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Single-crystal SiC has become the third-generation semiconductor material with the most development potential due to its many outstanding physical and chemical properties, but excellent surface quality is the prerequisite for its application. Therefore, atomic mechanism of chemical and mechanical mutual promotion in hydroxyl radical ·OH aqueous was researched through reactive molecular dynamics simulation for obtaining nano-smoothed surface with photocatalysis-assisted chemical mechanical polishing (PCMP). The behavior of nanoparticles promoting chemical reaction during the nanofinishing process was studied vias a single abrasive sliding on the surface of SiC. A combination method of mechanical action and chemical action was adopted to compare effect of material oxidation and material removal. Si/C atoms are mainly fractured or escaped in the forms of SiO, CO, chain, SiO2, and CO2, and more residual oxidation products were observed on the substrate. Furthermore, XPS and nanoindentation results also support the mechanism of chemical and mechanical mutual promotion in PCMP through the detection of the oxidized products and surface hardness. This process activated and removed the SiC materials and generated a smooth and non-damaged surface (Ra 0.269 nm and Rmax 0.807 nm). The research results may reveal the removal mechanism of Si/C atoms, and provide new theoretical and technical support for the ultra-precision machining of single crystal sapphire, silicon nitride and diamond etc.

In order to reveal the nanoscale friction behaviour and wear mechanism of 304 stainless steel during nano particles sliding, this study investigated the effects of sliding velocity and depth on the surface morphology, temperature, mechanical forces, coefficient of friction and sub-surface damage (SSD) of stainless steel by employing molecular dynamics simulations. The results demonstrate that the atoms symmetrically stack on both sides of the sliding grooves during the sliding process. Sliding friction, friction coefficient, defective atoms, phase changing degree and the length of dislocation line increases as the indentation depth of the abrasives, while sliding velocity had little impact on them. Temperature in sliding area and the squeezing effect distinctly increases with the indentation depth the abrasives, which leads more serious damage on the surface of workpiece. The damage layer with a sliding depth of 20 Å can reach about 57.2 Å at a sliding velocity of 100m/s, and it has a maximum value of 41.1 Å at a sliding distance of 50 Å. However, increasing sliding velocity can decline the surface SSD layer, which was at a sliding depth of 20 Å. The microscopic atoms evolution presented in the study uncovers the nano-sliding wear mechanism of stainless steel.

Aviation spherical plain bearing often undergoes serious wear due to its extreme and complex working condition. This paper presents a solution of vibration assisted strengthening and surface micro-texture for the wear of aviation spherical plain bearing to achieve the synergistic effects of surface property-improving and appearance-improving. On the basis of analysis the wear mechanism of spherical plain bearing systematically, it attempts to scientifically understand how the vibration assisted strengthening and micro texture can decrease the wear of spherical plain bearing by proposing the distribution function of asperity height and contact theory. The vibration assisted strengthening and micro-texture surface are prepared and the tribological property of friction pairs are investigated on the UMT TriboLab platform. The theoretical analysis and experimental results indicate that the flat-headed distribution of surface asperities is beneficial to improving the contact state and lubricant capability. The vibration assisted strengthening can effectively decrease the friction coefficient of frictional pairs to about 0.11 by decreasing the surface roughness of frictional pairs from about Ra 0.23μm to about Ra 70nm and increasing the micro hardness nearly by 54%. Static load, strengthening times and rotational speed of vibration assisted strengthening have obvious influences on the surface roughness and micro hardness of frictional pairs. Among three textures of micro groove, micro quadrate protrusion and micro quadrate pit, micro quadrate pit obtains a lowest friction coefficient and wear amount. Also the proposed graphene-oil lubricant presents excellent improvement of tribological properties and wear resistance performance of spherical plain bearings.