Structure and Dynamics of Shear Bands in Metallic Glasses and Nanophase Composites.

摘要

We have performed quantitative high-resolution transmission electron microscopy studies of the structure of shear bands in metallic glasses. We observe the formation of numerous nanometer-scale voids in shear bands produced under predominantly tensile loading. These void-like defects appear to result from the coalescence of excess free volume in the active shear band when the plastic flow ceases. By comparing the free energy of the shear band with that of the undeformed glass, we show that the void formation process is thermodynamically possible. The presence of the voids can explain several features of the mechanical behavior of metallic glasses, including the difference in plastic strain observed between tests conducted in uniaxial tension and those done in uniaxial compression.