Key Engineering Materials Vol. 866

Abstract: Effects of the electric inclusion in ferroelectrics on the stress and electric field concentration and polarization switching are investigated based on a phase field approach containing the time-dependent Ginzburg-Landau equation. To capture a clear physical picture with the simulation, the crack medium in the electric inclusion is taken into account explicitly as a crack fluid medium as water, oil or air in region. The simulations exhibit a macroscopic electric field concentration in the electric inclusion filled with air, and a significant influence on the domain evolution from the micro perspective, while the electric inclusion filled with water have little influence. The numerical calculations indicated that, when the dielectric constant inside the flaw are much smaller than the dielectric constant of the ferroelectric matrix, the electric field inside the crack medium are enhanced much higher than the applied electric loading. The result implies the domain evolution takes place with the minimization of total free energy, which involves the high electric field energy derived from the electric inclusion. Therefore, the crack fluid medium in ferroelectric plays in importation role in the effect on the non-uniform distribution of the stress and electric field.

Abstract: The powder compact was directly sintered by a pack boride process to prepare an Fe-based material having a boride layer. The effects of process parameters such as sintering temperature and sintering time on the microstructure and quality of the layer were studied. The thickness of the layer, surface hardness, phase composition and properties of friction and wear were also studied. The results show that the boride layer was mainly composed of Fe₂B, and its thickness is uniform and firmly bonded to the substrate. The thickness and hardness of the layer gradually increase with time and temperature. When the sintering temperature was higher than 1050°C, the more obvious holes and looseness would be appeared in the layer, which was not conducive to improve the properties of material. The thickness of the layer has the best value range with this method. Ensuring the thickness of the layer within a suitable range by controlling the sintering temperature, sintering time and other process parameters was beneficial to reduce the brittleness of the boride layer and improve the friction and wear properties of the material.

Abstract: In this paper, a series of chemical mechanical polishing (CMP) experiments for magnesia alumina (Mg-Al) spinel were carried out with different abrasives, and the materials removal rate (MRR) and surface quality was evaluated to explore their different effects. The scanning electron microscope (SEM) and laser particle size analyzer were also employed to test the micro-shape and size distribution of abrasives. Then, the mechanism of different effects with different abrasives was analyzed in CMP for Mg-Al spinel. Those experimental results suggest that different subjecting pressure ratios of abrasives to polishing pad with different abrasive are the key factors leading to difference polishing performances in CMP.

Abstract: Stainless steel will become one of the main substrate materials for flexible large-scale displays. As the substrate of the flexible displays, the biggest problem of stainless steel is that the surface roughness is too large. It is necessary to polish the surface of stainless steel with ultra-precision. Chemical mechanical polishing (CMP) technology will be one of the most practical processing technologies to make the surface of stainless steel ultra-smooth and damage-free. In this paper, the material removal rate (MRR) and surface roughness were studied based on the hydrogen peroxide oxidant and ferric chloride oxidant with different surfactants in chemical mechanical polishing (CMP) slurry by experiments. The results show that it can obtain the maximum of the MRR and the optimal surface quality when using 0.04 wt% sodium hexadecyl sulfate as the surfactant of the hydrogen peroxide-oxalic acid based polishing slurry and when using 0.2 wt% nonylphenol ethoxylate or 0.8 wt% OP-10 emulsifier as the surfactant of the of ferric chloride-oxalic acid based polishing slurry. The results of this study can provide a reference for further research on the chemical mechanical polishing of stainless steel.

Abstract: In this paper, the wear resistance of the different parameter (the tool rotation speed and feed speed) modified layer of the hot rolled 7075 aluminum alloy by the friction stir processing (FSP) were studied. The wear mechanism was explored by analyzing the surface morphologies of the modified layer after wear. The results showed that the wear resistance of 7075 aluminum alloy modified by FSP was superior to that of the base metal at different temperatures. The comprehensive wear resistance was better when the tool rotation speed and the feed speed were 500 rpm and 60 mm/min under different temperatures. Furthermore, the FSP parameters had a significant influence on the wear resistance of the modified layer. When the FSP parameters were too high or too low, the wear resistance would be reduced and the adhesive wear would appear. In addition, the modified layers obtained by different parameters received poor wear resistance when the temperature at high values.

Abstract: The depth of surface/subsurface damage layer is the key index of surface quality of sapphire. In this paper, that depth model of the surface/subsurface damage lay characterized by the crack length was established according to the mechanical theory of indentation fracture. The cutting relation between abrasive and workpiece and the difference of the depth of subsurface damage crack are analyzed. It is preliminarily estimated that the length of sub-surface damage crack of free abrasive sapphire is about 2.46 times that of fixed abrasive when considering only the contact hardness of abrasive grain under static load. Diamond abrasives with size of W20 were adopted to carry out experiments in free and fixed lapping methods. The results show that the surface/subsurface damage depth is 9.87μm and 3.63μm respectively. It is easier to obtain good sub-surface quality by using the fixed abrasive method than free abrasive at the same particle size.

Abstract: The oil soluble modified montmorillonite (MMT)/indium (In) composite nanoscale powders were prepared into four disperse systems by adding 1%, 2%, 3% and 4% to the base oil respectively. The friction properties of the 45 steel samples were tested by MMU-10G friction and wear testing machine, and the surface composition of the samples was analyzed by SEM and EDX. The mechanism that affects the tribological properties is compared and analyzed. The results show that the wear weight loss of the sample added with MMT/In nano powder is smaller than that in the base oil, and the average friction factor of the sample with 3% additions is 43.14% ,lower than that of the base oil, and the total wear is negative weightlessness.EDX analysis showed that the surface of the friction specimen was composed of Mg, Al and In repair membranes. The main mechanism of anti friction and friction reduction is that the composite powder will form a repair film on the surface of the friction pair during the friction process, and the repair layer can reduce the friction, compensate for the wear and play the role of resisting wear and reducing the effect of friction. With the increase of adding amount, the repair layer is gradually improved and the tribological performance is enhanced. But if the amount of addition is too high, the micro cutting and furrow effect of a large number of hard particles on the matrix and the new film will be greater than the compensation effect of the repair film, making the antiwear and antifriction properties decrease.

Abstract: In this paper, the tribological property of polyimide (PI) resin was improved by adding poly-p-phenylenebenzobisoxazole (PBO) fibers. The effects of PBO fiber volume fraction were studied by mechanics and tribology tests. The fracture and wear surfaces of PBO/PI composites were investigated by using scanning electron microscopy (SEM). The measurement showed that the flexural properties of composites reinforced by 10 vol% PBO fibers were lower than pure PI resin. With the increase of PBO fiber content, the flexural strength was first increase and then decrease. The frictional coefficient and wear rate of the PBO/PI composites varied with the variety of fiber content, and the optimum parameter was obtained at 20 vol%. The dominant wear mechanism and friction process were discussed on the basis of microscopic morphology analysis of wear surface of PBO/PI composite and the counterpart.