碳钢凝固过程中δ相横断面形状变化的研究

以Fe-0.15%C-0.8%Mn钢为研究对象,用激光共聚焦扫描显微镜原位观察了凝固过程中δ相的生长过程,并对δ相横断面形状的变化规律进行了研究。结果表明,在平均冷却速度为2℃·min-1的条件下,Fe-0.15%C-0.8%Mn合金凝固结束后δ相形成典型的蜂窝状组织。δ相径向生长时其半径随时间的变化规律不受周围钢液碳含量和过冷度的影响,均为开始时快速增大,而后增大幅度变慢。对于同一个δ相,随着半径与过冷度的增大,横断面形状稳定性下降,其形状呈由圆形逐渐变为椭圆形、类三边形、类四边形的变化规律。试验结果与理论预测结果基本吻合。     

基于质点逆向追踪的铝合金空心型材横断面温度的不均匀性

采用挤压金属质点逆向追踪方法,分析了铝合金空心型材挤压过程中型材横断面温度分布不均匀性的原因及主要影响因素。结果表明:挤压过程中质点在分流孔内流动时的温度变化对模孔出口处型材横断面温度分布不均匀性的影响较大,而在焊合室内和模孔内流动时,温度变化对模孔出口处型材横断面温度分布不均匀性影响较小;挤压过程中各项热流作用对型材横断面温度分布不均匀性的影响程度由大到小依次为摩擦热、塑性变形热以及金属与工模具间的传热;通过模具结构设计和挤压工艺参数合理化,可使空心型材横断面温度分布的不均匀性得到较大的改善。     

基于优化控制方法的水流量标准装置特性研究

水流量标准装置计量特性优化问题一直是流量领域研究的重点和难点。通过分析传统水流量标准装置结构及试验过程,指出存在的主要问题,利用新型单向换向、基于陷波器技术的脉冲相位补偿技术两种优化控制方法提升水流量标准装置的计量特性;同时对装置稳定性与流量稳定度的影响也进行了探讨。以静态质量法水流量标准装置为例,分别对传统装置、应用优化控制方法后的装置进行测量结果不确定度验证,证明应用优化控制方法后的装置扩展不确定度较传统装置降低了4‰(占原有扩展不确定度的1/5),方法效果显著,有良好的实用价值。     

基于阀门填料散逸性试验的API标准研究

基于常见的阀门泄漏原因,介绍了阀门试验国内标准,指出存在的主要问题是缺少专门针对阀门密封填料性能试验标准,现有阀门试验标准中对密封填料要求较低。介绍了API Std 622-2011《工艺阀门密封填料逸散性试验规程》,该标准阐述了阀门填料散逸性试验装置和试验程序、腐蚀性试验程序、材料性能试验程序,建立了阀门密封填料性能指标评价准则。借鉴该标准建立阀门填料产品规范,可补充完善阀门试验标准,减少阀门泄漏的可能性。最后提出了API Std 622-2011采标建议。     

基于标准模块的Handling技术

本文介绍了FESTO公司在Handling技术上的发展状况，模块化拼装技术以及专用选型软件PAA。     

万古霉素在老年感染患者体内的群体药代动力学研究

目的: 建立万古霉素在老年感染疾病患者体内的群体药代动力学模型,探讨其药代动力学特征及可能的影响因素。方法:71例老年感染患者的130个稳态血药浓度监测数据纳入本次研究,应用Phoenix NLME（Version 8.0）软件中的群体模块分析万古霉素静脉滴注后的血药浓度数据,估算相关药代动力学参数及其变异情况,构建万古霉素在老年患者中的群体药代动力学模型,并对最终模型进行验证。 结果:采用一房室模型拟合所收集的万古霉素血药浓度数据,表观分布容积V和药物清除率CL的群体典型值分别为33.44 L和2.16 L/h。协变量筛选结果显示,肌酐清除率Ccr对药物清除率CL有显著影响（P<0.01）。结论:本研究成功建立了万古霉素在老年感染疾病患者体内的群体药代动力学模型,最终模型可对个体药代参数做出精确的估计,Ccr对药物清除率CL有显著影响。     

基于标准球在铸件基准传递上的方法研究

通过标准球,实现三坐标测量和非接触式光学扫描测量数据的传递和验证,确定铸件基准.将标准球与铸件在同一坐标系中,使用非接触式光学扫描测量机进行扫描,根据产品三维模型进行拟合计算,得到理想的铸件尺寸状态,使标准球带有铸件坐标信息.根据标准球建立加工坐标系,通过基准目标的尺寸验证数据偏差是否满足加工要求,将理想的铸件尺寸状态...     

