Method and apparatus for thermal microhardness analysis

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Abstract
A method and apparatus are described to carry out microhardness measurements as a function of temperature on amorphous solids to investigate the glass transformation. The Vickers hardness number Hv of a typical well characterised inorganic glassy polymer a-Se has been monitored as a function of temperature with the heating rate kept constant during the measurements. In the glass transformation region, HV(T) was observed to go through a sharp fall. An empirical glass transition temperature, TG, was defined at the inflection point of HV(T) against T behaviour which depended on the heating rate, r. It is shown that the TG against r data can be used to study the structural relaxation processes which control the mechanical properties in the TG region. The activation energy for the structural relaxation process in a-Se, for example, was determined to be 2.77 eV over the temperature range 36-50 degrees C. The apparatus consisted of modifying a commercially available microhardness test instrument using a microcomputer and a data acquisition system, with an appropriate software and algorithm, to control the rate of heating of the sample.