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Expedient simulations and numerical modelling of forming processes depend on a good knowledge of the friction at the tool–sheet metal contact. The absolute value of the friction force or relative changes of this force due to changing conditions are vital input for a reliable numerical model. For that reason, a good selection of a laboratory experiment that can measure the friction under forming conditions is an essential step. This work is part of a large European Union project named ASPECT, which evaluates the friction force evolution in sheet metal forming as a result of changes in contact conditions. Simplified tribological lab-scale techniques showed an temperature dependence of friction opposite to what is measured in state-of-the-art macroscopic flat strip drawing tests. To understand and overcome this contradiction, a new method was developed to integrate the deformation aspect into a friction test; this approach assures closer resemblance to the actual forming conditions. The aim is to develop a method that measures the effect of temperature and speed on the resistance to sliding and deformation, and to provide an efficient prescreening and ranking of forming oils. [ABSTRACT FROM AUTHOR]

Considering that these elements will be essential for future generations, the major consuming countries must demand best practices throughout the life cycle of products that use potentially toxic elements, and, thereby, help to support the long-term sustainability of many species worldwide. Anthropogenic dissolved colloid/nanoparticle bound samarium, lanthanum and gadolinium in the Rhine River and the impending destruction of the natural rare earth element distribution in rivers. Relationship of the hair content of rare earth elements in young children aged 0 to 3 years to that in their mothers living in a rare earth mining area of Jiangxi. [Extracted from the article]

A method for the nucleation enhancement of nanocrystalline diamond (NCD) films on silicon substrates at low temperature is discussed. A sputter deposition of a Mo seed layer with thickness 50 nm on Si substrates was applied followed by an ultrasonic seeding step with nanosized detonation diamond powders. Hot-filament chemical vapor deposition (HF-CVD) was used to nucleate and grow NCD films on substrates heated up at 550 °C. The nucleation of diamond and the early stages of NCD film formation were investigated at different methane percentages in methane/hydrogen gas mixtures by atomic force microscopy, micro-Raman spectroscopy, scanning electron microscopy, and grazing incidence x-ray analyses in order to gain specific insight in the nucleation process of NCD films. The nucleation kinetics of diamond on the Mo-coated Si substrates was found to be up to ten times higher than on blank Si substrates. The enhancement of the nucleation of diamond on thin Mo interlayers results from two effects, namely, (a) the nanometer rough Mo surface shows an improved embedding of ultrasonically introduced nanosized diamond seeds that act as starting points for the diamond nucleation during HF-CVD and (b) the rapid carbonization of the Mo surface causes the formation of Mo2C onto which diamond easily nucleates. The diamond nucleation density progressively increases at increasing methane percentages and is about 5×1010 cm-2 at 4.0% methane. The improved nucleation kinetics of diamond on Mo interlayers facilitates the rapid formation of NCD films possessing a very low surface roughness down to ∼6 nm, and allows a submicron thickness control. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) of tungsten nitride carbide (WNxCy) on methyl-terminated self-assembled monolayers (SAMs) is investigated. SAM substrates provide extended transient regimes of different lengths, during which the WNxCy film growth is nonlinear. The extent of this offset from linear growth depends on the alkyl chain length. The film morphology is characterized by atomic force microscopy, which reveals island growth and fractal behavior. During the transient regime, WNxCy deposition shows nonconservative growth, as revealed by the low film density and a roughness exponent α of ∼0.4–0.5. During the linear growth regime, a conservative mechanism is observed, characterized by a higher, constant film density and α∼0.7. These observations do not apply to all ALD deposited films. In particular, ALD HfO2 films follow a conservative-type mechanism during the entire range of growth. [ABSTRACT FROM AUTHOR]

