Understanding And Improving The Toughening Mechanisms In Silicon Carbide Ceramics

Discovered by Edward G. Acheson about 1890, silicon carbide is one of the oldest materials and also a new material. It occurs naturally in meteorites, but in very small amounts and is not in a useable state as an industrial material. For industrial require ments, large amounts of silicon carbide must be synthesized by solid state reactions at high temperatures. Silicon carbide has been used for grinding and as an abrasive material since its discovery. During World War II, silicon carbide was used as a heating element; however, it was difficult to obtain high density sintered silicon carbide bodies. In 1974, S. Prochazka reported that the addition of small amounts of boron compounds and carbide were effective in the sintering process to obtain high density. It was then possible to produce high density sintered bodies by pressureless sintering methods in ordinary atmosphere. Since this development, silicon carbide has received great attention as one of the high temperature structural ceramic materials. Since the 1970s, many research papers have appeared which report studies of silicon carbide and silicon nitride for structural ceramics.

This book covers the area of tribology broadly, providing important introductory chapters to fundamentals, processing, and applications of tribology. The book is designed primarily for easy and cohesive understanding for students and practicing scientists pursuing the area of tribology with focus on materials. This book helps students and practicing scientists alike understand that a comprehensive knowledge about the friction and wear properties of advanced materials is essential to further design and development of new materials. The description of the wear micromechanisms of various materials will provide a strong background to the readers as how to design and develop new tribological materials. This book also places importance on the development of new ceramic composites in the context of tribological applications. Some of the key features of the book include: Fundamentals section highlights the salient issues of ceramic processing and mechanical properties of important oxide and non-oxide ceramic systems; State of the art research findings on important ceramic composites are included and an understanding on the behavior of silicon carbide (SiC) based ceramic composites in dry sliding wear conditions is presented as a case study; Erosion wear behavior of ceramics, in which case studies on high temperature erosion behavior of SiC based composites and zirconium diboride (ZrB2) based composites is also covered; Wear behavior of ceramic coatings is rarely discussed in any tribology related books therefore a case study explaining the abrasion wear behavior of WC-Co coating is provided. Finally an appendix chapter is included in which a collection of several types of questions including multiple choice, short answer and long answer are provided.

Ceramic materials are one of the most promising materials for wide variety of technical applications such as automotive, aerospace, medical, and other applications. They have very high strengths and high melting points relative to metals. However, low fracture toughness is one of the main barriers of ceramics prohibiting their wide-spread applications. This is because ceramics are mainly bonded with directional bonds which don't allow dislocations based deformation. Several attempts have been made to increase the toughness of ceramic materials without sacrificing significantly the other mechanical properties. Here three different types of SiC based ceramics have been computationally (atomistic and up-scaled modeling) developed and studied to understand the deformation mechanism. They are: (1) Nanodiamond reinforced SiC nanocomposites, (2) "carbon" enriched SiC nanostructures and (3) Diamond-SiC nanoscale multilayered films where fraction of "Si" atoms is replaced by "C" atoms. Initial results from atomistic level and subsequent continuum level studies show enhancement in both strength and toughness. Conventional strong but brittle ceramics can't be applied in many future engineering applications where the high stiffness of ceramics is very favorable but unavoidable low toughness is the disappointing point. The outcome of research is shows a successful indication of proposing computationally made a new class of ceramic materials with high hardness as well as desirable high toughness. It will increase the area of applications of ceramic materials and will meet the future demand of desired material properties.

Silicon carbides have major industrial uses as high temperature structural ceramic materials. These two volumes are translated from the Japanese and provide a comprehensive account of the seminal work going on in Japan.

Excerpt from Toughening Mechanisms in Ceramic Composites: Semi-Annual Progress Report for the Period Ending September 30, 1988 The achievement of higher efficiency heat engines and heat recovery systems requires the availability of high-temperature, high-performance structural materials. Structural ceramics and, more recently ceramic matrix composites have received particular attention for these applications due to their high strength and excellent resistance to corrosion, erosion and thermal shock. Even with these positive attributes, improved reliabil ity and extended lifetime under service conditions are necessary for strue tural ceramics and ceramic composites to gain wide industrial acceptance. This reliability is only achieved with improved knowledge of in-service damage modes and failure mechanisms, and the processing knowledge to improve this performance by microstructural modifications.' The inherent _problems are mechanical and chemical in nature and are enhanced by the high temperatures, reactive environments, and extreme thermal gradients and thermal cycling, to which these materials are subjected. With an objective of improved performance for heat engine/heat reccy ery applications, the nist program addresses these problems through a de termination and characterization of major toughening mechanisms in ceramic composites, examining both model crack-fiber systems and real composites. A key aspect of the program is a determination of the critical processing factors which influence microstructure and interfacial behavior in these materials, and which thereby influence these toughening mechanisms. The activities of the program are grouped under two major work areas, each designed to develop key data, associated test methods and companion predic tive models. The status of these two work areas are detailed below. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.

Method of improving the toughness of SiC-based ceramics. SiC, AlN, Al.sub. 2 O.sub. 3 and optionally .alpha.-Si.sub. 3 N.sub. 4 are hot pressed to form a material which includes AlN polytypoids within its structure.