Protective coatings are important for enhancing tribological behavior, preventing surface degradation, and reducing friction-induced energy losses during the operation of mechanical systems. Recently, tribocatalytically driven formation of protective carbon films at the contact interface has been demonstrated as a viable approach for repairing and extending the lifetime of protective coatings. Here, we study the effect of catalytic metals, specifically their composition and amount, on the tribocatalysis process. To achieve this, we test the tribological performance of electro-deposited amorphous CoNiP and CoCuP coatings in different hydrocarbon-rich environments. Our results indicate that the tribocatalytic repair of wear-induced damage is optimal when Ni and Cu are included in the Co-P matrix at 5 wt% Ni and 7 wt% Cu, respectively. Characterization of the wear tracks suggests that among the considered samples, the tribofilms formed on the surface of Co7CuP have the highest concentration of graphitic carbon, leading to a more significant reduction in the COF and wear rate. The carbon tribofilm formation was more pronounced in decane and synthetic oil than in ethanol, which is attributed to the difference in the length of the hydrocarbon molecules affecting viscosity and the lubricant film thickness during boundary lubrication sliding.

The performance and durability of high-pressure fuel systems in combustion engines are critical for consistent operation under extreme conditions. High-pressure fuel systems are traditionally lubricated with fuel that is compressed and delivered to the combustion chamber. However, lubrication with fuel presents significant challenges in these systems when used with low-viscosity fuels, leading to increased wear rates, especially in reciprocating contacts. This study delved into the tribological performance of steels of varying alloy content (annealed and hardened variants of AISI-52100, CF2, and D2) against alumina and hard 52100 counterbody materials in ethanol and decane environments. Friction and wear behaviors were evaluated, highlighting the influence of material interactions and environmental factors. Elastohydrodynamic lubrication analysis of the tested systems indicated that ethanol and decane form lubricating films of nanometer-scale thickness, confirming the boundary lubrication regimes of the performed tests. In summary, the tribological behavior trends were similar for alumina and 52100 counterbodies. Even though soft 52100 steel demonstrated low friction, its wear was the largest for both tested environments and counterface materials. Among all the tested materials, hard D2 experienced the lowest wear. 52100 and D2 steels showed opposite friction change behavior when comparing hard and soft samples, with lower friction observed for softer 52100 steel and harder D2 steel. Meanwhile, the wear was lower for harder candidates than for softer ones independent of the environment and counterbody material. Raman spectroscopy analysis of the formed wear tracks indicated the formation of carbon films with larger intensities of characteristic carbon peaks observed for more wear-resistant materials. These results suggest the synergistic effect of hardness and tribochemical activity in reducing the wear of materials.

The effects of a small addition of Ag and Ti on the thermal stability, mechanical properties, and tribological behavior of Zr-Co-Al bulk metallic glass (BMG) were investigated. A 5 at.% addition of Ag and Ti to the Zr-Co-Al base alloy improved the thermal stability and had no significant effect on the mechanical properties but considerably improved the wear behavior. The coefficient of friction decreased while the wear rate increased with increasing normal loads for all three alloys. Zr-Co-Al-Ti showed the best tribological performance among the studied alloys, with coefficient of friction and wear rate lower by a factor of four compared to Zr-Co-Al BMG. Predominantly oxidative wear was seen for the quaternary Zr-Co-Al-Ag and Zr-Co-Al-Ti BMGs at higher loads in contrast to abrasive and adhesive wear for the ternary Zr-Co-Al base alloy. These results highlight the potential of Ag and Ti micro-alloying for improving the mechanical and tribological properties of Zr-based amorphous alloys.

Molybdenum disulfide is the benchmark solid lubricant for dry and vacuum service, but its lubricity is affected by oxygen and water vapor. Hybridizing MoS₂ with Ti₃C₂Tₓ MXene produces macroscale superlubricity, yet the responsible mechanism has been established entirely from post-test characterization, which returns the end state of a tribological process and cannot establish the order in which events occurred. Here we close this gap by measuring friction and Raman spectra simultaneously during unidirectional sliding at 20 N across a factorial design spanning coating composition and atmosphere. Three of four conditions fail within 13.1 min; only Ti₃C₂Tₓ–MoS₂ in dry nitrogen sustains superlubricity (μ < 0.01) for 20 min. The A₁g/E₂g ratio, a measure of basal-plane texture, rises from a common initial 2.15–2.25 to 2.4 in both MXene coatings irrespective of atmosphere and in neither single-component coating, showing that texture development is governed by composition. That state persists twelve minutes in nitrogen but decays within four minutes in air at identical composition, establishing atmosphere as the determinant of retention. No MoO₃ forms in the surviving condition. Principal component analysis resolves a second, slower process continuing to 14 min, consistent with densification. Two-dimensional correlation analysis confirms this two-timescale structure: the asynchronous-to-synchronous ratio is 0.015–0.022 in failing conditions but 0.204 in the surviving one, and the asynchronous cross-peak sign reverses there alone, indicating that stacking reorganization precedes in-plane bond relaxation. All three failing conditions exhibit a spectroscopic precursor to frictional failure of 1.4–2.4 min, opening a pathway to in-operando failure prediction in solid-lubricated systems.

Advancement of nnext-generation aerospace systems is constrained by the poor tribological performance of nickel-based superalloys under extreme environments. Inconel 718 (IN718) offers exceptional strength, but its high coefficient of friction against most counterfaces and susceptibility to severe adhesive wear remain critical challenges. This study presents the design of self-lubricating metal matrix composites by integrating graphene nanoplatelets (GNPs) and molybdenum disulfide (MoS₂) directly into the superalloy matrix during laser powder bed fusion (LPBF). A parametric study identified stable processing parameters yielding 99.65% relative density. X-ray diffraction and electron backscatter diffraction reveal that the 2D materials induce a columnar-to-equiaxed transition via Zener pinning, reducing the area-weighted average grain diameter by 36.4% and raising microhardness to 411.8 HV, 23% above the baseline. Tribological testing at 25, 350, and 450°C against alumina shows marked stabilization of the sliding interface and up to 2 times reduction in wear when compared to baseline IN718. Nanoindentation mapping inside the wear tracks reveals hardness advantages of 94.5%, 110.5%, and 117.7% for the composite at the three temperatures. Raman and X-ray photoelectron spectroscopy establish that both materials form Cr- and Ni-rich spinel glaze layers, but only the composite retains the glaze as a continuous load-bearing layer, with crystalline MoS₂ and sp² carbon surviving intact within the same surface volume. The reinforcement therefore acts as a solidification modifier during manufacture, a load-bearing dispersion in the bulk, and a stabilizer of the protective oxide at the sliding interface. This multifunctional synergy advances the design of high-performance superalloy components for extreme environments.