拼焊板盒形件充液拉深的数值模拟

随着汽车行业对能源消耗和汽车尾气排放的要求,应用拼焊板成形技术显得越来越重要.以差厚拼焊板拉深方盒件为研究对象,采用板料成形分析软件DYNAFORM对充液拉深和传统拉深工艺进行分析和对比.研究发现,盒形件不同部位其焊缝有不同的移动趋势,传统拉深最大焊缝移动量发生在盒形件底部中心处,充液拉深件焊缝移动最大量发生在侧壁顶部,增大充液拉深凹模油腔的压力,可以有效地减少焊缝移动量和坯料的减簿量.     

甲基丙烯酸乙酯的"活性"/可控阴离子聚合

采用空间位阻大的引发剂1,1-二苯基己基锂(DPHLi),添加新型络合剂LiClO4,在-5℃,实现了活性阴离子聚合反应,获得分子量分布为1.05的单分散聚甲基丙烯酸乙酯(PEMA)。     

The effect of powders homogenisation conditions on the synthesis of yttrium aluminium garnet (YAG) by a solid-state reaction

The work presents results of research on the influence of the state of homogenisation of reagent powders i.e. aluminium oxide and yttrium oxide on the synthesis of yttrium aluminium garnet. Fine powders of commercial aluminium oxide and yttrium oxide were mixed in the same manner in a laboratory ball mill but under four different conditions. Three batches of powders were prepared in water of various pH values, selected on the basis of the zeta potential measurements, and one batch was prepared in propanol. They were consolidated by filter pressing and then sintered in air at a temperature from 900 °C to 1700 °C for 1 h, with heating rate of 5 °C/min. Samples were subjected to dilatometric studies, phase composition determination, measurement of apparent density and pore size distribution, as well as a microscopic examination. Mixing environment affected, to a given extent, almost all the features of green, and partially sintered materials as well as course changes of linear dimensions. As a result, the relative densities of samples sintered at a maximum temperature ranged from 58.31% to 98.25%. The highest density was achieved for the material originating from the suspension having a pH of 9.5, in which heterocoagulation occurred.     

Band gap engineering by substitution of S by Se in nanostructured CdS1−xSex thin films grown by soft chemical route for photosensor application

Ternary alloys of CdS_1−xSe_x (x=0, x=0.2, x=0.4, x=0.6, x=0.8, x=1) thin films were prepared on to glass substrates by a simple and economical soft chemical route (chemical bath deposition) at 50° to 80 °C in air. The as-grown films were characterized by optical and electrical measurement systems, X-ray diffraction (XRD), Energy dispersive X-ray analysis (EDAX) and SEM (scanning electron microscopy). The optical study reveals shift in the absorption edge towards the higher wavelengths, i.e. the band gap decreases as a function of ‘x’ (quantity of selenium in the bath). I–V measurement of CdS (resulted when x=0), CdS_1−xSe_x (x=0.2, x=0.4, x=0.6, x=0.8) and CdSe (resulted when x=1) thin films under dark and illumination conditions (60 W) were measured. Increase in photoconductivity is observed, suggesting its applicability in photosensor devices. Electrical resistivity shows semiconducting behavior and activation energy decreases. The XRD patterns reveals that deposited thin films have hexagonal mixed structure. EDAX confirmed the compositional parameters. SEM images showed uniform deposition of the material over the entire glass substrate.     

Onset coarsening-coalescence kinetics of γ-type related Al2O3 nanoparticles: Implications to their assembly in a laser ablation process

An onset coarsening-coalescence event based on the incubation time of cylindrical mesopore formation and a significant decrease of specific surface area by 50% and 70% relative to the dry pressed samples was determined by N₂ adsorption–desorption hysteresis isotherm for two Al₂O₃ powders having 50 and 10 nm in diameter respectively on an average and with γ-type related structures, i.e. γ- and its distortion derivatives δ- and/or θ-types with {1 0 0}/{1 1 1} facets and twinning according to transmission electron microscopy. In the temperature range of 1100–1400 °C, both powders underwent onset coarsening-coalescence before reconstructive transformation to form the stable α-type. The apparent activation energy for such a rapid coarsening-coalescence event was estimated as 241 ± 18 and 119 ± 19 kJ/mol, for 50 and 10 nm-sized particles, respectively indicating easier surface diffusion and particle movement for the latter. The size dependence of surface relaxation and onset coarsening-coalescence of the γ-type related Al₂O₃ nanoparticles agrees with their recrystallization–repacking upon electron irradiation and accounts for their assembly into nano chain aggregates or a close packed manner under the radiant heating effect in a dynamic laser ablation process.     

