The Deformation And The Evolution Of Shear Bands Of Vit1Amorphous Alloy Under High Pressure Torsion

Metallic glass is different with conventional crystalline metals in terms of atomicstructure, characterized by lacking long-range order. Metallic glass has very importantapplications in many areas as structural materials and functional materials because of itssuperior performance. Unfortunately, because metallic glass is zero-plastic at roomtemperature, its applications are limited seriously. Therefore, deed understanding of thedeformation behavior of metallic glass and its deformation ability has become the hottopic of common concern to scientists.The technology of high pressure torsion can reach more than50%strain forZr41Ti14Cu12.5Ni10Be22.5bulk metallic glass. After the pressure torsion, some properties ofmetallic glass have been tested such as the micro-hardness, nanoindentation and density.We use X-ray diffractometer (XRD), differential scanning calorimetry (DSC),transmission electron microscope (TEM), and other experimental methods to study theorganization structure change and analyze the effect of high pressure torsion of metallicglass.The results showed that no crystallization phase exists in the metallic glass and it stillkeeps the amorphous structure. The results of the micro-hardness, nanoindentation anddensity showed that strain softening occurred near the center of the samples and thehardness of the samples located away from the center position increased obviously for thehigh pressure torsion. The density of the samples decreased after the high pressure torsion.The experimental results show that excess free volume increased in the process of thelarge plastic deformation and the strain softening took place in the center of the samples,so the hardness of the samples decreased after the high pressure torsion. The density of thesample after the high pressure torsion occurred decline for the excess free volume in thesamples. The hardness of the sample rises mainly because of the cross shear bands thatstop the rapid spread of a single shear band in the process of deformationBulk metallic glass deforms at room temperature mainly through the formation andexpansion of shear bands. The evolution of shear bands of metallic glass in the process ofhigh pressure torsion has been observed by the SEM and the micro deformation mechanism of metallic glass has been analyzed. The SEM observation results show thatthe shear band by the compression and the secondary shear band by the torsion cross eachother, which prevents the single shear band rapidly growing and expanding. At last, thedeformation ability of metallic glass improved. High to diameter ratio is also an importantfactor that affects the plastic deformation ability of the metal glass. The smaller the aspectratio of bulk metallic glass, the stronger its deformation ability is. As the aspect ratio ofbulk metallic glass decreases, the shear band in the process of high pressure torsionbecomes more. The deformation of metallic glass becomes more homogeneous. Themutual influences between shear bands enhance, which inhibits the spread of shear bandsand improves deform ability and the strength.