基于多标准体系的注射模模块化设计方法研究

总结了注射模的结构和工艺特点,按照注射模结构将其划分为若干模块,建立了多标准体系零部件库,依据标准要求将设计参数、标准件数据和经验知识转化为计算机可存储识别编辑的数据,并开发了基于标准的模块化设计系统。系统在企业应用结果表明：降低了标准学习成本,固化了模具专家的设计经验,减少了设计师工作量与工作难度,也降低了模具设计对设计师个人经验的依赖,提高了工作效率。     

基于数据挖掘的厚板标准精轧道次模型研究

为了提高某厚板厂轧制产品的质量和轧机运行的稳定性,提出了利用决策树算法建立厚板精轧过程道次分配模型的新方法。该方法采用高维度数据可视化和数据挖掘对厚板精轧阶段的原始数据进行分析和挖掘,建立适应标准厚板轧制机组精轧道次的数据模型,实现厚板精轧道次规程的标准化,并为厚板精轧过程的限制参数提供推荐值。经现场模拟与在线应用,该厚板精轧标准道次模型有效地提高了轧制产品质量的稳定和轧机运行的安全。     

氨氯地平对老年高血压患者肾功能的影响

目的 了解老年高血压病患者血和尿β2 微球蛋白(β2-MG), 尿白蛋白(A Lb)、尿IgG 的变化及氨氯地平对其影响。方法 用放射免疫技术测定20 例正常人和48 例高血压患者氨氯地平治疗前后血尿β2-MG、尿ALb、尿IgG 等的变化。结果 老年高血压组血尿β2-MG、尿ALb、IgG 分别为(301±19)、(72±13) nmol·L^-1、(17±7)、(15±5) mg·L^-1,均高于正常人, 氨氯地平治疗12 w k 后上述指标分别为(201±20)、(29±11) nmol·L^-1、(9±4)、(9±6) mg·L^-1, 与治疗前相比均明显降低, P 均<0.01。结论 氨氯地平能降低老年高血压患者血和尿β2-MG, 尿ALb、IgG 浓度, 保护肾功能。     

基于特征的多模式CAPP系统的研究

构造了一种实用化的CAPP系统框架。该系统提供了检索式工艺生成，基于工艺模板的工艺生成，基于特征匹配的工艺生成，这三种决策方式功能并列在CAPP系统中，是相互关联的，较好地解决了CAPP系统的实用性和通用性问题。     

A study on the initial corrosion behavior of carbon steel exposed to outdoor wet-dry cyclic condition

The initial corrosion behavior of carbon steel subjected to outdoor wet-dry cyclic exposure and exposure under natural environments have been investigated. The weight loss results indicate a transition from corrosion acceleration to deceleration during the early stage of corrosion of carbon steel under both conditions. The corrosion kinetics under both conditions follow empirical equation D = Atⁿ. Outdoor wet-dry cyclic exposure significantly promoted the initiation but the rate of corrosion was about three times as fast. The morphology of corrosion surfaces and cross-section of rust layer have been examined using SEM and the compositions have been analyzed using XRD and EPMA.     

A study on the preparation of iron aluminium based intermetallic alloy by aluminothermic smelting technique

Iron aluminium based intermetallic alloys or iron aluminide alloys are usually made by conventional melting and powder processing routes. Melting is carried out either in vacuum induction melting or arc melting furnaces. However,the use of high vacuum and high temperature expensive furnaces, high cost associated with the procurement of pure individual metal components, operational problems during melting stages are some of the most deterrent factors in making these alloys by melting route. Powder processing route utilises atomised, carbonyl or rapidly solidified pre alloyed powders as starting materials and alloying is carried out either by mechanical alloying or reaction synthesis or by consolidation through hot isostatic pressing. This process also involves many processing steps and considerable expense. In the present investigation, it has been found possible to eliminate the above problems by adopting a simple aluminothermic reduction (thermit) smelting technique for the preparation of iron aluminide alloy of targetted composition Fe–16Al–5.46Cr–0.5V–0.05C (wt %) by the direct co-reduction of oxides of iron,chromium and vanadium in presence of carbon and excess aluminium. Incorporation of slag fluidizer CaO amounting to 10 wt % of total charge, aluminium, 10 wt % excess over stoichiometric requirement and carbon, double the theoretical amount have been found to be adequate to form the above alloy with maximum overall yield of 99.4 wt %. The compositional variation of alloying components like iron, chromium,vanadium, aluminium and carbon in the aluminothermically produced iron aluminide alloy from the target composition have been minimized under optimum experimental conditions. The reactions have been found to be well controlled, rapid and self-sustaining and are conducted in an off-furnace manner using a simple experimental set-up.Studies on composition and microstructure characterization, hot rolling behaviour and oxidation resistance of the said alloy points towards its suitability for use.     