The growth of tungsten nitride carbide (WNxCy) films obtained by atomic layer deposition using triethylboron, tungsten hexafluoride, and ammonia precursors is determined by the density and type of reactive sites. The film properties change as a function of thickness. On silicon dioxide and silicon carbide, growth is initially nonlinear such that the transient regimes are characterized by island formation, as evidenced by a parabolic tungsten growth curve extending to film thicknesses of up to 5 nm. Such films have low densities of ∼4–6 g cm-3 corresponding to only ∼30%–45% of the bulk density of ∼13.1 g cm-3 determined for a WN0.45C0.55 composition. X-ray reflectivity, thermal desorption, and elastic recoil detection spectroscopies reveal surface roughening and compositional and density differences close to the substrate surface. The offset from linear growth in the case of WNxCy films deposited on silicon dioxide is induced by the initial reaction of silanol and siloxane groups with triethylborane resulting in passivating ethylsilyl groups on the surface. A transient regime is not observed for WNxCy growth on hydrogen-terminated silicon with the initial growth being dominated by the reduction of tungsten hexafluoride to tungsten. On silicon nitride a short transient regime is observed relative to the carbide and oxide surfaces attributed to the enhanced binding of the triethylboron precursor. [ABSTRACT FROM AUTHOR]

This paper evaluated the internal stresses of different diamond and diamondlike carbon (DLC) coatings. For the diamond coatings, the stresses were determined using micro-Raman spectroscopy and x-ray diffraction (XRD), while the stresses of DLC films were determined with bent plate method. The internal stress was related to the structural properties of the coatings. Direct current plasma jet, combustion flame, and microwave chemical-vapor deposition processes were used to prepare the diamond coatings on the tungsten carbide or molybdenum substrates, while the DLC films were deposited on the silicon wafers with filtered cathodic vacuum arc process. From the Raman spectra of the diamond coatings, the compressive internal stresses were determined, which were related to the microstructure of the coatings. The results from XRD were comparable with those obtained from micro-Raman spectroscopy. Higher compressive residual stresses in the DLC films were noticed, which were also related to their chemical bonding nature as well as their microstructures. [ABSTRACT FROM AUTHOR]

A technique for wear sensing using a sacrificial layer with specific material properties has been developed successfully. This is achieved by recording the temperature evolution underneath the sacrificial organic layer during sliding tests, and by correlating the recorded temperature with a wear depth. Finite element modeling was used to calculate the contact temperature which spreads through the sacrificial layer under different sliding test conditions. Numerical simulation was used to determine the optimal parameters for the best correlation between temperature and wear depth. These parameters were used to select the appropriate sacrificial layer for wear sensing. Thus, an epoxy layer was implemented and experimental measurements were carried out to check the correlation between the measured temperature underneath the epoxy layer and wear depth. It was found that a low thermal conductivity of the sacrificial layer of less than 1 W/m K and a relative high thermal conductivity of the substrate, namely more than 4 W/m K are the optimal parameters for our thermal wear sensing system. The thickness of the sacrificial layer is also a crucial parameter and has to be taken into account when designing such a sensing system. [ABSTRACT FROM AUTHOR]

A [sup 59]Co NMR experiment has been used to investigate the structure of two series of Co films with thicknesses varying from 5 to 400 nm which were electrodeposited on Cu at the electrolyte pH value of 2.1 and 3.7, respectively. It was shown that the overall structure of studied Co films consists of a very good quality fcc phase and a heavily faulted hcp phase in about equal proportions. The exceptions are very thin Co layers (below 20 nm) where the hcp structure was stabilized at pH 3.7 and overpotential of 0.9 V. This effect is attributed to the formation of hexagonal cobalt hydroxide in the early stage of deposition, which acts as a buffer layer stabilizing Co hcp structure. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ni–Sn alloy intermetallic coatings with different Sn contents, were electrodeposited on Vanadis 23 steel substrates. Structural and chemical characterisation of these coatings was performed by x-ray diffraction, scanning electron microscopy and electron dispersive x-ray analysis. The as-plated Ni–Sn coatings were found to consist of a crystalline Ni solid solution with dispersed Ni–Sn intermetallic phases, whereas in certain cases bulk intermetallic coatings were obtained. The addition of Sn as an alloying element into electrolytic Ni coatings led to a significant increase of hardness and Young’s modulus of these coatings. In addition, the effect of a post-deposition heat treatment at 400°C for 1 h on the microstructure and mechanical characteristics of these electrolytic Ni–Sn alloy coatings was investigated. [ABSTRACT FROM AUTHOR]

