Nanomechanical testing of thin films to 950 °C

Nanomechanical testing has been a revolutionary technique in improving
our fundamental understanding of the basis of mechanical properties of
thin film systems and the importance of the nanoscale behaviour on their
performance. However, nanomechanical tests are usually performed in
ambient laboratory conditions even if the coatings being developed are
expected to perform at high temperature in use. It is important to measure
nanomechanical and tribological properties of materials under test
conditions that are closer to their operating conditions where the results
are more relevant. We can then better understand the links between
properties and performance and design advanced materials systems for
increasingly demanding applications. However, high temperature
nanomechanics is highly challenging experimentally and a high level of
instrument thermal stability is critical for reliable results. To achieve this
stability the NanoTest Vantage has been designed with (i) active heating of
the sample and the indenter (ii) horizontal loading to avoid convection at
the displacement sensor (iii) patented stage design and thermal control
method. By separately and actively heating and controlling the
temperatures of both the indenter and test sample there is minimal/no
thermal drift during the high temperature indentation and measurements
can be performed as reliably as at room temperature. Illustrative results
are presented for TiAlN, TiFeN, DLC and MAX-phase coatings. Above 500 °C
it is necessary to use Argon purging to limit oxidation of samples and the
diamond indenter, although the efficiency of this decreases over 750 °C. To
test at higher temperatures without indenter or sample oxidation an
ultra-low drift high temperature vacuum nanomechanics system (NanoTest
Xtreme) has been recently developed. Results with the vacuum system are
presented up to 950 °C.