2014 Volume 59 Issue 10 Pages 636-647
In order to elucidate the action mechanism of environmentally benign lubricant additives on Fe-Cr-Ni alloys, tribological tests using a sulfur-containing extreme pressure additive (polysulfide) and various compositions of Fe-Cr-Ni alloy materials under boundary lubrication regime were carried out, and then their surfaces were analyzed quantitatively by means of X-ray photoelectron spectroscopy (XPS). The results exhibited that a boundary lubrication film comprising of iron sulfide (FeS or FeS2) was formed on the materials containing low Cr or Ni, whereas that of nickel sulfide (mainly NiS) was formed on the materials containing high Cr or Ni. A relatively thick oxide layer was detected beneath the boundary lubrication film, which indicates that oxidation most likely due to dissolved oxygen in the lubricant also occurs in conjunction with sulfuring under the boundary lubrication condition. Nickel sulfide showed lower hardness compared to iron sulfide, which may be the main cause of the high friction and adhesion during the friction test in the case of high Cr or Ni alloy.
