CORRELATION BETWEEN DEFECT MORPHOLOGIES IN COATED FILM AND ENVIRONMENTAL DEGRADATION RESISTANCE OF PLASMA-SPRAYED CERAMIC COATINGS

为了利用陶瓷材料的高强度和化学稳定性等优良特性，要求加速发展陶瓷材料与其他各种材料的结合或结合技术。为了解等离子喷涂陶瓷涂层的性能，对等离子喷涂陶瓷涂层在腐蚀和循环加热条件下的各种退化特性进行了评价。然后，为了提高等离子喷涂陶瓷涂层在这些环境下的耐磨性能，采用NiCrAlY和ZrO2系统对涂层进行了封口处理、显微组织分级和喷涂气氛控制。然后，从不同角度对这些等离子喷涂涂层系统的环境降解特性进行了研究。结果表明，等离子喷涂氧化锆陶瓷涂层没有超强…。耐高温，尤其是在3%的氯化钠水溶液中。尤其是在陶瓷表层与底层NiCrAlY涂层的交界处，腐蚀尤为明显。因此，腐蚀电流是在水环境下发生在NiCrAlY涂层表面和内部的电化学反应产生的，这是由于水通过陶瓷表层的缺陷渗入界面而产生的。而且，人们认识到，微结构梯度涂层在腐蚀性能方面几乎没有改善。反之，密封处理后的腐蚀和氧化性能有很大的改善。对等离子喷涂涂层的缺陷率进行了评价，结果表明，低压等离子喷涂涂层具有较高的结合强度和细小的显微组织。因此，与大气等离子喷涂(APS)涂层相比，LPPS涂层具有更好的抗高温氧化性能。因此，本研究对APS涂层和LPPS涂层进行了循环加热和连续加热试验。研究了这两种涂层在循环加热条件下的降解特性。结果表明，经多次循环加热至1000ﾟC后，APS涂层顶层的ZrO2-8wt%Y_2O_3涂层出现少量裂纹，从而抑制了APS涂层的氧化。相反，在LPPS涂层中，在加热到1000ﾟC的几个循环后会产生许多微裂纹。LPPS涂层优先发生氧化，这是因为氧气通过这些裂纹进入涂层。从涂层中由于具有较大的维氏硬度而产生较大的热应力的观点来理解循环加热过程中微裂纹产生的控制因素。因此，热循环寿命与孔隙率变化引起的力学性能变化密切相关。较少

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 importantTo 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 … More 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