One Dimensional Silver‐based Nanomaterials: Preparations and Electrochemical Applications

One dimensional (1D) silver‐based nanomaterials have a great potential in various fields because of their high specific surface area, high electric conductivity, optoelectronic properties, mechanical flexibility and high electro‐catalytic efficiency. In this Review, the preparations of 1D silver‐based nanomaterials is classified by structure composed of simple silver nanowires/rods/belts/tubes, core‐shells, and hybrids. The latest applications based on 1D silver nanomaterials and their composite materials are summarized systematically including electrochemical capacitors, lithium‐ion/lithium‐oxygen batteries, electrochemical sensors and electrochemical catalysis. The preparation process, tailored material properties and electrochemical applications are discussed.     

Induktive Erwärmung von partikelverstärkten Stahlpresslingen in den thixotropen Temperaturbereich

The producers of powder metallurgy components are constantly making efforts to improve manufacturing processes and to extend the present ranges of their applications. One way to increase the complexity of powder metallurgy components is the combination of powder metallurgy and thixoforging. In contrast to the conventional process route, the powder‐pressed raw parts are heated up to the thixotropic temperature range in order to realise complex components in one process step. Additionally, the powder metallurgy combined with ceramic particles allows to produce Metal Matrix Composite (MMC) materials with improved mechanical properties compared to conventional materials. In this work basic experiments of the pressing and inductive heating of particle‐reinforced steel parts are examined.     

Multiscale Experimental Mechanics of Hierarchical Carbon‐Based Materials

Investigation of the mechanics of natural materials, such as spider silk, abalone shells, and bone, has provided great insight into the design of materials that can simultaneously achieve high specific strength and toughness. Research has shown that their emergent mechanical properties are owed in part to their specific self‐organization in hierarchical molecular structures, from nanoscale to macroscale, as well as their mixing and bonding. To apply these findings to manmade materials, researchers have devoted significant efforts in developing a fundamental understanding of multiscale mechanics of materials and its application to the design of novel materials with superior mechanical performance. These efforts included the utilization of some of the most promising carbon‐based nanomaterials, such as carbon nanotubes, carbon nanofibers, and graphene, together with a variety of matrix materials. At the core of these efforts lies the need to characterize material mechanical behavior across multiple length scales starting from nanoscale characterization of constituents and their interactions to emerging micro‐ and macroscale properties. In this report, progress made in experimental tools and methods currently used for material characterization across multiple length scales is reviewed, as well as a discussion of how they have impacted our current understanding of the mechanics of hierarchical carbon‐based materials. In addition, insight is provided into strategies for bridging experiments across length scales, which are essential in establishing a multiscale characterization approach. While the focus of this progress report is in experimental methods, their concerted use with theoretical‐computational approaches towards the establishment of a robust material by design methodology is also discussed, which can pave the way for the development of novel materials possessing unprecedented mechanical properties.     

制备工艺对Ag/SnO2材料力学性能的影响

采用粉末冶金和反应合成两种工艺制备了Ag/SnO2电接触材料,分析了两种工艺对显微组织的影响,发现反应合成法制备的Ag/SnO2材料经热挤压后,SnO2颗粒呈纤维状排列,颗粒细小,分散均匀,与基体浸润良好.断裂拉伸测试和分析表明,粉末冶金法制备的Ag/SnO2材料的拉伸断口形貌由许多互相连接的撕裂棱和韧窝组成,表现为韧断;而反应合成法制备的断口形貌韧窝更加细小,显示出近脆性断裂特征.最后比较了两种方法制备的Ag/SnO2材料的抗拉强度、延伸率、硬度等力学性能.     

Mechanical and physical properties of sintered YBCO-metal bulk composites with silver powder and fibres

Silver powder and continuous fibres were used in developing sintered YBa₂Cu₃O_7–x (YBCO)-metal composites because applications require further improvement in mechanical and physical properties of the bulk superconducting elements without affecting the critical current capacity. The weight ratios of silver powder to YBCO and silver fibre to YBCO were varied up to 50% and 5%, respectively, in the beam elements. The effect of silver addition on the density of the composite has been quantified. Stress-strain-critical current properties of bulk YBCO-metal composite elements were investigated in bending at 77 K. The addition of silver powder reduced the sintering temperature, increased the dimensional changes after sintering and also improved the strength, toughness and critical current capacity compared to the monolithic. Silver fibres, (aspect ratios varying between 70 and 110), aligned along the length of the element restricted the changes in dimensions of the composite after sintering and also influenced the stress-strain-current capacity relationship, strength and toughness of the composite to varying degrees. The mixture theory was used to predict the composite flexural strength based on the composition of the composite, constituent properties and porosity.     

