Formation of adsorbed and chemically reacted sulfur films on steel surfaces during sliding

Neat, thiophene, dimethyl disulfide and dibenzyl disulfide environments were tested for friction and wear with a pin-on-disk apparatus on two steels, ¡045 and 4142, the former not containing chromium and the latter containing chromium. In general, friction and wear were changed on introduction of the sulfur compound. Thiophene reduced wear and friction at room temperature while dimethyl disulfide was prowear under similar test conditions. Flow rate of the vaporous lubricant proved to be a dominant factor. Wear tracks were analyzed by SEM, AES, and EDAX. Significant sulfur could only only be found in the wear tracks and only once a surface layer was removed. Interestingly enough, the maximum sulfur concentration was located about 50 Á below the surface. This depth of 50 Á corresponds to the oxide layer. Hardly any sulfur was detectable above the oxide layer. The sulfur concentration decreased exponentially at depths greater than 50 Á.