Size-independent strength and deformation mode in compression of a Pd-based metallic glass

We present quasi-static, room temperature compression data for Pd 40Ni 40P 20 metallic glasses, with specimen sizes ranging from the submicron to several millimeters in diameter. We observe no change in deformation mode over this range. At all sizes, plastic flow is localized in shear bands, which are accompanied by sudden strain bursts. This metallic glass shows only a modest increase in strength in going from bulk to micrometer-sized specimens. We show that stress gradients in tapered specimens can complicate measurement of the yield strength of metallic glasses in microcompression. Estimates of yield strength based on the minimum cross-sectional area implicitly assume that yielding is controlled by a maximum effective shear stress criterion. An alternative is the shear plane yield criterion, in which the minimum shear stress on the shear band trajectory determines yield. Application of this criterion in tapered microspecimens reinforces the notion that metallic glasses possess relatively size-independent mechanical properties.