Advanced structural ceramics in aerospace propulsion.

Advanced structural ceramics are those ceramics intended for use as load‐bearing members. They are materials that combine the properties and advantages of traditional ceramics, such as chemical inertness, high temperature capability, and hardness, with the ability to carry a significant mechanical stress. Advanced structural ceramics are more expensive than traditional ceramics. Most of the advanced structural ceramics under development today are based on silicon nitride, Si3N4; silicon carbide, SiC; zirconia, ZrO2; or alumina, Al2O3. Advanced structural ceramics typically possess some combination of high temperature capabilities, high strength, toughness or flaw tolerance, high hardness, mechanical strength retention at high temperatures, wear resistance, corrosion resistance, thermal shock resistance, creep resistance, and long‐term durability. The relationship between processing and properties is especially critical for advanced structural ceramics because subsequent successful operation in severe environments often requires carefully controlled compositions and microstructures. Fabrication generally takes place in four steps: powder processing, consolidation/forming, densification, and finishing. The focus has been on applications for gas turbine, diesel, and spark‐ignited engines. Advanced structural ceramics are also under investigation for use in numerous other high performance applications including metal‐cutting and shaping tools, and various military applications. Exposure limits for silicon carbide and powders of zirconium compounds (including zirconium dioxide) have been established by ACGIH. The solid ceramics present no apparent health hazard.

Wear behavior on advanced structural ceramics: α-sialon matrix reinforced with β-sialon fibers

China has been following the research and development on advanced structural ceramics and ceramic engines for more than a decade. A National Project entitled “Advanced Structural Ceramics and Adiabatic Diesel Engine” was formulated in 1986. The principle program areas of this project are ceramic powder synthesis, material design and material processing, property and microstructure study, machining and joining, nondestructive evaluation, internal combustion engine component fabrication and low heat rejection diesel engine technology. The present paper is a short survey of what has been going on during the past 4 years.

In the paper the current innovations in automotive branches, including the development of propulsion systems in vehicles are described. Examples of the use of hybrid propulsion systems for three groups of vehicles: land, sea and air are presented. The concepts of technical solutions are described and the potential benefits of modifying traditional combustion systems are detailed.

Al-26 diffusion measurement in 2/1-mullite by means of Secondary Ion Mass Spectrometry

Ultra-precision grinding of structural ceramics by electrolytic in-process dressing (ELID) grinding

The travelers attended the 33rd ASME International Gas Turbine and Aeroengine Congress and Exposition. V.R. Bullington staffed the exhibits for the Ceramic Technology for Advanced Heat Engines Project and distributed informational materials to the attendees. V.J. Tennery presented a paper; in addition, he organized and presented the US portion of a technical status review for the Executive Committee, IEA Annex II (including US research being conducted within the IEA Annex II agreement on advanced structural ceramics). Finally, Dr. Tennery made a technical presentation on the proposed research plan for an Annex III agreement on structural ceramics.

The application of fracture mechanics to advanced technical ceramics was initiated nearly 30 years ago. It was heralded by an international conference at the Pennsylvania State University in 1973. Unbridled optimism prevailed as many believed that the coupling of fracture mechanics with ceramics would enable high temperature advanced ceramics to find extensive structural applications. Unfortunately, there were a number of barriers to the use of ceramics as structural materials, even with the application of fracture mechanics. The use of brittle ceramics in structural applications faced major challenges. These included: (1) the absence of a reliable data base of materials properties, (2) the lack of appropriate standards for the determination of the properties of these materials, (3) a lack of any rational, fracture mechanics based design methodology for brittle ceramics, and (4) the high costs of producing and utilizing structural parts from advanced ceramics. These were serious deficiencies that inhibited the achievement of successful applications of ceramics. Fracture mechanics tests provided a basis for the design methodology and also provided understanding of the basics of the fracture process in brittle ceramics. It informed the engineering community that ceramic fracture toughnesses were low, < 10 MPa√m and that there were serious problems with slow crack growth and fatigue. The presence of rising R-curve behavior was observed and related to the crack tip's following wake region. Cyclic fatigue was confirmed to exist and related to the presence of a rising R-curve. Today, the promise of structural ceramics remains mostly unfulfilled, except for a few niche applications that are nonetheless encouraging. In addition, there have been significant advances in the properties and integrity of structural ceramics over the past three decades. Advanced structural ceramics are better than ever. This can be attributed to the use of fracture mechanics concepts to identify the microstructural processing defects and then improve the processing methodology to eliminate those defects. There have also been major advances in the development of standards applied to ceramics in which ASTM has played a major role. Unfortunately, we still have not learned to design with brittle ceramics and the cost of their utilization in structural applications remains prohibitively high.

