The Plastic Deformation Of Metallic Glass Ribbons By Ball Milling

Metallic glasses, owing to their superior mechanical properties, are considered as potential engineering material and have attracted much interest recently. However, metallic glasses often fail catastrophically along a single shear band at room temperature and this has been a major bottleneck of their wide application. Obviously, the shear bands have a determinative affect on the plasticity for metallic glasses and it is significantly important to study the formation and morphology of shear bands. At present, during the inhomogeneous plastic deformation process for metallic glasses, the loadings, which are often performed under a single stress and once deformation, are relatively simple. However, material in real application is often subjected to random stress and multiple effects, but seldom research for metallic glasses in this area has been reported. Especially the plastic deformation in metallic glasses caused by ball milling hasn't been reported in the literature. Therefore, it is important to study metallic glass deformation under random and multiple effects in planetary ball milling. Moreover, this will provide important information from both basic scientific research and real application aspects.In this study, Zr64.13Cu15.75Ni10.12Al10 metallic glass ribbons are deformed in planetary ball milling. Both the XRD and TEM results indicate that during the balling milling process, the samples always maintain amorphous structure and neither phase separation nor crystallization forms in the shear band regions. The DSC results imply that the average free volume content increases with increasing milling time and this probably reflects that the shear band density increases with increasing ball milling time. The SEM observation results show that, the shear bands distribute unevenly in the surface for the samples milled in short time; for the samples endured relatively long time milling, it is difficult to observe the shear bands because of the damage on the sample surface caused by friction and wear. During the milling process, the samples are mainly grinded thin, and then severely deformed accompanying fragmentation, and finally broken into spherical powders of about 1μm diameter. The samples may also be bended back and forth during the milling process owing to the repeated impact of the milling balls. As a result, a layered morphology forms at the direction perpendicular to the sample surface.The metallic glass ribbons will endure plastic deformation under random and multiple loading during the ball milling process, and thus the shear bands with different kinds of morphology form on the sample surface. In addition, high density of shear bands with spacing less than 100 nm can be observed in some regions of the sample surface and this demonstrate that it is possible to produce nano-glasses by inhomogeneous plastic deformation on metallic glass. In some local areas of the sample surface, shear bands with special morphology including grass-like and layer-like can be observed. According to our analysis, the grass-like shear bands are probably caused by friction, and the layer-like shear bands may possibly be caused by repeated bending.