Synthesis and structural properties of Mo-S-N sputtered coatings

Abstract

Transition-metal-dichalcogenide coatings provide low friction because of characteristic low shear strength along the basal plane of the lamellar structure; however, the material can easily degrade through exfoliation and poor adhesion to the metallic substrates. In this work, an innovative approach was employed to improve the coating's adhesion. A secondary plasma source was used during deposition to generate an additional charged particle flux which was directed to the growing film independently of the magnetron cathode. Therefore, Mo-S-N solid lubricant films were deposited by DCMS from a single molybdenum disulphide (MoS 2 ) target in a reactive atmosphere. Nitrogen was introduced during the deposition with increasing partial pressures, resulting in a high N 2 content in the doped films (37 at. %). The variation in incident ion energy and flux of energetic species bombarding the growing film allows for the control of the S/Mo ratio through selective re-sputtering of sulphur from the film. The S/Mo ratio was progressively increased to the range of 1.2-1.8, having gradient from metallic layer upto-the lubricious sulphide. Combining the ion bombardment with nitrogen incorporation, cohesive critical load (Lc1) reached 38N, 10 times more than MoS 2 coating. Observation using HRTEM revealed an amorphous structure and strong bonding with the substrate.

Mechanical Properties and Vacuum Tribological Performance of Mo–S–N Sputtered Coatings

“…With the increase in N content, the increasing values of the wear rate and COF were attributed to the reduced S/Mo ratio (∼0.7) which hindered the formation of the well-ordered tribo-film at the contact area leading to the failure of coating. Similar works were also reported by Nossa et al 41 In our previous work, 29 Mo−S−N coatings were deposited using a novel hybrid deposition approach to improve the composition, compactness, structure, and adhesion. It was observed that the use of the secondary plasma source allowed the N ion bombardment of the growing film.…”

“…The pure sputtered MoS 2 coating showed the lowest hardness values of 0.5 GPa because of its low packing density 47 and columnar morphology, in agreement with the previous study. 29 The hardness of the films increased to 1.5 GPa (Mo−S−N10, 18 atom % N) as soon as nitrogen was introduced in the chamber. The hardness continued to increase with further additions of nitrogen.…”

“…This was done to enhance the adsorbed gas removal. The schematic diagram of the deposition chamber, secondary plasma source, deposition parameters detail, and the main characterization results (composition, morphology, microstructure, crystal structure, and adhesion) of the coatings can be found in ref 29. The roughness measurements were performed using a contact mode atomic force microscope, manufactured by Nanosurf AG (Liestal, Switzerland).…”

“…It is expected that these properties will contribute to the excellent mechanical and tribological behavior of the deposited films. 29 Therefore, this study is a continuation of the previous work focusing on the exploration of the mechano-tribological properties for real industrial requirements. It is well-known that the contact stresses in many tribological applications are relatively low, that is, in the range of 10−150 MPa, for example, in journal bearings.…”

High Performance Space Lubrication of MoS2 with Tantalum

“…The interface of MoS 2 with the steel substrate can often be a point of failure by delamination due to the abrupt change in material properties causing stress concentrations at the interface. [ 44 ] To address this, adhesion layers are often employed as seen for the thick WC layer of MoS 2 +WC and very thin layers for MoS 2 +Ta and MoS 2 +Ti. Figure 1E–H shows the cross‐sectional high‐resolution transmission electron microscopy (HRTEM) images of the four coatings inset with the selected area electron diffraction (SAED) pattern.…”