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PROCESSING OF ADVANCED CERAMIC COMPOSITES

Roy W. Rice Naval Research Laboratory, Washington, D.C. 20375

Code 6360

ABSTRACT The field of ceramic composites is reviewed as an outstanding example of where more sophisticated chemistry can aid ceramic processing. Processes reviewed, mostly from work of the author and colleagues, include use of solution, polymer and high temperature chemistry, e.g. in sol-gel, polymer pyrolysis, solid state, and chemical vapor deposition processes. Future needs and opportunities for chemistry in ceramic processing are also discussed, e.g. coating part or all the matrix or its precursor onto the particulates or fibers of the resultant composite.

INTRODUCTION Ceramic composites have been attracting increasing interest and study; particularly composites for improved mechanical behavior, but the opportunities for electrical and electronic ceramic composites are at least as 1 great.( ) While composites used for their mechanical performance may pose some new design challenges, the substantial opportunities they offer for improved mechanical reliability is the driving force for their development, i.e. they have resulted in mechanical properties that were felt unlikely, or undreamed of, 5 to 15 years ago. Ceramic composites are an outstanding example of both the need for, and the results achievable from, applying more sophisticated chemistry to their processing. This paper surveys a number of ceramic composite developments illustrating a variety of contributions of chemistry to their processing along with some future processing needs and opportunities. Examples are drawn mostly from the experience and current work of the author and his colleagues, with a few key examples drawn from other investigators. While the focus is on composites for mechanical properties, most of the processing approaches are also pertinent to electrical and electronic composites. II. A.

SURVEY OF CERAMIC COMPOSITE PROCESSING AND RESULTS Particulate Composites

Our first major application of chemistry to composite processing was the processing of A1 2 0 3 -Zr0 2 composites by mixing an A12 0 3 and a Zr0 2 sol then gelling, crushing, calcining, and subsequently hot pressing the resultant powder. As discussed elsewhere this sol-gel approach resulted in a far more homogeneous composite than could be achieved by conventional mixing and hot pressing of A1 2 0 3 and Zr0 2 powders (Fig. 1), and was apprently the first demonstration of fracture strengths which increased along with 2 fracture toughness in this system.( ,3) Such sol-gel processing is only one example of a broad spectrum of applications of lower temperature, more traditional aqueous (or non-aqueous) chemistry to ceramics. This potential for lower temperature chemistry should not obscure the equally important opportunity for higher temperature chemistry applicable to many composite needs, as illustrated by BN particulate composites. Mat.

Res.

Soc.

Symp,

Proc.

Vol.

32 (1984)

Published by Elsevier Science Publishing Co., Inc.

338

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