| Budget Amount *help |
¥5,600,000 (Direct Cost: ¥5,600,000)
Fiscal Year 1996: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1995: ¥4,200,000 (Direct Cost: ¥4,200,000)
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| Research Abstract |
To utilize superior characteristics of ceramics such as high strength and chemically stable properties, accelerative developments of technologies concerning binding or combining ceramic materials with other various materials are requested. For this meaning, ceramic coating technologies are just now becoming extremely important
To make clear the performance of plasma-sprayd ceramic coating, evaluations of various degradation characteristics of plasma-splayd ceramic coatings were conducted under corrosion and cyclic heating conditions. Then, to improve resisting characteristics of plasma-sprayd ceramic coating in these environments, sealing treatment, micro-structural grading and control of spraying atmosphere were conducted employing NiCrAlY and ZrO_2 system. Then, several investigations concerning environmental degradation characteristics of these plasma-sprayd coating system, were conducted from various view points. As a result, plasma sprayd zirconia ceramic coating do not have superi
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or resistance especially in 3%NaCl aqueous solution. And, corrosion was especially recognized in the boundary layr between ceramic top coat and undercoated NiCrAlY layrs. Therefore, the corrosion current was generated by electrochemical reactions that was occurred on the surface and in the inner part of NiCrAlY layr under the aqueous environment which was brought about by the penetration of water into interface through defects of ceramic top coat layr. And, it was recognized that micro-structural graded coating shows little improvements in corrosion properties. On the contrary, sealing treatment shows much improvement in corrosion and oxidation characteristics. Then, some evaluations of defect ratio in plasma-spray coating were conducted.
Recently, it has been indicated that Low Pressure Plasma Spray (LPPS) coating has higher adhesive strength and minute microstructure. For this reason, LPPS coating has been expected to have better high temperature oxidation resistance compared with Atmospheric Plasma Spray (APS) coating Therefore, in this study, cyclic and continuous heating tests of APS coating and LPPS coating were conducted. The degradation characteristics of these two types of coatings under cyclic heating conditions were investigated. As a result, a few cracks were generated in the top coated ZrO_2-8wt%Y_2O_3 layr of the APS coating after several cycles of heating to 1000ﾟC.Therefore, oxidation of the APS coating has been suppressed. On the contrary, in the case of LPPS coatings many microcracks were generated after several cycles of heating to 1000ﾟC.Oxidation of LPPS coatings preferentially occurred due to oxygen coming into coated layrs through these cracks. The governing factor of microcrack generation in the cyclic heating process was understood from the view point of larger thermal stress generation in the rop coated ZrO_2 -8wt%Y_2O_3 layr in the case of LPPS coating due to having larger Vickers hardness. Therefore, the thermal cycle life was closely correlated to the mechanical properties change due to porosity change. Less
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