基于SLM的18Ni-300模具钢工艺参数优化

设计了以激光功率、扫描速度、扫描间距、铺粉厚度为因素的正交实验,研究了SLM 成型18Ni-300 模具钢粉末过程中各个工艺参数对成型件致密度的影响规律,并进行了工艺参数优化。实验表明,在选定范围内,成型件致密度随激光功率的增加先增大后减小?随扫描速度的增加持续减小?随扫描间距的增加先增加后减小?随铺粉厚度的增加持续减小。最优工艺参数组为激光功率260 W、扫描速度500 mm/ s、扫描间距0.11 mm、铺粉厚度0.02 mm 时,成型件致密度99.99%,为所有实验中的最优值。     

In-situ investigation of melting characteristics of waste selective catalytic reduction catalysts during harmless melting treatment

Selective catalytic reduction(SCR) catalyst waste is a hazardous solid waste that seriously threatens the environment and public health.In this study,a thermal melting technology is proposed for the treatment of waste SCR catalysts.The melting characteristics and mineral phase transformation of waste SCR catalysts blended with three different groups of additives were explored by heating stage microscopy,thermogravimetric analysis/differential scanning calorimetry(TG/DSC) analysis,thermodynamic simulation,and X-ray diffraction(XRD) analysis;heavy metal leaching toxicity was tested by inductively coupled plasma-atomic emission spectrometry(I CP-AES) analysis.The results indicated that the melting point of waste SCR catalysts can be effectively reduced with proper additives.The additive formula of 39.00% Fe_2 O_3(in weight),6.50% CaO,3.30% SiO_2,and 1.20% Al_2 O_3 achieves the optimal fluxing behavior,significantly decreasing the initial melting temperature from 1223℃ to1169℃.Furthermore,the whole heating process of waste SCR catalysts can be divided into three stages:the solid reaction stage,the sintering stage,and the primary melting stage.The leaching concentrations of V,As,Pb,and Se are significantly reduced,from 10.64,1.054,0.195,and 0.347 mg/L to 0.178,0.025,0.048,and 0.003 mg/L,respectively,much lower than the standard limits after melting treatment,showing the strong immobilization capacity of optimal additives for heavy metals in waste SCR catalysts.The results demonstrate the feasibility of harmless melting treatments for waste SCR catalysts with relatively low energy consumption,providing theoretical support for a novel method of disposing of hazardous waste SCR catalysts.     

Wear performance of metal parts fabricated by selective laser melting: a literature review

Selective laser melting (SLM) is one type of additive manufacturing which produces metal parts by powder bed fusion. Since the materials undergo repeated and sharp heating/cooling cycles, the SLMed parts have unique microstructures. The relations among SLM processing parameters, resultant microstructures, and mechanical properties have been investigated by many researchers. However, the wear performance of SLMed materials under various contact conditions has not been carried out until recently. This paper is a presentation of previous and recent research related to wear performance. This is a crucial aspect if SLM is to be expanded to produce friction pairs. Wear rates and mechanisms of the SLMed materials under dry, boundary lubrication, cavitation erosion, and corrosion conditions are discussed and compared with conventionally processed (CP) materials. SLMed materials benefit from fine grains and high hardness, which have higher wear resistance than CP materials. Moreover, a unique tribo-layer on the surface of the SLMed part is found to protect the bulk material under boundary lubrication conditions. An optimized combination of processing parameters increases part density, which further improves the wear resistance. Future work includes studying the influence of pores on the deforming and lubricating behaviors from dry conditions to different lubrication regimes. The final target is to actively control the processing parameters to obtain desirable material properties for improving wear performance.     

