WEAR REDUCTION BY PYROLYTIC CARBON ON TRIBOSURFACES

Sliding tests with a pin-on-disc tribometer and both sliding and rolli ng tests with a modified four-ball tester at bulk temperatures of abou t 500-degrees-C and initial contact pressures of about 2.2 GPa have de monstrated up to 80% reductions of friction and wear with silicon nitr ide surfaces when a stream of ethylene is directed into the conjunctio n region. The effects are even more pronounced when the ethylene is pr enucleated by a flow over a coil of nichrome wire electrically heated to about 800-degrees-C and located about 30 cm upstream of the exit no zzle. Steel and Ni-plated steel are lubricated by this method even mor e efficiently and at lower temperatures. The underlying mechanism is p robably analogous to that of hydrocarbon pyrolysis by flash photolysis , which was studied by Porter in the 1950s, with the rapid heating to the ''flash temperatures'' and subsequent cooling occurring naturally in friction contacts. The observation that pyrolysis of hydrocarbons t o solid carbon occurs in two stages, nucleation and particle growth, h as allowed their physical separation, the former taking place in the e thylene stream and the latter in the frictional contact some distance away.