Materials Science Forum Vol. 1036

Abstract: The mechanical properties and microstructure of the A356-T6 wheel hub based on low pressure die casting-hot flow forming process were analyzed by means of optical microscopy (OM), scanning electron microscopy (SEM) and tensile tests. Results showed that the size of the eutectic region and the morphology of the Si phase were the main factors affecting the mechanical properties and fracture morphology of the wheel hub. There was a uniform distribution of eutectic area and fine Si phase morphology in the microstructure of the upper rim and lower rim, moreover, the ultimate tensile strength and yield strength of the upper rim reached 282.4MPa and 185.1MPa, respectively. The fractures were mainly composed of fine quasi-cleavage platform and dimple. The microstructure of the rim showed a long strip along the deformation direction and the eutectic structure and Si particles were uniformly distributed. Irregular polygonal eutectic regions and coarse rod-like Si particles were accumulating in the spoke, causing a serious decrease in mechanical properties, especially in the spoke center and spoke R angle.

Abstract: The effects of different tempering temperatures on the microstructure evolution and mechanical properties of the new low-alloy ultra-high-strength 45CrNiSiMnMoVA steel after quenching were investigated by mechanical property tests, SEM and TEM. The results show that a complex phase organization consisting of martensite/ lower bainite of the tested steel after treated at 920°C×1h+(320~380)°C×4h was obtained, and the partition interface of the lath martensite bundle became blurred from clear with the increase of tempering temperature; In the proposed tempering temperature range, the toughness of the alloy has become better while maintain the strength without decreasing basically, and when the tempering temperature is 350°C, the alloy has the optimal comprehensive mechanical properties of strength, plasticity and toughness together. The analysis concluded that the strong toughening of the tested steel was mainly attributed to the coupling effect of the alloying elements in the steel and the composite toughening of the nano-precipitated phases, among other aspects.

Abstract: Ti-Ni based shape memory alloys (SMAs) are of excellent shape memory effect, superelasticity and damping property. These properties of the alloys can be fully displayed only after proper heat treatment. In this paper, the research progresses of the effect of the heat treatment on the microstructure, phase composition, phase transformation behaviors and shape memory properties in Ti-Ni based SMAs are reviewed, the correlation influence mechanism is summarized, and the future research directions in this field are pointed out. It is expected to provide reference for the development of Ti-Ni based SMAs and their heat treatment technologies.

Abstract: Silicon-based anode materials have been widely discussed by researchers because of its high theoretical capacity, abundant resources and low working voltage platform,which has been considered to be the most promising anode materials for lithium-ion batteries. However,there are some problems existing in the silicon-based anode materials greatly limit its wide application: during the process of charge/discharge, the materials are prone to about 300% volume expansion, which will resultin huge stress-strain and crushing or collapse on the anods; in the process of lithium removal, there is some reaction between active material and current collector, which creat an increase in the thickness of the solid phase electrolytic layer(SEI film); during charging and discharging, with the increase of cycle times, cracks will appear on the surface of silicon-based anode materials, which will cause the batteries life to decline. In order to solve these problems, firstly, we summarize the design of porous structure of nanometer sized silicon-based materials and focus on the construction of three-dimensional structural silicon-based materials, which using natural biomass, nanoporous carbon and metal organic framework as structural template. The three-dimensional structure not only increases the channel of lithium-ion intercalation and the rate of ion intercalation, but also makes the structure more stable than one-dimensional or two-dimensional. Secondly, the Si/C composite, SiOx composite and alloying treatment can improve the volume expansion effection, increase the rate of lithium-ion deblocking and optimize the electrochemical performance of the material. The composite materials are usually coated with elastic conductive materials on the surface to reduce the stress, increase the conductivity and improve the electrochemical performance. Finally, the future research direction of silicon-based anode materials is prospected.

