Abstract

Within a Brite Euram project thick thermal barrier coatings for combustor applications were produced by plasma spraying of yttria partially stabilised zirconia (ZrO2 + 8 wt.% Y2O3). The material properties of such coatings strongly depend on their microstructure which can be altered by manipulating the parameters controlling the plasma spraying process. Covering a variation of possible microstructures, the coatings considered had a thickness of about 2 mm and were six to eight times thicker than the coatings currently in service. This investigation was concerned with an evaluation of the thermophysical and mechanical properties of these coatings and their correlation with the microstructure and the plasma spray parameters. Particular attention was paid to the influence of coating segmentation, microcracking and porosity. The experimental work included the measurement of the thermal diffusivity using the laser flash technique, thermal expansion measurements, and the determination of flexural strength and Young's modulus by means of a specially constructed four-point bend rig. Since some of the samples considered were sprayed according to a partially factorial test plan a statistical evaluation of the material data was possible yielding the correlation between process parameters and material properties.

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