Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-08-29
2003-09-02
Jenkins, Daniel J. (Department: 1742)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S539500
Reexamination Certificate
active
06613462
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method to form a shaped article from separate bodies. In one embodiment, the method produces a shaped composite article from bodies of dissimilar materials such as a composite article comprised of a cermet and a ceramic.
BACKGROUND OF THE INVENTION
Ceramics and ceramic-metal composite (i.e., cermet) are usually formed by powder metallurgical methods. A ceramic is an inorganic nonmetallic material, such as an oxide, carbide, nitride, boride, silicide or alloy thereof. A cermet is a material containing a ceramic and a free metal, such as a cemented tungsten carbide. In forming a ceramic or cermet, a powder or powder mixture is shaped into a porous body (i.e., greenware) by techniques, such as pressing or slip casting. The greenware is then heated to remove volatile materials, such as water and plastic binders, and, subsequently, heated to a higher temperature to form a dense body. The greenware typically displays a linear shrinkage of about 15 percent. The shrinkage may vary within the part due to differing powder compaction, such as between regions having significantly different cross-sectional areas. When the shrinkage between two areas is too large, the part tends to crack during heating.
Several methods have been employed to make complex shaped cermet and ceramic bodies via powder metallurgical techniques. Techniques that have been employed include machining of the greenware (e.g., spark plugs) and injection molding (e.g., turbocharger rotors). Greenware machining causes significant loss of material and, generally, cannot form highly complex or small parts due to, among other things, the fragility of the greenware body. Injection molding requires expensive tooling and heating of the molded body for long times to remove plastic additives needed to form the body.
Recently, U.S. Pat. No. 5,333,520 disclosed complexed shaped cermets made by uniaxially pressing two or more shapes that are placed upon each other with the joint between them lying essentially horizontally and, subsequently, sintering to form a complex shaped body. The two bodies may be of differing composition, but when the compositions are different, the shrinkage must be similar to avoid breakage, thus limiting the body compositionally.
Composite structures of metal, ceramics and cermets have also been formed by pressing, in a die, differing powder compositions to form a composite green body (shaped porous powder compact). The composite green body has regions that are comprised of different powder compositions. The green body is then sintered to form a dense body. Examples of this technique are described in U.S. Pat. Nos. 4,329,175; 4,372,404 and 4,602,956.
Because each of the techniques described above requires the sintering of a powder compact having differing compositions, the interface between regions in the body is dictated by the sintering. Because of the time and temperature it takes to sinter, the interface between regions tends to be diffuse. The variation of composition is also limited by the sintering shrinkage between the differing powder compositions.
Therefore, it would be desirable to provide a method of forming a complex shaped or composite body of a metal, ceramic, cermet or combination thereof that avoids one or more of the problems of the aforementioned methods.
SUMMARY OF THE INVENTION
A first object of the invention is a method for preparing a consolidated shaped article comprising:
placing a plurality of separate bodies in an arrangement, such that each separate body is in contact with at least one other separate body to form an aggregate body, and wherein at least one of the separate bodies is essentially dense and the separate bodies are comprised of a material selected from the group consisting of a ceramic, a cermet and a metal and
consolidating the aggregate body at a consolidating temperature, superatmospheric pressure and time at temperature and time at superatmospheric pressure sufficient to form the consolidated shaped article, wherein (i) the consolidating temperature is a temperature that fails to form a liquid within at least one separate body, (ii) at least a portion of the time at superatmospheric pressure is at the consolidating temperature and (iii) the consolidated shaped article has a density of at least about 95 percent of theoretical density.
A second object of this invention is a consolidated shaped article comprised of (i) a cermet body directly chemically bonded to (ii) a ceramic body selected from the group consisting of a carbide and a carbonitride.
A third object of this invention is a consolidated shaped article comprised of (i) a cermet body directly chemically bonded to (ii) a ceramic body and having (iii) an interface that has a thickness of at most about 2 mm between said cermet and ceramic body.
The instant method may be used to make complex shaped bodies of metals, cermets, ceramics and combinations thereof. The method may be used to fabricate items, such as drill bits, rock drilling inserts, knives, rotor blades and tubes.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a method for forming complex shaped articles that may be comprised of dissimilar materials, wherein the interface between the materials may be very narrow. Dissimilar materials, herein, are materials having different chemistry, different microstructure or combination thereof. Examples of dissimilar material pairs include different compounds (e.g., ceramic:metal) different metals (e.g., Ni alloy:steel), different ceramics (e.g., aluminum oxide:zirconium oxide), differing cermets (e.g., a cemented carbide having a large carbide grain size versus a cemented carbide having a small carbide grain size and a cemented carbide having a large amount of binder metal versus a cemented carbide having a small amount of binder metal).
The method first involves placing a plurality of separate bodies in an arrangement, such that each separate body is in contact with at least one other separate body to form an aggregate body. As an illustration, three separate bodies having the same cube shape may be placed one on top of each other forming a columnar aggregate body having a top, middle and bottom separate body. The same three cube shaped separate bodies may be placed such that one cube shaped body rests on top of two bottom cube shaped separate bodies to form a triangular shaped aggregate body.
A separate body, herein, means a body that supports its own weight and defines its own shape (i.e., does not conform to another shape such as a coating). “Supports its own weight,” herein, means the body may be handled by hand without substantially deforming or breaking (i.e., the body has the same shape before and after handling). Thus, the separate body, herein, precludes, for example, foils (e.g., graphite foil and metal foil), thin wires, threads and a coating on a substrate.
In forming the aggregate body, at least one of the separate bodies is essentially dense. “Essentially dense,” herein, means a separate body having a density of at least about 90 percent of theoretical. Preferably said separate body has a density of at least about 93 percent, more preferably at least about 95 percent, even more preferably at least about 98 percent, and most preferably at least about 99 percent of theoretical density. Herein, the theoretical density is the theoretical density described on page 530 of
Introduction to Ceramics
2
nd
Ed
., W. D. Kingery et al., John Wiley and Sons, New York, 1976. Preferably each of the separate bodies of the aggregate body is essentially dense. More preferably each of the separate bodies has a density of at least about 95 percent, even more preferably at least about 98 percent and most preferably at least about 99 percent of theoretical density.
The separate bodies are comprised of a material selected from the group consisting of a ceramic, cermet and metal. A ceramic, herein, is an inorganic nonmetallic material, such as an oxide, nitride, carbide, boride, silicide, mixtures of these and inorganic alloys of these (e.g.,
Dubensky Ellen M.
Kelto Clifford A.
Macki James M.
Ness Eric A.
Nilsson Robert T.
Dow Global Technologies Inc.
Jenkins Daniel J.
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