Optical system for microscopic observation and strain measurement at high temperature

A system of optical microscopy has been developed for high-temperature direct observation and strain measurement. Observations at high temperatures are carried out using a UV CCD camera and UV illumination while thermal radiation is cut off by a UV light transmission filter. Observation of a Vickers indentation on polycrystalline α-Al₂O₃ revealed that sufficient image contrast was maintained up to 1400 °C. The potential of the proposed system for strain measurement via digital image correlation was evaluated through measuring the thermal strain of polycrystalline α-Al₂O₃; the obtained coefficient of thermal expansion agreed well with the reported values. (paper)