This work focuses in investigating the effect of cold deformation on the cathodic hydrogen charging of 5083 aluminum alloy. The aluminium alloy was submitted to a cold rolling process, until the average thickness of the specimens was reduced by 7% and 15%, respectively. A study of the structure, microhardness, and tensile properties of the hydrogen charged aluminium specimens, with and without cold rolling, indicated that the cold deformation process led to an increase of hydrogen susceptibility of this aluminum alloy. [ABSTRACT FROM AUTHOR]

Nanometric magnetite ( nm-FeO) particles were prepared by the reverse co-precipitation synthesis method, obtaining particle sizes that ranged from 4 to 8.5 nm. In their synthesis, the concentration of iron salts of ferric nitrate, Fe(NO)⋅9HO, and ferrous sulfate, FeSO⋅7HO, were varied relative to the chemical reaction volume and by using different surfactants such as oleic acid (OA) and hexadecyltrimethylammonium bromide (CTAB). The nm-FeO particles were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy (MS), magnetic and X-ray diffraction (XRD) measurements. Typical asymmetrical and/or broad lines shapes appeared in all Mössbauer spectra of the as prepared samples suggesting strong magnetic inter-particle interactions, reducing these interactions to some extent by gentle mechanical grinding. For the smallest particles, maghemite instead of magnetite was the main preparation product as low temperature Mössbauer and magnetic measurements indicated. For the intermediate and largest particles a mixture of magnetite and maghemite phases were produced as the saturation magnetization values of M ∼ 60 emu/g indicated; these values were measured for most samples, independently of the coating surfactant concentration, and according to the ZFC-FC curves the blocking temperatures were 225K and 275K for the smallest and largest magnetite nanoparticles, respectively. The synthesis method was highly reproducible. [ABSTRACT FROM AUTHOR]

Presents a study that discussed the sol-gel preparation of high-temperature superconducting oxides. Methodology; Examination of the thermogravimetric and differential thermal analysis; Comparison of the electrical resistivity of the superconductors.

This work presents a study on the effects of hydrogen dilution and boron doping on the formation of Si-C and Si-H bonds during the deposition of hydrogenated amorphous silicon carbon alloy films by plasma-enhanced chemical vapor deposition. Low power densities of 25 mW/cm² and 50 mW/cm², high pressure of 1.5 Torr, temperatures of 150 °C and 200 °C, and methane-silane gas flow ratios of 0.70 and 0.85 were chosen in order to obtain suitable films for biomedical and biological applications. FTIR spectroscopy, UV-Vis spectroscopy, atomic force microscopy and electrical dark conductivity measurements were carried out to characterize the films. The results show that hydrogen dilution decreases CHn groups in the films and increases the Si-C and Si-H bond densities, whereas B-doping decreases the Si-C and Si-H bond densities. Undoped films with optical band gap of 2.47 eV and conductivity around of 5×10-10 S/cm, and B-doped films with a root mean square roughness of about 1 nm and a conductivity of the order of 10-6 S/cm were obtained. [ABSTRACT FROM AUTHOR]

80-μm-thick nanostructured coatings consisting of a Ni solid solution, NiSn, NiSn, and metastable NiSn intermetallic phases were deposited via supersonic cold spraying onto inconel 718 alloy substrates. These coatings have complex nanostructured metallurgical phases as revealed by transition electron microscopy, scanning electron microscopy, and x-ray diffraction techniques. Their mechanical properties were determined by nanoindentation measurements. Furthermore, the wear behavior of these nanostructured sprayed coatings was compared to the one of the industrial bulk or sprayed coated benchmark materials. It was found that the nanostructured coatings exhibit higher wear resistance than the industrial benchmarks, thanks to an appropriate balance of hard intermetallic phases and soft Ni matrix, as well as to their nanostructuring. Their frictional characteristics under reciprocating sliding are mainly determined by the formation of an oxide-based tribo-layer, which was analyzed by x-ray photoelectron spectroscopy. The role of intermetallic phases in these coatings on the friction and wear is also discussed. [ABSTRACT FROM AUTHOR]

