Cold Spray Deposition of MoS₂- and WS₂-Based Solid Lubricant Coatings

• Published in: Lubricants
• Main Authors: Jeffrey R. Lince, Peter Woods, Eric Woods, Wai H. Mak, Scott D. Sitzman, Andrew J. Clough
• Format: Article
• Language: English
• Published: MDPI AG 2024-06-01
• Subjects: solid lubrication; anti-wear coatings; dry-film lubricants; cold spray; spacecraft; tribology
• Online Access: https://www.mdpi.com/2075-4442/12/7/237

The cold spray deposition technique has been used to produce a new class of solid lubricant coatings using powder feedstocks of the metal disulfides WS₂ or MoS₂, either pure or mixed with Cu and Ni metal powders. Friction and cycle lives were obtained using ball-on-flat reciprocating tribometry of coated 304 SS flats in dry nitrogen and vacuum at higher Hertzian contact stresses (S_max = 1386 MPa (201 ksi)). The measured friction and thickness of the coatings were much lower than for previous studies (COF = 0.03 ± 0.01 and ≤1 µm, respectively), which is due to their high metal disulfide:metal ratios. Cu-containing metal sulfide coatings exhibited somewhat higher cycle lifetimes than the pure metal sulfide coatings, even though the Cu content was only ~1 wt%. Profiling of wear tracks for coatings tested to 3000 cycles (i.e., pre-failure) yielded specific wear rates in the range 3–7 × 10⁻⁶ mm³N⁻¹m⁻¹, similar to other solid lubricant coatings. When compared to other coating techniques, the cold spray method represents a niche that has heretofore been vacant. In particular, it will be useful in many precision ball-bearing applications that require higher throughput and lower costs than sputter-deposited MoS₂-based coatings.