Nanoindentation and contact-mode imaging at high temperatures
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Technical issues surrounding the use of nanoindentation at elevated temperatures are discussed, including heat management, thermal equilibration, instrumental drift, and temperature-induced changes to the shape and properties of the indenter tip. After characterizing and managing these complexities, quantitative mechanical property measurements are performed on a specimen of standard fused silica at temperatures up to 405 °C. The extracted values of hardness and Young’s modulus are validated against independent experimental data from conventional mechanical tests, and accuracy comparable to that obtained in standard room-temperature nanoindentation is demonstrated. In situ contact-mode images of the surface at temperature are also presented.
I. INTRODUCTION
With significant recent advances in instrumented nanoindentation testing, it has become possible to routinely measure the mechanical properties of small structures, such as are relevant to microelectronics, microelectromechanical systems, and coatings.1–9 For many such applications, it is desirable to measure nanomechanical properties at elevated temperatures (i.e., at relevant service temperatures), but nanoindentation has historically been a room-temperature mechanical testing technique. Although non-instrumented “hot hardness” tests have been used on coarser scales for decades,10–15 experimental efforts in high-temperature indentation with load and depth instrumentation have been relatively few. A brief summary of the experimental studies on this topic to date is given in Table I, focusing on the technical conditions of the tests reported. Those studies involving relatively large indentation depths (>1 m) are denoted as “microscale” studies and differentiated from generally higherresolution “nano-scale” studies. Examining Table I, it is clear that the existing studies on elevated-temperature nanoindentation are inhomogeneous, involving different apparatuses, different temperature ranges, and a host of different materials. The properties or physical phenomena under investigation also vary considerably across this literature. For example, Farber et al.16,17 have focused on larger
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0080 J. Mater. Res., Vol. 21, No. 3, Mar 2006
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microscale indentations and have studied the energetics of plastic deformation. Lucas and Oliver18,19 performed various indentation creep experiments to extract powerlaw exponents, while Beake, Smith et al.,20–22 and Volinsky et al.23 have looked at the hardness and modulus of various materials at elevated temperature. Recently, a number of authors have studied discrete events under the indenter tip at elevated temperatures, including the displacement burst associated with the elastic-plastic transition in crystals24–27 as well as shear band formation in metallic glasses.28 Across all of these various properties and topics, most of the reported studies are concentrated at relatively low temp
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