高孔率金属材料延伸率的估算方法

基于各向同性高孔率材料的结构特征进行理论推导,得出了由孔率计算高孔率金属延伸率的方法,并用泡沫镍作相应的实验验证。结果表明：高孔率金属（孔率在80％以上）的延伸率随其孔率增大而有所增大,估算值与实测结果基本一致。     

承受扭矩和剪切时开口多孔金属的孔棱失效

以高孔率的三维网状多孔金属(即开口多孔金属)为研究对象,建立其简化结构失效模型。分析多孔构件在扭转和剪切载荷形式作用下由于孔棱发生拉断、剪切和屈曲而引起的失效模式,系统地研究上述两种承载条件下这类多孔体构件受到载荷作用而导致孔棱失效时名义载荷与孔率的数理关系。在此基础上,进一步研究此类材料在不同载荷作用下发生各种孔棱失效模式的载荷条件。结果表明,这些失效模式与多孔金属的材质指标、孔率及承受的载荷大小等因素均有关系,这种关系也可以进行相应的具体数理表征。     

三维网状泡沫金属杨氏模量和泊松比的数理表征

杨氏模量和泊松比是工程材料最为基本的两个力学指标.多孔金属是一种兼具功能和结构双重属性的优秀工程材料,采用"八面体分析模型",研究了三维网状泡沫金属的这两个性能指标,发现其表观杨氏模量与多孔体的孔率有比较复杂的数理关系,而其表观泊松比则是一个与孔率无关的特征材料常数.     

泡沫材料在多向拉伸载荷作用下的力学模型

以各向同性的三维网状高孔率泡沫金属为研究对象,根据其简化结构模型,推导得出该类材料在多向拉伸破坏时3个名义主应力与孔率四者之间的数理关系。通过推演得出的有关关系式,还可进一步得出泡沫金属在多向受力状态下使用时的强度设计判据。     

泡沫金属在双向承载条件下的力学性能

根据各向同性三维网状泡沫金属的简化结构模型,建立该类材料的双向拉伸力学分析模型.利用该力学模型推出泡沫金属在双向拉伸破坏时两向名义应力与孔率3者的数学关系式,并在此基础上进一步得出该类材料在承受双向载荷时的安全判据.当双向承受的名义应力相等时,还可得到泡沫金属在双向等荷承载条件下的载荷强度与孔率的数学关系.这些关系式通过泡沫镍为例的有关实验数据证明是相当实用的.而由本理论体系可得出对多孔体双向承载条件的安全性判断,这似乎是Gibson和Ashby的有关模型理论所未触及或难以做到的.     

泡沫金属双向等速拉伸载荷强度与孔率的近似关系

以各向同性的三维网状高孔率泡沫金属为对象，提出双向等速拉伸过程中载荷强度与其孔率的数学关系。结果表明，以泡沫镍为例的有关实验数据，能较好地用该数学关系式来描述。     

泡沫金属力学性能的若干问题

泡沫金属在结构方面的应用口益增多，其力学性能随之显得越来越重要。本文列举了该材料的一些结构用途，在强化其力学性能研究意识的同时，提出了泡沫金属双向拉伸性能研究的基础性和必要性。并从其应用发展趋势、制备方法和结构特点出发，指出该材料双向力学性能与孔率关系研究的重要意义。     

基于聚苯乙烯新2D降解模型的消失模铸件加工过程研究

针对消失模铸造过程中泡沫密度、涂层透气性以及泡沫降解温度问题,提出了热传递、泡沫降解和气体扩散的二维模型。考虑了泡沫和熔融金属间的辐射和热传导,对金属表面和泡沫表面进行了追踪,计算了气隙体积和压力;结合能量守恒和几何相关性,定义了在金属填充过程中消退的泡沫表面;将间隙中的气体流动看成楔形流,并将层状不可压缩楔形流的努塞尔特数用于该过程。为了将模型应用于实例,使用算法对具有自由边界的熔融金属流动进行了仿真。仿真结果显示,新二维模型在铸造过程中,泡沫密度、涂层透气性以及泡沫降解温度越大,压力就会越大,导致金属充模时间更长。     

