This paper summarizes the basic properties of ceramic materials for thermal barrier coatings. Ceramics, in contrast to metals, are often more resistant to oxidation, corrosion and wear, as well as being better thermal insulators. Except yttria stabilized zirconia, other materials such as lanthanum zirconate and rare earth oxides are also promising materials for thermal barrier coatings.

Ceramic materials for thermal barrier coatings

Silicon-based ceramics are the leading candidates for high temperature structural components in next generation gas turbine engines. One key drawback of silicon-based ceramics for such an application is volatilization of the protective silica scale in water vapor and the resulting rapid ceramic recession. Therefore, the realization of Si-based ceramics components in advanced gas turbine engines depends on the development of protection schemes from water vapor attack. Currently, plasma-sprayed external environmental barrier coatings (EBCs) are the most promising approach. In the late 1980s and early 1990s a wide range of refractory oxide materials were tested as coatings on Si-based ceramics to provide protection from hot corrosion. After the discovery of silica volatilization in water vapor in the early 1990s, the focus of EBC development research has been shifted towards the protection from water vapor attack. Experience learned form the earlier coating developmental effort provided the foundation upon which more complex and advanced EBC coatings have been developed. This paper will discuss the brief history and the current status of EBC development for Si-based ceramics with the main focus on water vapor protection.

Current status of environmental barrier coatings for Si-Based ceramics

A steady‐state model for the resistivity of composites is presented, based on the idea that the resistance through a composite is the result of a series of a large number of resistors combined in series and parallel. There are three separate contributions to the resistance: constriction resistance at the contacts, tunneling resistance at the contacts, and the intrinsic filler resistance through each particle, with tunneling resistance generally dominating the magnitude of the overall resistance. The model predicts resistivity increases with increasing filler hardness and/or elastic modulus and insulating film thickness, while resistivity decreases with increasing particle size and intrinsic stress. The room‐temperature dc resistivity behavior of conductor‐filled silicone rubber composites was investigated to verify the model. Comparison of the model to this experimental data showed that good agreement could be obtained for filler materials in which the tarnish layer was a known quantity for a given powder...

Resistivities of conductive composites

Ceramics are a distinct class ofmaterials whose properties range from extreme hardness to unique electrical behavior. New methods of creating thin films of complex oxides and electronic ceramics allow the integration of these properties with semiconductor technology and raise the possibility of a new range of electronic devices.

https://science.sciencemag.org/content/sci/247/4946/1056.full.pdf

Ceramic Thin Films: Fabrication and Applications

This feature article explores the concept of creating functionally graded metal-ceramic composite microstructures for thermal barrier coatings used in gas-turbine applications. From a thermomechanical perspective, this concept offers the possibility of significantly improving the life and reliability of thermal barrier coatings. However, prior research reveals that progress has been somewhat limited because of the oxidative instability exhibited by some metal-ceramic composite microstructures. The present study addresses some of the materials criteria and research issues associated with preparing chemically stable, yet mechanically durable, graded metal-ceramic microstructures for realistic application environments.

Concept of Functionally Graded Materials for Advanced Thermal Barrier Coating Applications

This report assesses the current status and future potential for the application of ceramic coatings in advanced diesel and turbine engines A previous report describes the authors findings in greater detail Ceramics, in contrast with metals, generally exhibit better structural and thermal capabilities at high temperatures In general, ceramics are more resistant to creep, oxidation, corrosion, erosion, and wear, as well as being better thermal insulators The benefits of thermal barrier coatings on the hotter side of diesel or turbine engine components are well-documented, and thermal barrier coatings are one of several applications of ceramics that are being pursued actively for heat engines Ceramic coatings are being considered for diesel engine cylinder liners, piston caps, valve faces and seats, piston rings, and other parts and for turbine components such as combustors, blades, stators, seals, and bearings

Ceramic coatings for advanced heat engines - A review and projection

The current status and future potential for application of ceramic coatings to diesel and turbine engine components was assessed Properties are tabulated for numerous materials from the oxide, carbide, nitride, and boride families Several coating deposition processes are described and compared, including plasma spraying, electron beam evaporation, sputtering, chemical vapor deposition, sol-gel, ion, and laser techniques We emphasize zirconia thermal-barrier coatings, but coatings for wear and erosion resistance, lubrication, chemical protection, seals, and interfaces were also addressed Coating characterization methods, particularly those for measuring adherence and defects, are reviewed We conclude that the use of coatings will expand in the future, permitting higher performance and more reliable heat engines

G.A. Cerny

Papers

Ceramic coatings for advanced heat engines - A review and projection

Ceramic coatings for heat engine materials: status and future needs