Fracture of metal/ceramic interfaces

The present paper examines metal/ceramic interfaces. Energy release rates are calculated with the finite element method for different elastic–plastic material laws of the metal. The local strain field of the metal is measured during a four-point bending test with an optical method and compared with results from the simulations. The aim of the work is to understand the influence of interface strength and material properties on the energy release rate.     

The adhesion of metal/alumina interfaces

Cylinders of copper and nickel have been melted under various conditions to form sessile drops on alumina plaques. The resultant metal/ceramic adhesion at room temperature has been measured using the commonly adopted test in which the drops are pushed off the ceramic plaques. The stress system involved in the test has been analysed and it has been shown that the standard interpretation of the test, as a measure of interfacial shear strength, is not valid; the revised interpretation makes it a measure of adhesion in tension. Results for the Cu/Al₂O₃ and Ni/Al₂O₃ systems show that non-wetted interfaces can be strong and have strengths that are independent of contact-angle changes caused by wetting-temperature variations.     

The strength of metal/alumina interfaces

The room-temperature strengths of interfaces formed by melting aluminium, cobalt, gold, iron, nickel, palladium, silver, and uranium in contact with alumina have been measured. Correlations were sought between the strengths and the physical properties of the systems. Metals which formed void-free interfaces and were not subject to martensitic transformations bonded well to alumina. Metals subject to martensitic transformations (cobalt and uranium) were virtually non-adherent at room temperature.     

Thermal conductance of metal interfaces at low temperatures

In the present work the dependence of the heat transfer coefficient between Cu and Sn, Cu and Pb, and Cu and W on the temperature and an external magnetic field has been measured. The preparation of the metal-metal junctions has been performed by melting so that a close contact at the interface was guaranteed. The heat transfer coefficient has been found by a steady-state measuring method. In the case of the Cu-Pb junction the heat transfer coefficient could be measured both in the superconducting and normal states. For all the metal—metal junctions in the normal state a linear temperature dependence of the heat transfer coefficients on the temperature has been found. In the superconducting state a strong reduction of the heat transfer coefficient has been observed. In addition, a theoretical calculation of the heat transfer coefficient on metal-metal interfaces is given. First we consider the scattering of electrons on a steplike potential barrier between two gases of free electrons. Then the thermal conductance due to scattering in an alloy layer is calculated. Such an alloy layer may arise from diffusion during the contact preparation. Comparison of these two cases with the experiments shows the thermal conductance at the interface is mainly determined by the electron scattering on lattice irregularities in the diffusion layer.     

A molecular perspective of water at metal interfaces

Water/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as corrosion, lubrication, heterogeneous catalysis and electrochemistry. Although many fields have contributed to rapid progress in the fundamental knowledge of water at interfaces, detailed molecular-level understanding of water/solid interfaces comes mainly from studies on flat metal substrates. These studies have recently shown that a remarkably rich variety of structures form at the interface between water and even seemingly simple flat surfaces. In this Review we discuss the most exciting work in this area, in particular the emerging physical insight and general concepts about how water binds to metal surfaces. We also provide a perspective on outstanding problems, challenges and open questions.     

Surface analysis of polysiloxane/metal oxide interfaces

The interfaces between various types of silane-based primers and abraded mild-steel surfaces have been investigated using two surface-specific techniques in an attempt to ascertain the bonding mechanism between primer and metal. The XPS technique gave semi-quantitative information about the relative concentrations of primer and exposed steel while the SSIMS technique enabled the chemical state of the first few monolayers of surface to be elucidated. From some primer/metal systems the presence of FeSiO⁺ radicals was detected by SSIMS and it was found that the environmental resistance of structural adhesive joints, employing the various silane-based primers, could be directly related to the presence or absence of this radical.     