铸造法制备泡沫金属材料

泡沫金属是一种集力学性能、热电性能、声学等性能于一体的宏观结构一功能一体化的环保材料，由于其巨大的应用前景，在工业领域，特剐是汽车和航空航天领域受到了越来越广泛的重视。泡沫金属的制备方法很多，与其它制备方法相比，基于金属熔体的铸造法具有产量大、成本相对低廉、易于工业生产等优点，因而已被广泛研究并已部分实现了产业化。本文对当前应用于泡沫金属研究领域的几种铸造方法的工艺过程进行了详细介绍，并分析了其优缺点。     

泡沫金属的制备工艺及应用

根据泡沫金属制备过程中金属的状态,将泡沫金属的制备方法归类为：熔体凝固法、固态烧结法、金属沉积法,并按此分类对泡沫金属常用制备工艺进行了介绍。泡沫金属具有轻质、高孔隙率、电磁屏蔽等性能,按照功能用途和结构用途2方面对其应用领域进行了介绍。     

Functional Characterization of Shape Memory CuZnAl Open-Cell Foams by Molten Metal Infiltration

In the recent years, the research for novel materials with tailored mechanical properties, as well as functional properties, has encouraged the study of porous and cellular materials. Our previous work proposed and reported about the possibility to manufacture open-cell metal foams of CuZnAl shape memory alloy by liquid infiltration in a leachable bed of silica-gel particles. This innovative methodology is based on cheap commercial consumables and a simple technology, focusing on intermediate-density low-cost foams with interesting cost/benefits ratio. Microstructural analyses on foamed specimens showed uniform microstructure of ligaments and a very regular and well reproducible open-cell morphology. Moreover, calorimetric analysis detected a thermo-elastic martensitic transformation in the foamed material. In this study, a CuZnAl shape memory alloy was considered and tested to clarify possible effects of the foaming process on the functional properties of the material. Morphological, calorimetric, and thermo-mechanical analyses were carried out. The results show that it is possible to produce metal foams of CuZnAl shape memory alloy with different functional properties and able to recover mono-axial compressive strains up to 3%.     

金属含量对Co-TiO2纳米颗粒复合薄膜微观结构及其性能的影响

目的使Co-TiO_2纳米颗粒复合薄膜同时具备高的磁化强度及电阻率,从而实现更好的高频软磁特性。方法通过磁控共溅射的方法,在不同金属靶功率下制备了Co-TiO_2纳米颗粒复合薄膜,并探究金属含量对薄膜的微观结构、表面形貌、电学和静态磁学性能的影响。结果薄膜中的金属颗粒被非晶态的TiO_2分散。金属含量的增加可以显著提高纳米颗粒薄膜中金属颗粒的结晶性,降低薄膜电阻率,并且通过改变金属含量,可使薄膜逐渐从超顺磁态向铁磁态转变,达到精确调控纳米颗粒复合薄膜的磁学和电学性能的目的。结论在金属含量达到54%时,实现了高电阻率和高饱和磁化强度共存,有望得到具有高频软磁特性的纳米颗粒复合薄膜。     

Electrochemical evaluation of sintered aluminium – ceramic cenospheres composites

The corrosion behaviour of cenospheres metal matric syntactic foams of different compositions in 3.5?wt-% NaCl aqueous solution at ～25°C was investigated. The electrochemical properties of the composites were assessed experimentally, employing potentiodynamic polarisation and electrochemical impedance spectroscopy measurements. Appropriate equivalent electrical circuits were proposed. Results showed that the corrosion rate is higher for the metal matrix syntactic foams compared to pure sintered aluminium. As the volume fraction of cenospheres increases cenospheres fragments and the presence of reaction zones seems to have a greater effect on the corrosion behaviour of the composites compared to the presence of unintended porosity.     