Abstract: X-ray diffractometer, field emission scanning electron microscope (SEM, Hitachi S-4800), laser confocal micro-region Raman spectrometer and vibration sample magnetometer were used to systematically study the effects of polyethyleneimine concentrations and exposure time on the morphology and size of ZnO nanowire arrays. The photoelectric property and the relationship between the morphology of nanowire arrays and ferromagnetism at room temperature were also analyzed. Under 15 min exposure time, when the polyethyleneimine concentration is 2.25 g / L, the obtained ZnO nanowire array film exhibits the smallest size, the optimal density and vertical orientation. According to the study of luminescence and room temperature magnetism, it is shown that the optical and ferromagnetic property are related to the variation tendency of oxygen defects and surface defects of the ZnO nanowires.

Abstract: LED healthy light source by using a blue LED chip to excite phosphor was prepared successfully. Four kinds of LED commercial phosphors (cyan phosphor with a peak wavelength of 498 nm, green phosphor with 520 nm, yellow-green phosphor with 546 nm, and red phosphor with 628 nm) were selected that could be excited by blue light. A series of experimental studies were carried out on the different amounts of glue, different powder-glue ratio, different combinations of phosphors, and the influence of different driving currents. Trough the optimization of the experimental scheme, we obtained a LED healthy light source spectrum with luminous efficiency higher than 124 lm/w, color rendering index higher than 80, color temperature around 4000 k. These spectra are in good agreement with the full spectrum of sunlight, and the spectral continuity and uniformity are better, which accord with the requirements of bright (dark) vision, and the proportion of the blue spectrum is less than 2.4%, which meets the high quality and healthy lighting requirements of safety and comfort.

Abstract: With the development of flexible optoelectronic devices, transparent conductive films (TCFs) based on nanowires provide wide concern. The low preparation cost and high-efficiency assembly characteristics make them occupy a very important position in scientific research and industrial application. In practical applications, TCFs in optoelectronic devices often do not need to cover the whole device, but only need to be prepared in part areas. At this time, patterned TCFs need to be prepared. In this paper, four kinds of patterning methods of TCFs are introduced, and the advantages and disadvantages of each method are analyzed.

Abstract: Since the performance of silver metal oxide (Ag/MeO) electrical contact materials directly affects the reliability and service life of switching apparatus, the related research on high-performance Ag/MeO electrical contact materials has not stopped. And with the rapid development of switching apparatus, higher and higher requirements are put forward for the performance of Ag/MeO electrical contact materials. Thanks to low and stable contact resistance, short arc burning time, good resistance to high current impulse (3000-5000 A) and good anti-arc erosion, silver zinc oxide (Ag/ZnO) more than just serves as an indispensable environmentally friendly alternative to silver cadmium oxide (Ag/CdO) electrical contact material, and has become one of the important research hotspots of Ag/MeO in recent years. Nevertheless, Ag/ZnO is suffering the increasingly serious challenges, especially the poor processability and electrical properties due to the easy segregation of zinc oxide (ZnO) during the process of preparation, which urge scholars at home and abroad to seek favorable methods to optimize the Ag/ZnO. As yet, impressive strides have been made in optimization the preparation process, nano-technology and additive modification of materials, and research on the failure mechanism of materials. Aiming to provide reference for optimizing Ag/ZnO electrical contact material, this review retrospects the research progress in Ag/ZnO electrical contact materials in recent years, and expounds the preparation methods, processing technology, modification research and failure mechanism of Ag/ZnO, and points out the future development directions of Ag/ZnO.

Abstract: Graphene coating is a new type of coating made by using the unique structural properties of graphene. It has broad application prospects of anticorrosive coatings, conductive coatings and heat-dissipating coatings. In order to study the development of graphene coating technology research, we use CiteSpace information visualization software, based on the literature of 8 813 articles in the research and application of graphene coatings in Web of Science database from 2010 to 2018. From the perspective of literature measurement, we apply the knowledge map to research the national, discipline and related hotspot analysis of graphene coating research, cited literatures and research frontier status. By comparing and analyzing the literature information on the field of graphene coating research and application at home and abroad, the research progresses and development trend of graphene coatings can be evaluated from the disciplinary distribution and research fronts. It is pointed out that the wear resistance of graphene coatings is the focus of the future research.