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In this work, the effects of the developed oil-in-water (O/W) based nanolubricants containing TiO 2 nanoparticles (NPs) on the tribological behaviour of oxidised high-speed steel (HSS) were studied, using pin-on-disc tests. The pin was made of HSS and, prior to the wear test, was oxidised to form a scale layer on the surface. The results show that the TiO 2 NPs in the O/W lubricant can achieve an excellent reduction of the coefficient of friction (COF) and improve the anti-wear properties of pins with oxidised surfaces. The TiO 2 NPs in the nanolubricant were found to have the filling and tribo-sintering effects. The NP aggregation around the contact area was observed with higher TiO 2 NP concentrations in the nanolubricant, revealing a larger NP aggregation area. Based on the results and analysis, the mechanism about the effects of the TiO 2 NPs in the O/W based nanolubricant on the wear and COF were well explained. [ABSTRACT FROM AUTHOR]

A ball-on-disk tribometer was employed to evaluate the lubrication performance and mechanisms of innovative TiO 2 nano-additive water-based lubricants. Two experimental methods were applied to determine the optimal mass fraction of TiO 2 . In the method I, lubricants were added onto the worn disk tracks at a predetermined time interval. In the method II, the disks were immersed in the lubricants continuously during the whole process of tribological tests. The results both indicate that the water-based lubricants can significantly reduce the coefficient of friction (COF). The 0.8 wt% TiO 2 lubricant demonstrates excellent tribological properties including the lowest COF and the strongest wear resistance under all lubrication conditions. The lubrication mechanisms are attributed to the rolling and mending effects of the TiO 2 nanoparticles. [ABSTRACT FROM AUTHOR]

Electron backscatter diffraction (EBSD) of the microtexture in the tertiary oxide scale after hot rolling were investigated. The surface asperity flattening and grain refinement of Fe 3 O 4 were produced at a thickness reduction of 28% and a cooling rate of 28 °C/s. Microtexture development of Fe 3 O 4 manifests as a strong θ fibre parallel to oxide growth, including the {100}<001> and {001}<110> textured components, whereas the {0001}<10 1 ̅ 0> component dominates in α -Fe 2 O 3 as the favoured basal slip. The tribological effect of α -Fe 2 O 3 at the contact surface of steel and rolls was considered at low and high thickness reductions. The propagation of cracks along the Fe 3 O 4 grain boundaries could create a dish to collect nanoparticles during lubrication and thereby changed the wear rates. [ABSTRACT FROM AUTHOR]

Abstract SiC-graphene nanosheets (GNSs) core-shell nanoparticles were incorporated into alumina matrix composites. The composites showed refined grain sizes, increased toughness and hardness. Ball-on-disk wear tests were conducted and the results demonstrated that the coefficient of friction was reduced by 29.4%, and the wear rate was reduced by 90.1% for the composite containing 5 vol % SiC and 1 vol % GNSs at 90 N in comparison to monolithic alumina. These results are superior to Al 2 O 3 -graphene composites documented in the literature. The microstructure and topography of the wear scars were examined to understand the wear behaviour. GNSs-rich tribofilms were observed on the wear scar. The contributing mechanism of the self-lubricating and wear-resistance performance was explored. Highlights • The composites showed excellent wear-resistant and self-lubricating performance. • The reduction effect of the nanofiller on friction tends to be more significant under higher loads. • The enhancement is attributed to the improved microstructure, mechanical properties and GNSs-rich tribofilms. [ABSTRACT FROM AUTHOR]