Table of ContentsIntroductionHigh
Temperature Nanoindentation – The Importance of Isothermal ContactMechanical Properties of Solid Oxide Fuel Cell Glass-Ceramic Seal at
High TemperaturesHigh Temperature Microcompression and
Nanoindentation in VacuumAbout Micro Materials
The year 2011 proved that high temperature nanoindentation is a potential
growth area in materials science. The function and operation of the NanoTest
instrument from Micro Materials Ltd (MML) at temperatures up to 750°C has been
well established and has also been recognized, implying that the challenge
to the nanomechanical community is no longer in the acquisition of reliable
data, but in the interpretation of the resulting data produced.
In 2011, numerous papers were published in the area of high temperature
nanoindentation. This article will provide a summary of selected work from users
of the MML
NanoTest system, which was the only instrument to produce publications
featuring data above 200°C. This article will précis experiments carried out at
temperatures above 600°C only.
High Temperature Nanoindentation – The Importance of
N.M. Everitt, M.I. Davies & J.F. Smith
A major issue in high temperature nanoindentation is stability of the
instrument and the need to reduce drift during testing. This is important for
accuracy of hardness and modulus data, and also for long-duration creep data.
A key focus area in the last few years has been the evaluation of heat flow
and stability during the indent itself, when the indenter material is brought
into contact with the sample. It makes logical sense that the diamond must be
heated as well as the sample in order to ensure isothermal contact and prevent
unwanted system instability, and this paper demonstrates this.
Finite element analysis modelling was utilized to offer a qualitative view of
how the thermal picture develops under a diamond indenter without controlled
heating of the diamond. In the case of a low-conductivity sample such as fused
silica, the thermal gradient below the indenter tip can be relatively
insignificant, whereas with a high-conductivity sample such as gold, only a
small region of the sample reaches thermal equilibrium with the tip. As a
result, a very steep thermal gradient is formed in the sample.
Such a thermal gradient will cause heat flow between the sample and the
indenter immediately after the indenter moves into the sample, causing unwanted
contraction/ expansion of both during indentation, and thus inaccuracy in
The model results were validated by comparing results obtained by heating the
indenter either indirectly by contact with the sample or utilizing a separate
heater for the indenter (an isothermal contact method).
Figure 1a displays a nanoindentation curve obtained on a gold sample at
300°C, using a method where the heater is heated indirectly by prolonged contact
with the sample prior to indentation. The curve seems to exhibit negative creep,
with the unloading curve crossing the loading curve. This is due to instrument
drift. Figure 1b shows how this can be prevented by heating the tip separately
so that contact is isothermal.
Figure 1. Figures1a (left) shows a nanoindentation curve
acquired on a gold sample at 300°C, using a method where the heater is
indirectly heated by prolonged contact with the sample prior to indentation. The
curve appears to exhibit negative creep, with the unloading curve crossing the
loading curve. This is as a result of instrument drift. Figure 1b
(right) shows how this can be avoided by heating the tip separately so that
contact is isothermal.
Nanoindentation results were shown for experiments on fused silica at
temperatures up to 600°C, and annealed gold at temperatures up to 300°C. The
results showed that indentation without separate indenter heating produced
unacceptable thermal perturbation in the system, whereas the isothermal contact
method maintained acceptable thermal drift and displayed values of modulus and
hardness that compared well with those in the literature.
Mechanical Properties of Solid Oxide Fuel Cell Glass-Ceramic
Seal at High Temperatures
J. Milhans, D. Li et al
This group at Georgia Tech recently published NanoTest data describing the
mechanical properties of solid oxide fuel cell glass-ceramic seal material, G18.
Hardness, modulus and creep properties were investigated via depth-sensing
nanoindentation at room temperature, and then at temperatures of 550, 650 and
Results proved a decrease in modulus with increasing temperature, with
considerable decrease above the glass transition temperature, while hardness
generally decreased with increasing temperature as shown in Figure 2.
Figure 2. Hardness measurements show that aging the G18
sample for longer improved stability.
Creep data acquired over 120s at a maximum load of 120mN showed that creep
increased with increasing temperature, but then decreased with further aging as
shown in Figure 3.
Figure 3. High temperature creep data for G18 aged for 4
The tip heating used by the NanoTest ensures superior instrument stability
even at these very high temperatures, allowing such creep data to be obtained.
High Temperature Microcompression and Nanoindentation in
S. Korte, R.J. Stearn, J. Wheeler, W.J. Clegg
Nanoindentation is now used commonly as a method of studying micropillar
At high temperatures it is essential to test in an inert environment so as to
minimise oxidation effects. Also, impurities in inert gases can cause problems
so that testing in vacuum can also be desirable. NanoTest users in
Cambridge have altered their instrument to allow it to be used in a vacuum
chamber, allowing high temperature nanoindentation in a vacuum environment.
By carefully controlling the temperatures of the indenter tip and the sample,
the group was able to carry out flat punch indentations of gold, a good thermal
conductor, over several minutes at 665°C in vacuum.
This tip heating capability also allowed thermal stability to be once again
re-established in site-specific microcompression experiments. This allowed
compression of nickel superalloy micropillars up to sample temperatures of 630°C
with minimal levels of oxidation after 48 h. Furthermore, the measured Youngs
modulus, yield and flow stresses were consistent with literature data.
NanoTest capabilities that made this work possible include the following:
- The MML NanoTest uses an exclusive horizontal loading mechanism, meaning
electronics and measurement hardware are free from the influence of heat
convection. This, combined with the separate heating of both sample and
indenter, ensure makes the NanoTest stand out as the only option for high
- Patented PID loop control of the heating mechanisms ensures excellent
temperature stability, enabling long duration creep tests.
About Micro Materials
Established in 1988, Micro Materials Ltd are manufacturers of the innovative
NanoTest system, which offers unique nanomechanical test capability to materials
researchers for the characterisation and optimisation of thin films, coatings
and bulk materials. The current model, the NanoTest Vantage was launched on June
This information has been sourced, reviewed and adapted from
materials provided by Micro Materials.
For more information on this source, please visit Micro