查看更多>>摘要：In this study, the effects of AlxCoCrFeNiCu high entropy alloy (HEA) binder on the phase composition, microstructure, hardness, fracture toughness and abrasion resistance of Ti(C, N) cermets prepared by powder metallurgy method were investigated by X-ray diffraction, scanning electron microscopy, mechanical properties and abrasion test. The results showed that the sintered Ti(C, N) cermets exhibit homogeneous core-shell microstructure at 1500 degrees C when HEAs with 0.2 at% aluminum were added. The Vickers hardness and fracture toughness of cermet with Al0.2CoCrFeNiCu could reach the peak value of 2235 Kg/mm(2) and 10.51 MPa *m1/2 and the fracture morphology showed mixture fracture. The Ti(C, N) cermets with HEA binder exhibited good friction and wear properties.
查看更多>>摘要：This study is focused on obtaining a comprehensive understanding of the influence of geometry - size and shape - on the indentation response of a large set of piezoelectric small-volume structures such as nanoislands, nanowires and thin films. Using three-dimensional finite element modeling, the complex interplay between the properties of the indented materials and the indentation response of piezoelectric micro- and nanostructures is analyzed. It is demonstrated that: (i) In general, the indentation response of thin film structures tends to be much stiffer than that of the piezoelectric nanoisland and nanowires, resulting in more charges being generated during the indentation of the thin-film structures. (ii) The indentation of the piezoelectric nanowire structures with a spherical indenter whose radius is substantially larger than the width of the nanowires, introduces a combination of deformation modes - structural bulging and indentation-induced compression. The combined effect of two deformation modes produces a maximum in the charges generated during the indentation process on a nanowire structure with a particular aspect ratio (i.e., wire width/wire height), which is greater than that produced in nanoisland and thin films structures with the same characteristic size.
查看更多>>摘要：alpha-Si3N4 nanowires were formed by a simple chemical vapor deposition (CVD) method using Si and SiO2 as raw materials without the addition of metal catalyst. The effect of reaction temperature on the phase composition and morphologies of the nanowires were analyzed by XRD and SEM. The experimental results indicate that a suitable reaction temperature is essential for the final products. At 1400 degrees C, small amount of target products were obtained, and some irregular particles were attached on the surfaces of nanowires. When the temperature increased to 1450 degrees C, the nanowires were mainly composed of alpha-Si3N4 phase, they had smooth surfaces with diameters fluctuating from 50 to 200 nm and lengths from hundreds to thousands of microns. At further high reaction temperature (1500 degrees C), beta-Si3N4 phase was observed and the nanowires had larger diameters, this was negative for obtaining purity alpha-Si3N4 nanowires. The growth process of alpha-Si3N4 nanowires was dominantly governed by the vapor-solid mechanism.
查看更多>>摘要：We prepared aluminum-silicon-rare earth (Al-Si-Re) elements alloys for electrical contact applications. Three Si weight percentages (wt.%) - 10%, 20% and 30% - were used, and rare earth (Re) elements were kept at 0.35 wt.%. The spraying forming process was adopted, and high-pressure hot isostatic pressing (HIP) was conducted to obtain the bulk materials from the as-deposited billets. The electrical conductivity of alloys with 10% and 20% Si reached 40% International Annealed Copper Standard (IACS). The hardness of Al-Si alloys significantly increased with Si content and HIP processing times. The hardness of alloy with 30% Si reached similar to 90 HV. Meanwhile, HIP reduced weight loss in the wear resistance by reducing the microcracks and materials removal. The current study proposes an approach to manufacture Al-Si alloys with high electrical conductivity and high wear resistance.
