Reducing corrosion and wear has been a challenge to metal components in marine environments for a long time. However, the problems of high cost and low efficiency hinder the discovery of new anti-tribocorrosion multiprincipal element alloys (MPEA). This study reported a significant reduction in both wear and corrosion of single-phase CoCrNi MPEA through in situ laser-directed energy deposition (L-DED), which had only half the tribocorrosion rate of prealloyed samples. Furthermore, the structural evolution mechanism of in situ samples was revealed at different scales, and the interaction mechanism of tribocorrosion was clarified in detail. The results show that in situ samples had finer cells and higher microhardness due to solid solution strengthening and nanoprecipitation strengthening. The higher Cr2O3/Cr(OH)3 ratio, higher Rct, and lower Ipass indicated a denser and more protective passive film of the in situ samples. Furthermore, the in situ sample demonstrated superior tribocorrosion resistance, which was mainly due to a lower corrosion-intensified wear loss (WC) value. Moreover, the load intensified the material loss of interactions between wear (W) and corrosion (S). This work will provide breakthroughs in the wear–corrosion trade-off of MPEA design and promote the application of anti-tribocorrosion MPEAs in marine equipment.
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Molybdenum disulfide (MoS2) is a multifunctional material primarily used in lubrication, electronics, and catalysis. MoS2 films are widely utilized in the aerospace industry due to their excellent lubrication properties. These films are applied in aircraft landing gear, engine components, and moving parts of spacecraft to ensure efficient operation and minimize frictional wear. However, under high-temperature conditions, MoS2 films are susceptible to oxidation into molybdenum trioxide, significantly degrading their lubricating performance and restricting their applicability in high-temperature environments.
Herein, MoS2 films were enhanced by doping them with amorphous carbon to improve their mechanical properties and high-temperature tribological performance. Using direct-current magnetron sputtering, medium-frequency magnetron sputtering, and high-power pulsed composite sputtering techniques, MoS2-C composite films were fabricated. The effects of doping amorphous carbon and its concentration on the microstructure, mechanical properties, and tribological performance of MoS2 films were thoroughly investigated.
The results revealed that the MoS2-C composite films exhibited a preferential orientation of the (002) crystal plane. Amorphous carbon incorporation into the MoS2 matrix resulted in a dense and uniform structure while reducing surface roughness. This structural modification enhanced the mechanical and tribological properties of the films. Doping MoS2-C composite films with an optimal amount of amorphous carbon significantly improved their mechanical properties. Their nanohardness and elastic modulus reached 5.50 and 82.53 GPa, respectively, while substrate adhesion strength increased to 8.30 N, approximately 3.6 times higher than that of pure MoS2 films. These improvements suggest that amorphous carbon addition enhances the mechanical strength and durability of the films. At room temperature, both MoS2 and MoS2-C composite films exhibited poor tribological performance, primarily due to the infiltration of moisture molecules from air into the MoS2 interlayers. This results in MoS2 oxidation, compromising the lubrication properties of the films. Meanwhile, the tribological performance of MoS2-C composite films substantially improved in a vacuum environment, attributed to the isolation from oxygen, preventing oxidation and allowing the films to maintain their lubricating properties. Under high-temperature conditions (100 ℃-300 ℃), MoS2-C films outperformed pure MoS2 films by maintaining a lower friction coefficient. MoS2-C films with 37.41% atomic percentage of carbon exhibited the lowest wear rate of 9.75×10-8 mm/(N·m) while showing a friction coefficient of 0.008 at 200 ℃, which is the lowest value among all samples. Notably, at 300 ℃, pure MoS2 films quickly failed due to oxidation, whereas MoS2-C composite films retained a lower friction coefficient and longer wear life. This improvement is primarily attributed to the incorporation of carbon, which effectively inhibits MoS2 oxidation in high-temperature environments.
MoS2-C composite films exhibit enhanced wear resistance and load-bearing capacity at elevated temperatures. These findings suggest that doping amorphous carbon into MoS2 films significantly improves their tribological and mechanical properties, especially under high-temperature conditions. MoS2-C composite films demonstrate excellent wear resistance and prolonged service life, making them promising for high-temperature lubrication applications. By optimizing the carbon content, it is possible to further enhance the high-temperature lubrication performance of MoS2 films while maintaining their excellent mechanical properties. This provides new possibilities for developing advanced tribological coatings that effectively perform under harsh operating conditions.
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Based on the density functional theory (DFT), we investigate the friction properties of inevitable oxidized black phosphorus (o-BP). o-BP with the weaker interlayer adhesion exhibits their great potential as a solid lubricant. At the zero load, the friction property of o-BP is adjusted by its oxidation degree. Expressly, ultra-low friction of P4O2 (50% oxidation, O : P = 2 : 4 = 50%) is obtained, which is attributed to the upper O atoms with lower sliding resistance in the O channel formed by lower layer O atoms. More attractive, we observe superlubricity behavior of o-BP at the critical load/distance due to the flattening potential energy surface (PES). The flattening PES is controlled by the electrostatic role for the high-load (P4O3, O : P = 3 : 4 = 75%), and by the electrostatic and dispersion roles for the low-load (P4O2). Distinctly, the transform from ultra-low friction to superlubricity state of black phosphorus (BP) can be achieved by critical oxidation and load, which shows an important significance in engineering application. In addition, negative friction behavior of o-BP is a general phenomenon (Z > Zmin, Zmin is the interlayer distances between the outermost P atoms of minimum load.), while its surface-surface model is different from the fold mechanism of the tip-surface model (Z0 < Z < Zmin, Z0 is the interlayer distances between the outermost P atoms of equilibrium state.). Thus, this phenomenon cannot be captured due to the jump effect with instability of the atomic force microscopy (AFM) (Z > Zmin). In summary, o-BP improves the friction performance and reduces the application limitation, comparing to graphene (Gr), MoS2, and their oxides.
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Graphene oxide (GO) nanosheets and onion-like carbon (OLC) nanoparticles were synthesized from natural graphite powder and candle soot, respectively, and characterized by transmission electron microscopy and Raman spectroscopy. The lubricating performances of GO and OLC as lubricant additives in water were comparatively evaluated using a ball-on-disc tribometer. The effects of sand blasting of a steel disc on its morphology and tribological property were evaluated. The results show that the two nanomaterials, GO and OLC, when used as lubricant additives in water effectively reduce the friction and wear of the sliding discs, which is independent of the disc surface treatment. On applying heavy loads, it is observed that GO exhibits superior friction-reducing and anti-wear abilities compared to those of OLC—a trace amount of GO can achieve a lubricating ability equivalent to that of an abundant amount of OLC. Furthermore, it is observed that sand blasting cannot improve the wear resistance of the treated steel disc, even though the hardness of the disc increased after the treatment. The possible anti-wear and friction-reducing mechanisms of the GO and OLC as lubricant additives in water are discussed based on results for the wear surfaces obtained by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy
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