Development of a WS2-Based Solid Lubricant Wear-Resistant Coating on Stainless Steel by Laser-Assisted Cold Spray Process

Abstract With advancements in space technology, efficient solid lubricants are being sought after for the reliable operation of instruments in space. This article describes the development of a solid lubricant coating composed of tungsten disulfide (WS2)-blended 15-5 precipitation hardening stainless steel (15-5 PH SS) on SS304 substrate using a laser-assisted cold spray (LACS). During the deposition, the temperature of the laser-irradiated zone was kept below the melting temperature of both the substrate and the powder, and the powder carrier gas pressure was kept sufficiently high to impart enough pressure to the powder particles to get plastically deformed on impinging on the laser-heated substrate to deform and form the coating in a solid state, while minimizing WS2 evaporation. The significant presence of WS2 in the coating was confirmed by the phase and microstructure analyses. The coating surface had 372 MPa of compressive residual stress due to the peening effect of impinging particles, and the average hardness varied between 400 HV0.05kgf and 500 HV0.05kgf, which was double the hardness of the SS304 substrate. A ball-on-disk wear test of the coating, against a WC counter surface, exhibited a coefficient of friction and wear-rate of 0.05 and 0.11 × 10−5 mm3/N m, indicating approximately 10 times lower friction and over 330 times lower wear-rate compared to the substrate values of 0.52 and 36.2 × 10−5 mm3/N m, respectively. The synergistic effect of embedded WS2, along with the hard stainless steel (SS) particles, contributed to the improved tribological performance.