Mechanical assessment of ultrafine-grained nickel by microcompression experiment and finite element simulation
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nedikt Moser EMPA Thun, Swiss Federal Institute for Materials Testing and Research, Laboratory for Materials Technology, 3602 Thun, Switzerland; and Suisse Technology Partners Ltd., 8212 Neuhausen, Switzerland
Peter Gumbsch Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), 76021 Karlsruhe, Germany; and Fraunhofer Institute for Mechanics of Materials IWM, 79108 Freiburg, Germany
Oliver Kraftb) Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), 76021 Karlsruhe, Germany (Received 16 May 2011; accepted 14 July 2011)
Over the past two decades, nanoindentation has been the most versatile method for mechanical testing at small length scales. Because of large strain gradients, it does not allow for a straightforward identification of material parameters such as yield and tensile strength, though. This represents a major drawback and has led to the development of alternative microscale testing techniques with microcompression as one of the most popular ones today. In this research, the influence of the realistic sample configuration and unavoidable variations in the experimental conditions is studied systematically by combing in-situ microcompression experiments on ultrafine-grained nickel and finite element simulations. It will be demonstrated that neither qualitative let alone quantitative analyses are as straightforward as they may appear, which diminishes the apparent advantages of microcompression testing.
I. INTRODUCTION
Over the past two decades, nanoindentation has been the most versatile method for mechanical testing at small length scales. Because of large strain gradients, it does unfortunately not allow for a straightforward identification of material parameters such as yield and tensile strength. This represents a major drawback for the use of nanoindentation in the assessment of mechanical properties of materials. This limitation together with significant progress in micromachining has led to the development of alternative microscale testing techniques with microcompression1 as one of the most popular ones today. The focused ion beam (FIB) technique is probably the most established method for fabricating pillars in (sub)micrometer dimensions. To date, a variety of FIB machined materials have been studied by microcompression,2 including single crystalline pure metals and alloys, nanoporous and nanocrystalline metals, and amorphous metals. Microcompresa)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-policy DOI: 10.1557/jmr.2011.248 266
J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
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sion promises to probe intrinsic materials properties as a function of decreasing sample size without the interference of strain gradients.3 In general, a conventional nanoindenter with a flat-
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