A new method for analyzing data from continuous depth-sensing microindentation tests
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A new parameter, hardness/modulus2 (H/E2), has been derived from the equations used to calculate the hardness and elastic modulus from data taken during continuous depth-sensing microindentation tests. This paper discusses the use of this parameter to treat the data obtained from a sample whose surface roughness was of the same scale as the size of the indents. The resulting data were widely scattered. This scatter was reduced when the data were plotted in terms of H/E2 versus stiffness. The effect of surface roughness on the hardness and elastic modulus results is removed via stiffness measurements, provided single contacts are made between the indenter and the specimen. The function relating the cross-sectional area of the indenter versus the distance from its point is not required for calculation of H/E2, but the hardness and modulus cannot be determined separately. The parameter H/E2 indicates resistance to plastic penetration in this case.
I. INTRODUCTION
Interest in determining the mechanical properties of thin films, coatings, and ion beam treated surfaces has prompted a re-examination of the microindentation hardness technique in recent years. Conventional measurements of the properties of thin films or surface layers that are free from the influence of the substrate require very shallow indents, since the elastic/plastic stress field extends to distances several times the depth of an indentation. Accurate measurement of the dimensions of very small indentations may be difficult and therefore errors may be introduced into the calculated hardness values. The usual microhardness techniques yield hardness values which are obtained from the applied load and a contact area that is determined from the dimensions of the residual indentation. To overcome the area measurement problems, a mechanical properties microprobe (MPM) with depth-sensing capability has been developed.1 In this technique, the plastic depth is determined from the load-displacement curves2 such as the one shown in Fig. 1. With accurate information on the shape of the indenter, the indent's projected area can be calculated as a function of the plastic depth.1 The elastic properties as well as the hardness of the material under examination may be calculated from such data.2 These calculations are based on assumptions which require that the test surface be smooth to dimensions much smaller than the indent depth. As a result, data obtained from samples with rough surfaces show considerable scatter. Since it is sometimes necessary to a)Guest,
University of Tennessee, Knoxville, Tennessee.
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