Self-repairing Layer Research Articles

Modified Graphene/Muscovite Nanocomposite as a Lubricant Additive: Tribological Performance and Mechanism

Modified graphene/muscovite (MGMu) nanocomposite was synthesized with muscovite (Mu) and silane coupling agent modified graphene oxide through a simple hydrothermal method that exhibited excellent dispersion stability in oil. Compared with the base oil sample, the average friction coefficient and wear scar diameter of the MGMu oil sample decreased by 64.4 and 20.0%, respectively, and the microhardness of its wear scar was increased by 16.1%. The MGMu showed better tribological performance than its individual component due to the synergetic effect between the two components. The lubrication mechanism was proposed according to the morphology, chemical composition, and microhardness of the surface of wear scars. MGMu as an oil additive could fill between the friction pairs, cling to some asperities, and occur relative sliding between unit layers, thus playing a role in lubrication. It was found that MGMu would react with the surface of the friction pair during the friction process to generate Fe2O3, SiO2, SiC, and new aluminosilicate, which formed a self-repairing layer with high hardness. This chemically reactive film exhibited a lower shear strength, which made the oil sample containing MGMu have a lower coefficient of friction.

Self-repairing and tribological behaviour of steel–steel friction pairs lubricated with an oil with magnesium silicate hydrosilicate as additive

Magnesium silicate hydrosilicate (MSH) was added into a lubricating oil as an additive for testing self-repairing capability of a friction pair when it is lubricated. A systemic examination of the structure and chemical composition of the surfaces with self-repairing layers was carried out with an expectation of reducing the wear and even fully repairing the surfaces through the newly grown layers. The wear behaviour of the surfaces, including that having the deposited self-repairing layers, was examined with reference to the lubricated steel friction pairs, being loaded under different working conditions. The treated surfaces and their chemical composition were examined using scanning electron microscopy (SEM) and EDS/XRD, respectively. The results showed that the level of the concentration of the additive in the lubricating oil does not affect the chemical composition of the self-repairing layer formed, and lubricating oil with 1.0% MSH is an optimal concentration value for reducing friction and wear for the friction pairs examined. At the same time, the grown self-repairing layers become more uniform as the duration of sliding between the two parts in a friction pair increases.

Self-repairing mechanism and surface characterization of compressor vanes lubricated with oil added with magnesium silicate hydroxide nanorods

Using magnesium silicate hydroxide as additive of lubricating oils for reducing friction in engineering equipment/machinery has been researched intensively. However, some mechanism relating to the growth of the self-repairing layers on the won surfaces is still not clearly explained. At the same time, using magnesium silicate hydroxide (MSH) in the form of nanorods showed great promise in reducing friction and wear. In this study, surface-modified MSH in the form of nanorods was used as additive of polyolester oil (POE) which was then used for the lubrication of compressor vanes. The sample parts were studied on the morphology and the microstructure of the self-repairing layer in a great depth. The results showed that self-repairing layers with different thicknesses were generated on the worn surfaces when the POE with 1 wt.% nanorods-MSH was used. It was found that the self-repairing layers consist of organic–inorganic composite membranes, and with increase of working time of the compressor vanes, the self-repairing layers become denser and thicker, while their micro-structural form remains to be similar. The situ-repairing capability of the metal surfaces (roller-vane pair of the compressor) enforced by the MSH nanorods is very significant, indicating high potential for industrial applications where boundary and mixed lubrications are needed.

Self-Repairing Characteristics of Serpentine Mineral Powder as an Additive on Steel–Chromium Plating Pair under High Temperature

Friction and wear experiments on steel–chromium plating pairs were carried out with nanoscale serpentine (a magnesium silicate mineral) as a lubricating oil additive at 400°C. The tribological test results showed that self-repairing protective layers formed on the contact surfaces of both the steel matrix and hard chromium coating. Field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the morphology and elements of self-repairing layers were in accordance with that of serpentine. A generation mechanism of the layer was proposed that suggests that isomorphic replacement between Fe/Cr and serpentine mineral silicate occurs, which is the wear mechanism of the tribochemical reaction.

Long-term surface restoration effect introduced by advanced silicate based lubricant additive

Long-term effect (up to 300h) of an advanced silicate based lubricant additive on the tribological properties is studied using a newly designed pin-on-disk tester. With the additive, the coefficient of friction was reduced by ∼40%. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) examinations showed that a smooth and high C-content outer layer was formed on the specimen surfaces, suggesting possible formation of diamond-like carbon (DLC) films. Using nano-hardness measurements, the hardness of the layer on the disk and the pin were 10.2GPa and 16.7GPa respectively. Wear loss and ferrographic analyses indicated that a “negative wear” occurred when the additive was applied, suggesting the debris particles were captured by the specimen to form a self-repairing layer.

Comparative tribological properties of magnesium hexasilicate and serpentine powder as lubricating oil additives under High temperature

Friction and wear experiments were carried out with nanoscale serpentine (magnesium silicate mineral) and magnesium hexasilicate powder as lubricating oil additives at 400°C. The tribological test results showed that the self-repairing protective layers could be well formed on the contact surfaces, whether nanoscale serpentine or magnesium hexasilicate powder was added into lubricating oil. The SEM and EDAX analysis demonstrate that the morphology and elements of both self-repairing layers are in accordance with each other. The research results indicate that the essence of self-repairing of serpentine power is isomorphic replacement and tribochemical reaction between magnesium silicate and metal matrix.

Characterization and auto-restoration mechanism of nanoscale serpentine powder as lubricating oil additive under high temperature

Friction and wear experiments were carried out with nanoscale serpentine (a magnesium silicate mineral) and heat-treated serpentine as lubricating oil additives at 400 °C. The tribological test results showed that the self-repairing protective layers could be well formed on the contact surfaces, whether nanoscale serpentine or heat-treated serpentine powder was added into lubricating oil. SEM and EDAX analysis demonstrate that the morphology and elements of self-repairing layers are in accordance with that of serpentine. A generation mechanism of the layer was proposed from the view of isomorphic replacement theory in mineralogy and petrology, and friction-induced chemical reaction.