查看更多>>摘要：The effects of polishing pressure, polishing speed and pH value of the polishing slurry on the chemical activity of quartz glass, the material removal rate (MRR) and surface roughness (Ra) of the workpiece were studied. Using MRR and Ra as evaluation indexes, three factors and four levels of the orthogonal test were used to perform chemical mechanical polishing on quartz glass. By measuring the contact angle between the polishing slurry and workpiece, the influence of different polishing slurries on the chemical activity of quartz glass surface was studied. The processing mechanism of CMP quartz glass was analyzed. The order of important factors affecting MRR of quartz glass was: pressure > rotation speed > pH value; the order of significant factors affecting Ra of quartz glass was: pressure > pH value > rotation speed. The optimum polishing process parameter combination of the MRR was: pressure 27.58 kPa, rotation speed 85 rpm, pH value 12; the optimum polishing process parameter combination of the Ra was: pressure 13.79 kPa, rotation speed 85 rpm, pH value 12. The MRR and Ra of the workpiece are evaluated from the mechanical action of pressure and speed and the chemical action of polishing slurry on the workpiece. The results proved that the effect of the alkaline polishing solution on MRR and Ra of quartz glass is more significant than that of the acidic polishing slurry.
查看更多>>摘要：The SiC single-crystal substrate with ultrasmooth and damage-free properties has potential applications in the field of optoelectronics and microelectronics. Lapping is one of the important processes for ultraprecision machining of the SiC single-crystal substrate. The lapping quality has an important impact on the surface quality, processing time, processing cost and processing efficiency of the subsequent chemical mechanical polishing (CMP) of the SiC single-crystal substrate. In this paper, four kinds of lapping pastes with different ingredients were prepared. The tribochemical action and mechanism of the oxidant in the lapping paste were studied. The results show that NaOH can be used as an oxidant for the tribochemical mechanical lapping of the SiC single crystal. Under the catalysis of iron oxide and frictional force, the tribochemical reaction between the SiC single-crystal substrate and the oxidant NaOH occurred and the silicon oxides (such as SiO2), gaseous carbon oxides and other reactants were produced. The surface energy of the SiC substrate was reduced and the material removal rate was improved effectively. These results can provide a reference for further research on the mechanism of tribochemical mechanical lapping.
查看更多>>摘要：In this study, the problems of the low deposition rate and bath instability in chemical deposition can be effectively solved by using the pulsed current-assisted chemical deposition process when preparing Ni-P alloy coating. Orthogonal experiments were designed by changing the average current density, pulse frequency and duty ratio of the pulses to study their effects on the deposition rate and hardness of the coatings. Compact Ni-P coating with uniform surface morphology and good performance was prepared by parameter optimization. The results show that our method can greatly improve the deposition rate while ensuring the surface quality and performance of the deposited layer.
查看更多>>摘要：In this research, four titanium-doped zinc oxide (TZO) thin films were deposited on quartz glass substrates by radio frequency (RF) magnetron sputtering. Three of the samples were annealed at 400 degrees C for 40 mins in N-2, Ar and vacuum, respectively. The microstructure and photoelectric properties of the films were characterized. The results showed that annealing in different atmospheres has a significant effect on the microstructure and photoelectric properties. The structure of all the annealed films remained polycrystalline, with a c-axis preferred orientation, and the crystallization quality was improved. In addition, the photoelectric properties were also significantly improved by annealing with the average transmittance in the visible region exceeding 90%, the resistivity reaching 3.32 x 10(-4)Omega.cm. The conductivity enhancement was mainly attributed to the increased mobility of carriers. Annealing in argon had the best effect. Finally, the resistivity of all the samples experienced an initial negligible change followed by an increase as the temperature was raised from 10 to 350 K.
查看更多>>摘要：Corrosion resistance is of practical importance for the application of 2205 duplex steels in chemical industries. For taking an insight into pitting corrosion behavior, electrolysis was employed to distinguish the 2205 duplex steel samples. In the following, X-ray diffraction, scanning electron microscopy and electron backscattering diffraction are used to characterize the regions with superior and inferior corrosion performance, thus constructing the relationship between the microstructure and their corrosion behavior.
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