LUBRICIOUS-SURFACE SILCON-NITRIDE RINGS FOR HIGH-TEMPERATURE TRIBOLOGICAL APPLICATIONS

FRICTIONAL LOSSES ACCOUNT FOR A LARGE PERCENTAGE OF THE TOTAL MECHANICAL POWER LOSS IN ENGINES. THEREFORE, SLIDING SURFACES WITH LOW FRICTION, HIGH WEAR RESISTANCE, AND LONG LIFETIMES REPRESENT AN ENABLING TECHNOLOGY FOR FUTURE TRANSPORTATION SYSTEMS. THIS PROJECT WILL INVESTIGATE AN ENTIRELY NEW CLASS OF CERAMIC-MATRIX-COMPOSITE (CMC) RINGS AND CYLINDERS, WITH A GRADED DISTRIBUTION OF CERAMIC COMPOUNDS NEAR THE SLIDING-WEAR INTERFACE. THE SELECTIVE CERAMIC REINFORCEMENTS WILL CONVERT TO LOW-FRICTION AND LOW-WEAR LUBRICIOUS OXIDES DURING HIGH-TEMPERATURE AIR EXPOSURE. LONG-WEAR-ENDURANCE LIFETIMES OF THE CMC SURFACES WILL RESULT, DUE TO THE SELF-LUBRICATING, REPLENISHABLE NATURE OF THE REINFORCEMENTS WHICH ARE INCORPORATED IN THE MATRIX TO LARGE DEPTHS. PHASE I WILL DEMONSTRATE INNOVATIVE FABRICATION METHODS THAT INCLUDE: (1) CENTRIFUGAL SPINNING OF A SLURRY OF TITANIUM NITRIDE (TIN) REINFORCEMENTS AND SILICON MATRIX POWDERS WHICH WILL BE FIRED AND NITRIDED TO PRODUCE A TIN OUTER-SURFACE-REINFORCED SILICON NITRIDE (SI3N4) RING, AND (2) INFILTRATION OF A GRADED POROSITY SI3N4 CYLINDER LINER WITH TI MOLTEN WHICH WILL BE SUBSEQUENTLY CARBURIZED TO FORM A TITANIUM CARBIDE (TIC) INNER-SURFACE-REINFORCED SI3N4 CYLINDER LINER. TEST SPECIMENS WILL BE SUBJECTED TO MICROSTRUCTURAL EXAMINATIONS AND MICROHARDNESS MEASUREMENTS. SLIDING WEAR TESTS WILL BE PERFORMED ON MATING SPECIMENS FROM THE RINGS (TIN/SI3N4) AND CYLINDERS (TIC/SI3N4) IN 800 DEGREES CENTIGRADE AIR, TO ENHANCE PISTON RING-ON-CYLINDER LINER CONTACT. COEFFICIENTS OF FRICTION, WEAR RATES, AND LUBRICATION MECHANISMS WILL BE ESTABLISHED. IN PHASE II, NEAR-NET SHAPE FABRICATION OF RINGS AND CYLINDERS WILL BE STUDIED THROUGH THE USE OF CONTROLLED GEOMETRIC DIES.