Yanwei Sui

Influence of Brazing Technology on the Microstructure and Properties of YG20C cemented carbide and 16Mn steel joints

Cu-Mn-Zn brazing filler metal was used to study the vacuum brazing of YG20C cemented carbide and 16Mn steel. Then the effects of brazing temperature on the structural properties and element distribution at joints were explored separately through scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and three-point bending test. The results showed that Cu-Mn-Zn brazing filler metal can efficiently wet both YG20C cemented carbide and 16Mn steel. The bending strength of the seam was maximum at the temperature of 960 °C and at the brazing filler metal thickness of 0.2 mm.

Co3O4 nanocrystals derived from a zeolitic imidazolate framework on Ni foam as high-performance supercapacitor electrode material

A binder-free method was adopted to obtain a Ni foam/Co3O4 electrode. The Co3O4 nanocrystals with an average size of 15–25 nm deliver a high specific capacitance of 1680 F g−1 at a current density of 0.5 A g−1 in 1.0 M KOH electrolyte. Of particular note, the electrode exhibits a high capacitance retention rate of 58.3% at a current density of 15 A g−1 with excellent electrochemical stability (15.9% specific capacitance loss after cycling 1000 times) even at high current density (5 A g−1), suggesting its promising application as a high-performance supercapacitor electrode material.

Multilayer hexagonal silicon forming in slit nanopore

The solidification of two-dimensional liquid silicon confined to a slit nanopore has been studied using molecular dynamics simulations. The results clearly show that the system undergoes an obvious transition from liquid to multilayer hexagonal film with the decrease of temperature, accompanied by dramatic change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the cooling process, some hexagonal islands randomly appear in the liquid first, then grow up to grain nuclei, and finally connect together to form a complete polycrystalline film. Moreover, it is found that the quenching rate and slit size are of vital importance to the freezing structure of silicon film. The results also indicate that the slit nanopore induces the layering of liquid silicon, which further induces the slit size dependent solidification behavior of silicon film with different electrical properties.

An Asymmetric Supercapacitor Based on Activated Porous Carbon Derived from Walnut Shells and NiCo2O4 Nanoneedle Arrays Electrodes

A facile method was utilized to convert a common biomass of walnut shells into activated porous carbon by carbonization and activation with nitricacid treatment. The obtained activated carbon (WSs-2) exhibited excellent electrochemical performance with high specific capacitance of 137 F · g-1 at 1 A · g-1 and super cycling performance of 96% capacitance retention at 5 A · g-1 after 5000 cycles. In addition, NiCo2O4 nanoneedle arrays with good electrochemical properties were successfully prepared by a simple hydrothermal method. An aqueous asymmetric supercapacitor (ASC) device based on WSs-2 and NiCo2O4 was assembled, which delivered 21 Wh · kg-1 at a power density of 424.5 W · kg-1, and maintained 19 Wh · kg-1 at power density of 4254 W · kg-1 as well as excellent cycling stability of 99.3% capacitance retention after 5000 cycles at 4 A · g-1. Through this method, low-cost, environmentally friendly and large-scale carbon materials can be fabricated and applied in supercapacitor electrodes.

Effects of pouring temperature on interfacial reaction between Ti-47.5Al-2.5V-1Cr alloy and mold during centrifugal casting

Pouring temperature and time are the most important influencing factors on interfacial reaction during the centrifugal casting. When cast at high temperatures, the crucible becomes brittle and prone to cracking, and shows a low stability. In this paper, we studied the centrifugal casting of Ti-47.5-Al-2.5V-1Cr alloy, and explored the effects of pouring temperature on the interfacial reaction. Castings at 1 600, 1 650, and 1 700 °C were obtained by controlling the other parameters constant in the experiments. The microstructure, elemental distribution, thickness of the reaction layer and phase composition of the castings at the interface were studied. The results show that the thickness at the interfacial reaction layer is increased by raising the pouring temperature. The elements in the mold and the matrix were double-diffused and reacted at the interface during the casting process, and formed solid solutions with the precipitation of many new phases such as Al2O3 and TiO2. The roughness of interface structure and layer thickness of reaction increase with the rise of temperature, and the interfacial reaction is more intense. There is a minimum layer thickness of the reaction layer that is 80 μm when the temperature is 1 600 °C.

