Posted on 20/05/2010

This paper describes micropillar compression tests carried out by Dr Sandra Korte and Prof Bill Clegg at the University of Cambridge, UK. Using a flat punch indenter mounted on an MML NanoTest system, tests were carried out on MgAl2O4 spinel, at a range of temperatures from room temperature to 400°C. The spinel deformed plastically at 200°C and above without a confining pressure. The yield stresses measured were consistent with those obtained elsewhere by compressing larger crystals under a high confining pressure, suggesting that micropillar compression has the potential to be a useful technique for studying plastic flow in brittle materials.

Compression of such micropillars requires an extremely stable system. The NanoTest ensured this stability at high temperature by using heaters in both the sample stage and diamond tip. This minimises thermal drift, thereby allowing micro-compression tests to be carried out at reasonably low strain rates.

The authors state ‘Both sample and tip heaters are required to minimize thermal drift … In both cases the rate was constant over the 20s period. The values obtained were 0.15 and 0.20 nm/s at 200 and 400^oC respectively.’

NanoTest capabilities that made this work possible:

The MML NanoTest uses a unique 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 temperature measurements.   PID loop control of both indenter and sample heating ensure excellent temperature stability, thus long duration creep tests.