High-temperature friction performances of graphite blocks (GBs) and zinc phosphate impregnated graphite blocks (IGBs) were evaluated under various friction temperatures. The surface of IGB exhibited extremely lower average friction coefficient values, that was 0.007 at 400 °C and 0.008 at 450 °C, in comparison to that of GB (0.13 at 400 °C and 0.16 at 450 °C, respectively). The worn surface of IGB in the high-temperature friction test was smoother and more complete than that of GB. The wear under high temperature and load caused the transformation of zinc pyrophosphate to zinc metaphosphate and the formation of a continuous large-area boundary lubrication layer combined with graphite and metallic element on the wear surface. The superior tribology property of IGB could be attributed to the digestion of iron oxides by tribo-chemical reactions and passivation of the exposed dangling covalent bonds. Specifically, the layered structure generated on the IGB wear interface effectively decreased the adhesive forces and prevented the surface from serious damage.
In this work, we have successfully prepared carbon quantum dots with abundant edge-OH (CQDs-OH) via hydrothermal reaction , and then the zwitterionic dopamine sulfonate (ZDS) was self-assembled onto CQDs surface via chemical bond between the catechol group of ZDS and the edge-OH of CQDs. Due to the good dispersion stability of quantum dots endowed by ZDS, CQD-ZDS exhibits excellent lubricating effect as a water-based lubricating additive. Meanwhile, the tribochemical reaction induced by CQD-ZDS can form a stable carbon and metal oxide protective film on the wear surface. Compared with pure water, the average friction coefficient (COF) decreases from 0.5 to 0.11. The hydration process of ZDS modified CQDs is simulated by molecular dynamics simulation, and its lubricating mechanism is explored.
Oleylamine (hereinafter referred to as OM)-modified CeO 2 nanoparticles were synthesized by a one-pot pyrolysis method. The tribological properties of the as-prepared CeO 2 nanoparticles as the lubricant additive in poly-alpha olefin (PAO) were investigated with a four-ball machine, and their lubricating mechanism was discussed in relation to worn surface analyses by SEM, EDS, and XPS. Findings indicate that these nanoparticles exhibit good dispersibility as well as excellent anti-wear ability in PAO. This is because OM-modified CeO 2 nanoparticles can catalyze the oxidation of metallic Fe to form ferrite oxide-containing tribo-film. Under the condition of ASTM D2266-2001, the same lowest WDS was obtained at the concentration of 0.2 wt% and 1.8 wt%. When the concentration of CeO 2 is 0.2 wt%, a compact catalytic oxidation tribo-film is formed, which has more outstanding long-term anti-wear ability. When 1.8 wt% CeO 2 is added, the tribo-film formed is the combination of catalytic oxidation film and ceria deposition film, which has more significant bearing capacity.
Reducing alloy friction to achieve ultra-low friction is a valuable approach to save energy and reduce pollution from oil use, which is a major challenge for researchers. This study introduces a successful method to achieve ultra-low friction in Ti-6Al-4 V using a hydrated lubricant composed of hydroxyethyl cellulose (HEC). And the effects of speed and concentration on lubricating were investigated. It was found that excessive sliding speeds may lead to lubricant detachment and consequent friction increase, indicating that the adsorption ability of HEC needs to be enhanced in future studies. In addition, when the concentration exceeds 5 wt%, wear loss tends to stabilize across tests with different concentrations, while the friction force increases with rising concentrations. Based on these findings, microscopic studies were conducted to investigate the mechanism of friction reduction. Notably, distinct topographic features resembling ‘valleys’ and ‘plateaus’ were identified on the wear scars in a nanoscale scope. The movement of the surfaces induces the hydrated HEC lubricant to flow from the lower valleys to the higher plateaus, suggesting elastohydrodynamic lubrication mechanisms to form robust films. The valleys serve as lubricant reservoirs, while the plateau tops support the lubricant films to prevent contacts between Ti-6Al-4 V and Si 3 N 4 . The schematic illustrations depict the microscopic mechanisms for achieving of ultra-low friction on Ti-6Al-4 V alloy.
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