Nanoindentation and contact-mode imaging at high temperatures

Abstract

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.

Hot nanoindentation in inert environments

“…Of the components in this assembly, the diamond indenter tip itself is almost certainly not responsible for the drift that we measure in our experiments. As noted elsewhere 33 , the very high thermal conductivity of diamond suggests that it should be heated quickly and achieve a roughly constant temperature throughout its volume, as long as it is in contact with a hot sample. Second, the displacements we measure in drift are not plausibly ascribed to thermal expansion of diamond: at a test temperature of 300 o C the unload drift rate is 1.2 nm s -1 ( Figure 5A), or 12 nm in total drift displacement over the 10 second measurement time.…”

“…At elevated temperatures, however, temperature gradient variation can be more severe and thermal effects such as thermal expansion of the tip and surrounding components are expected to amplify drift, making accurate property measurement more challenging. In our group's prior work on high temperature nanoindentation in air 33 , for example, the average drift rate after equilibration increased two orders of magnitude (0.01 to 1 nm s -1 ) between room temperature and 405 o C.…”

“…The tip ( Figure 2C) is instead heated through thermal transfer from the sample via conduction (during indentation) and convection (when indenting in gas) from the hot sample, as discussed in Ref. 33 . After each indentation, the tip remains in contact with the surface as the stage translates to the next indentation position.…”

“…With the addition of a heat source, there is potential for larger thermal gradients and fluctuations in the load frame, thus leading to higher drift rates, increased variation in drift rate from one nanoindentation to the next, and even a progression of drift rate over the duration of a single test. A previous report from our group 33 showed that thermal drift can be adequately managed during testing in air up to 400°C with appropriate equilibration; however, the trend of increasing thermal drift rate with temperature observed there raised concerns for the viability of high quality testing at higher temperatures. Universally achieving nano-scale indentations at higher temperatures (and thus expanding the envelopes in Figure 1), requires instrumentation advances in two arenas: 1) minimizing or eliminating oxidation and 2) successful management of thermal drift and noise 47 .…”

Bend Testing of Silicon Microcantilevers from 21°C to 770°C

“…This article is published with open access at Springerlink.com 750°C. [21][22][23][24][25] For high-quality nanoindentation experiments to be performed, it is necessary to accurately know the area function for the indenter tip. As discussed by Wheeler et al, 23,26 high-temperature experiments can quickly blunt indenter tips whether made from diamond or another hard material such as cubic boron nitride.…”