Advanced Materials Research Vol. 1017

Abstract: Interest in carbon-fiber-reinforced plastic (CFRP) has been growing for the last several years. CFRP, a composite material made of carbon fibers and resins, has high mechanical characteristics and is well known as a difficult-to-cut material. During the process of drilling or cutting of CFRP, tool wear and delamination occur frequently. In this study, the authors developed a milling tool for CFRP using polycrystalline diamond, and the cutting performance of the developed tool was investigated.

Abstract: A microstructured surface was created on a steel surface by whirling electrical discharge texturing (WEDT) since it was considered that the microstructures could act as lubricant reservoirs to assist the formation of a lubricating film, resulting in reduced friction. In this study, friction tests under engine oil were carried out over a range of loads and sliding speeds. In addition, the surface characteristics of the microstructured surface were also investigated to optimize the friction characteristics of the textured surface through pin-on-disc friction tests. It was found that under the mixed lubrication condition near the boundary condition, textured surfaces with texture-area ratio of approximately 6% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient. However, a texture-area ratio of approximately 4% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient under the mixed lubrication condition near the elastohydrodynamic lubrication condition. It was considered that when the normal load decreased, the lubrication region changed from the mixed lubrication condition to the hydrodynamic lubrication condition, which meant that the actual contact surface area decreased. The decrease in the actual contact surface area with decreasing texture-area ratio led to a reduction in the friction coefficient. Finally, it was clarified that the friction coefficient was reduced under the optimized conditions of the microstructured surface through a pin-on-disc friction test.

Abstract: The tribo-electrochemical performance of polycrystalline silicon was studied by Tafel polarization curves and electrochemical impedance spectroscopy (EIS), based on which the electrochemical mechanical planarization (ECMP) simulating test was done to investigate the effects of applied potentials on friction and material removal rate (MRR) with an ECMP simulating tester. According to the research, a suitable anode polarization potential is advantageous to promote the forming of passivation film with better corrosion inhibition in alkaline CeO₂ polishing liquid, and forming of passivation film on silicon surface can increase both the friction between polishing pad and specimen and the MRR of silicon. This result provides theoretical supports and experimental bases for ECMP of silicon wafer to increase its polishing efficiency.

Abstract: In the present study, the long-duration frictional and wear performance of the MCD/DLC (Micro-crystalline Diamond / Diamond-like Carbon) bilayered film are investigated under water-lubricating conditions. All friction tests are carried out on a rotation “ball-on-plate” tribotester where the MCD/DLC is slid against with a Φ 6.0 mm Si₃N₄ ball and the whole sliding contact is immersed in deionized water during the sliding process. A full factorial experimental plan is conducted with four sliding velocities ranging from 0.126 to 0.503 m/s and four normal loads from 2 to 8 N. The duration of each sliding process is 24 h. For the sake of comparability, conventional MCD and NCD (nanocrystalline Diamond) films are also adopted under each sliding condition. The results show that the stable coefficient of friction (COF) of MCD/DLC film is ranging from 0.025 to 0.12 under the water-lubricating condition, comparable with the NCD film but much lower than that of single-layered MCD film; in contrast, the top-layered DLC film does not show beneficial effect on enhancing the sliding stability of single-layered diamond films. Moreover, its specific wear rate is estimated at the level of 10^-8 mm³N^-1m^-1, higher than that of MCD or NCD films. The sliding interface is under boundary lubrication condition, high normal load causes more prominent mechanical interactions between two contacted surfaces and thus produces a smoother and cleaner equilibrium sliding interface, which finally results in the decreasing tendency of stable COF as the load rises. Comparatively, the sliding velocity does not exhibit evident influence on the stable COF of the MCD/DLC film.