It has been demonstrated that persistent organic pollutants (POPs) can affect the immune system of mammals and birds. In this study, the concentration of different POPs and leukocytes in blood samples from three chinstrap penguin (Pygoscelis antarctica) populations was analysed in order to assess the impact on haematological parameters. Using blood sample smears, basophils, eosinophils, heterophils, lymphocytes and monocytes were quantified. Mature and immature red blood cells were counted and cell alterations in both white and red blood cells were analysed. At the same time, whole blood was analysed for POPs. The results showed that contaminants, such as dichlorodiphenyltrichloroethane and its metabolites (ΣDDT), as well as polychlorinated biphenyls (ΣPCB), had significant correlations to eosinophils, lymphocytes and heterophils. This indicates possible immunohaematological alterations derived from exposure to such contaminants. Cytological alterations were also observed, such as cytotoxic granules, toxic heterophils, and atypical and granulated lymphocytes, which would demonstrate that these seabirds are being exposed to stress agents that could be producing some alterations at a leukocytary cellular level. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the relationship between the osteoblastic cells behavior and biotribocorrosion phenomena on bioactive titanium (Ti). Ti substrates submitted to bioactive anodic oxidation and etching treatments were cultured up to 28 days with MG63 osteoblast-like cells. Important parameters of in vitro bone-like tissue formation were assessed. Although no major differences were observed between the surfaces topography (both rough) and wettability (both hydrophobic), a significant increase in cell attachment and differentiation was detected on the anodized substrates as product of favorable surface morphology and chemical composition. Alkaline phosphatase production has increased (≈20 nmol/min/mg of protein) on the anodized materials, while phosphate concentration has reached the double of the etched material and calcium production increased (over 20 µg/mL). The mechanical and biological stability of the anodic surfaces were also put to test through biotribocorrosion sliding solicitations, putting in evidence the resistance of the anodic layer and the cells capacity of regeneration after implant degradation. The Ti osteointegration abilities were also confirmed by the development of strong cell-biomaterial bonds at the interface, on both substrates. By combining the biological and mechanical results, the anodized Ti can be considered a viable option for dentistry. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 103B: 661-669, 2015. [ABSTRACT FROM AUTHOR]

A retrospective case-control study of patients who had undergone cataract extraction at a Spanish hospital over a 13-year period was conducted to identify the risk factors for developing post-operative endophthalmitis (POE). During the study period, the type of antibiotic prophylaxis was changed from subconjunctival gentamicin to the addition of both vancomycin and gentamicin to the irrigating solution. The overall incidence of POE was 0·19% (35 cases/18 287 operations). For the period prior to the change in antibiotic prophylaxis, the incidence rate of POE was 3·4 cases/1000 operations while in the latter period the incidence rate decreased to 0·34 cases/1000 operations. All patients who presented a virulent microorganism had a final visual acuity worse than 20/200. The only significant risk factor identified was the type of prophylaxis used (odds ratio 1·97, 95% confidence interval 0·94–4·14, P = 0·07). There were no significant differences between cases and controls although choice of surgeon approached significance. [ABSTRACT FROM AUTHOR]

This study was performed in order to investigate a possibility to obtain Co-W microbumps via electrochemical routes, because this alloy recently has gained attraction as a novel barrier against copper diffusion. In order to be applied in flip-chip technology, barrier layers should be void-free and uniformly deposited on the entire area of a die to ensure high reliability and high performance of wafer bump-solder interface. To meet these requirements, a set of potentiostatic and galvanostatic electrodeposition was carried out from a citrate electrolyte, at pH 5 and at room temperature. The tests done confirm that void-free Co-W bumps with a uniform tungsten content along the bump can be obtained by potentiostatic and galvanostatic electrodeposition. Successful electrodeposition of Cu/Co-W/Sn layers with good adhesion between them and uniformity on the entire array of bumps also was obtained. The XPS data confirm that electrodeposited Co-W layers can act as a good barrier between Sn and Cu. [ABSTRACT FROM AUTHOR]

