The onset of plasticity in nanoscale contact loading

Abstract

We report studies of strained‐layer semiconductor superlattice structures under nanoindentation. Coherency strain reduces the yield stress at room temperature, from 6 GPa in unstrained material to 3 GPa in the most highly strained structures. The dependence of the yield stress on the design parameters of the superlattice structures shows that the onset of plastic deformation under an inhomogeneous stress is a cooperative process that takes place simultaneously across a finite volume more than 150 nm across. In this way, we demonstrate a new yield criterion, of which the key feature is that it is to be averaged over a finite volume. This provides a natural explanation of the indentation‐hardness size effect.