds as a source of antioxidants affected by fortification with selenium

The work aimed to determine the potential of selenium incorporation into seeds of selected species of Ocimum spp. after fortification with a foliar solution of sodium selenate at a concentration of 50 g Se · ha−1. In a 2-year trial, the selenium content was determined by electrothermal atomic absorption method with Zeeman background correction. Modified spectrophotometric method (2,2-diphenyl-1-picrylhydrazyl [DPPH] assays) was used to rate the potential of oxidation– reduction components of basil seeds (AA). The total polyphenol content (TPC) was determined spectrophotometrically using the Folin–Ciocalteu reagent and gallic acid (GA) as the standard solution. The results of experiments showed that the selenium biofortification significantly (p < 0.05) increased the content of selenium in basil seeds (17-fold increase in comparison with controlled variant in case of Tulsi, 12-fold in ‘Cinamonette’ and 12-fold in ‘Dark Green’ when compared with control). The basil seeds represented a valuable source of polyphenols (1414.61–1681.75 μg GA · g−1 dried weight [d.w.]) with multiple times higher antioxidant activity (23.50–28.97 mmol Trolox · kg−1) in comparison with common tested horticultural crops (e.g. peas, tomato and pumpkin). Significant influence of fortification was not found in AA and TPC values. Fortification was not significantly reflected in AA and TPC values. In addition to its very strong reproductive function, healing and religious purposes, the basil seed is used as a functional food due to its high content of bioactive compounds