Monday, October 5, 2009

Nanostructured Low-Cr Cu-Cr Coatings Provides High Temperature Oxidation Resistance

Southwest Research Institute (San Antonio, TX) scientists Kuang-Tsan Kenneth Chiang, James H. Arps, and Ronghua Wei developed a method of preventing oxidation of copper alloys at high temperatures by deposition of a nano-structured, low-chromium copper-chromium protective coating to copper-alloy components. The coatings are applied by an ion beam assisted, electron beam physical vapor deposition and consist of copper and chromium particles having a diameter of about 10 nm, according to U.S. Patent 7,592,051. The coated copper-alloy components are produced by deposition methods. The coatings may be deposited as one or more discrete layers each of copper and chromium, or alternatively as one or more layers of a copper-chromium mixture. The coatings have a thickness of less than about 25 microns. The so coated copper-containing components exhibit enhanced oxidation resistance at high temperatures

Copper-based alloys and composites are candidate materials for high heat flux structural applications because of their high thermal conductivity and high-temperature strength. Such applications include hot gas walls for combustion chambers and surfaces of nozzle ramps for rocket engines and for the next generation launch vehicles. Other applications include protective coatings for heat exchangers in commercial power generation systems and firearm barrels.

A major limitation to the use of any of these copper-based materials, however, is their rapid oxidation at elevated temperatures. In addition, copper-alloy rocket engine combustion chamber linings have been found to deteriorate when exposed to cyclic reducing/oxidizing (redox) environments, which are a consequence of the combustion process. This deterioration, known as blanching, can be characterized by increased roughness and burn-through sites in the wall of the combustion chamber lining and can seriously reduce the operational lifetime of the combustion chamber. Southwest Research Institute’s coatings display excellent oxidation resistance under high temperature oxidative conditions and perform as well as coatings requiring greater layer thickness and higher levels of chromium.

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