Additives for property modification in ceramic composite bodies

Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing

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501 96, 501 99, 501102, 419 12, 419 14, 419 15, 419 16, C04B 3558, B22F 326

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054037905

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates generally to a novel method of manufacturing a ceramic composite body, for example, a ZrB.sub.2 -ZrC-Zr composite body (hereinafter referred to as "ZBC" composite body). More particularly the present invention relates to a method for modifying the resultant properties of a ceramic composite body, by, for example, minimizing the amount of porosity present in the composite body. The composite body comprises one or more boron-containing compounds (e.g., a boride or a boride and a carbide) which has been made by the reactive infiltration of a molten parent metal into a bed or mass containing boron carbide, an additive material, and optionally one or more inert fillers, to form the composite body. Particular emphasis is placed upon modifying the properties of a ZBC composite body (e.g., reactively infiltrating a mass containing boron carbide with a zirconium parent metal). However, the methods disclosed herein are believed to be generic to a number of different parent metals.


BACKGROUND ART

In recent years, there has been an increasing interest in the use of ceramics for structural applications historically served by metals. The impetus for this interest has been the relative superiority of ceramics, when compared to metals, with respect to certain properties, such as corrosion resistance, hardness, wear resistance, modulus of elasticity and refractory capabilities.
However, a major limitation on the use of ceramics for such purposes is the feasibility and cost of producing the desired ceramic structures. For example, the production of ceramic boride bodies by the methods of hot pressing, reaction sintering, and reaction hot pressing is well khown. While there has been some limited success in producing ceramic boride bodies according to the above-discussed methods, there is still a need for a more effective and economical method to prepare dense boride-containing materials.
In addition, a second major limitation on the use of ceramics for structural applications is that ceramics generally exhibit a lack of toughness (i.e., damage tolerance, or resistance to fracture). Such lack of toughness tends to result in sudden, easily induced, catastrophic failure of ceramics in applications involving rather moderate tensile stresses. This lack of toughness tends to be particularly common in monolithic ceramic boride bodies.
One approach to overcome the above-discussed problem has been the attempt to use ceramics in combination with metals, for example, as cermets or metal matrix composites. The objective of this known approach is to obtain a combination of the best properties of the ceramic (e.g., hardness and/or stiffness) and the best properties of the metal (e.g., ductility). While there has been some general success in the cermet area in the production of boride compounds, there still remains a need for more effective and economical methods to prepare dense boride-containing materials.


DESCRIPTION OF COMMONLY OWNED U.S. PATENTS AND PATENT APPLICATIONS

Many of the above-discussed problems associated with the production of boride-containing materials have been addressed in commonly owned and co-pending U.S. patent application Ser. No. 07/551,306, filed on Jul. 12, 1990, in the names of Terry Dennis Claar et al, which is a continuation-in-part of U.S. patent application Ser. No. 07/446,433, filed on Dec. 5, 1989, in the names of Terry Dennis Claar et al., as a continuation of commonly owned U.S. patent application Ser. No. 07/296,771, which issued on Dec. 5, 1989, as U.S. Pat. No. 4,885,130. U.S. patent application Ser. No. 07/296,771, was a continuation-in-part of U.S. patent application Ser. No. 07/137,044, filed on Dec. 23, 1987, and now allowed, in the names of Terry Dennis Claar et al., which was a continuation-in-part of U.S. patent application Ser. No. 07/073,533, filed in the names of Danny R. White, Michael K. Aghajanian and T. Dennis Claar, on Jul. 15, 1987, and entitled "Process for Preparing Self-Supporting Bodies and Products Made Thereby". The above-discussed s

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