Carbon diffusion in steels: A numerical analysis based on direct integration of the flux

In the early 1970s, Professor Dayananda developed a technique for the direct integration of fluxes from the concentration profiles in vapor-solid diffusion couples to determine diffusion coefficients and atomic mobilities. As part of a project to control and optimize the industrial carburization process in mild- and low-alloyed steels, a modified integration analysis was applied to determine the mass transfer coefficient in the gas boundary layer and carbon diffusivity in austenite. Because carbon flux and surface carbon content vary with time during single-stage carburizing even with a fixed carbon potential in the atmosphere, a mass balance at the gas-solid interface must serve as a boundary condition. This article discusses the numerical modeling of gas carburizing, and focuses on calculating the mass transfer and carbon diffusivity parameters using the simulated concentration profiles. This approach validates the proposed method by comparing the calculated parameters with those used in simulation. The results were compared with previous determinations and predictions reported in the literature. This article was presented at the Multicomponent-Multiphase Diffusion Symposium in Honor of Mysore A. Dayananda, which was held during TMS 2006, the 135th Annual Meeting and Exhibition, March 12–16, 2006, in San Antonio, TX. The symposium was organized by Yongho Sohn of University of Central Florida, Carelyn E. Campbell of National Institute of Standards and Technology, Richard D. Sisson, Jr., of Worcester Polytechnic Institute, and John E. Morral of Ohio State University.     

A Comprehensive Overview on the Latest Progress in the Additive Manufacturing of Metal Matrix Composites: Potential,Challenges, and Feasible Solutions

Nowadays, as an emerging technology, additive manufacturing(AM) has received numerous attentions from researchers around the world. The method comprises layer-by-layer manufacturing of products according to the 3D CAD models of the objects. Among other things, AM is capable of producing metal matrix composites(MMCs). Hence, plenty of works in the literature are dedicated to developing different types of MMCs through AM processes. Hence, this paper provides a comprehensive overview on the latest research that has been carried out on the development of the powder-based AM manufactured MMCs from a scientific and technological viewpoint, aimed at highlighting the opportunities and challenges of this innovative manufacturing process. For instance, it is documented that AM is not only able to resolve the reinforcement/matrix bonding issues usually faced with during conventional manufacturing of MMCs, but also it is capable of producing functionally graded composites and geometrically complex objects. Furthermore, it provides the opportunity for a uniform distribution of the reinforcing phase in the metallic matrix and is able to produce composites using refractory metals thanks to the local heat source employed in the method. Despite the aforementioned advantages, there are still some challenges needing more attention from the researchers. Rapid cooling nature of the process, significantly different coe fficient of expansion of the matrix and reinforcement, processability, and the lack of suitable parameters and standards for the production of defect-free AM MMCs seem to be among the most important issues to deal with in future works.     

A study on microreplication of real 3D-shape structures using elastomeric mold: from pure epoxy to composite based on epoxy

In this paper, a new replication technique for a real 3D microstructure was introduced, in which a master pattern was made of photo-curable epoxy using a microstereolithography technology, and then it was transferred onto an epoxy-copper particle composite. A helical gear was selected as one of the real 3D microstructure for this study, and it was replicated from a pure epoxy to an epoxy composite. In addition, the transferability of the microreplication process was evaluated, and the properties of the epoxy composite were compared to that of the pure epoxy, including hardness, wear-resistance and thermal conductivity.     

Influence of irregularities in the electrolyte on the cathodic protection of steel: A numerical and experimental study

This paper shows how the last algebraic matricial form can be obtained when the finite element method is used to approximate the potential distribution of a cathodic protection system that includes low conductivity irregularities in the electrolyte away from, close to and directly on the cathode. In order to study the influence of the resistivity of these irregularities on the possibilities of steel protection, five conductivities were analysed. The numerical results, validated with COMSOL® Multiphysics, show the importance of considering irregularities in the domain in order to prevent systems from becoming unprotected. The experimental data agrees with the theoretical data.     

The effect of alloying elements on the dislocation climbing velocity in Ni: A first-principles study

By using density functional theory calculations in conjunction with the climbing images nudged elastic band method, the effects of alloying elements Re, W, Mo, Cr, Co and Ru on the velocity of dislocation climbing in gamma Ni were studied. The results shed a light on the mechanism of these elements suppressing the dislocation motion by connecting the stacking fault energy and the migration activation energy of vacancy with the dislocation climbing velocity. It is found that the elements can decrease the stacking fault energy of Ni and raise the migration activation energy of vacancy. The changes of these two energies result in the increase of the formation energy and the diffusion activation energy of the jog, thus the dislocation climbing is restricted. The results also reveal that the influences of alloying elements on dislocation climbing velocity depend on the characters of dislocations.     

水溶液体系中制备纳米银线的研究

在水溶液体系中,以蔗糖为还原剂、NaCl为前驱体络合剂、PVP为表面活性剂,通过水热反应制备得到了直径大约为40 nm,线径分布均匀、分散性良好的纳米银线。有效解决了目前多元醇有机体系下制备纳米银线洗涤困难,反应条件苛刻,后处理繁琐等问题。系统研究了还原剂用量、还原剂种类、Cl^-/Ag⁺摩尔比、卤化物种类和表面活性剂种类对于产物形貌的影响。结果表明,当还原剂蔗糖的用量为0.18 g,PVP的相对分子质量为58000,选择Na Cl作为络合剂,且Cl^-/Ag⁺摩尔比控制在1.26时,制备的纳米银线形貌均一,纯度较高,纳米线长径比大于1000。