Wetting and spreading of liquid metals on ZrB2-based ceramics

The possibility to exploit commercially the peculiar characteristics of refractory metallic and ceramic materials and in particular of Zirconium diboride ceramics—a class of promising materials for high temperature applications—often depends to a great extent on the ability to join different ceramics one to the other or to special metallic alloys. As the behaviour of a metal-ceramic joint is ruled by the chemical and the physical properties of the interface, the knowledge of wettability, interfacial tensions and interfacial reactions is mandatory to understand what happens at the liquid metal-ceramic interface during joining processes. In the framework of an extensive study aimed at evaluating the wettability and the interfacial characteristics of different metal-ceramic systems, the behaviour of ZrB₂ in contact with liquid Ag and its alloys (Cu, Ti, Zr, Hf) has been studied. ZrB₂ pure, with different sintering aids or “alloyed” with other ceramic materials (SiC, Si₃N₄), have been used. The wetting and spreading experiments have been performed by the sessile drop technique under controlled atmospheres. The wetting and spreading characteristics and the interfacial reactions are discussed as a function of time, compositions of the ceramic and of the alloy involved. The interfacial morphologies, analysed by SEM and EDS, show the presence of regular interfaces and adsorption layers and of different bulk phases which are interpreted in terms of the relevant phase-diagrams.     

Structure induced wide range wettability:Controlled surface of micro-nano/nano structured copper films for enhanced interface

The wettability of materials used in the production of devices employed in various technological domains have attracted significant attentions.Therefore,it is important to design the surfaces of these materi-als such that they can provide the required surface free energy and simplify the interfacial structure.Herein,various Cu films with a highly controllable surface wettability and a wide range of contact angles ranging from 6° to 152° were fabricated,and the corresponding mechanism was discussed.A wide range of wettability was realized by controlling the surface structure of the Cu film.The nanogap structure of the vertical nanowire-array film led to a high surface free energy.Similarly,the oblique nanowire-array film increased the surface free energy;however,the surface free energy was dependent on the size of the nanowires rather than on the nanogaps owing to the crystallinity of the film.Additionally,cluster-nanowire-array films were designed to realize a wettability transition from hydrophilicity to hydrophobicity with a constant surface free energy.The Cu foam possessed a superhydrophilic surface owing to its high porosity,whereas the cluster-nanoparticle structure possessed a superhydrophobic surface.In addition,we noted that the structure-induced wettability played an important role in tuning the semiconductor and metal interfacial stress and simplifying the interfacial structure.Furthermore,the outstanding electrical conductivity of the Cu films indicates its promising potential as an electrode.The structure-induced wettability proposed in this study can be applied for a wide range of materials,particularly for films used for advanced applications.     

Mechanical properties of the interface of gelcoat resin–composite materials and improvements via surface treatment methods

A gelcoat resin was applied to improve the surface properties of composite materials. Combinations of a gelcoat with a glass/epoxy or carbon/epoxy result in a prime composite structure. Prior to application, however, the mechanical properties of these bonds should be studied. Three material pairs, glass/epoxy-gelcoat (GEG), carbon/epoxy-gelcoat (CEG), and glass/polyester-gelcoat (GPG), were studied to experimentally determine the interfacial properties. Then, four surface treatment methods were applied to the GEG and CEG composite, and the resulting materials were investigated to assess potential improvements to the interfacial properties. Three tests, single-leg bending, peel, and single lap joint, were carried out, and experimental results were combined with equations to obtain the strength or energy. It was observed that the strength or energy of the GPG material was higher than that of the GEG and CEG. After the surface treatment, the energy and strength of the interfaces had increased over that of the values of the untreated surfaces.     

The effect of interfacial energy and phase fraction on the particle shape and the dihedral angles in two-phase small particles containing a cusp-oriented interface; computational model

The equilibrium shape and dihedral angles at the solid–liquid–vapor tri-junctions of two-phase alloy small particles containing a cusp-oriented interface were modeled as a function of phase fraction, surface energy and the interfacial energy. The calculation was applied to different combinations of surface and/or interfacial energies to demonstrate the various possible particle shapes and dihedral angles that result for two-phase particles. The dihedral angles at the tri-junction vary with the phase fraction, due to the coupling between the relative amounts of each phase, interfacial energy relative to the two surface energies and the equilibrium conditions at the tri-junction. These features can be used to find the ratio of the interfacial energy to the surface energies of two-phase particles for any state of matter.     

