Understanding the Influence of Sample Preparation Methods upon Nanoindentation Response

When nanoindentation testing is performed, a number of assumptions are made in order to employ the governing contact mechanics models and formulations associated with this form of indentation-based characterization. For example, one fundamental assumption is that a specimen studied by way of instrumented indentation has a surface finish that is perfectly flat, smooth, and orthogonally oriented below the nanoindenter tip without the presence of any degree of tilt. However, when nanoindentation testing is performed experimentally, changes in sample preparation methods and setup procedures can result in tilted surfaces with varying levels of surface roughness. Prior research has attempted to correct for sample tilt analytically and formulate models that can introduce parameters for surface roughness into the conventional methodology to analyzing load-displacement data; this work will not only build upon such prior approaches, but will also explicitly study the nanoindentation response as a function of preparation method. More specifically, variations in indentation response will be examined for the same materials when they are mounted in various epoxies and resins to inspect the possible effect of mounting material compliance upon modulus data. Additionally, samples will be prepared using vibratory polishing, mechanical polishing, ion beam polishing and electrochemical means in order to explore the effect each procedure has on the recorded hardness. Three nanoindentation systems will be used during the course of this work: the iMicro Pro and in-situ NanoFlip (Nanomechanics Inc., now KLA Corporation, Oak Ridge, TN, USA), as well as the Nano Indenter G200 (Keysight Technologies, Santa Rosa, CA, USA). Indenter tips with varying geometries, from Berkovich to cono-spherical diamond tips with different radii, will be utilized. Additional characterization and analysis will be performed using scanning electron microscopy, confocal microscopy, and x-ray diffraction.