Elevated temperature, in situ indentation with calibrated contact temperatures

Stable, elevated temperature indentation requires the indenter tip and the sample to be in thermal equilibrium to prevent thermal displacement drift due to thermal expansion. However, temperature feedback on the sample and/or indenter temperatures comes from thermocouples which are not generally located at the contacting surfaces. Thus, a temperature gradient exists between the thermocouple and the contact surfaces. In this work, two procedures for calibrating the surface temperature of the indenter tip via thermocouple indentation and Raman spectroscopy are demonstrated at temperatures between 25 degrees C and 150 degrees C. Good agreement is found between the two methods, and thermal drift is observed to be minimal at the calibrated temperatures. A linear relationship is also demonstrated between measured temperature shifts during contact and heat flow calculated from thermal conductivity, contact area and thermal gradient.