The subject matter of this application is related to copending and commonly owned U.S. patent applications, which include the following: Ser. No. 818,943, filed Jan. 15, 1986, and its ancestor applications (now abandoned), all in the name of Marc S. Newkirk et al. and entitled "Novel Ceramic Materials and Methods for Making the Same". These applications disclose the method of producing self-supporting ceramic bodies grown as the oxidation reaction product from a parent metal precursor. Molten parent metal is reacted with a vapor-phase oxidant to form an oxidation reaction product, and the metal migrates through the oxidation reaction product toward the oxidant thereby continuously developing a polycrystalline ceramic body of the oxidation reaction product. The ceramic body can be produced having metallic components and/or porosity, which may or may not be interconnected. The process may be enhanced by the use of an alloyed dopant, such as in the case of an aluminum parent metal oxidized in air. This method was improved by the use of external dopants applied to the surface of the precursor metal as disclosed in commonly owned and copending U.S. patent application Ser. No. 822,999, filed Jan. 27, 1986, and its ancestor applications (now abandoned), all in the name of Marc S. Newkirk et al. and entitled "Methods of Making Self-Supporting Ceramic Materials".
The subject matter of this application is also related to that of commonly owned and copending U.S. patent application Ser. No. 819,397, filed Jan. 17, 1986, which is a continuation-in-part of Ser. No. 697,876, filed Feb. 4, 1985 (now abandoned), both in the name of Marc S. Newkirk et al. and entitled "Composite Ceramic Articles and Methods of Making Same". These applications disclose a novel method for producing self-supporting ceramic composites by growing an oxidation reaction product from a parent metal into a permeable mass of filler, thereby infiltrating the filler with a ceramic matrix.
Further developments of the foregoing methods enable the formation of ceramic composite structures which (1) contain therein one or more cavities which inversely replicate the geometry of a shaped precursor parent metal, and (2) have a negative pattern which inversely replicates the positive pattern of a parent metal precursor. These methods are described, respectively, (1) in Commonly Owned U.S. patent applications Ser. No. 823,542, filed Jan. 27, 1986, in the name of Marc S. Newkirk et al., entitled "Inverse Shape Replication Method of Making Ceramic Composite Articles and Articles Obtained Thereby", and (2) in Commonly Owned U.S. patent application Ser. No. 896,147, filed Aug. 13, 1986, in the name of Marc S. Newkirk and entitled "Method of Making Ceramic Composite Articles with Shape Replicated Surfaces and Articles Obtained Thereby."
A feature useful in the methods of the above-mentioned commonly owned patent applications to produce a net shape ceramic body, including composite bodies which retain essentially the original shape and dimensions of the filler or preform, is to minimize or inhibit ceramic matrix overgrowth of defined surface boundaries. Overgrowth of the surface boundaries can be substantially prevented by controlling the infiltration of the polycrystalline ceramic matrix to any defined surface boundaries, which may be accomplished such as by using a predetermined quantity of parent metal, establishing within the preform more favorable oxidation kinetics than those outside the preform, exhausting the oxidizing atmosphere at some point in the process, or lowering the reaction temperature at some point in the process. Any of these steps may require close control or vigilance to obtain essentially no polycrystalline overgrowth of any defined surface boundary, and still may not produce the most desirable net or near net shape, or may require additional machining or finishing to create acceptable tolerances in a finished part.
Methods were developed of making ceramic composite structures having a pre-selected shape or geometry. These methods include the utilization of a shaped preform of permeable filler into which the ceramic matrix is grown by oxidation of a parent metal precursor, as described in commonly owned U.S. patent application Ser. No. 861,025, filed May 8, 1986, in the name of Marc S. Newkirk et al. and entitled "Shaped Ceramic Composites and Methods of Making the Same". Another method of making such shaped ceramic composites includes the utilization of barrier means to arrest or inhibit the growth of the oxidation reaction product at a selected boundary to define the shape or geometry of the ceramic composite structure. This technique is described in commonly owned U.S. patent application Ser. No. 861,024, filed May 8, 1986, in the name of Marc S. Newkirk et al. and entitled "Method of Making Shaped Ceramic Composites with the Use of a Barrier".
The entire disclosures of all of the foregoing Commonly Owned Patent Applications are expressly incorporated herein by reference.
The present invention provides another method for establishing a surface boundary on a ceramic composite which is desirable in forming net shape ceramic composites, particularly with larger, single-piece bodies or bodies with complicated geometry.