Continuous manufacturing of fiber-reinforced metal matrix composite wires — technology and product characteristics

A new continuous processing method is presented for the production of continuous-fiber-reinforced metal matrix composite (MMC) wires. The process currently yields MMC wires with the diameter of 0.5–1.6 mm at a maximum speed of 0.3 m/s for (fiber)–(metal) combinations of (Al₂O₃, Si–Ti Carbide, SiC, Carbon)–(Aluminum, 2024A1, 6061A1) with a fiber volume fraction of 0.50–0.65. The process operation, mechanical/materials characteristics of the MMC wires as well as their relationships are described as an overview of the new materials processing technology.     

Molybdenum Oxides – From Fundamentals to Functionality

The properties and applications of molybdenum oxides are reviewed in depth. Molybdenum is found in various oxide stoichiometries, which have been employed for different high‐value research and commercial applications. The great chemical and physical characteristics of molybdenum oxides make them versatile and highly tunable for incorporation in optical, electronic, catalytic, bio, and energy systems. Variations in the oxidation states allow manipulation of the crystal structure, morphology, oxygen vacancies, and dopants, to control and engineer electronic states. Despite this overwhelming functionality and potential, a definitive resource on molybdenum oxide is still unavailable. The aim here is to provide such a resource, while presenting an insightful outlook into future prospective applications for molybdenum oxides.     

Hypervelocity impact damage to Ti–6Al–4V meshes reinforced Al–6Mg alloy matrix composites

An Al–6Mg alloy matrix composite reinforced with Ti–6Al–4V meshes was fabricated by pressure infiltration method; its damage behaviors impacted by hypervelocity aluminum projectiles were investigated. Results showed that the thin Ti_f/Al–6Mg composite target exhibits better protection efficiency and energy absorption ability than Al–6Mg alloy target. With projectile sizes increasing, bulge and spallation were observed on the back of the composite target. The Ti–6Al–4V meshes were tensed and deformed drastically in the spallation region, where micro-damages such as interfacial debonding and cracks were dominant. Shear localization was the primary failure characteristic for thin Al–6Mg alloy target. The adiabatic shear bands were observed near the crater of Al–6Mg alloy, not in Ti_f/Al–6Mg composite target. It was ascribed to the Ti–Al interfacial bonding strength and the high temperature strength for Ti–6Al–4V alloy.     

Thermal fatigue behaviour and damage development in Al‐Alloys 6061 an 6061‐metal matrix composites

Metal matrix composites (MMC) have become important materials in many technical fields. But above all there is a high amount of failures due to alternating stresses because of temperature changes. In this investigation the thermal fatigue behaviour of two metal matrix composites with different particle contents and their base material without particles are compared. It is shown that there are three main parameters influencing lifetime: the maximum temperature of the cycles, the particle content and the particle size. An increasing of these parameters means a decreasing of the cycle numbers before damage occurs.     

Laser surface coating of Mo–WC metal matrix composite on Ti6Al4V alloy

Laser surface alloying of Mo, WC and Mo–WC powders on the surface of Ti6Al4V alloys using a 2 kW Nd-YAG laser was performed. The dilution effect upon the microstructure, microhardness and wear resistance of the surface metal matrix composite (MMC) coating was investigated. With a constant thickness of pre-placed powder, the dilution levels of the alloyed layers were found to increase with the incident laser power. The fabricated surface MMC layer was metallurgically bonded to the Ti6Al4V substrate. The microhardness of the fabricated surface layer was found to be inversely proportional to the dilution level. The EDAX and XRD spectra results show that new intermetallic compounds and alloy phases were formed in the MMC layer. With the existence of Mo content in the pre-placed powder, the β-phase of Ti in the MMC coating can be retained at the quenching process. With increasing weight percentage content of WC particles in the Mo–WC pre-pasted powder, the microhardness and sliding wear resistance of the laser surface coating were increased by 87% and 150 times, respectively, as compared with the Ti6Al4V alloy. The surface friction of the laser-fabricated MMC coatings was also decreased as compared with the worn Ti6Al4V substrate.     

