亀裂を有するセラミックスの高温腐食雰囲気中の強度

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The purpose of this paper is to report on the strengthening mechanism of corroded and/or eroded ceramics at elevated temperature. A study was conducted on the effect of surface cracks on the fracture strength of ceramics used for the lower-quality fueled gas turbine or diesel engine. In general, in order to remove the surface defects or to form into correct shape the ceramic materials has been machined at a great cost and a waste of time. Even if the materials were carefully machined their surface would be attacked under service conditions of gas turbine to the extent of considerable damages by corrosive ashes and such an effort consequently seems to be useless. The experiments were carried out on the fracture strengthes by bending stress and tensile stress under the various test conditions. Partially stabilized zirconia, silicon carbide and silicon nitride were used for test specimens. In these materials the silicon nitride was mainly used in this study. The tests were performed in the range of 650 to 1200℃ for 1.5 hours to 150 hours with and without corrosive ash. Vanadium pentoxide and /or sodium sulfate were applied on the surface of bending test specimen and tensile test specimens were exposed to combustion gas flow containing sulpher and sodium. In order to simulate mechanical surface defects on the specimens, Vickers hardness indentation method or blast erosion damage was applied as quantitative tool. Conventional bending machine with an electric furnace and burner rig with a tensile loading apparatus were used in fracture strength tests. The experimental results show that the existence of artificial corrosive ash containing sodium sulphate or hold in low quality fueled combustion gas, the fracture strength of cracked specimen is comparable to the non cracked or smooth specimen and hadn't any scattering among the results. On the other hand on a electric furnace test the bending strength of cracked specimen applying sodium sulfate had considerable scattering under the similar test condition. It seems this difference depends on whether the molten salt enter into the cracks or not. In the case of burner rig test, a dynamic pressure activate entering of gaseous or liquid molten salt into the cracks, but on the electric furnace the sodium sulfate didn't always dissolve sufficiently or not active. Some experimental facts likely supporting this hypothesis were obtained with EPMA. These results mean that at least on lower-quality fueled gas turbine engine the high quality finishing work on the blade surface is useless rather than insignificant.
独立行政法人海上技術安全研究所の論文
1995-07-30

亀裂を有するセラミックスの高温腐食雰囲気中の強度

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