Influence of carbon nanotubes and dispersions of SiC on the physical and mechanical properties of pure copper and copper‐nickel alloy

This paper investigates the physical and mechanical properties of copper‐nickel alloy (at 50 wt.%–50 wt.%) and pure copper, mixed with various types of reinforcement materials such as carbon nanotubes (0.5 wt.%–2 wt.%) as nanoparticles, silicon carbide (1 wt.%–4 wt.%) as microparticles. The acquired composite specimens characteristics were estimated such as microstructure, density, electrical and thermal conductivity, hardness, and compression stress properties to determine the suitable reinforcement percentage that has the best physical and mechanical properties with different main matrix material whether copper‐nickel mechanical alloying or pure copper powder. The micron‐sized silicon carbide and nanosized carbon nanotubes were added to improve the mechanical and physical properties of the composite. The electrical and thermal conductivity of pure copper alloy enhanced compared with the copper‐nickel alloy matrix material. The hardness and compression yield stress of both pure copper and copper‐nickel composites have enhancement values and for copper‐nickel base composites hardness and compression yield stress have enhanced with the most positive enhancement values to examined an optimum percentage of reinforcing material.     

Processing of Net‐shaped Nanocrystalline Fe‐Ni Material

Development of nanoparticulate materials technology is essential to processing of highly functional nanoparticulate materials and components with small and complex shape. This paper provides an overview on our recent investigations on the processing of net‐shaped nanocrystalline Fe‐Ni powder and related material property such as mechanical property. The key‐processing concept is the synthesis of nanopowders and subsequent consolidation with controlled microstructure by using powder injection molding (PIM) process. Especially, the pressureless sintering process is inevitable for consolidation of the PIMed nanopowder. The present review focuses on the densification process and related mechanical property of the PIMed Fe‐Ni nanopowder in association with microstructural evolution and diffusion process.     

Microstructural and Nano‐Mechanical Characterisation of Multicomponent Composites Nanocrystalline Matrix

Multicomponent, Ti‐based, in situ formed composites with a nanocrystalline matrix are a promising new type of material for structural applications. The materials exhibit an excellent combination of mechanical properties resulting from the composite microstructure. This paper contains a detailed introduction to such materials and a review of the most recent developments in the specific areas of microstructural and nano‐mechanical characterization.     

Synchrotron‐Based Micro‐CT and Refraction‐Enhanced Micro‐CT for Non‐Destructive Materials Characterisation

X‐ray computed tomography is an important tool for non‐destructively evaluating the 3‐D microstructure of modern materials. To resolve material structures in the micrometer range and below, high brilliance synchrotron radiation has to be used. The Federal Institute for Materials Research and Testing (BAM) has built up an imaging setup for micro‐tomography and ‐radiography (BAMline) at the Berliner storage ring for synchrotron radiation (BESSY). In computed tomography, the contrast at interfaces within heterogeneous materials can be strongly amplified by effects related to X‐ray refraction. Such effects are especially useful for materials of low absorption or mixed phases showing similar X‐ray absorption properties that produce low contrast. The technique is based on ultra‐small‐angle scattering by microstructural elements causing phase‐related effects, such as refraction and total reflection. The extraordinary contrast of inner surfaces is far beyond absorption effects. Crack orientation and fibre/matrix debonding in plastics, polymers, ceramics and metal‐matrix‐composites after cyclic loading and hydro‐thermal aging can be visualized. In most cases, the investigated inner surface and interface structures correlate to mechanical properties. The technique is an alternative to other attempts on raising the spatial resolution of CT machines.     

Laser ablation of diamond fibres and a diamond fibre metal matrix composite

Continuous chemical vapour-deposited diamond-coated fibres with tungsten wire or SiC fibre cores are attractive for reinforcing metals and ceramics. The fibres have been embedded in Ti-6A1-4V alloy to produce a diamond fibre-reinforced composite. Both the fibres and the composite material are extremely difficult to cut without damage by conventional mechanical methods. The use of a Nd-YAG laser to cut these materials is described.     

A micromechanical fracture analysis to investigate the effect of healing particles on the overall mechanical response of a self‐healing particulate composite

A computational fracture analysis is conducted on a self‐healing particulate composite employing a finite element model of an actual microstructure. The key objective is to quantify the effects of the actual morphology and the fracture properties of the healing particles on the overall mechanical behaviour of the (MoSi₂) particle‐dispersed Yttria Stabilised Zirconia (YSZ) composite. To simulate fracture, a cohesive zone approach is utilised whereby cohesive elements are embedded throughout the finite element mesh allowing for arbitrary crack initiation and propagation in the microstructure. The fracture behaviour in terms of the composite strength and the percentage of fractured particles is reported as a function of the mismatch in fracture properties between the healing particles and the matrix as well as a function of particle/matrix interface strength and fracture energy. The study can be used as a guiding tool for designing an extrinsic self‐healing material and understanding the effect of the healing particles on the overall mechanical properties of the material.     