Fatigue behaviour characterization of the fibre-matrix interface

The fracture behaviour of FRP composite materials is significantly influenced by the behaviour of the fibre-matrix interfacial bond. Thus far interfacial bond mechanical characterization has been based upon the critical strength and critical fracture energy of debonding. Characterization of the fatigue behaviour of the interfacial debonding process, however, may be more valuable for composite design and fibre-matrix selection. A fracture mechanics model of interfacial bond fatigue based on the mode II strain energy release rate (G _II) is presented. An expression forG _II is derived for a single fibre in matrix cylinder model. By fitting the model to single fibre pull-out fatigue test data, fatigue crack propagation plots for specific fibre-matrix combinations can be drawn. These should prove useful for the development of fatigue resistant FRP composite materials.     

Subsurface particle monolayer and film formation in softenable substrates: Techniques and thermodynamic criteria

We have previously shown that subsurface particulate monolayers form rather generally when inorganic materials are appropriately deposited onto softenable organic polymer substrates. Here we analyse, in terms of the surface free energies, the thermodynamic stability on soft substrates of the various conceivable subsurface structures versus the possible above-surface configurations. For both rigid preformed particles and flexible growing clusterd (as occur in vacuum deposition), the tendency for complete immersion is determined by the same inequality among the various surface and interfacial tensions. Estimates of these parameters predict a completely embedded structure to be thermodynamically favourable for most inorganic materials on organic polymer substrates, with generally a partially embedded structure predicted for organic materials. Although, with vacuum deposition of the particle material, subsurface structure formation is often limited by kinetic factors (associated with substrate temperature and deposition rate)), we describe a variety of other fabrication techniques by which such structures can indeed be fabricated with remarkable generality from preformed particles. Moreover, with organics, completely—rather than partially—embedded structures can be formed, if particles are spread on the surface of the polymer and the system is exposed to a suitable solvent vapour. This can be rationalized in terms of the above- mentioned inequality, provided that appropriate surface and/or interfacial tensions are calculated for this situation. Continuous subsurface films are predicted to become thermodynamically favourable during vacuum deposition, compared with embedded particulate structures, when particle coalescence becomes too slow to keep the projected-area coverage below certain maximum levels. This is expected as the particles exceed some minimum size, and we confirm this prediction experimentally.     

Environment,pollution, energy and materials

In this paper it is tried to deal with materials from the ecological point of view, that means regarding futural shortance of energy, materials and water and the problems of pollution and waste. After the introduction which puts the problem, it is tried in the first chapter to give data on the capital, income and consumption of materials and of the energy including the limits of increasing energy-production. In the second chapter it is tried for some building materials belonging to the metals, the ceramic materials and the polymers, to give preliminary data about the demand of energy and water necessary for the chain: raw material—building material—building product and about the emission of pollutants during this chain. Pollution also influences the service-lifetime of building materials, which is dealed with in the last stage of materials: waste and what can be done with it; while finally some remarks are made regarding the management of environment.     

Nanotribology, nanomechanics and nanomaterials characterization

Nanotribology and nanomechanics studies are needed to develop fundamental understanding of interfacial phenomena on a small scale and to study interfacial phenomena in magnetic storage devices, nanotechnology and other applications. Friction and wear of lightly loaded micro/nanocomponents are highly dependent on the surface interactions (a few atomic layers). These structures are generally coated with molecularly thin films. Nanotribology and nanomechanics studies are also valuable in the fundamental understanding of interfacial phenomena in macrostructures and provide a bridge between science and engineering. An atomic force microscope (AFM) tip is used to simulate a single-asperity contact with a solid or lubricated surface. AFMs are used to study the various tribological phenomena that include surface roughness, adhesion, friction, scratching, wear and boundary lubrication. In situ surface characterization of local deformation of materials and thin coatings can be carried out using a tensile stage inside an AFM. Mechanical properties such as hardness, Young's modulus of elasticity and creep/relaxation behaviour can be determined on micro- to picoscales using a depth-sensing indentation system in an AFM.     

