Instrumented indentation microscope: A powerful tool for the mechanical characterization in microscales
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T. Miyajima Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Shimo-shidami, Moriyama-ku, Nagoya 463-8560, Japan (Received 19 March 2006; accepted 3 May 2006)
An instrumented indentation microscope was constructed and applied to the measurements of the Meyer hardness and the elastic modulus of several engineering materials ranging from ductile metals to brittle ceramics. Because of the in situ optical observation and determination of the indentation contact area that is synchronized to the indentation load versus depth relation, the mechanical properties determined on the indentation microscope are precise and reliable without any undesirable approximations and assumptions required for estimating the contact area. It is also demonstrated that the instrumented indentation microscope is capable of determining in a quantitative manner the in situ contact profiles of impression (sinking-in/piling-up profiles). The present work suggests that the instrumented indentation microscope will be a powerful tool in the science and engineering of indentation contact mechanics.
I. INTRODUCTION
In instrumented indentation tests, the most critical issue is the rigorous as well as the precise determination of the contact area Ac during the continuous measurement of indentation load P versus penetration depth h both in the loading and the unloading processes.1 The reliability of any mechanical characteristic parameters (contact hardness and elastic modulus in the time-independent elastic/elastoplastic regime and viscoelastic parameters and functions in the time-dependent regime) determined in instrumented indentation tests always as well as directly linked to the test conditions or the analyses in which how precisely Ac is estimated or approximated. In general, there have been no experimental ways for directly determining Ac, except for transparent materials such as inorganic glasses, in which the through-thickness observations of contact behaviors have often been conducted. 2–5 The Oliver–Pharr approximation (OPapproximation) that is based on an elastic assumption for the P-h unloading path has widely been utilized for estimating Ac in elastoplastic indentation,6 though the a)
Address all correspondence to this author. e-mail: [email protected] This author was an editor of this journal 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/publications/jmr/policy.html. DOI: 10.1557/JMR.2006.0276 2298 J. Mater. Res., Vol. 21, No. 9, Sep 2006 http://journals.cambridge.org Downloaded: 14 Jul 2014
approximation includes a crucial underestimate for Ac of ductile materials in which the pileup of hardness impression is significant.5,7 Furthermore, the OP-approximation leads to a fatal error in the estimated Ac when we apply it to coating/substrate composites.8–11 As an example, for a soft and ductile film coated on a hard and brittle substrate, the indentation-i
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