Abstract
A technique for measuring the coefficient of thermal expansion (CTE) of ceramic protective coatings from 25 °C to 1400 °C is proposed. The surface of a self-standing mullite coating heated in a furnace was observed by a scanning laser microscope which detects only the blue laser light reflected from the sample surface as an image source and thereby eliminates the effect of thermal radiation. Images with constant contrast independent of temperature without halation by thermal radiation were obtained. The series of images from 25 °C to 1400 °C was used for the digital image correlation and the thermal strain was measured for each temperature; the CTE was calculated from the data as a function of temperature. The reliability of the measurement was confirmed through the CTE measurement of a c-plane sapphire plate and practically applied to the measurement of a mullite coating. For cases in which a self-standing coating cannot be obtained, we also proposed a method of CTE measurement for a coating adhered to a substrate, with consideration for the effect of substrate constraint.
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