Influence of the material removal mechanisms on hole integrity in ultrasonic machining of structural ceramics

In archaeological studies of ceramic materials, nondestructive evaluation (NDE) methods are needed to better understand the nature and evolution of ceramic fabrication techniques [1] and even to authenticate ancient ceramics [2]. The desired data are similar to those sought in modern fine ceramics, especially advanced structural ceramics [3]. X-ray imaging technologies, developed to characterize structural ceramics, were applied to three samples, a modern and two archaeological ceramics, in order to obtain fabrication information. They were imaged using various X-ray image receivers: electrostatic receivers (Xeroradiography Xerox 125 and 175, Xerox Medical Systems, Pasadena CA), photostimulable phosphors (Fuji Photo Film Co., Japan, 1985 Prototype System FCR-101), and high-resolution industrial X-ray film (Kodak, Rochester, N.Y.). Ultrasound and dye penetrants had failed to reveal methods of manufacture in the ancient ceramics because of their highly porous fabric (1).

Microstructure and mechanical properties of a SiC containing advanced structural ceramics

The development of a computerized database on advanced structural ceramics can play a critical role in fostering the widespread use of ceramics in industry and in advanced technologies. A computerized database may be the most effective means of accelerating technology development by enabling new materials to be incorporated into designs far more rapidly than would have been possible with traditional information transfer processes. Faster, more efficient access to critical data is the basis for creating this technological advantage. Further, a computerized database provides the means for a more consistent treatment of data, greater quality control and product reliability, and improved continuity of research and development programs.A preliminary system has been completed as phase one of an ongoing program to establish the Structural Ceramics Database system. The system is designed to be used on personal computers. Developed in a modular design, the preliminary system is focused on the thermal properties of monolithic ceramics. The initial modules consist of materials specification, thermal expansion, thermal conductivity, thermal diffusivity, specific heat, thermal shock resistance, and a bibliography of data references. Query and output programs also have been developed for use with these modules. The latter program elements, along with the database modules, will be subjected to several stages of testing and refinement in the second phase of this effort. The goal of the refinement process will be the establishment of this system as a user-friendly prototype.Three primary considerations provide the guidelines to the system’s development: (1) The user’s needs; (2) The nature of materials properties; and (3) The requirements of the programming language. The present report discusses the manner and rationale by which each of these considerations leads to specific features in the design of the system.

10 - Operational sustainability assessment of multipower source traction drive

Advanced structural ceramics have been increasingly used in automotive, aerospace, military, medical and other applications due to their high temperature strength, low density, thermal and chemical stability. However, the Grinding of advanced ceramics such as alumina is difficult due to its low fracture toughness and sensitivity to cracking, high hardness and brittleness. In this paper, surface integrity and material removal mechanisms of Alumina ceramics ground with SiC abrasive belts, have been investigated. The surface damage have been studied with scanning electron microscope (SEM). The significance of grinding parameters on the responses was evaluated using Signal to Noise ratios.This research links the surface roughness and surface damages to grinding parameters. The optimum levels for maximum material removal and surface roughness been discussed.

The primary goal in the development of advanced structural ceramics has been to provide high-strength, corrosion-resistant materials for use in high-temperature, aggressive environments. Much of the developmental effort has focused on heat exchangers for use in industrial gas- or coal-fueled systems with temperatures on the order of 1200 to 1400°C. while ceramics are often popularly described as inert to chemical degradation, the corrosion resistance of these materials actually ranges from excellent to very poor, depending especially on the compositions of the environment and the material. Understanding these dependencies is critical to the development of a materials selector expert system for advanced ceramics. The present paper examines the development of a set of rules for a material selector expert system based on relations among composition, microstructure, transport processes, operating conditions, and corrosion. The concurrent information requirements that must be provided in a computerized materials property database are discussed also.