Tao Wang

CrN_x coatings with a low nitrogen content below 31.7 at.% were deposited using closed field unbalanced magnetron sputtering by varying the N₂:Ar flow ratio. A dense and column-free CrN_x coating was obtained at a nitrogen content of 14.8 at.%, whereas the other CrN_x coating were all columnar structured. The column-free CrN_x coating was composed of two types of structures: an N-incorporated Cr(N) solid solution matrix with a high number of point defects and a Cr(N) matrix with dispersed Cr₂N nanocrystallines. The pinning effect of Cr₂N nanocrystallines and point defects in Cr(N) grains are responsible for the formation of a column-free CrN_x coating. The columnar-free CrN_x coating exhibits a high hardness of 33.7 GPa, which is comparable to the hardness of Cr₂N coating but 2.6 times larger than that of the Cr coating. It also has significantly better corrosion resistance than both Cr and Cr₂N coating, with a corrosion current density of 4.1 × 1.0⁻⁹ A/cm² that was only 1/20 than that of Cr coating.

MoS_x-Ti composite coatings with different S/Mo ratios were prepared by varying the substrate bias voltage of magnetron sputtering. It was found that the S/Mo ratio of the as-deposited MoS_x-Ti coating decreased gradually from 1.7 to 1.3 as substrate bias voltage increased from −30 V to −110 V. The MoS_1.7-Ti coating exhibits a nanocrystalline and amorphous phase mixed structure while the other MoS_x-Ti coatings were all amorphous structured. The hardness of the MoS_x-Ti coatings increased from 8.8 GPa to 9.8 GPa as the S/Mo ratio decreased from 1.7 to 1.3. The MoS_x-Ti coatings with the S/Mo above 1.4 exhibit COF with values smaller than 0.07 at RH of 50% and increased wear rate in the magnitude of ∼10^–7 mm³ Nm⁻¹. The tribological behavior of the MoS_x-Ti coatings were determined by the formation of the imperfect crystalline MoS₂ tribofilm. With the decrease of the S/Mo ratio, the increased defects in imperfect crystalline MoS₂ tribofilm lead to quicker consumption of the tribofilm during the trio-test, which result in a higher wear rate.