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 sulp hurization. The anti-scuffing, friction-reducing, and wear-resistant behavi or of these sulphurized surfaces were investigated systematically using a b all-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 an d boundary films. Sulphide layers improved anti-scuffing properties remarka bly at low sliding velocities, and exhibited good friction-reducing and wea r-resistant effects. During friction the sulphide layer promoted the growth of oxide, and iron sulphide could be decomposed and regenerated to form Fe S again on the rubbing surface. An appropriately thick sulphide layer optim izes the sulphur-to-oxygen concentration in the boundary film resulting in the highest load-bearing capacity, and shows that thicker sulphide layers a re unnecessary. (C) 2001 Elsevier Science B.V. All rights reserved.