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

► The two-step treatments, supersonic fine particles bombarding (SFPB) surface nanocrystallization and low temperature ion sulfurization, were employed to modify the surface of 1Cr18Ni9Ti steel. ► The SFPB treatment induced grain refinement and martensitic phase transformation in the surface layer, and thus increased the surface activity and hardness significantly. A compact and uniform FeS solid lubrication film formed on the nanocrystalline layer after sulfurization. ► A special structure of “inside hard & outer soft” surface layer can be obtained on the treated (after SFPB and sulfurizing treatments) 1Cr18Ni9Ti and thus show excellent tribological properties in various atmospheric pressures.