Dual-chemiresistor GC detector employing monolayer-protected metal nanocluster interfaces

The synthesis and testing of two gold-thiolate monolayer-protected (nano)clusters as interfacial layers on a dual-chemiresistor vapor sensor array are described. Responses (changes in dc resistance) to each of 11 organic solvent vapors are rapid, reversible, and linear with concentration at low vapor concentrations, becoming sublinear at higher concentrations. Limits of detection (LODs) range from 0.1 to 24 parts per million and vary inversely with solvent vapor pressure. When configured as a GC detector and used to analyze 0.5-L preconcentrated samples of the 11-vapor mixture, the array provides LODs of < or = 700 parts per trillion for most vapors, comparing favorably with those from an integrated array of polymer-coated surface acoustic wave sensors configured and tested similarly. This first report on the use of such an array as a GC detector shows that the combination of response patterns and GC retention times improves capabilities for vapor recognition compared to the sensor array alone or to single-detector GC systems. Spray-coated nanocluster thin films can be deposited reproducibly and exhibit response stability in air that ranges from fair to excellent for up to several months. Scaling the active device area down by a factor of 16 has no significant effect on sensitivity. Implications of these results for portable vapor sensing systems are discussed.     

Reinforcement coatings and interfaces in aluminium metal matrix composites

The interface between the matrix and reinforcement plays a crucial role in determining the properties of metal matrix composites (MMC). Surface treatments and coating of the reinforcement are some of the important techniques by which the interfacial properties can be improved. This review reports the state of art knowledge available on the surface treatments and coating work carried out on reinforcements such as carbon/graphite, silicon carbide (SiC) and alumina (Al2O3) and their effects on the interface, structure and properties of aluminium alloy matrix composites.The metallic coatings improved the wettability of reinforcement but at the same time changed the matrix alloy composition by alloying with the matrix. Ceramic coatings reduce the interfacial reaction by acting as a diffusion barrier between the reinforcement and the matrix. Multilayer coatings have multifunctions, such as wetting agent, diffusion barrier and releaser of thermal residual stress. The roles of reinforcement coating as a means of in situ hybridising and in situ alloying are described.     

Adhesion along metal–polymer interfaces during plastic deformation

In this paper a numerical study is presented that concentrates on the influence of the interface roughness that develops during plastic deformation of a metal, on the work of adhesion and on the change of interface energy upon contact with a glassy polymer. The polymer coating is described with a constitutive law that mimics the behavior of Poly-Ethylene Terephthalate. It includes an elastic part, a yield stress, softening and hardening with increasing strains. For the interface between the metal and the polymer a mixed-mode (mode I and II) stress-separation law is applied that defines the interface energy and an interaction length scale. At the onset of deformation the surface of the substrate has a self-affine roughness characterized by the so-called Hurst exponent, a correlation length and an rms roughness amplitude, that evolves as a function of increasing strain. The findings are the following: the interface energy decreases until the strain at yield of the polymer coating. Interestingly, after yielding as the polymer starts to soften macroscopically, the decreasing average stress levels result in partial recovery of the interface energy at the interface. At higher strains, when macroscopic hardening develops the recovery of the interface stops and the interface energy decreases. The effect of coating thickness is discussed as well as the physical relevance of various model parameters.     

Ice/metal interfaces: fracture energy and fractography

Results are presented of the fracture tests of ice/metal interfaces in an attempt to utilize fracture mechanics to characterize the failure of ice/solid adhesion. The four-point bending delamination specimen was used to measure the fracture energy of ice/aluminium and ice/steel joints at — 15 °C. The interfacial fracture energy was found to be dependent on ice type and formation procedure of the ice/metal composites. Crack growth was in a manner of asymmetrical bursting, and both cohesive and adhesive failure mechanisms were observed. Although the fracture of ice/metal interfaces was brittle in nature, the evidence of dislocation slip in ice crystals, as revealed by etching and replicating, suggests that microplastic deformations occur in the ice component.     

