Determination of the true projected contact area by in situ indentation testing

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Determination of the true projected contact area by in situ indentation testing Gaylord Guillonneau1,a), Jeffrey M. Wheeler2, Juri Wehrs3, Laëtitia Philippe3, Paul Baral4 Heinz Werner Höppel5, Mathias Göken5, Johann Michler3

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Laboratory for Mechanics of Materials and Nanostructures, Empa, Swiss Federal Laboratories for Materials Testing and Research, Thun CH-3602, Switzerland; and Ecole Centrale de Lyon, Laboratoire de Tribologie et Dynamique des Systèmes, Université de Lyon, 69134 Ecully Cedex, France 2 Laboratory for Mechanics of Materials and Nanostructures, Empa, Swiss Federal Laboratories for Materials Testing and Research, Thun CH-3602, Switzerland; and Laboratory for Nanometallurgy, Department of Materials Science, ETH Zürich, Zürich CH-8093, Switzerland 3 Laboratory for Mechanics of Materials and Nanostructures, Empa, Swiss Federal Laboratories for Materials Testing and Research, Thun CH-3602, Switzerland 4 Ecole Centrale de Lyon, Laboratoire de Tribologie et Dynamique des Systèmes, Université de Lyon, 69134 Ecully Cedex, France 5 Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Materials Science and Engineering, Institute I: General Materials Properties WWI, 91058 Erlangen, Germany a) Address all correspondence to this author. e-mail: [email protected] Received: 21 February 2019; accepted: 1 July 2019

A major limitation in nanoindentation analysis techniques is the inability to accurately quantify pile-up/sink-in around indentations. In this work, the contact area during indentation is determined simultaneously using both contact mechanical models and direct in situ observation in the scanning electron microscope. The pile-up around indentations in materials with low H/E ratios (nanocrystalline nickel and ultraﬁne-grained aluminum) and the sink-in around a material with a high H/E ratio (fused silica) were quantiﬁed and compared to existing indentation analyses. The in situ projected contact area measured by scanning Eelectron Mmicroscopy using a cube-corner tip differs signiﬁcantly from the classical models for materials with low H/E modulus ratio. Using a Berkovich tip, the in situ contact area is in good agreement with the contact model suggested by Loubet et al. for materials with low H/E ratio and in good agreement with the Oliver and Pharr model for materials with high H/E ratio.

Introduction Instrumented indentation allows the measurement of the mechanical properties of a material by means of applying controlled deformation using a speciﬁed indenter tip geometry. The classical indentation hardness tests, e.g., Brinell or Vickers, allowed the measurement of hardness by determining the contact area after the test performed at a set load [1, 2]. This is straightforward to measure at the micro-millimeter scale, but at smaller scales, optical measurements lack the required precision. To allow indentation measurements at smaller scales, instrumented nanoindentation devices were developed. Nanoindentation is now commonly used to measure the mechanical properties of mate

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