Mechano-Chemical Surface Modification with Cu₂S: Inducing Superior Lubricity

Advances toward low friction surfaces are in growing demand from many economic sectors for energy efficiency and environmental safety. However, the traditional approach of multi-grade oil formulation is limited by its inability to induce pollution-free generation of uniform oil-retaining films needed to improve surface lubricity. Here, a direct route to the formation of a surface layer of superior lubricity is presented as an alternative to the use of oil additives for friction reduction. The deformation-induced generation of a surface film consisting of low-shear-strength oil-retaining compounds is obtained via supplying chemically beneficial elements during a widely used surface finishing mechanical treatment. An ultra-low friction coefficient of about 0.01 is obtained with base oil lubrication after tailoring the surface chemistry by shot peening using a mixture of Cu₂S and Al₂O₃; this result opens new horizons for surface engineering.