Influence of different carbon nanotubes on the mechanical properties of epoxy matrix composites – A comparative study

Carbon nanotubes (CNTs) in general are considered to be highly potential fillers to improve the material properties of polymers. However, questions concerning the appropriate type of CNTs, e.g., single-wall CNTs (SWCNT), double-wall CNTs (DWCNT) or multi-wall CNTs (MWCNT), and the relevance of a surface functionalisation are still to be answered. This first part of the study focuses on the evaluation of the different types of nanofillers applied, their influence on the mechanical properties of epoxy-based nanocomposites and the relevance of surface functionalisation. The nanocomposites produced exhibited an enhanced strength and stiffness and even more important, a significant increase in fracture toughness (43% at 0.5 wt% amino-functionalised DWCNT). The influence of filler content, the varying dispersibility, the aspect ratio, the specific surface area and an amino-functionalisation on the composite properties are discussed and correlated to the identified micro-mechanical mechanisms.     

Polymer matrix wave-transparent composites:A review

With the rapid development of electronic information technology,antenna systems in the fields of avia-tion,aerospace,transportation,and 5 G communication services are becoming more and more intensive and accurate.Polymer matrix wave-transparent composites with lightweight,low dielectric constant(e)and dielectric loss tangent(tanδ),high temperature resistance,and excellent mechanical properties are urgently needed in order to ensure high-fidelity transmission of electromagnetic wave and protect antenna systems from external interference.This review introduces the wave transmission mechanism,key compositions(polymer matrix&reinforced fibers),and several typical testing methods for dielec-tric properties of polymer matrix wave-transparent composites,mainly elaborates the latest research progress and achievements of polymer matrix wave-transparent composites from polymer matrix,rein-forced fibers and their surface functionalization methods,and presents the key scientific and technical problems that need to be solved urgently in the application of polymer matrix wave-transparent com-posites in the antenna systems.Finally,the future development trends and application prospects of the polymer matrix wave-transparent composites are also proposed.     

Electrocatalytic N‐Doped Graphitic Nanofiber – Metal/Metal Oxide Nanoparticle Composites

Carbon‐based nanocomposites have shown promising results in replacing commercial Pt/C as high‐performance, low cost, nonprecious metal‐based oxygen reduction reaction (ORR) catalysts. Developing unique nanostructures of active components (e.g., metal oxides) and carbon materials is essential for their application in next generation electrode materials for fuel cells and metal–air batteries. Herein, a general approach for the production of 1D porous nitrogen‐doped graphitic carbon fibers embedded with active ORR components, (M/MO_x, i.e., metal or metal oxide nanoparticles) using a facile two‐step electrospinning and annealing process is reported. Metal nanoparticles/nanoclusters nucleate within the polymer nanofibers and subsequently catalyze graphitization of the surrounding polymer matrix and following oxidation, create an interconnected graphite–metal oxide framework with large pore channels, considerable active sites, and high specific surface area. The metal/metal oxide@N‐doped graphitic carbon fibers, especially Co₃O₄, exhibit comparable ORR catalytic activity but superior stability and methanol tolerance versus Pt in alkaline solutions, which can be ascribed to the synergistic chemical coupling effects between Co₃O₄ and robust 1D porous structures composed of interconnected N‐doped graphitic nanocarbon rings. This finding provides a novel insight into the design of functional electrocatalysts using electrospun carbon nanomaterials for their application in energy storage and conversion fields.     

Thermal stress relaxation in magnesium matrix composites controlled by dislocation breakaway

In metal matrix composites (MMCs) thermal stress relaxation can be achieved either by interface debonding, crack propagation or by dislocation motion. The present paper shows that in the case of magnesium matrix, interface thermal stresses are relaxed by dislocation motion. Moreover the results obtained by mechanical spectroscopy prove that this dislocation motion is controlled by a solid friction mechanism, which is not thermally activated. This point is very interesting for the development of MMCs, which exhibit a high damping capacity over a wide frequency range. Dislocation hysteretic motion in the magnesium matrix is evidenced by the dependence of the mechanical loss on the stress amplitude. The obtained relationship obeys perfectly to the Granato–Lücke model for dislocation breakaway.     

Metal matrix composites. A bird’s eye view

Composite materials, in general, have so far been used mainly for structural applications. However, with regard to metal matrix composites, interest is growing on account of their physical properties. Indeed, customer requirements in this field cannot always be met by traditional materials. This paper first presents a brief overview of the interaction between fabrication, microstructure and properties of metal matrix composites. Further, some changes in the strategy for modelling and designing these materials are discussed. Finally, future prospects are outlined.     

