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Thermal Barrier Coatings T he concept of thermal engines. These large engines, coatings is accomplished by a barrier coating, or TBC, ranging from 1700 to 6700 process developed by the involves placing a thermal horsepower, are used in Caterpillar Technical Center in insulating layer of material stationary electric power gener- Peoria. High quality coatings between a metallic engine ation and marine applications. are ensured by a fully automat- component and the hot gas Cat 3600 engines can be config- ed plasma spray cell (below) heat source to reduce heat ured for optimized operation that includes computerized transfer to the component. on distillate fuels or for running plasma spray equipment capa- Such coatings, applied by plas- on the heaviest fuel available. ble of monitoring and control- ma spray processing in thin Heavy fuels contain high ling all spray variables, a films typicallym easuring less amounts of sulphur and vanadi- six-axis robot for manipulating than a millimeter, have been um that, at high combustion the spray gun, and a laser temperatures, form corrosive gauge for monitoring coating compounds on exhaust valves. thickness as it is built up. With high vanadium fuels, the Caterpillar and NASA are life of an engine valve can be continuing their collaboration, reduced to as little as 50 hours extending thermal barrier coat- AN AEROSPACE ENGINE without design measures to ing technology to other applica- minimize the temperature of the tions, such as heavy duty truck exhaust valve. Caterpillar's engines. For this application, I COMPONENT COATING answer is use of watercooled they are testing TTBCs (thick used for years to coat metal TECHNOLOGY IS components of gas turbine and I rocket engines for aircraft and spacecraft. Lewis Research EXTENDED TO Center is a world leader in developing TBC technology. NON-AEROSPACE USE The successful employment of TBCs in aerospace applica- \ tions has sparked interest in applying them to non- aerospace turbines and diesel engines. One company that has conducted extensive I research in this area is Caterpil- lar Inc., Peoria, Illinois, a lead- ing manufacturer of earthmoving equipment and heavy duty diesel engines. Caterpillar has been actively pursuing application of ceramic coatings to high temperature components of diesel engines, valve inserts, a corrosion resis- thermal barrier coatings),w hich aided by technical assistance tant Nimonic 80A material in are as thick as four millimeters. from Lewis Research Center and the exhaust valves, and a 'ITBCs applied to pistons and contractual support from the unique ceramic coating on the engine heads insulate the Department of Energy. exhaust valve head (left above) engine, raise the combustion The cooperative efforth as to control temperatures, temperature and increase the resulted in use of ceramic ther- extend valve life and reduce engine's fuel efficiency. ma1 barrier coatings on Caterpil- operating cost. lar Series 3600 production Application of the ceramic lndustrlal Product~v~etynd Manufaclurinp Technology