SOLID LUBRICATION BY DECOMPOSITION OF CARBON-MONOXIDE AND OTHER GASES

Extended duration high temperature (above 500 degrees C) lubrication o f silicon nitride sliding and rolling contacts was accomplished by sol id carbon deposited and replenished via the decomposition of carbonace ous gas streams directed towards the tribological surfaces. Injection of carbon monoxide-hydrogen mixtures can lead to reductions in high te mperature friction and wear of silicon nitride sliding contacts by fac tors of up to 10 x and 500 x respectively from the unlubricated case. Similar lubrication is attained by various hydrocarbon gas mixtures, w hile only a ten-fold reduction in wear is attained by a carbon dioxide -hydrogen mixture. Effective lubrication can be modeled as a favorable balance between carbon deposition from the gas phase and removal by w ear. This model is based on the dependencies of solid lubricant deposi tion and removal processes on temperature, sliding speed, normal load, decomposition activation energy, gas flow rate, and tribosystem prope rties. The model is checked by the mapping of regions where measured f riction indicates that lubrication by CO-H-2 mixtures is adequate, and the identification of a boundary representing the onset of marginally effective lubrication.