Alumina dispersed FeCuAl-based nanostructured cermet coatings were deposited from nanostructured powders by atmospheric plasma spraying on low carbon steel substrates. Nanostructuring was retained in the deposited coatings which exhibit up to four distinctive phases as revealed by electron microscopy. In this study, the friction behavior of the distinctive phases at nano-normal load scale was investigated alongside their contribution to the overall friction behavior at macro-normal load scale. Friction behavior at nano-normal load scale was investigated by lateral force microscopy, whereas conventional tribometers were used for investigations at micro and macro-normal loads. It appeared that, the friction measured at nano-normal loads on individual phases is dictated by both composition and hardness of the corresponding phases, and thus influences the overall friction behavior of the coatings at macro-normal loads. Moreover, the coefficient of friction at macro-normal loads differs from the one at nano-normal loads, and deviates from Amonton's friction law. [ABSTRACT FROM AUTHOR]

Thin silica coatings may be used as pretreatments for steel sheet, offering temporary corrosion protection and promoting adhesion of organic coatings. For use as ready to paint product, silica coated steel has to possess also good corrosion properties after deformation and successive paint application. In this paper, we investigate the forming limit curve for flame assisted chemical vapour deposited silica coated steel sheet with respect to corrosion properties after paint application. We find good corrosion properties up to a strain of 10%, indicating a high tolerance towards deformation. Evaluation of the silica coated steel sheet by scanning electron microscopy shows that severe failure takes place at high levels of deformation, but only at a fraction of the surface. Adhesion, cracking as well as deadhesion and flaking of the very thin films (15-50 nm) was furthermore investigated by scratch testing. [ABSTRACT FROM AUTHOR]

Tribocorrosion plays an important role in the lifetime of metallic implants. Once implanted, biomaterials are subjected to micro-movements in aggressive biological fluids. Titanium is widely used as an implant material because it spontaneously forms a compact and protective nanometric thick oxide layer, mainly TiO2, in ambient air. That layer provides good corrosion resistance, and very low toxicity, but its low wear resistance is a concern. In this work, an anodizing treatment was performed on commercial pure titanium to form a homogeneous thick oxide surface layer in order to provide bioactivity and improve the biological, chemical and mechanical properties. Anodizing was performed in an electrolyte containing β-glycerophosphate and calcium acetate. The influence of the calcium acetate content on the tribocorrosion behaviour of the anodized material was studied. The concentration of calcium acetate in the electrolyte was found to largely affect the crystallographic structure of the resulting oxide layer. Better tribocorrosion behaviour was noticed on increasing the calcium acetate concentration. [ABSTRACT FROM AUTHOR]

Nanostructured molybdenum disulfide thin films were deposited on various substrates by direct current (DC) electrolysis form aqueous electrolyte containing molybdate and sulfide ions. Post deposition annealing at higher temperatures in the range 450- 700°C transformed the as-deposited amorphous films to nanocrystalline structure. High temperature X-ray diffraction studies clearly recorded the crystal structure transformations associated with grain growth with increase in annealing temperature. Surface morphology investigations revealed featureless structure in case of as-deposited surface; upon annealing it converts into a surface with protruding nanotubes, nanorods, or dumbbell shape nanofeatures. UV-visible and FTIR spectra confirmed about the presence of Mo-S bonding in the deposited films. Transmission electron microscopic examination showed that the annealed MoS2 films consist of nanoballs, nanoribbons, and multiple wall nanotubes. [ABSTRACT FROM AUTHOR]

For the first time thick (∼8 μm) Cu/Co-W multilayered coatings with individual layers ranging from 5 to 200 nm were electrodeposited from a single bath. The content of tungsten in rich-in Co-W layers was controlled by varying current densities in a citrate-borate bath. Continuous Multi-Cycle (CMC) nanoindentation technique was used to analyze mechanical properties of those deposits. Optical examination of the indented zone revealed the absence of cracks inside and outside the indentation area in the interval of the normal loads used. The hardness of Cu/Co-W multilayers varied with the bi-layer period and the electrodeposition parameters. The Cu/Co-W multilayers showed an increased hardness compared to that of Co-W coatings electrodeposited under the same conditions. [ABSTRACT FROM AUTHOR]

The work considers the effect of additives of hardening submicron silicon carbides and heat treatment on the fretting corrosion in NaCl solution of nickel-phosphorus (NiP) coatings produced by electrolytic deposition. Tests are performed at amplitudes 100 and 500 μm. Pitting reveals the abrasive nature of the wear of all of the studied coatings. Introduction of silicon carbides into NiP coatings increases the number of pits in fretting corrosion. The pitting of NiP coatings is distributed regularly over the subsurface and pits are not so numerous. As the loading grows, fretting corrosion intensifies, though the friction coefficient declines in the majority of cases. [ABSTRACT FROM AUTHOR]