Abstract: The composition and phase transformation of oxide scale in cooling process (after hot rolling) of rolled microalloyed steels affect tribological features of rolled strip and downstream process, and the produced steel surface quality. In this study, physical simulation of surface roughness transfer during cooling process with consideration of ultra fast cooling (UFC) was carried out in Hille 100 experimental rolling mill, the obtained oxide scale was examined with SEM to show its surface and phase features. The results indicate that the surface roughness of the oxide scale increases as the final cooling (coiling) temperature increases, and the flow rate of the introduced air decreases. The cracking of the surface oxide scale can be improved when the cooling rate is 20 °C/s, the strip reduction is less than 12 %, and the thickness of oxide scale is less than 15 μm, independent of the surface roughness. A cooling rate of more than 70 °C/s can increase the formation of retained wustite and primary magnetite precipitates other than the precipitation of α-iron. This study is helpful in optimising the cooling process after hot rolling of microalloyed steels to obtain quality surface products.

Abstract: In previous study, the quantitative measurement method of contact stiffness of the joint considering real contact area is developed by experimental approach. However, the measurement of contact stiffness needs special device and skillful measuring technique. Therefore, in this paper, simplified calculation method with material properties and profile data of surface roughness obtained by profilometer is considered. As a result, real contact area, contact stiffness and contact spring stiffness calculated from specific wavelength of rough surface are near agreement with experimental value. Hence, it is revealed that there is dominant configuration in surface roughness.

Abstract: Archard wear theory, which describled the relationship between wear volume and material hardness, coasting distance and loading, was the classical theory of tribology problem. According to Archard wear theory, bionic lead rail was compared with ordinary lead rail based on ABAQUS software in the same conditions. Friction and wear property of bionic lead rail were studied, including the maximum contact surface, the distribution of working point of friction force and transformation law of friction force. The results indicated that the maximum contact surface of bionic friction pair decreased obviously and the variation of contact surface was steady. The distribution of working point of friction force for ordinary lead rail was relatively concentration. The distribution of working point of friction force for bionic lead rail was relatively dispersion. Friction force for bionic friction pair decresed to some extent, but the peak friction force was relatively larger.

Abstract: A new polishing method by using fixed soft abrasive film is proposed to polish the end-face of the optic fiber connector. In order to study the wear property of the fixed soft abrasive film, the Particle Flow Code program was employed to simulate the interaction of surface topography. The discrete element model of the optic fiber connector and the fixed soft abrasive film were established. Through the interaction of the surface of two models, the process of contact and friction between the fixed soft abrasive film and the end-face of the optic fiber connector could be simulated. Simulation results showed that the main factors affecting the wear of the fixed soft abrasive film were pressure and speed, which mainly affected the normal stress and the tangential stress respectively. And the wear of the surface was mainly related to pressure and speed. The greater the speed and pressure were, the more serious wear of the fixed soft abrasive film was.

Abstract: The grinding heat directly affected workpiece surface in the grinding process and it might produce some defects such as crack and burn. Meanwhile wear debris generated in the grinding process could easily embed grinding wheel blowhole and caused clogging and passivation. So it was particular important to avoid defects and improve the grinding workpiece surface integrity effectively. This paper established an incompressible turbulent fluid spray model based on the study of the existing airflow and the grinding fluid distribution in the grinding zone. Then according to different grinding fluid supply parameters established the two-phase gas liquid spray flow model by using CFD(computational fluid dynamics), simulated and calculated the model, compared the mass flow rate of the grinding fluid flow field with different spray distances, heights, speeds and spray angles in the grinding zone and determined the most reasonable spraying jet position. At the last, through researching on the workpiece surface integrity experiment, it provided an experimental basis to determine the most suitable spray jet position and verify the rationality of supply parameters selection.

Abstract: Needs of precision optical mirrors are increasing in the astronomical space telescope. In the space having extremely large temperature differences, the aspheric optical mirror made of low thermal expansion ceramic is very effective in reducing the focus errors due to the thermal expansion. In order to develop the mirror made of a new low thermal expansion ceramic, parabolic mirror of the ceramic is ground and polished to test. By the grinding and polishing test, changes of form deviation profiles and surface roughness profiles are evaluated and machinability of the proposed ceramic is studied.