Indentation size effects in the nano- and micro-hardness of fcc single crystal metals

This paper presents the results of the experimental study of nano- and micro-indentation size effect on selected (0 0 1) oriented face-centered cubic (fcc) crystals (Ni, Au and Ag). Following a detailed description of experimental techniques and correction factors, indentation size effects in (0 0 1) oriented Au, Ag and Ni single crystals are elucidated. Material pile-up phenomena are discussed before analyzing the results within the context of mechanism-based strain gradient plasticity (SGP) theories. Microstructure length scales are calculated based on the analysis. These are shown to vary with indentation size. A bi-linear behavior is shown to describe the indentation size effects between the micro- and nano-scales. This is rationalized by considering the limiting cases of plastic deformation by source-limited and established dislocation substructures. A multi-scale framework is proposed for modeling small contacts.