Mussel-inspired block copolymer lithography for low surface energy materials of teflon, graphene, and gold

Mussel-inspired interfacial engineering is synergistically integrated with block copolymer (BCP) lithography for the surface nanopatterning of low surface energy substrate materials, including, Teflon, graphene, and gold. The image shows the Teflon nanowires and their excellent superhydrophobicity.     

Adaptive finite element remeshing in a large deformation analysis of metal powder forming

In this paper, a general framework for the finite element simulation of powder forming processes is presented. A large displacement formulation, based on a total and updated Lagrangian formulation and an adaptive finite element strategy based on error estimates and automatic remeshing techniques are utilized. To describe the constitutive model of the highly non‐linear behaviour of powder materials, an elliptical cap model based on a hardening rule to define the dependence of the yield surface on the degree of plastic straining is applied. The interfacial behaviour between the die and powder is modelled by using a plasticity theory of friction in the context of an interface element formulation. Finally, the powder behaviour during the compaction of a set of complex shapes are analysed numerically. The simulation of the deformation is shown as well as the distribution of relative density contours at different time stages. The results clearly indicate that the algorithm makes it possible to simulate the powder forming problems efficiently and automatically. Copyright © 1999 John Wiley & Sons, Ltd.     

Novel organic monotectic alloy and its thermal,physicochemical, and microstructural studies

The phase diagram study of an organic analogue of a nonmetal–nonmetal system involving 4-bromochlorobenzene and resorcinol shows the formation of a eutectic and a monotectic. The phase equilibrium shows the large miscibility gap region with the consolute temperature 143.0 °C. Growth kinetics of the eutectic, the monotectic and the pure components studied at different undercooling, suggests the applicability of Hillig–Turnbull’s equation. For binary materials and parent compounds, the heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated from the enthalpy of fusion values determined by the DSC method. The solid–liquid interfacial energy shows the applicability of Cahn’s wetting condition. The effects of solid–liquid interfacial energy on solidification behaviour of monotectic alloy have also been discussed. The microstructures of monotectic and eutectic show the uniform array of droplets and broken lamella, respectively.     

Three dimensional simulation of microstructure evolution for ceramic tool materials

The observation and scientific quantitative characterization of three dimensional microstructure evolution during sintering process of ceramic tool materials is important to investigate the influence of nano-particles on mechanical properties. The relationship between microstructure and mechanical properties of ceramic tool materials can be established to direct the development of nano-composite ceramic tool materials by the research of the grain growth, grain boundary migration, distribution of nano-particles and microstructure densification at the different sintering temperature and pressure. In this paper, a 3D Monte Carlo model of three-phase nano-composite ceramic tool material is built and applied to simulate the microstructure evolution during sintering process. In this model, the grain boundary energy of each phase and interfacial energy between two phases are taken into consideration as the driving forces for grain growth. The sintering temperature and pressure are successfully coupled into the Monte Carlo simulation model. The microstructure evolution of defect free three-phase nano-composite ceramic tool materials is successfully simulated at different sintering temperature and pressure. The simulation results show that the higher the sintering temperature is, the faster the grain growth. However, the sintering pressure has little effect on the grain growth.     

Antiplane shear crack problem in bonded materials with a graded interfacial zone

In this paper the interface crack problem for two elastic half spaces bonded through a nonhomogeneous interfacial zone is considered. It is assumed that the medium is under antiplane shear loading. The problem is solved for two different interfacial zone models that may approximate the actual diffusion bonded materials or homogeneous solids bonded through a functionally gradient material. Extensive results are obtained by varying the stiffness and the interfacial zone thickness to crack length ratios. Also, for various limiting cases the behaviour of the stress intensity factors and the strain energy release rates are studied.     