开孔泡沫铝导电性的研究

本文采用加压渗流方法制备开孔结构的泡沫铝,并通过调整工艺参数改变泡沫铝的孔径和相对密度.采用“直流四端电极”法测量了不同参数泡沫铝的电阻,研究开孔泡沫铝的导电性随其相对密度和孔径的变化规律.实验结果表明：随着相对密度的提高,开孔泡沫铝的电导率增大,且电导率随相对密度的改变呈指数关系变化;当相对密度参数基本相同时,随着泡沫铝孔径的减小,由于在制备过程中产生的结构缺陷增多,其电导性下降.     

Transfer of Wire Arc-Sprayed Metal Coatings onto Plastic Parts

By means of In-Mold-Metal-Spraying (IMMS), metal coatings deposited by means of arc spraying process (ASP) can be transferred onto plastic parts during injection molding, thus realizing an efficient production of metallized plastic parts. Parts produced by means of IMMS can be used in electrical applications. In the current study, the electrical resistivity of coatings applied with different feedstock materials was determined. As a starting point, pressurized air is used as atomizing gas for ASP. In contrast to Zn coatings, Cu coatings applied with pressurized air exhibit a significantly higher electrical resistivity in comparison with massive material. One possible reason is the more pronounced oxidation of Cu particles during ASP. Therefore, N₂ and a mixture of N₂ and H₂ were used as atomizing gas. As a result, the electrical resistivity of coatings applied by means of IMMS could be significantly reduced. Furthermore, standoff distance, current and pressure of the atomizing gas were varied to investigate the influence of these process parameters on the electrical resistivity of Zn coatings using a full factorial experiment design with center point. It can be observed that the electrical resistivity of the Zn coatings increases with decreasing current and increasing standoff distance and pressure.     

Preparation of open-cell metal foams by investment cast

1. Introduction Metal foams are a new kind of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. They are potential materials for lightweight structures, energy absorption, and thermal management applications. They can be divided into closed and open cell structures (sponges). For sponges, the typical applications of these open-cell materials so far are heat exchangers, filter elements, acoustic absorbers, stiffening elements, crash absorb…     

Investigation of the spark cycle on material removal rate in wire electrical discharge machining of advanced materials

The development of new, advanced engineering materials and the need for precise and flexible prototypes and low-volume production have made the wire electrical discharge machining (EDM) an important manufacturing process to meet such demands. This research investigates the effect of spark on-time duration and spark on-time ratio, two important EDM process parameters, on the material removal rate (MRR) and surface integrity of four types of advanced material: porous metal foams, metal bond diamond grinding wheels, sintered Nd-Fe-B magnets, and carbon–carbon bipolar plates. An experimental procedure was developed. During the wire EDM, five types of constraints on the MRR due to short circuit, wire breakage, machine slide speed limit, and spark on-time upper and lower limits are identified. An envelope of feasible EDM process parameters is generated for each work-material. Applications of such a process envelope to select process parameters for maximum MRR and for machining of micro features are discussed. Results of Scanning Electron Microscopy (SEM) analysis of surface integrity are presented.     

Effectiveness of electrically assisted solid-state pressure joining using an additive manufactured porous interlayer

A solid-state pressure joining using resistance heating as a heat source and adopting an additive manufactured metal porous interlayer between joining specimens is demonstrated. During the joining of 316L stainless steel cylindrical specimens, an electric current is directly applied to the joint under continuous axial compression. Defect-free joints are successfully fabricated with a lower joining pressure when applying the porous interlayer with a lower compressive strength and higher electric resistivity. The microstructural analysis confirms that the porosity is eliminated as a result of the compressive deformation during joining, and recrystallization takes place in the interlayer.     

Effects of Zr, Mo and Y-Doping on Microstructure and Mechanical, Electrical Properties of Au-Pd Binary Alloy

在Au-Pd系中分别加入Zr、Mo、Y3种稀有金属元素,研究稀有金属元素的加入对Au-Pd合金组织结构及力学和电学性能的影响。合金在真空高频炉中熔炼。首先用X射线衍射仪和金相显微镜对合金的显微组织和结构进行分析,用电桥、涡流导电仪测量合金的电阻率,用拉力试验机测量合金的力学性能。结果表明稀有金属元素的加入可以有效地细化合金的显微组织,并且提高合金的熔点、密度、力学性能和电阻率,但是合金的加工性能有所降低。