Long-Term Tribological Performance of Tungsten Disulfide-Blended Inconel 625 Coating Fabricated Via Laser-Assisted Cold Spray

Abstract Self-lubricant coatings are widely used in tribological applications, particularly under extreme conditions such as high speed, high load, and long-term operations. To evaluate the long-term performance of such coatings, a 12.5-hour reciprocating tribological study was conducted on a tungsten disulfide (WS2)-blended Inconel 625 (In625) coating. The coating was deposited on an SS304 substrate using an in-house-developed laser-assisted cold spray setup. Microstructural analysis revealed the presence of In625, WS2, Cr2S3, and tungsten (W) phases within the coating matrix. Initial tribological testing for 30 min demonstrated that the coating reduced the coefficient of friction (COF) to 0.31, nearly half that of the uncoated substrate (0.58). Subsequently, prolonged testing over 12.5 h confirmed that the COF of the coating remained stable, maintaining the same low value observed during the shorter test. Scanning electron microscopy and elemental mapping on the wear track indicated that the coating exhibited excellent adhesion, with no significant peeling off after 12.5 h of wear testing. Additionally, analysis of the wear counterpart showed the transfer of sulfide phases from the coating, facilitating the formation of a lubricating layer on both the coating and the counterpart. This transfer of lubricious phases was beneficial in achieving a low and stable COF. Furthermore, the wear-rate of the coating was significantly lower than that of the substrate (17 times), with the wear-rate decreasing over time. These results highlight the coating's potential for enhanced durability and performance in severe tribological applications.