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This paper describes an experimental program that investigated the friction and wear behavior of ceramic materials considered for use for piston rings and cylinder liners in high-temperature, low-heat rejection diesel engines. Candidate materials include silicon carbide, silicon nitride, titanium carbide, nickel-molybdenum bonded titanium carbide cermets, and partially stabilized zirconia (PSZ); and ceramics whose surfaces have been modified by the ion beam mixing of several oxide-forming metal ions including chromium, cobalt, nickel, and a double layer of nickel and titanium. Friction and wear testing is performed in two stages. Various material couples are tested using laboratory bench tests (pin-on-disk) in simulated diesel environments at 800°C, in order to determine those couples most likely to be successfully applied to actual engine operating conditions. Cylinder liners and piston rings are produced from those materials, and tested under actual operating conditions in one of two test rigs: a heated, single-cylinder test rig designed by Southwest Research Institute (SwRI) for ceramic engine component analysis; and a single-cylinder research engine. The various testing procedures and equipment are described, and the advantages and disadvantages of the test methodology are discussed. The results of testing to date are reviewed and discussed. Bench tests have shown that most unmodified ceramic couples have relatively high wear rates, and coefficients of friction above about 0.25. Certain combinations of pins and ion-beam modified disks, however, produce coefficients of friction as low as 0.06 with minimal wear, characteristics close to those required for liquid lubricated metal couples run at much lower temperatures. Promising combinations include titanium carbide on titanium-nickel modified silicon nitride, and titanium carbide cermet on titanium-nickel or cobalt modified PSZ. These materials were fashioned into cylinder liners and piston rings for testing in the test rig and in the research engine. Details of these engine tests are presented, and plans and suggestions for future testing and research are discussed.
ceramics, diesel engine, friction, high temperature engine, low-heat rejection engine, ion beam mixing, ion implantation, surface modification, high temperature lubrication, wear
Southwest Research Institute, San Antonio, TX