The effect of grain boundary (GB) defects on the tribological properties of MoS2 has been investigated by molecular dynamics (MD) simulations. The GB defects-containing MoS2 during scratching process shows a lower critical breaking load than that of indentation process, owing to the combined effect of pushing and interlocking actions between the tip and MoS2 atoms. The wear resistance of MoS2 with GB defects is relevant to the misorientation angle due to the accumulation of long Mo-S bonds around the GBs. Weakening the adhesion strength between the MoS2 and substrate is an efficient way to improve the wear resistance of MoS2 with low-angle GBs.

Pure MoS2 coatings are easily affected by oxygen and water vapor to form MoO3 and H2SO4 which cause a higher friction coefficient and shorter service life.

The effects of in-plane prestrain on the anti-pressure and anti-wear performance of monolayer MoS2 have been investigated by molecular dynamics simulation. The results show that monolayer MoS2 observably improves the load bearing capacity of Pt substrate. The friction reduction effect depends on the deformation degree of monolayer MoS2. The anti-pressure performance of monolayer MoS2 and Pt substrate is enhanced by around 55.02% when compressive prestrain increases by 4.03% and the anti-wear performance is notably improved as well. The improved capacities for resisting the in-plane tensile and out-of-plane compressive deformation are responsible for the outstanding lubrication mechanism of monolayer MoS2. This study provides guidelines for optimizing the anti-pressure and anti-wear performance of MoS2 and other two-dimension materials which are subjected to the in-plane prestrain.

A novel polyphosphate lubricant was used and evaluated during hot (ferrite) rolling of an interstitial-free (IF) steel. The texture evolution of these rolled IF steels have been examined by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) measurements. The polyphosphate lubricant shows an improved lubrication performance in terms of the texture optimization compared with lubricating oil and with unlubricated conditions. The γ-fiber texture is enhanced, and less shear texture is produced. This microstructure is responsible for enhanced drawability of ferrite rolled IF steels. The very high thermal stability of the polyphosphate enabled its use at very high temperatures (from 700 to 800 °C). Rolling temperature exerted limited influence on the resulting rolling texture evolution. The polyphosphate lubricant stabilizes the surface texture and reduces the gradient of shear texture through the thickness. The in-grain shear bands are reduced significantly (48.5%) compared with the unlubricated condition. Measured grain orientations indicate that the favorable texture of {111}<112> along the γ-fiber is developed while the undesired α-fiber texture of {001}<110> is effectively suppressed.

Hot rolling of titanium alloy currently is carried out without lubrication because of the surface defects. In order to explore an effective lubrication scheme to reduce friction and wear during hot rolling of titanium alloy, a mixed graphene-incorporating lubricant has been proposed to study its lubrication performance and mechanism. The tribological experiments were carried out by ball-disk friction and wear tester under hot-rolling parameters. Scanning electron microscopy (SEM), X-ray energy spectrum analyzer (EDS), X-ray powder diffractometer (XRD) and Raman analysis were used to analyse the surface and cross-section of the wear marks on the samples after the tribological experiments. The results show that the friction coefficient decreases up to about 35% compared with tests under dry and lubricated conditions. The surface quality of the wear marks is improved significantly after applying the proposed lubricant. The graphene which is embedded in the phosphate film can be effectively applied as a lubricating material to strengthen the lubricating film with less combustion loss at high temperatures. A chemical- and mechanical-induced lubrication mechanism for the hot rolling of titanium sheets has been proposed due to the synergistic lubrication effect of the graphene, ZrO2 nano particles and phosphate. It is of great significance and potential value to apply this proposed lubricant as an effective way to reduce the wear, friction and oxidation during the hot-rolling process of titanium alloy.