Densification of transparent yttrium aluminum garnet (YAG) by SPS processing

Nano-size YAG powder co-mixed with 0.25 wt.% LiF was used to fabricate transparent polycrystalline YAG specimens by means of the Spark Plasma Sintering (SPS) technique. The presence of the LiF additive in the initial nano-powder allows obtaining fully dense disc shaped (up to 4 mm thick) transparent specimens at the outcome of a 2 h treatment at 1300 °C. The presence of LiF plays a key role in the mass transport related effects during the densification of YAG to full density and also in the elimination of the residual carbon contamination, allowing reaching a level of optical transmittance close to the theoretical value.     

Tape casting of strontium and cobalt doped lanthanum chromite suspensions

Lanthanum chromite (LaCrO₃) is currently the most widely studied material as interconnector layers for solid oxide fuel cells (SOFC). The complexity of microstructures and geometries of SOFC devices, which are usually built-up by lamination of the different constitutive layers, make it necessary a precise control of processing parameters to achieve the desired combination of properties. Much effort has been devoted to the processing of electrodes and electrolytes but the other layers, such as that of interconnecting material, have received scarce attention. This work deals with the preparation and optimisation of the rheological behaviour of concentrated suspensions of Sr- and Co-doped LaCrO₃ and the subsequent tape casting to produce homogeneous thin sheets to be used in the SOFC stack.The starting powder was produced by combustion synthesis from the corresponding nitrates and urea as a fuel, and had a final composition of La_0.80Sr_0.20Cr_0.92Co_0.08O₃. These powders were dispersed in ethanol with commercial copolymers (Hypermer, KD6) to solids loading of up to 58 wt%. The binding system (BS) consisted of a mixture of a binder, polyvinyl butyral-co-vinyl alcohol-co-vinyl acetate (PVA-PVAc), and two plasticizers, polyethyleneglycol (PEG400) and benzylbutylphthalate (BBP). The effect of the binding system content and the binder-to-plasticizer ratio on the tape casting performance and the characteristics of the green and the sintered tapes, were studied, as well as the influence of the casting parameters (casting speed and blades height).     

Strengthening mechanisms of a new 700 MPa hot rolled Ti-microalloyed steel produced by compact strip production

A new hot rolled titanium-microalloyed steel with yield strength of 700 MPa has been developed by CSP (compact strip production) process based on commercial weather resistant steel. EBSD results showed that the average size of its grains with high angle boundaries (>15°) was 3.3 μm. High-density dislocations and large number of nanometer particles were observed in the steel product by TEM. X-ray analysis on the electrolytically extracted phase from the steel indicated that fraction of MX phase was 0.0793 wt%, in which the particles smaller than 10 nm accounted for 33.7%. The contribution of precipitation hardening resulting from nanometer particles was calculated as approximate 158 MPa. The commercial weather resistant steel, reference steel for comparison with 450 MPa yield strength, was also prepared and investigated. It can be concluded that grain refinement is still a major strengthening mechanism in this high strength steel, but precipitation hardening of nanometer TiC precipitates is the dominant factor to increasing the yield strength in new developed steel compared with the reference steel.     

The dielectric properties of epoxy/AlN composites

In this paper, AlN ceramic powder is chosen to be mixed with epoxy to form epoxy/AlN composites, the effects of the content of AlN filler on the physical and dielectric properties of epoxy/AlN composites are developed. From the SEM observation, the particles of self-synthesized AlN powder, obtained by using combustion method, is less uniformity and the average particle size is about 3.12 μm. Only the AlN phase can be detected in the XRD patterns of the epoxy/AlN composites. The more AlN powder is mixed with epoxy, the higher crystal intensity of AlN phase will exist in the XRD patterns. As the content of AlN powder in the epoxy/AlN composites increases from 5 to 40 wt.%, the dielectric constant increases from 6.52 to 7.28 (measured at 1 MHz). The loss tangent of epoxy/AlN composites is slightly increased as the measured frequency increases. Moreover, the epoxy/AlN composites in this investigation show less pores as compared to other literatures. The results indicate that the fabrication process has an apparent effect on the decrease of porosities, and the composites with a low porosity will lead to a low loss tangent.