Lubrication of Silicon Nitride in a Simulated Turbine Exhaust Gas Environment

Testing has been conducted on silicon nitride (Si3N4) in simulated engine exhaust gas environments in four-ball rolling contacts and pin-on-disk sliding contacts to 590°C. Utilizing a steel race, the depth of the. wear track formed at the Si3N4/Si3N4 rolling contact in the presence of exhaust gas was roughly one-half that formed in the presence of N2 alone. Deposition of lubricous microcrystalline graphite carbon from CO within the exhaust was confirmed by Raman spectroscopy. Removal of H2O from the exhaust gas further reduced rolling wear. Exhaust gas alone provided no benefit to Si3N4/Si3N4 sliding contacts, where the rate of wear greatly exceeds the rate at which lubricous carbon may deposit from the exhaust environment. As compared to that measured in the presence of N2 alone, the directed admixture of hydrocarbon (C2H2) to the exhaust gas enhanced the lubrication of Si3N4 with reductions of up to 25-fold in rolling wear, 650-fold in steady-stale sliding wear rate and 20-fold in sliding friction.