Effect of colloidal silica on the strength and energy absorption of glass fiber/epoxy interphases

Prior research has demonstrated that fiber-sizings can be designed to yield composite materials that simultaneously possess high energy absorption and structural properties. The improved mechanical properties resulted from control of the fiber surface chemistry and nano-scale topological features within the fiber–matrix interphase. The present study further explains the role of sizing chemistry and surface roughness on composite material performance. Model and commercial glass fiber epoxy specimens were fabricated using these fiber sizing systems resulting in interphase regions with varied surface topology and chemical functionality. Micromechanical measurements were performed using the microdroplet adhesion test method to quantify the fiber–matrix interfacial properties. Improvement in energy absorption and interfacial shear strength due to the presence of the nano-scale silica were quantified. Inspection of the failure modes revealed that the existence of colloidal silica promotes crack propagation along a more tortuous path within the interphase that results in progressive failure and contributes to increased energy dissipation.     

定向凝固钛铝合金熔体与铸型界面反应研究展望

钛铝合金是性能优异的高温合金,在航空航天领域有广泛的应用前景,但由于其熔体具有较高的活性,制备时熔体与所有已知的铸型材料会发生不同程度的反应,限制了钛铝合金铸件的发展.定向凝固技术作为制备高精度钛铝合金的新工艺,使铸件组织定向排列,可以进一步提高钛铝合金的使用性能,因此如何调控凝固过程中钛铝合金熔体与铸型材料间的界面反应成为目前有关定向凝固钛铝合金研究的一个热点.从目前国内外关于钛铝合金熔体与铸型材料间界面反应的研究出发,综述了定向凝固过程中铸型材料、涂层成分、工艺参数及合金元素等对界面反应的影响,介绍了界面反应的理论水平,系统收集了界面反应的各项研究结果.     

Der Pendelfurcher – ein Prüfgerät zur Untersuchung des Formänderungsverhaltens duktiler Werkstoffe bei dynamischer Beanspruchung

The pendulum furrower – a test device for the investigation of the deformation behaviour of dilatable materials at dynamical loading Within this contribution a new test device is presented, allowing the investigation of the deformation behaviour of dilatable materials at shock loading. The base equipment is a commercial pendulum striking apparatus, equiped with a Brinell ball at the end of the pendulum. From the adjustable feeding of the rigid fixed flat specimen and the pendulum path through the material of the specimen follows automatically an arc-shaped wearing track. By means of the energy of friction, registered during the oscillation of the pendulum and the following measuring of the volums of the furrows new special charakteristic values of the materials can be find out.     

Pressure-induced transition-temperature reduction in ZnS nanoparticles

The study of the structural transition in nanoscale materials is of particular interest for their potential applications. In the present study, we have observed a lower temperature T = 250?°C for the phase transition from the sphalerite structure to the wurtzite structure in ZnS nanoparticles under a pressure of 1?GPa, as compared to those, T = 400 and 1020?°C, for ZnS nanoparticles and bulk ZnS under normal pressure, respectively. The reduced transition temperature is attributed to the applied pressure leading to tight particle-particle contacts, which change the surface (or interfacial) environment of the nanoparticles and thus their surface (or interfacial) energy.     

Effect of filler surface morphology on the impact behaviour of hydroxyapatite reinforced high density polyethylene composites

Instrumented falling weight impact tests have been carried out to characterize the impact behaviour of hydroxyapatite reinforced high-density polyethylene composite (HA-HDPE) in order to use this biomaterial in skull implants. The effects of HA filler surface morphology and volume fraction on the fracture toughness were studied, and fracture mechanism investigated. Impact resistance was found to be markedly improved by using a sintered grade HA filler with smooth particle surface instead of spray dried grade HA with rough surface. SEM examination of impacted fracture surfaces revealed that the improvement of impact resistance was due to the stronger interfacial bonding between smooth HA particles and HDPE polymer matrix compared with that between rough HA and HDPE, which results in more energy absorption during impact and hence better fracture resistance.     

Peculiarities of the mechanical response of heterogeneous materials with highly deformable interfaces

Peculiarities of the deformation and fracture of heterogeneous materials with a large fraction of interfacial regions (interfacial materials) under the action of complex alternating loads have been studied by computer-aided simulation. The dependence of the character of fracture, deformability, dissipation of the applied energy, and strain distribution in the material bulk on the frequency of cyclic loading was determined. High-frequency vibrations at a frequency much greater than that of the natural oscillations may significantly increase the deformability of interfacial materials.