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Multilayered boron nitride/silicon nitride fiber coatingsMultilayered boron nitride/silicon nitride fiber coatings description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090088038, Multilayered boron nitride/silicon nitride fiber coatings. Brief Patent Description - Full Patent Description - Patent Application Claims
The Government of the United States of America may have rights in the present invention as a result of Contract No. NAS3-26385 awarded by the National Aeronautics and Space Administration. The present invention relates to multilayered boron nitride/silicon nitride (BN/Si3N4) coatings and to a method and a system for forming such coatings. Composite coatings are used in a number of gas turbine engine applications. It is important for these coatings to demonstrate resistance to recession and high temperature oxidation stability. One of the problems with ceramic matrix composites is the instability of the fiber matrix interface to oxidation. The use of boron nitride as a replacement for carbon has showed an improvement in resistance to high-temperature oxidation. However, it is common knowledge that the oxidation resistance of CVD boron nitride fiber coatings in the presence of moisture is considerably lower. CVD boron nitride fiber coatings have been known to degrade at room temperature in the presence of moisture. There has been an investigation on the effect of alternating layers of SiC and carbon in SiC/SiC composites. It has been found that in such a system the room temperature mechanical properties are similar to a SiC/SiC composite fabricated with a normal carbon interface. However, when the composite is prestrained beyond the proportional limit (so that the matrix was micro-cracked) and subjected to high temperature oxidation, the composite exhibits brittle mechanical properties. This has been attributed to the removal of the carbon interface by oxidation. In order to enable this type of system to work in elevated temperature applications, a material with a greater oxidation resistance than carbon has to be substituted. Some speculated that boron nitride could be substituted for the carbon. The major problem with such a substitution however is in the processing of the material. Boron nitride is usually fabricated by reacting a boron halogen with ammonia. The deposition of SiC is affected by the presence of ammonia. Therefore, the deposition of boron nitride has to be carried out in a separate reactor. This results in extra heating/cooling cycles in the process and additional handling of the part from one reactor to the other. This makes a boron nitride/silicon carbide multilayering concept unattractive. Coatings provided by the present invention exhibit improved high temperature oxidation stability. In accordance with the present invention, there is provided a composite which broadly comprises a substrate having a surface and at least one layer of a BN/Si3N4 coating on the substrate surface. The coating preferably is formed by alternative layers of a BN material and a Si3N4 material. In a preferred embodiment of the present invention, the substrate is a cloth material with fibers, such as SiC fibers, woven therein. Further, in accordance with the present invention, a method for forming a coating having high temperature oxidation stability broadly comprises the steps of placing a substrate in a reaction chamber, heating the substrate to a deposition temperature, and forming at least one coating layer on the substrate. The forming step comprises introducing ammonia and nitrogen into the reaction chamber, introducing a boron halogen precursor into the reaction chamber, stopping the flow of the boron halogen precursor, and introducing a silicon halogen precursor into the reaction chamber. Still further, in accordance with the present invention, a system for forming a coating having a high temperature oxidation stability broadly comprises a reaction chamber for holding the substrate to be coated and means for forming a multilayered BN/Si3N4 coating on the substrate. Other details of the multilayered boron nitride/silicon nitride fiber coatings of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings, wherein like reference numerals depict like elements. Continue reading about Multilayered boron nitride/silicon nitride fiber coatings... Full patent description for Multilayered boron nitride/silicon nitride fiber coatings Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Multilayered boron nitride/silicon nitride fiber coatings patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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