Pressurelessly sintered zirconium diboride/silicon carbide composite bodies and a method for producing the same

Abstract

A method of sintering a ZrB2—SiC composite body at ambient pressures, including blending a first predetermined amount of ZrB2 powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities. Next the blended powders are mixed to yield a substantially homogeneous powder mixture and a portion of the substantially homogeneous powder mixture is formed into a green body. The body is fired to a first temperature, wherein substantially all surface oxide impurities are reduced and / or volatilized to substantially eliminate oxides from the green body, and the body is heated to a second temperature and sintered to yield a composite body of at least about 99 percent theoretical density and characterized by SiC whisker-like inclusions distributed substantially evenly in a ZrB2 matrix.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The invention relates generally to the field of zirconium diboride ceramics, and, more particularly, to a pressurelessly sintered primarily zirconium diboride ceramic body and a method for making the same.BACKGROUND OF THE INVENTION[0002]Traditionally, zirconium boride and composites thereof, such as zirconium boride / silicon carbide composites, have been fabricated by a hot pressing process. Mixtures of zirconium boride and silicon carbide powders are placed in a pressure vessel and are subjected to elevated pressures while heated to high temperatures, typically in an inert atmosphere or under vacuum. Alternately, ZrB2 / SiC composites may be formed by reaction hot pressing precursors such as metallic Zr, Si powders and boron carbide (B4C) powder (instead of SiC and ZrB2 powder precursors). In either technique, the lack of self-diffusion and low driving forces for sintering and densification inherent in the materials is compensated for through the...

AI Technical Summary

Benefits of technology

[0005]The present invention relates to a method of sintering ZrB2/SiC bodies at ambient pressures, as well as to control of the microstructure of the so-produced ZrB2/SiC bodies.

[0006]One object

Problems solved by technology

Although hot pressing is not required per se for the sintering of ZrB2 / SiC composites, sintering without the application of elevated pressures results in weak bodies characterized by densities only about 90 percent of theoretical and having poor thermal and mechanical properties.

Therefore, the densified bodies so produced are limited by the constraints of the hot pressing die to simple shapes and moderate sizes.

Further, hot pressing techniques require expensive hot pressing facilities and provide a slow rate of production.

Moreover, the bodies produced by hot pressing techniques are simple and unfinished, thus typically requiring further diamond machining in order to produce a finished end product.

Such machining adds considerable time and financial cost.

In the hot pressing processes, the attendant high pressures are necessary to provide sufficient driving force for substantial densification to occur, since the mixed ZrB2 and SiC powders alone lack sufficient self-diffusion characteristics when heated to sintering temperatures.

The use of high sintering pressures addresses this problem by providing an externally generated driving force to the system, but also adds complexity and cost to the fabrication of ZrB2 / SiC bodies.

Further, the application of high pressure adds inherent geometrical constraints that limit the bodies so formed to simple geometric shapes.

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