Characterisation of mechanical properties of electrochemically deposited thin silver layers

Abstract

In the present work, mechanical properties of electrochemically deposited thin silver layers with known thickness over brass substrates were investigated. For determination of mechanical properties of the layers, a method was used which is novel compared to those traditionally used in practice (in which, for example, a tensile test is carried out on a deposit after removal of the deposited layer from the substrate). The method developed and reported here is a combination of microindentation experimentation and numerical simulations and gives the opportunity to obtain mechanical properties of thin layers without their removal from the substrate. Vickers' microindentation experiment of the silver layer was realized and as a result, led to experimental a load–displacement curve. After that the process of microindentation was modelled numerically by means of finite element method. The numerically obtained load–displacement curve was compared with the experimental one and the result shows good correlation between numerical and experimental curves. For some kinds of layers, which are difficult or impossible to strip away from the substrate, this method reported in this paper is the only one feasible.     

The chemical structure and stability of plasma-deposited thin hydrocarbon layers on polyethylene

AbThe surfaces of polyethylene (PE) films were modified by deposition of layers from acetylene/ethylene monomer gases in a low-pressure radio-frequency plasma. The chemical structure of the plasma-deposited layers and their long-term stability were studied by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurements. These studies have shown that the plasma-deposited layers consist mainly of amorphous, short-chain, functional C_xH_y structures with aryl units. As the reactive radical centers formed during the plasma process are susceptible to further reaction with atmospheric oxygen and water, the chemical stability of these layers was investigated. This stability is ensured over the long-term, although an increase in the number of functional groups is obtained over time. It was demonstrated that the post-reactions reach a state of equilibrium after a few weeks.     

Production of Si55 Al20 Fe10 Ni5 Cr5 Zr5 bulk amorphous alloy by hot pressing

Abstract

The temperature dependence of the relative density was examined for a Si₅₅ Al₂₀ Fe₁₀ Ni₅ Cr₅ Zr₅ alloy which was produced by hot pressing of the amorphous powder during heating up to various temperatures under a critical pressure of 1·5 GPa through a heating/pressing cycle. The density of the compacts increased with increasing temperature and reached a maximum near the crystallisation temperature of 698 K. The relative density of the compacts reached 98·3% at the critical condition of 1·5 GPa and 687 K. The hardness value of the bulk specimen was 940 HV(10 gf, 0·098 N), corresponding to that of the amorphous ribbon. Exposure to higher temperatures resulted in the precipitation of the crystalline phase. The present results indicate that Si based alloys can be produced in a compact form with a low fraction of voids by hot pressing the amorphous powder.     

Ultra-Thin Polymer Layer Deposition by Aerosol–Dielectric Barrier Discharge (DBD) and Electrospray Ionization (ESI) at Atmospheric Pressure

Polyolefins are chemically inert and do not adhere well to metals, polymers or inorganics. To overcome this problem, polyolefin surfaces were modified thermally, plasmachemically, or by flame treatment with different oxygen-containing groups, however, unfortunately, such treatments were accompanied by undesired, adhesion lowering polymer degradation. To solve this dilemma, solutions of synthetic polymers and copolymers were prepared, sprayed into the barrier discharge or electrosprayed without discharge and deposited as thin adhesion-promoting layers. The deposited polymer layers from poly(vinylamine), poly(ethylene glycol)–poly(vinyl alcohol) copolymers and poly(acrylic acid) were endowed with monotype functional groups. Using the aerosol — dielectric barrier discharge only a fraction of functional groups survived the deposition process in contrast to the electrospray in which all functional groups were retained.     

Interfacial structure and bond strength of ultrasonic brazed Al–304 stainless steel dissimilar joints

Abstract

A filler alloy (Zn–14 at.-%Al) was used to join aluminium to 304 type stainless steel by ultrasonic brazing at 673 K for different ultrasound application times. Different reaction layers could be observed at the interface, containing Fe–Al, Fe–Zn, and Al–Zn solid solutions. As the amount of these solid solutions increased at the interface, there was a gradual improvement in the joint bond strength. The maximum bond strength of 146 MPa was obtained for the Al–304 joint brazed at 673 K for 3 s ultrasound application time. A critical remaining thickness of the filler alloy after ultrasonic application improves the interfacial joining. Extending the ultrasound application time beyond 3 s causes a bulk escape of the brazing alloy from the interface and leads to a direct interaction between aluminium and 304, which increases the possibility of forming intermetallics, and consequently decreases the joint bond strength.     

