Electrodeposition of Tribological Molybdenum Disulfide Coatings on Stainless Steel

MoS 2 is an excellent solid-state lubricant for applications in space systems. Among various methods for MoS 2 deposition, electrodeposition has the potential advantage over vapor deposition methods in achieving coatings on parts with complex geometries. This presentation will describe methods to electrodeposit smooth, crack-free, low-friction, and wear-resistant coatings of MoS 2 on stainless steel at room temperature. The MoS 2 films can be directly deposited on stainless steel without the need for anodic pretreatments or an adhesion layer, giving a low surface roughness comparable to that of the polished steel surface. The incorporation of stabilizing additives to the deposition bath not only enables the long-term stability of the solution under ambient environment, but also improves the uniformity of the coating over the substrate surface while maintaining a consistent S:Mo ratio of 2:1 across the thickness of the film. Additionally, coatings deposited from additive-free baths are amorphous, whereas those produced with additives are a composite of both amorphous and crystalline MoS 2 regions. Coatings deposited with or without bath additives both display initially high friction and long run-in times but achieve low steady-state coefficients of friction and wear rates comparable to MoS 2 coatings prepared by physical vapor deposition. Post-deposition mild annealing of the electrodeposited films under inert gas substantially reduces the initial friction and run-in times. Ongoing efforts to adopt the electrodeposition method for coating small parts with complex geometries such as pins and bearings will also be presented, as well as detailed information about the chemical composition and mechanistic roles of the additives in the improved deposition bath, methods to prevent film cracking during drying, and the role of mild thermal annealing.