Microstructure and vacuum tribological properties of 1Cr18Ni9Ti steel with combined surface treatments

A sulfide film was fabricated on the nanocrystalline layer of 1Cr18Ni9Ti stainless steel by a two-step method of supersonic fine particles bombarding (SFPB) and low temperature ion sulfurization treatments. The microstructure and mechanical properties of the nanocrystallized surface and the sulfide film were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy (equipped with EDS), augur energy spectroscopy, X-ray photoelectron spectroscope, and nano-indenter. The tribological behaviour of the treated (after SFPB and sulfurizing treatments) 1Cr18Ni9Ti steel in vacuum was investigated on a ball-on-disk tribometer. The results showed that, randomly oriented equiaxial nanograins with the mean grain size less than 30 nm were formed in the top surface layer of the SFPB treated sample, and a compact and uniform sulfide film mainly composed of FeS was obtained after the succedent sulfurizing treatment. Compared to the original 1Cr18Ni9Ti steel, the treated surface revealed lower friction coefficient and better wear resistance in vacuum, and the variation of tribological properties with atmospheric pressure of the treated samples was not significant. The dominant wear mechanisms of the treated 1Cr18Ni9Ti in vacuum were abrasive wear and fatigue wear.