Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
1999-03-09
2001-01-16
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S698000, C428S687000, C428S325000, C428S335000
Reexamination Certificate
active
06174605
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to carbon—carbon composites, and more particularly to a method for joining carbon—carbon composites parts with minimum surface preparation.
2. Description of the Prior Art
Joining of carbon—carbon composites becomes increasingly important as new technology developments demand larger and more complex geometries. Available joining methods are limited to bonding with adhesive materials, alloy brazing, diffusion bonding, and welding. Joints produced by bonding with adhesive materials or alloy brazing are only suitable for low to intermediate temperature applications, well below the temperature capability of the carbon—carbon composites. Diffusion bonding using refractory metals or compounds usually requires quite careful joining surface preparations of essentially porosity free carbons as well as long heating times at very high temperatures (often >2000° C.) under high pressures. Welding requires even higher joining temperatures, and the joints produced are poor and exhibit low strength. U.S. Pat. No. 5,021,107 describes a process for joining finely finished carbon—carbon composites requiring a joint interlayer thickness of 25-100 micrometers. That process requires rather careful surface preparation and high joining temperatures close to the melting point (TMP, Tungsten is approximately 344° C.) of the joint interlayer material. Furthermore, the strength of the joints, which is low, was not specified in the patent. There is a strong technical need for a process for joining common carbon—carbon composites which requires minimal surface preparation and produces joints having high strength and high temperature application capability. Further needed is a process that produces reliable joints at low temperatures under low pressures.
SUMMARY OF THE INVENTION
The present invention provides for the joining of carbon—carbon composites by a reactive-bonding process that requires minimal surface preparation. Generally stated, the process is used for joining two carbon—carbon composite parts, and comprising the steps of: (a) preparing a reactive-bonding compound layer having a thickness ranging from about 25 to 2500 micrometers and a dimension matching the smaller faying surface of the carbon—carbon parts to be joined, the compound layer being comprised of fine particle sized, carbide-forming metallic ingredients and carbon, and having a composition that is nonstoichiometric, metal-rich; (b) assembling the carbon—carbon parts and the reactive-bonding layer to form a setup in which the reactive-bonding layer becomes the joint interlayer between the parts; and (c) heating the setup under a compressive pressure in either a vacuum or an inert gas atmosphere for a time and at a temperature sufficient to complete a bonding reaction which is produced within said joint interlayer and between said interlayer and said carbon—carbon composite parts.
More specifically, in the process of the invention, the joint interlayer is made from a nonstoichiometric mixture of metallic ingredients and carbon, with a joint thickness greater than 25 micrometers. Since the carbon surface is not highly finished, the joint layer is expected to be 25 to 2500 micrometers. The presence of this thick interlayer requires that the thermal expansion of the joint be matched well with that of carbon—carbon and homogeneity of the interlayer composition. In the reaction bonding process of this invention, this effect is accomplished by careful selection of the metallic ingredient together with carbon and selection of the particle sizes so that diffusion and complete reaction can occur within a preselected time and temperature range. In this manner there is provided a high quality joint at temperatures as low as 1500° C. and diffusion time as small as ½ hour or less. The homogeneous interlayer thus formed exhibits high joint strength due to the superior thermal expansion match with carbon—carbon. As a result, the joining operation requires a lower capital investment and has a lower operating cost. Energy savings is another benefit afforded by the process of this invention. Advantageously, the surfaces of the two parts to be joined need not be specially prepared, as long as the surface roughness is below as much as 2500 micrometers. The elimination of the surface preparation step simplifies the joining process and results in cost savings as well as the reduction of production cycle times. The joint layer is sandwiched between the two surfaces and the assembly is held together under some pressure while being heated to a temperature and for a time sufficient to facilitate the completion of the bonding reaction. Such a joining operation can usually be accomplished within 30 min. at a temperature considerably lower than half the melting point of the metallic ingredients in the joint interlayer. High joint strength is assured by selecting metal-carbon ingredients so that the thermal expansion mismatch is minimized. The joint shear strength of the products produced by the process of the invention is much higher than the interlaminar shear strength of the carbon—carbon composites. Advantageously, the products of the present invention are suitable for use at elevated temperature as high as 2800° C.
REFERENCES:
patent: 3946932 (1976-03-01), Peterson
patent: 4032607 (1977-06-01), Schulz
patent: 4514240 (1985-04-01), Heraud
patent: 4748079 (1988-05-01), Thebault
patent: 4892790 (1990-01-01), Gray
patent: 5021107 (1991-06-01), Holko
patent: 5457151 (1995-10-01), Graef et al.
patent: 5474849 (1995-12-01), Graef et al.
patent: 5837081 (1998-11-01), Ting et al.
Narasimhan Dave
Xue Liang An
Allied-Signal Inc.
Jones Deborah
Resnick Jason
Zak, Jr. Esq. William J.
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