Indentation Size Effects in the Nano and Microhardness of FCC Single Crystal Metals

Abstract

This paper presents the results of the experimental study of nano and micro indentation size effect on selected (001) oriented face centered cubic (FCC) crystals (Ni, Au, and Ag). Following a detailed description of experimental techniques and correction factors, indentation size effects in (001) 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.

Keywords:

• Bi-linear behavior
• Geometrically necessary dislocations (GND)
• Hardness
• Indentation size effects
• Material pile-up
• Micro-electro-mechanical systems (MEMS)
• Nano- and micro-indentation
• Statistically stored dislocations (SSD)
• Strain gradient plasticity

ACKNOWLEDGMENTS

This research was partially supported by the National Science Foundation (MRSEC Program) through the Princeton Center for Complex Materials (DMR 0213706). Partial support was also received from the NSF funded US-Africa Materials Institute at Princeton University (DMR 0231418). Appreciation is extended to the NSF Program Managers, Dr. Ulrich Strom and Dr. Carmen Huber for their encouragement and support.