Advanced Thermal Barrier Cotings by the Sol-Gel Process

The sol-gel process as been proven to prepare chemically uniform, high-purity, Yttria-stabilized zirconia (YSZ) powders. Ceramic powders can also be synthesized by solution-based spray pyrolysis (SP) process. Plasma can be used as one of the pyrolysis methods for SP process. Therefore, by a combination of plasma spray and sol-gel solution-based SP process, the powders can be calcinated by the plasma flame and deposited onto the substrates directly. Due to the ultra-bigb temperature of plasma flame, the drying, decomposition, and sintering stages in SP process can be done simultaneously. Metal powders can be blended into the sol-gel solution, which will be coated a layer of ceramic precursor spontaneously. After pyrolysis in plasma flame, micro-composite powders with ceramic surface coating and metal core can be achieved and deposited on the substrates with the fine ceramic powders from the sol-gel solution at the same time. By subsequently changing the concentration of sol-gel solution or the ratio of metal powder/solution, composition gradient can be builtup easily. The process of making functionally gradient coatings, either gradient in chemical composition or in microstructure, can be done continuously. Lower process cost and fast process time with improving performance of the functionally gradient TBC can be expected. This sol-gel plasma-spray can also provide many advantages such as simple process, low-cost, flexibility on controlling microstructure and chemical composition, and fast throughput. Successful development of this sol-gel plasma-spray can provide a revolutionally processing technique of making ceramic coatings and functionally gradient materials. The applications can be on thermal barrier coatings, antiwear and anticorrosion coatings, high strength materials, electrical and optical materials and devices, and many others. The low-cost nature of the sol-gel process can guarantee the popularity of this sol-gel plasma spray process. The flexibility on microstructure and composition can even create new applications that can not be achieved by the traditional processes.