Plastic zone evolution in Al-2 wt% Si metal films on silicon and sapphire substrates was studied using nanoindentation and atomic force microscopy (AFM). AFM was used to measure the extent of plastic pileup, which is a measure of the plastic zone radius in the film. It was found that the plastic zone size develops in a self-similar fashion with increasing indenter penetration when normalized by the contact radius, regardless of film hardness or underlying substrate properties. This behavior was used to develop a hardness model that uses the extent of the plastic zone radius to calculate a core region within the indenter contact that is subject to an elevated contact pressure. AFM measurements also indicated that as film thickness decreases, constraint imposed by the indenter and substrate traps the film thereby reducing the pileup volume.
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The authors would like to thank J.A. Schneider, formerly of Sandia National Laboratories and currently at Mississippi State University, for performing the x-ray diffraction experiments. D.E.K. and N.R.M. gratefully acknowledge the support of the United States Department of Energy (U.S. DOE) under Contract No. DE-AC04-94AL85000. W.W.G. and A.A.V. gratefully acknowledge the support of the Center for Interfacial Engineering at the University of Minnesota under Grant No. NSF/CDR-8721551 and the U.S. DOE under Contract No. DE-FG02/96ER45574.