Corrosion resistance of AA2219 aluminium alloy: electrochemical polarisation and impedance study

Abstract

The addition of copper increases the strength of aluminium, but decreases the localised corrosion resistance of the metal to seawater as the copper containing intermetallics exhibit different electrochemical properties from the matrix. The main requirement of corrosion resistance could be met through the surface modification by removing the copper rich phase. The present work involves investigations of the influence of prior copper removal treatment on the pitting and general corrosion resistance of AA2219 alloy containing a high copper content in different initial thermal tempers. Significant improvement in the pitting and general corrosion resistance after surface copper removal treatment was evident from the results of electrochemical polarisation and the impedance tests. Attempts were also was made to modify the surface further, with a conversion layer of cerium as an alternative to the chromate coating.     

Weak boundary layers on wood surfaces

Adoption of the weak boundary layer (WBL) concept in wood adhesion science and a general extension of the concept are suggested. A distinction is made between a chemical weak boundary layer (CWBL) and a mechanical weak boundary layer (MWBL). Definitions of both CWBL and MWBL are proposed. On wood, a CWBL is caused mainly by extractives migrating to the wood surface after machining, whereas an MWBL is caused mainly by the machining operation itself or by degradation of the fibres at the surface, in practice mainly by natural (UV) light irradiation. Sawn endgrain and planed side-grain surfaces of softwoods have been studied by scanning electron microscopy [SEM and environmental SEM (ESEM)]. Both sawn and planed wood surfaces are deformed to a depth of 0.1-0.2 mm to such an extent that one cannot expect the same strength at the surface as in the intact wood material. The crushed and damaged surface can be expected to contain failure initiation sites when the glueline, especially in an end-grain joint, or a coating is exposed to stresses. Furthermore, this crushed and damaged surface can be expected to be a barrier for adhesives and coatings to penetrate into the material and anchor to intact wood material. A comparison between microtomed and sawn end-grain surfaces has shown that the damaged fibres seem, to some extent, to improve the glue joint performance, using a conventional glue. Reasons for this are discussed.     

Deformation and fracture of adhesive layers constrained by plastically-deforming adherends

The use of an embedded-process zone (EPZ) model to investigate the mode I cohesive parameters for plastically-deforming, adhesively-bonded joints is demonstrated in this paper. It is shown that for the particular systems investigated, the cohesive parameters are consistent with an adhesive layer deforming in accordance with its bulk constitutive properties (as constrained by the adherends). In other words, these systems provide examples where the cohesive tractions exerted by an adhesive layer can be calculated simply from considerations of the constrained deformation of the adhesive. Consistent with such calculations, the peak stress in the adhesive layer decreases as the level of the constraint decreases (either with an increase in the thickness of the adhesive layer or with a decrease in the thickness of the adherends). It is also shown that owing to a compensating effect in which the critical displacement for failure varies with the constraint, the energy absorbed by the adhesive layer (the 'intrinsic' toughness of the joint) is essentially independent of the geometry in these systems.     

Effect of heat treatment on corrosion behaviour of deposited Fe–40Al intermetallics

Abstract

A study using electrochemical techniques of the susceptibility to corrosion in 0·1M NaCl solution (pH 3) of atomised and deposited Fe–40Al (at.-%) intermetallic material at room temperature is reported. Specimens were heat treated at temperatures of 600 and 900°C for 24 and 72 h. Potentiodynamic polarisation, linear polarisation resistance, potential–time, and electrochemical current noise data were collected. The untreated material displayed higher corrosion resistance than the heat treated material. In the treated material, the corrosion resistance increased with both the time and temperature of heat treatment. Also, untreated material was more susceptible to pitting corrosion than heat treated material. As the temperature or the time of heat treatment was increased, the material became more resistant to pitting. This improvement in resistance to pitting was related to a decrease in surface defects, such as pores and cracks, and an increase in grain size. Thus, heat treatment lowered the number of active sites and helped the material to establish a more protective film.     

Oxidising type inhibitors for protection of aluminium and steel surfaces in sodium chloride solutions

Abstract

Photoelectron spectroscopy was used to study the composition of surface films formed on aluminium and steel when protected from corrosion in aqueous chloride media by inorganic inhibitors of the MeO^2?₄ oxidising type and by mixtures of these and monoethanolamine (MEA). The surface condition plays a significant role in the protection of aluminium. In the adsorption of molybdate on to an etched surface reduction of Ma(VI) to Mo(IV) occurs whereas on an unetched surface, as also for a steel surface, no reduction occurs. In the case of chromate, reduction to Cr( III) took place on steel and on aluminium. Synergism was established in the inhibition of corrosion of steel by a combination of inorganic oxidisers and MEA and a study made of this phenomenon.