循环剪切对岩石节理形貌与力学行为影响实验研究

为研究岩石节理在循环剪切作用下的物理力学特性变化规律,对节理试件进行了不同法向荷载下的循环剪切试验,并对节理表面形貌进行了测量研究。结果表明:随着循环剪切次数的增加,节理表面最高点与最低点之间的垂直距离迅速减小,试件所施加的法向荷载越大则会增加节理表面形貌的劣化程度,节理表面的劣化主要发生在第1次剪切过程。节理峰值抗剪强度与残余强度均随剪切次数增加而减小,第2次剪切以后节理剪切曲线峰值点消失,峰值抗剪强度几乎与残余抗剪强度相等。同时,随着形貌特征的劣化,节理剪胀随着剪切次数的增加而减小。     

Influence of polarized bias and porous silicon morphology on the electrical behavior of Au-porous silicon contacts

INTRODUCTION Porous silicon (PS) attracts the attention of many researchers due to the possibility of developing PS based devices, including optoelectronics, photo re- sistors, solar cells and light emitting diodes (Balucani et al., 1999; Palma et al., 1999a; Stievenard and Deresmes, 1995). To integrate PS into electronic circuits or to develop PS based devices, the electrical properties of this material must be studied thoroughly. It is a difficult case because this material has a ve…     

衬底温度对金刚石膜选择性沉积的影响

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Influence of ash composition on the sintering behavior during pressurized combustion and gasification process

To determine the ash characteristics during fluidized bed combustion and gasification purposes, the investigation of the impacts of chemical composition of Jincheng coal ash on the sintering temperature was conducted. A series of experiments on the sintering behavior at 0.5 MPa was performed using the pressurized pressure-drop technique in the combustion and gasification atmospheres. Meanwhile, the mineral transformations of sintered ash pellets were observed using X-ray diffractometer (XRD) analyzer to better understand the experimental results. In addition, quantitative XRD and field emission scanning electron microscope/energy dispersive X-ray spectrometer (FE-SEM/EDS) analyses of ash samples were used for clarifying the detailed ash melting mechanism. These results show that the addition of Fe₂O₃ can obviously reduce the sintering temperatures under gasification atmospheres, and only affect a little the sintering temperature under combustion atmosphere. This may be due to the presence of iron-bearing minerals, which will react with other ash compositions to produce low-melting-point eutectics. The FE-SEM/EDS analyses of ash samples with Fe₂O₃ additive show consistent results with the XRD measurements. The CaO and Na₂O can reduce the sintering temperatures under both the combustion and gasification atmospheres. This can be also contributed to the formation of low-melting-point eutectics, decreasing the sintering temperature. Moreover, the fluxing minerals, such as magnetite, anhydrite, muscovite, albite and nepheline, contribute mostly to the reduction of the sintering temperature while the feldspar minerals, such as anorthite, gehlenite and sanidine, can react with other minerals to produce low-melting-point eutectics, and thereby reduce the sintering temperatures.     

镧对A356铝合金组织的影响

对比研究了添加不同添加量镧处理后A356铝合金的组织变化．结果表明：镧对A356铝合全晶粒细化效果不明显,但对二次枝晶间距有一定影响,当添加量达到0．35％时使合金的二次枝晶间距减小至17．41um．镧对A356铝合金的变质作用比较明显,当镧添加量≥0．05％时,硅颗粒呈部分变质形态．镧对合金中气孔影响很大,合金微观组织中气孔很少．     

Microencapsulation of immunoglobulin Y: optimization with response surface morphology and controlled release during simulated gastrointestinal digestion

Journal of Zhejiang University-SCIENCE B - Immunoglobulin Y (IgY) is an effective orally administered antibody used to protect against various intestinal pathogens, but which cannot tolerate the...     

激光处理对切口棒料疲劳性能的影响

疲劳断料是一种新的分离材料方法 .通过对棒料进行切口并施加旋弯载荷 ,可人为制造疲劳 .为了进一步提高断裂的效率 ,采用激光对棒料切口的根部进行了处理 ,处理后的棒料疲劳周次大大降低 .通过分析实验结果得到 :棒料的疲劳受硬化区形状影响 ,具有较小轴向尺寸和较大径向尺寸的硬化区会促进疲劳 .硬化区的形状可以通过调整激光处理参数来控制 .     