EBSD – orientation analysis of monocrystalline diamonds used for diamond metal composites – Influence of sample preparation

This paper focuses on a new field of application for the EBSD‐technique. Generally, EBSD‐mappings are performed on different metal alloys used for quality assurance and to get information about the microstructure regarding grain orientation, grain size and distribution. In contrast, the orientation determination of monocrystalline diamond grains with an EBSD system is not a conventional method. Thus, this work describes the EBSD testing sequence in detail and illustrates the preparation of orientation data for a statistical design. Furthermore, dependencies of the sample preparation, alignment to the detector, and the analyzed position on the diamond on the quality of the Kikuchi‐patterns, respectively on the indexing rates, have been scrutinized. Finally, the orientation obtained of each tested diamond sample has been utilized in a statistical design to show a direct influence of the crystal orientation on the wear behavior of the diamond grains.     

Influence of the microstructure on the deformation behaviour of metal–matrix composites

In this contribution, investigations of the influence of the microstructure on the macro-, meso- and micro-effects in metal–matrix composites are presented by direct combination of experiment and simulation. The aim of the presented work consists in an improved understanding of the mechanical behaviour of heterogeneous materials by combining information of different length scales.     

WC–Co particulate reinforcing Cu matrix composites produced by direct laser sintering

Experimental investigations on the development of the WC–10%Co particulate reinforcing Cu matrix composite material have been conducted using direct laser sintering. The chemical compositions and microstructures of the laser processed material have been characterized using X-ray diffraction (XRD), energy disperse X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), and atomic force microscope (AFM). An excellent interfacial bonding between the reinforcement and the matrix was obtained. The WC reinforcing particulates typically had two distinct morphologies, i.e., partially dissolved and smoothed or completely dissolved and refined. The effects of the WC–Co content on the microstructural characteristics and resultant properties of the laser sintered parts have been studied. It was found that lowering the amount of WC–Co resulted in the insufficient reinforcement, while at a higher amount of WC–Co the significant agglomeration of the WC reinforcing particulates occurred. A homogeneous sintered structure with a high average hardness of HV_0.1384.6 was obtainable using 30 wt.% WC–Co.     

From the History of Science to the History of Knowledge – and Back

The history of science can be better understood against the background of a history of knowledge comprising not only theoretical but also intuitive and practical knowledge. This widening of scope necessitates a more concise definition of the concept of knowledge, relating its cognitive to its material and social dimensions. The history of knowledge comprises the history of institutions in which knowledge is produced and transmitted. This is an essential but hitherto neglected aspect of cultural evolution. Taking this aspect into account one is led to the concept of extended evolution, which integrates the perspectives of niche construction and complex regulative networks. The paper illustrates this concept using four examples: the emergence of language, the Neolithic revolution, the invention of writing and the origin of mechanics.     

Fracture behaviour of 2D-weaved, silica–silica continuous fibre-reinforced, ceramic–matrix composites (CFCCs)

Significantly improved fracture resistance (in terms of fracture toughness and fracture energy) can be imparted to monolithic ceramics by adopting composite design methodology based on fibre reinforcement technology. The present paper describes the fracture behaviour of one such fibre-reinforced material, namely the silica–silica based continuous fibre-reinforced, ceramic–matrix composite (CFCC) in two orthogonal notch orientations of crack divider and crack arrester orientations. Different fracture resistance parameters have been evaluated to provide a quantitative treatment of the observed fracture behaviour. From this study, it has been concluded that the overall fracture resistance of the CFCC is best reflected by total fracture energy release rate (J_c), which parameter encompasses most of the fracture events/processes. The J_c values of the composite are found to be more than an order of magnitude higher than the energy values corresponding to the plane strain fracture toughness (J_KQ, derived from K_Ic, the plane strain fracture toughness) and >200% higher than elastic–plastic fracture toughness (J_Ic). Apart from this, the composite is found to exhibit high degree of anisotropy in the fracture resistance and also, a significant variation in the relative degree of shear component with crack extension.     

Micromechanical modelling and experimental investigation of random discontinuous glass fiber polymer–matrix composites

Videomeasurements were used to estimate the damage in chopped random glass fiber polymer–matrix composites. In order to predict the overall mechanical behaviour, voiding evolution induced by fiber debonding is incorporated into a micromechanics-based constitutive model. The comparison between the experimental data and the numerical predictions shows a very good agreement.