United Technologies Corporation

Richard D Veltri

Francis S Galasso

Philip J Birbara

Roy Fanti

Karl M Prewo

David A Condit

John J Brennan

Mel I Mendelson

Raymond L Taylor

CVD Si.sub.3 N.sub.4 can be made by placing a substrate (2) inside a CVD reactor (4) having an interior and interior walls (6). The interior walls of the reactor are include a high temperature metal selected from the group consisting of Mo, Nb, Rh, Hf, Ta, W, Re, and Ir. An inert gas is flowed through the reactor (4) and the pressure inside the reactor is reduced to less than about 40 kPa. The substrate (2) and interior of the reactor (4) are heated to a temperature between about 1200.degree. C. and about 1700.degree. C. A reactant gas mixture of a silicon halide and an excess of a nitrogen-containing compound is flowed into the reactor such that the silicon halide reacts with the nitrogen-containing compound to form Si.sub.3 N.sub.4. The high temperature metal on the interior walls (6) of the reactor (4) inhibits the formation of Si.sub.3 N.sub.4 on the interior walls of the reactor so the majority of the Si.sub.3 N.sub.4 forms on the substrate (2).

Method of making CVD Si.sub.3 N.sub.4

Chemical vapor deposition (CVD) techniques for forming tough silicon carbide (SiC) matrix composites. The introduction of methyldichlorosilane (MDS) to a reactor containing a fiber preform which been flushed with a noble gas, causes the formation of a carbon layer around the fibers. The carbon interlayer improves the fracture toughness of the composite.

CVD SiC matrix composites containing carbon coated fibers

Gas turbine engine carbon-carbon composite components having multilayer coatings resulting in components resistant to oxidation at temperatures greater than 2500.degree. F. A first multilayer coating comprises a pack derived silicon carbide coating covered with a chemical vapor deposition layer of silicon nitride. A second multilayer coating comprises a layer of pyrolytic graphite covered with a pack derived silicon carbide coating covered with a chemical vapor deposition layer of silicon nitride. The third multilayer coating comprises a layer of chemical vapor deposition applied silicon carbide covered with a pack derived silicon carbide coating covered with a chemical vapor deposition layer of silicon nitride. Carbon fibers are carbonized or graphitized, formed into woven structures which are stacked in a prepreg with impregnating resin, pyrolyzed and optionally graphitized to form an engine component, and then coated with the above-described layers to achieve an engine component highly resistant to oxidation at elevated temperatures.

Gas turbine composite parts

Amorphous boron-carbon alloy cutting tool bits and methods of making them are described. The tool bits can be composites of conventional hard alloys containing the amorphous boron carbon alloy in a first layer over a conventional hard alloy layer such as cobalt bonded tungsten carbide. The amorphous boron carbon alloy used is preferably produced in bulk with a grain size less than 30 .ANG. and ground into a powder. The tool bits are produced by cold compressing, in a tool bit die, the lower layer material at about 2000 psi followed by hot compressing the composite containing the added amorphous boron carbon alloy powder at about 1350.degree.-1500.degree. C. The resultant cutting tool bit has a cutting lifetime at least four times that of conventional carbide cutting tool bits even when cutting such things as nickel superalloys at speeds in excess of 125 surface feet per minute (SFM).

Amorphous boron-carbon alloy tool bits and methods of making the same

Method of making amorphous boron carbon alloy cutting tool bits

An improved mirror substrate, that is particularly adapted for use as a laser mirror, has significantly improved transverse strength and polishability and a method of making the same. The composite comprises graphite fibers coated with an oxidized silicon carbide layer. The coated fibers alternate with layers of glass to form a composite, preferably having a central plane of symmetry across its central plane.

Composite mirror substrate

A method for repairing a multilayer coating on a carbon-carbon composite having a CVD silicon nitride outercoating by applying a coating of CVD silicon nitride. It has been found that if a multilayer coating containing CVD silicon nitride on a carbon-carbon composite is broken the entire composite will fail to survive at elevated temperatures due to oxidation. However, the deposition of silicon nitride on such a composite will affect repair such that the newly coated composite will substantially resist oxidation at temperatures up to 1750.degree. C. and above. Preferably the coated composite is maintained at a temperature of about 1500.degree. C. and a gaseous mixture containing silicon tetrafluoride and anhydrous ammonia is passed over the composite at a partial pressure of the reactant gases less than about 10 millimeters mercury.

Method for repairing a multilayer coating on a carbon-carbon composite

Articles and method for containing molten nickel and methods for making the former. The material used is a high density silicon nitride that is very resistant to the corrosive properties of molten nickel alloys. The composition needed to produce such a containing article comprises polycrystalline silicon nitride containing (by weight) about 0.6% to about 8% alumina, about 15% yttria and about 2% to about 5% silica or amorphous silicon nitride containing about 2% to about 6% alumina, and about 15% yttria and about 2% to about 5% silica. The articles are formed by cold pressing and sintering methods. These articles are particularly useful in processes for molding and (RSR.TM.) spinning molten nickel alloys.

High density, sintered silicon nitride containing articles and methods

An erosion resistant composite material is described comprising silicon nitride rod reinforced nickel alloy, where the silicon nitride is cold pressed and sintered and substantially nonreactive with the alloy at high temperatures. The silicon nitride can either be polycrystalline or amorphous containing alumina, 15% yttria and about 2% to about 5% silica. Three to 8% alumina is used in the case of polycrystalline silicon nitride and 2% to 6% alumina is used in the case of amorphous silicon nitride.

Silicon nitride reinforced nickel alloy composite materials

Carbon-carbon composite materials are provided with significantly enhanced oxidation resistance by the formation of a SiC coating. The coating is produced from a pack containing a small but effective amount of boron. The balance of the pack is preferably based on Al.sub.2 O.sub.3, SiO.sub.2, and Si. The composite to be coated is embedded in the pack and heated to an elevated temperature. The boron addition provides a conversion SiC coating having enhanced resistance to oxidation.

Deposition of improved SiC coatings on carbon-base materials

The process of making an article of chemically vapor deposited silicon nitride on a pattern at high temperature including the use of methane to reduce the grain size of the deposited compound.

Manufacture of hollow CVD silicon nitride articles

Carbon-carbon composites are prepared to receive a subsequent protective coating by having a thin layer (1 to 5 mils) of pyrolytic graphite applied to its surface. The graphite layer improves the performance of subsequent protective coatings and is especially useful on carbon-carbon composites having a positive coefficient of thermal expansion.

Pyrolytic graphite pretreatment for carbon-carbon composites

A multilayer coating system for the protection of carbon-carbon composites is described. The coating includes an inner layer of SiC produced by diffusing Si into the carbon substrate (0.5 to 30 mils thick), and at an outer layer of CVD (chemically vapor deposited) SiC (5 to 30 mils thick). Such a coating successfully protects carbon-carbon materials from oxidation at temperatures up to 2500.degree. F. (1371.degree. C.) and above.

Composite silicon carbide coatings for carbon-carbon materials

A multilayer coating system for the protection of carbon-carbon composites is described. The coating includes an inner layer of SiC (produced by a conversion process in which Si is diffused into the carbon substrate) and an outer layer of CVD (chemically vapor deposited) Si.sub.3 N.sub.4. Such a coating provides exceptional oxidation resistance, to 2500.degree. F. (1371.degree. C.) and above, for carbon-carbon materials. Optionally, preliminary coatings of CVD SiC or pyrolytic graphite can be applied prior to application of the inner layer of SiC.

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East Hartford, CT, United States of America

Richard D Veltri