Polymer electrolytes and interfaces in solid-state lithium metal batteries

The polymer electrolyte based solid-state lithium metal batteries are the promising candidate for the high-energy electrochemical energy storage with high safety and stability. Moreover, the intrinsic properties of polymer electrolytes and interface contact between electrolyte and electrodes have played critical roles for determining the comprehensive performances of solid-state lithium metal batteries. In this review, the development of polymer electrolytes with the design strategies by functional units adjustments are firstly discussed. Then the interfaces between polymer electrolyte and cathode/anode, including the interface issues, remedy strategies for stabilizing the interface contact and reducing resistances, and the in-situ polymerization method for enhancing the compatibilities and assembling the batteries with favorable performances, have been introduced. Lastly, the perspectives on developing polymer electrolytes by functional units adjustment, and improving interface contact and stability by effective strategies for solid-state lithium metal batteries have been provided.     

A thermodynamic analysis of ceramic oxide/liquid metal interfaces

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Atomistic simulation of misfit dislocation in metal/oxide interfaces

In this work, we use a Chen–Möbius inversion method to get the interatomic potentials for metal/oxide interfaces, and then study the misfit dislocation in a series of interfaces, including Au/MgO, Rh/MgO and Ni/MgO. The calculation shows that dislocation line always prefers at the first monolayer of metal side, with metal on top of Mg at the dislocation core, and metal on top of O at the interface coherent area. Also, the Burgers vector for these interfaces is determined at two cases. For Rh/MgO and Ni/MgO, it keeps the value of . But for Au/MgO, it changes from to a[1 0 0] as the number of monolayers in metal side increases. This work shows a theoretical understanding of misfit dislocations in metal/oxide interfaces, from dislocation structure, density to Burgers vector orderly, and gives some hints to experiments.     

Tensile strength of composites with brittle reaction zones at interfaces

A theoretical model of the longitudinal strength of brittle fibre-reinforced composites with brittle reaction zones was presented for both cases of strongly and weakly bonded fibre/brittle zone interfaces. First, on the basis of the fracture mechanics, a model of the strength of the fibres coated with strongly adhering brittle zones was proposed as a function of the thickness of the brittle zones. Next, the conditions under which debonding occurs at the interfaces were investigated with the aid of the shear lag analysis proposed by Cox. The theoretical model was then examined using composites with strongly and weakly bonded interfaces. The proposed model agreed fairly well with the experimental results. Finally, the permissible thickness of the brittle zone below which no reduction in fibre strength appears was calculated, using the proposed theory, under the condition of strong interfacial bonding, for carbon, boron and silicon carbide fibres which are of practical use. The calculated values of the thickness were smaller than 1 m.     

Quantum chemical calculation of electron transfer at metal/polymer interfaces

Calculation of contact charging at metal/polymer interfaces were performed by a quantum chemical method (DV-Xa). In the calculation, model clusters with dangling bonds were used. The model clusters showed surface states in the density of states (DOS), the electron transfer occurred at the contact interfaces between polymer and Al. Then, 0.3 nm was a reasonable value as the contact distance in the present simulation.Contact electrifications between PTFE and six metals, such as Pt, Au, Cu, Al, Pb and Ca were simulated. The charge transferred from the metal to PTFE depended on the work function of the metals, and had a gap in range of 4.25–4.28 eV. According to the gap of metals were classified into two groups. If Fermi level of a metal is lower than the lowest unoccupied molecular orbital (LUMO) level of PTFE, the electrons of the metal transfer to the surface state (interface state). Electrons in the other metals with a higher Fermi level move into the conduction band of PTFE.     

On eliminating deposition-induced amorphization of interfaces in refractory metal multilayer systems

Multilayer thin films with refractory metal components are susceptible to solid state amorphization. It is an objective to minimize this interfacial reaction in order to ensure smooth layering and compositionally abrupt interfaces. These features are desirable for maximum reflectivity in X-ray optic applications such as projection lithography as well as neutron supermirror applications. This goal is achievable when the deposition process is optimized to thermalize the sputtered neutrals. Low working gas pressures (below 5 m Torr) and large source-to-substrate distances (more than 12 cm) typically provide the proper conditions to form dense sputter deposits without adatom-induced, interfacial amorphization. The interfaces of Mo/Si and Ni/Ti multilayers are examined with high resolution electron microscopy for samples sputter deposited under thermalized conditions. It is shown to be possible to produce crystalline, refractory metal layers in the as-deposited structure without amorphous interfacial regions.