Measuring, Evaluating, and Describing Pile-Up and Sink-In During Nanoindentation of Thin Films on Substrates

Abstract

Nanoindentation is a valuable tool for extracting material properties such as elastic modulus and hardness at the nanoscale. Knowing material properties at this scale enhances the use of thin films in protective coatings and various electronic applications. It is essential that material behavior is well-known before manufacture to ensure material selection will prevent catastrophic failures. The research presented here has led to the creation of a model that extracts elastic modulus from the film or substrate, termed the Zhou-Prorok model, and has been tested on a wide variety of film/substrate combinations. Other researchers have been concerned with a change in area when the film and substrate have different elastic moduli; phenomena such as sink-in or pile-up can occur, leading to a difference in contact area, the crucial term used to calculate the material properties. The model, however, is not affected elastically, and it is hypothesized that the plastic properties are the only effect on the pile-up and sink-in. Within this work, new methods are outlined to characterize and measure projected pile-up and sink-in. Additionally, yield stress was controlled prior to indentation, and pile-up was then examined across a variety of plastically deforming substrates with metallic films. Overall, this research contributes a number of new findings of pile-up and sink-in related to plasticity, and improves the field of nanoindentation as this new information can be utilized for the most accurate extraction of material properties from simple small-scale nanoindentation tests.