Applied Surface Science, Vol.181, No.1-2, 61-67, 2001
Effect of sulphide layers on the tribological behavior of steels under boundary lubrication conditions
Sulphide layers were prepared on the surface of AISI 1045 steel by ion sulphurization. The anti-scuffing, friction-reducing, and wear-resistant behavior of these sulphurized surfaces were investigated systematically using a ball-on-disc wear tester with engine oil as a lubricant. SEM, EDX, XPS, and AES were used to examine the morphologies and compositions of wear scars and boundary films. Sulphide layers improved anti-scuffing properties remarkably at low sliding velocities, and exhibited good friction-reducing and wear-resistant effects. During friction the sulphide layer promoted the growth of oxide, and iron sulphide could be decomposed and regenerated to form FeS again on the rubbing surface. An appropriately thick sulphide layer optimizes the sulphur-to-oxygen concentration in the boundary film resulting in the highest load-bearing capacity, and shows that thicker sulphide layers are unnecessary.