WEAR-INDUCED CHANGES IN THE RAMAN, INFRARED, AND FLUORESCENCE-SPECTRAOF SILICON-NITRIDE SURFACES

Commercial alpha-silicon nitride plates and balls used in simulated sl iding bearing tests were found to fluoresce under 514.5-nm argon-ion l aser excitation after heating to above 350 degrees C in a stream of ar gon, Wear track areas fluoresced much more intensely than their surrou ndings, When small concentrations or ethylene or other carbonaceous ga s were added to the argon stream, carbonaceous deposits formed primari ly in the wear track in amounts roughly paralleling the fluorescence i ntensity, Some of the deposits were lubricating carbon and some nonlub ricating silicon oxycarbide. Continuous high-temperature lubrication w as possible by balancing deposit removal by wear with surface-chemical deposit formation rates, Raman, infrared, fluorescence, and other spe ctroscopies helped explain the process, Defect energy stales within th e large silicon nitride energy gap and dangling bonds appear to play a role.