Microstructure of iron sulfide layer as solid lubrication coating produced by low-temperature ion sulfurization

FeS is an excellent solid lubricant due to its hexagonal structure, low shear strength, and high melting point. A new low-temperature ion sulfurization technology was developed to produce a sulfide layer of varying thickness on AISI 1045 and AISI 52100 steels. It has many advantages compared with the electrolytic process. Metallography, an SEM equipped for energy-dispersive X-ray spectroscopy, and X-ray spectroscopy, and X-ray diffraction were used to examine the microstructure of sulfide layers and their structural depth-profiles. The results showed that the sulfide layer was loose and porous, and no transition layer was found between it and the substrate. The sulfide layer was composed of iron sulfide and substrate phases. The former included mainly FeS and FeS2. On the top of the sulfide layer, only FeS2 appeared. FeS was found to become more abundantly with increasing depth below the surface, whereas FeS2 was found in greater quantities in thicker sulfide layers.