WEAR RESISTANT SULFUR FILMS ON HARD BALL-BEARING STEEL STUDIED BY AUGER-ELECTRON SPECTROSCOPY AND SPUTTER PROFILING, INCLUDING FACTOR-ANALYSIS

Tribological procedures with hard SAE(b)) 52100 steel elements (hardness of 850 Vickers or above) leading to scoring resistant surfaces with sulfur films have been monitored with Auger electron spectroscopy and sputter profiling. For hard SAE 52100 steel with clean and dry surfaces, a criterion for scoring resistance is a static friction coefficient of 0.73-0.76. These surfaces are found to consist of an approximately 30-angstrom-thick upper region of oxide and sulfur. Sulfur was added to the lubricant in one of the steps of the procedure, after the end of which the majority of it (85%) was found to be bound to iron as in FeS. The formation of this sulphide film is the key to scoring resistance. For other, nonscoring resistant surfaces resulting from various unsuccessful procedures, only oxide films were formed, and no sulfur had been taken up by those surfaces. The sulfur film on a scoring resistant surface was shown to slow initial oxidation compared to a surface stripped of this film. Wear of hard steel surfaces in sliding contacts, without any sulfur in the surface region, was shown to occur through oxidation, with a release of oxide debris. Thus, oxides are not beneficial to scoring resistance.