Novel corn cob-like Fe3O4@Ni3S2 as high-performance electrode for supercapacitors

Corn cob-like Fe3O4@Ni3S2 nanocomposites was synthesized through a facile two-step hydrothermal process. The precursor was obtained by a facile calcination of a Fe-MOF template, then, nickel sulfide coated on iron oxide composites were synthesized using a hydrothermal method. In addition, the fabricated Fe3O4@Ni3S2 electrode revealed a great electrical performances with a maximum specific capacitance of 1200Fg−1 at 1Ag−1, a capacitance retention of 83% could be observed after 1000 cycles at a great charge–discharge current density of 5Ag−1. We believed that the excellent performance might be ascribed to the synergistic effect between the Fe3O4and Ni3S2. Thus, the results demonstrate the corn cob-like Fe3O4@Ni3S2 composite is prominent candidate in the field of supercapacitor applications.

Microstructure and friction performance of copper film fabricated by ion implantation assisted electroless plating on PTFE

Abstract The polytetrafluoroethylene (PTFE), which was implanted with Ni ion to different energy and doses, fabricated metallic structures by selective electroless copper plating. The characteristic and microstructure of the copper film were studied using SEM and X-ray diffraction. Friction performance of the interface between copper film and basal body of PTFE was tested with a CETR UMT-2 (CETR Co., Campbell, CA, USA) multifunction micromechanics instrument. The test loads were 10, 20 and 40 N, while the line velocity was 8 mm s−1, and the frequency of data acquisition was 1 Hz. The Ni ion implantation replaces the complicated electroless plating surface pretreatment, and it is an assisted technique of electroless plating of copper on the surface of PTFE and plate Cu directly on its surface. Continuous, prepressing and uniformity plating was obtained with proper technique parameters and the dosage of Ni+. The frictional performance comprehensive property of copper film was remarkably influenced by different plating methods, annealing treatment and testing loads under unlubricated condition. The friction coefficients and wear rates changed with the varied load. Annealing treatment improves the tightness and uniformity of the copper film, while it decreases its cavity. Friction performance of copper film was thus increased. The mechanisms of friction and wear of copper film under different test conditions are also discussed.

Dandelion-like nickel/cobalt metal-organic framework based electrode materials for high performance supercapacitors

Metal-organic frameworks (MOFs), serving as a promising electrode material in the supercapacitors, have attracted tremendous interests in recent years. Here, through modifying the molar ratio of the Ni2+ and Co2+, we have successfully fabricated Ni-MOF and Ni/Co-MOF by a facile hydrothermal method. The Ni/Co-MOF with a dandelion-like hollow structure shows an excellent specific capacitance of 758 F g-1 at 1 A g-1 in the three-electrode system. Comparing with Ni-MOF, the obtained Ni/Co-MOF has a better rate capacitance (89% retention at 10 A g-1) and cycling life (75% retention after 5000 circulations). Besides, the assembled asymmetric supercapacitor based on Ni/Co-MOF and active carbon exhibits a high specific energy density of 20.9 W h kg-1 at the power density of 800 W kg-1. All these results demonstrate that the mixed-metal strategy is an effective way to optimize the morphology and improve the electrochemical property of the MOFs.

Wear behavior of in-situ TiC particles reinforced aluminum matrix composite

The microstructure, tensile property and wear resistance of 7075 aluminum matrix composite reinforced with TiC particles prepared by in-situ reaction casting were investigated. The effect of TiC reinforcement on wear behavior was analyzed. The wear mechanism was also discussed. A micro-mechanism model of reaction kinetics for synthesis of TiC was acquired. Results show that TiC could increase the tensile and yield strength, but decrease the elongation. Besides, TiC particles improve the property of wear resistance of 7075 aluminum alloy. The wear mechanisms include abrasive wear and adhesive wear in wear test process.