Al-Si合金第二相形貌变化及其对断裂行为的影响

用光学显微镜和扫描电镜(SEM)观察Al-Si合金中硅相形貌在固溶过程中的变化, 并研究了此变化对合金力学性能和断裂行为的影响. 结果表明: 固溶初期 (250 min), 硅相发生缩颈、钝化、溶断并伴随长大; 在固溶中期(250～400 min), 其形貌没有发生显著变化, 仅球化程度更高; 600 min后, 硅相的长大是受扩散控制的粗化过程, 且符合LSW粗化模型; 同时由于出现棱角小面及搭接特征使硅相形貌有所恶化. 定量金相测量及回归分析说明硅相的形貌对合金的力学性能和断裂行为有显著影响.     

金膜表面光栅制备中飞秒激光参数的影响

为了研究飞秒激光参数对制备金膜表面光栅的影响, 设计搭建了飞秒激光干涉微加工实验装置, 经衍射光栅得到的两束相干光在金膜表面诱导出微光栅.借助原子力显微镜研究在不同的脉冲能量密度、脉冲个数、波长等条件下制备的光栅形貌, 测得光栅的周期和线宽.研究发现, 飞秒激光参数对光栅形貌的影响显著, 制备光栅的最佳波长为800 n...     

Influence of surface roughness on the color of dental-resin composites

This study deals with the influence of surface roughness on the color of resin composites. Ten resin composites (microfilled, hybrid, and microhybrid) were each polished with 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers. The roughness parameter (R _a) was measured using a Plμ confocal microscope, and field-emission scanning electron microscope (Fe-SEM) images were used to investigate filler morphology. Color was measured using a spectroradiometer and a D65 standard illuminant (geometry diffuse/0° specular component excluded (SCE) mode). Surface roughness decreased with grit number and was not influenced by filler size or size distribution. A significant influence of R _a on lightness (L*) was found. Lightness increased with decreases in roughness, except for specimens that underwent polishing procedure 4 (PP4; 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers consecutively). Generally, it was found that surface roughness influenced the color of resin composites. The composites that underwent PP1 (500-grit SiC paper) exhibited significant differences in chroma (C*), hue (h°), and lightness (L*) compared to composites that underwent PP3 (500-grit, 1 200-grit, and 2 000-grit SiC papers consecutively) and PP4. Color difference (ΔE*) between the polishing procedures was within acceptability thresholds in dentistry.     

柠檬酸还原法制备金溶胶中反应物配比和加料顺序的影响

为研究柠檬酸还原法制备金溶胶的反应过程中2种反应物柠檬酸钠和氯金酸的加料顺序和物质的量比对金溶胶的尺寸及其分布的影响规律,按照设定的物质的量的比值将一种反应物的浓溶液加入到另一反应物的沸腾的稀溶液中,继续煮沸10~15min均可以制备金溶胶。结果表明,将柠檬酸钠浓溶液加入氯金酸稀溶液中制备的金溶胶颗粒的尺寸较大,当柠檬酸钠和氯金酸的物质的量的比值为4~6时制备的粒径分布均一,直径为13.8~18.2nm;将氯金酸浓溶液加入柠檬酸钠稀溶液中制备的金溶胶颗粒的尺寸相对小,调整柠檬酸钠和氯金酸的物质的量的比值,尺寸在7.2~10.4nm调节,且尺寸分布更为均一。这2种加料顺序制备的金纳米颗粒均为多面体单晶结构,说明金纳米颗粒具有相似的生长过程,这种加料顺序对金溶胶尺寸及其分布的影响主要与氯金酸根和柠檬酸根的发生还原反应开始时金离子周围的pH环境有关。     

Influence of postpartum shock controllability on subsequent maternal behavior in rats

Responses of mother rats were observed 24 h before and 24 and 72 h after exposure to one of three 8-day postpartum treatments: shock escape training, yoked inescapable shock, or restrained with no shock. In contrast to those in the other two groups, the dams given inescapable shock showed slower speed to approach the nest, shorter durations of being on the nest, and lower frequency and shorter total duration of oral contact with their pups. These dams also retrieved their pups less frequently, but this measure, as well as the frequency of leaving the nest, did not result in significant differences between groups. Since the traditional interpretations of the learned-helplessness effect were not entirely able to account for these findings, the observed uncontrollable-stress-produced changes in maternal behavior were examined from an ethological perspective.     