Crack‐Tip Stress Field and Fatigue Crack Growth Monitoring Using Infrared Lock‐In Thermography in A359/SiCp Composites

Abstract: This paper deals with the study of fracture behaviour of silicon carbide particle‐ reinforced aluminium alloy matrix composites (A359/SiCp) using an innovative non‐destructive method based on lock‐in thermography. The heat wave, generated by the thermo‐mechanical coupling and the intrinsic energy dissipated during mechanical cyclic loading of the sample, was detected by an infrared camera. The coefficient of thermo‐elasticity allows for the transformation of the temperature profiles into stresses. A new procedure was developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue. The thermographic results on the crack growth rate of A359/SiCp composite samples with three different heat treatments were correlated with measurements obtained by the conventional compliance method. The results obtained by the two methods were found to be in agreement, demonstrating that lock‐in thermography is a powerful tool for fracture mechanics studies. The paper also investigates the effect of heat treatment processing of metal matrix composites on their fracture properties.     

Characterisation of barium titanate-silver composites, part I: Microstructure and mechanical properties

The paper presents an investigation of the influence of silver particles on the microstructure and mechanical properties of barium titanate. Barium titanate-silver composites have been prepared by ball milling precursor powder constituents; followed by drying, sieving and calcination prior to powder compaction. After sintering the green compacts, microstructural analysis was undertaken involving measurement of grain size, silver particle size, phase composition and phase content. Characterisation of mechanical strength, toughness, hardness and stiffness was also undertaken. Reaction product phases between silver and barium titanate could not be detected. The dispersed silver particles were shown to inhibit densification. Silver particles below 1 μm in size were intragranular and attached to domains. The size of the intergranular silver particles increased with silver content. An increase in silver content improved whereas strength, hardness and stiffness decreased, while toughness was unchanged.     

The Manufacture of Resorbable Suture Material from Magnesium – Drawing and Stranding of Thin Wires

With the aid of multiple wire drawing passes, the magnesium alloys ZEK100, MgCa0.8, and AL36 were reduced to monofilament wires possessing diameters between 0.5 and 0.1 mm. These filaments were subsequently twisted into poly‐filament suture material using stranding. In order to analyze the microstructural constituents and the mechanical‐tribological properties, metallographic specimens were prepared and tensile tests were performed on both monofilament as well as poly‐filament wire strands. Appropriate parameters were ascertained for the wire drawing process with regard to forming rate, temperature, and heat treatment. During the investigations, the alloy ZEK100 exhibited particularly interesting mechanical properties which, owing to its high tensile strengths (up to 550 MPa for monofilament) and fracture strains (up to 30% for poly‐filament), are comparable to those of conventional polymer‐based suture materials. In addition to this, integrating a core (internal, individual wire) into the poly‐filament mesh of wire strands represents an interesting alternative for future research in which structures composed of different materials, and the advantages of combining their properties are brought into particular focus.     

The statistical second‐order two‐scale method for mechanical properties of statistically inhomogeneous materials

A class of random composite materials with statistically inhomogeneous microstructure, for example, functionally graded materials is considered in this paper. The microstructures inside a component are gradually varying in the statistical sense. In view of this particularity, a novel statistical second‐order two‐scale (SSOTS) method is presented to predict the mechanical properties, including stiffness, and elastic limit. To develop this method, the microstructures of statistically homogeneous, and inhomogeneous materials are represented. In addition the SSOTS formulas are derived based on normalized cell depending on the position variables by a constructing way, and the algorithm procedure is described. The mechanical properties of the different inhomogeneous materials are evaluated. The numerical results are compared with the experimental findings. It shows that the SSTOS method is effective. Copyright © 2010 John Wiley & Sons, Ltd.     

Neuartige Faserverbunddrähte für die Leistungselektronik

Novel fibre reinforced wires for power electronics The use of power electronics within the scope of mechatronic applications as well as the increasing integration of components lead to increased requirements concerning their mechanical and thermal reliability. Today contact making in power electronics is mostly done by aluminum thick wire bonding. This process is highly productive, however the life time of power electronic components is meanwhile predominantly limited by the durability of these wire bonds. The thermal mismatch between the wire material and the connected components is one cause. A new starting point, in order to improve the reliability, is the application of new fibre reinforced metal matrix composite (MMC) wires with increased reliability under thermo‐mechanical stress. In the context of a research project MMC bond wires of different material combinations and arrangements were manufactured. Aluminum wires with copper fiber reinforcement as well as Copper wires containing FeNi36 fibre reinforcement have successfully be drawn to a final diameter of 300 μm. The fibre reinforcements should reduce the coefficient of thermal expansion and improve the mechanical strength. By aluminium copper MMC the electrical conductivity is increased as well. Measurements of the produced MMC wires confirmed these expectations. The manufacturing of the MMC took place on the basis of wire material of different diameters. These wires were stacked in capsules in different arrangements and material combinations. Subsequently, the capsules were either hot‐isostatically pressed or directly extruded. In such a way produced composites have been manufactured by rotary swaging and wire drawing into bond wires and after that tested.     