粗糙表面对薄样品热传导的影响

在半经典输运理论的基础上分析了不同粗糙表面的薄样品热传导性质，比较了样品在不同方向上的热导率(热阻率)。     

短脉冲紫外激光辐照下硅材料表面剥离过程研究

利用紫外激光对硅材料进行加工时需要估算硅材料表面剥离深度、温度分布与入射光功率密度的关系。激光与硅材料相互作用涉及多种复杂的物理现象，直接利用现有理论进行计算，确定相应的温度分布和剥离深度十分困难。文章探讨了在不同功率密度范围内，根据激光与物质相互作用主要形式的不同，建立相应的估算方法。实践证明，在一定功率密度范围内，估算值较好地符合了实验测定数据。     

实际塑性铰链位置对延性框架行为的影响

研究目的：研究方法：通过有限元分析和极限分析,研究了在纵向和横向载荷下钢框架的最大负荷和坍塌模式,并考虑了塑性铰链住轴向力和弯曲力矩的作用下住实际旋转时的运动学。在垂直和水平方向载荷共存的情况下,基于轴向力和弯曲力矩的交互作用,研究延性框架的极限载荷和坍塌模式对产生于塑性铰链的真实运动学的敏感性。通过两个基本的案例和通过成功地评估非线性有限元分析和直接实施的极限分析步骤,并利用MATHEMATICA,揭示了其敏感性。 在标准规程的框架下,即使在最简单的案例中,极限分析的主要结果也会考虑在坍塌时的运动学,这与设计和加固的目的都是相关的。如果没有对所有的结构元件的轴向力和弯曲力矩的交互作用进行合理的计算,塑性铰链的定位计算可能得出不正确的坍塌机理和误导性的安全系数。就具体方面而言,本文清楚地表明,在设计新的结构或者为现有结构进行加固时,即使是使用看起来已经非常完备的经典步骤,也必须非常小心。本文的模型可以为处理规程设计的执业工程师和标准化委员会提供参考。     

Influence of family structure and school variables on behavior disorders of children

The purpose of this study was to examine the influence of family structure and school variables on behavior disorders of children. The sample consisted of 1,162 white elementary school children. General information was obtained from school records, and ratings on behavior disorders were obtained from teachers. Data were analyzed using multiple regression analyses of variance. Results indicated that grade in school, sex, social class, ordinal position in the family, and teacher were important variables in the determination of behavior disorders. Whether or not the children were living with both of their natural parents, number of children in the family, if the children were in special education classes, and whether the children were older than usual for their grade in school were less important or were unimportant. The results, especially those that were not expected, were discussed.     

浅部缩径缺陷对单桩竖向承载特性的影响

为了探究浅部缩径缺陷对单桩竖向极限承载力的影响规律,设计了包含1根完整桩和9根带有浅部缩径的缺陷桩在内的10组室内模型试验,并进行相应的有限元数值模拟,获得了10根桩的桩顶荷载-沉降曲线。结果表明:在单桩浅部含有缩径长度不大于完整桩桩长的10%且缩径处桩径不小于完整桩桩径的80%时,或者单桩含有缩径长度不大于完整桩桩长的2.5%时,浅部缩径对单桩竖向极限承载力基本无影响;当单桩含有的缩径长度为完整桩桩长的2.5%～10%,且缩径处桩径小于完整桩桩径的80%时,单桩竖向极限承载力降低约20%;在未达到单桩竖向极限承载力之前,所有单桩桩顶荷载-沉降曲线呈线性变化;达到单桩竖向极限承载力之后,含有较大程度浅部缩径缺陷桩的曲线斜率较完整桩偏大。