Preparation of the Silver-Superconductor Composite by Deposition of the Silver Nanoparticles in the Bismuth Cuprate Superconductor

BiSCCO (Bi–Sr–Ca–Cu–O) is high temperature superconductor with a lot of possible applications. Interfaces between superconductors and metal conductors are one of the technological problems. In this work, silver-superconductor composite was prepared by using flow of silver nanoparticles suspension in DMF (N,N-dimethylformamide) through superconductor’s pore system. Silver nanoparticles were prepared by reaction of silver nitrate with DMF. Properties of prepared composite were measured by SEM charting, XRD and critical current measurements. SEM chart showed uniform distribution of silver across sample. XRD and critical current measurements validated superconducting properties of prepared composite. In the future, materials based on this method could be used as an interface between superconductors and metals or as a base for superconducting composite with much better mechanical properties.     

Mikrostrukturelle und mechanische Eigenschaften von laserstrahlgeschweißtem Magnesiumfeinblech AZ31‐HP mit und ohne Zusatzwerkstoffe

Microstructural and mechanical properties of laser welded sheets of magnesium AZ31‐HP with and without filler wires This paper describes Nd:YAG laser beam welding experiments carried out on rolled 2.5 mm thick magnesium sheet AZ31‐HP. For the butt welds in flat position, filler wires AZ31X and AZ61A‐F were used, diameter 1.2 mm. The microstructure and mechanical properties of the different laser beam welded joints were examined and compared with one another. The obtained results show that the laser beam welding of AZ31‐HP sheet is possible without hot crack formation, both without and with filler wires. The determined tensile strength, ductility, fracture toughness and microhardness of laser beam welded joints without filler wire were not effected by AZ31X nor AZ61A‐F. By use of these filler wires loss of zinc was minimized and the shape of weldments was optimized. The values of fracture strength, yield strength and microhardness of the joints and base material are quite similar. It is found that the ductility of the joints is lower than the base materials due to the heterogeneous microstructure of the fusion zones and geometrical notches of the weld seams. Both, weld and base material of AZ31‐HP, showed stable crack propagation. Furthermore, for base material slightly lower fracture toughness values CTOD than for the joints were determined.     

Effect of SiC‐Reinforcement and Equal‐Channel Angular Pressing on Microstructure and Mechanical Properties of AA2017

This article deals with powder metallurgical production and modification of properties of a composite material based on an age‐hardenable Al–Cu alloy. The main objective is to improve the mechanical properties by particle reinforcement and equal‐channel angular pressing (ECAP). Our approach makes use of four hardening mechanisms: precipitation hardening, particle reinforcement, strain‐hardening, and grain boundary hardening associated with an ultrafine‐grained microstructure produced by ECAP. The main processing steps are high‐energy ball milling, hot‐isostatic pressing, extrusion, heat treatment, and a single ECAP pass. Microstructures are analyzed by optical microscopy, scanning electron microscopy, and scanning transmission electron microscopy. The mechanical properties are characterized by hardness measurements and quasi‐static tensile testing. Our experimental results show that the proposed processing route results in a nearly homogeneous distribution of SiC particles in the matrix. The combination of particle reinforcement and ECAP leads to an improvement of ultimate tensile strength by almost 300 MPa compared to the unreinforced alloy. A subsequent heat treatment leads to a further increase in hardness and strength that can be related to changes in the defect structure. Our study provides detailed information on how processing steps, microstructures, and mechanical behavior are interrelated in this technologically relevant class of materials.     

Nature‐Inspired Lightweight Cellular Co‐Continuous Composites with Architected Periodic Gyroidal Structures

Shell‐core cellular composites are a unique class of cellular materials, where the base constituent is made of a composite material such that the best distinctive physical and/or mechanical properties of each phase of the composite are employed. In this work, the authors demonstrate the additive manufacturing of a nature inspired cellular three‐dimensional (3D), periodic, co‐continuous, and complex composite materials made of a hard‐shell and soft‐core system. The architecture of these composites is based on the Schoen's single Gyroidal triply periodic minimal surface. Results of mechanical testing show the possibility of having a wide range of mechanical properties by tuning the composition, volume fraction of core, shell thickness, and internal architecture of the cellular composites. Moreover, a change in deformation and failure mechanism is observed when employing a shell‐core composite system, as compared to the pure stiff polymeric standalone cellular material. This shell‐core configuration and Gyroidal topology allowed for accessing toughness values that are not realized by the constituent materials independently, showing the suitability of this cellular composite for mechanical energy absorption applications.