The present work studies the effect of reinforcing additives of submicron-size silicon carbide and thermal treatment on fretting wear of nickel-phosphorus (NiP) electroplated coatings. The tests are conducted under a 500-μm shear of the friction contact. The tribotests show that all coatings under study undergo abrasive-oxidative wear. Thermal treatment is found to reduce the friction coefficient and wear rate of the coatings under fretting, whereas the increased content of the SiC additive leads to increased friction coefficient and wear rate. The annealed NiP coatings have a lower wear rate compared to the composite NiP-SiC coatings. [ABSTRACT FROM AUTHOR]

Biofilm formation is widely reported in the literature as a problem in the healthcare, environmental, and industrial sectors. However, the role of biofilms in sliding contacts remains unclear. Friction during sliding was analyzed for titanium covered with mixed biofilms consisting of Streptococcus mutans and Candida albicans. The morphology of biofilms on titanium surfaces was evaluated before, during, and after sliding tests. Very low friction was recorded on titanium immersed in artificial saliva and sliding against alumina in the presence of biofilms. The complex structure of biofilms, which consist of microbial cells and their hydrated exopolymeric matrix, acts like a lubricant. A low friction in sliding contacts may have major significance in the medical field. The composition and structure of biofilms are shown to be key factors for an understanding of friction behavior of dental implant connections and prosthetic joints. For instance, a loss of mechanical integrity of dental implant internal connections may occur as a consequence of the decrease in friction caused by biofilm formation. Consequently, the study of the exopolymeric matrix can be important for the development of high-performance novel joint-based systems for medical and other engineering applications. [ABSTRACT FROM PUBLISHER]

The effect of submicron silicon carbide frictional strengthening admixtures and heat treatment on the wear process of nickel phosphide coatings obtained by electrolytic deposition is studied. Despite the heat treatment and admixtures of silicon carbides, the wear of the coatings is of abrasion-oxidizing nature; in the case of NiP-SiC composite coatings, the oxide films formed during the friction process do not exhibit the shield effect; these films show a considerable effect on the wear of silicon-free NiP coatings. The silicon carbide admixtures increase the hardness of the electrolytic coatings but prevent the oxide films formed in the frictional process from attaching to the contact surface. Annealing of the coating reduces the wear rate. In the process of heat treatment, the crystalline phase NiP is formed in the NiP matrix, increasing the coating hardness. At the same time, in the process of annealing of NiP-SiC composite coatings, the NiP matrix cracks around the silicon carbides. As a result, silicon carbides are extracted in the frictional process and the wear rate of the NiP-SiC composite coating grows. [ABSTRACT FROM AUTHOR]

The main aim of this work was to study the simultaneous wear-corrosion of titanium (Ti) in the presence of biofilms composed of Streptococcus mutans and Candida albicans. Both organisms were separately grown in specific growth media, and then mixed in a medium supplemented with a high sucrose concentration. Corrosion and tribocorrosion tests were performed after 48 h and 216 h of biofilm growth. Electrochemical corrosion tests indicated a decrease in the corrosion resistance of Ti in the presence of the biofilms although the TiO2 film presented the characteristics of a compact oxide film. While the open circuit potential of Ti indicated a tendency to corrosion in the presence of the biofilms, tribocorrosion tests revealed a low friction on biofilm covered Ti. The properties of the biofilms were similar to those of the lubricant agents used to decrease the wear rate of materials. However, the pH-lowering promoted by microbial species, can lead to corrosion of Ti-based oral rehabilitation systems. [ABSTRACT FROM PUBLISHER]

By means of electron microscopy, EDX analysis, and tribotesting, there is found a correlation between the composition, morphology, and properties of Co-Mo-P alloy coatings deposited at direct current from a citrate electrolyte containing ammonium hypophosphite in a current density range of 1–15 A/dm2, at temperatures of 28 and 60°C, and pH of 4–6. It is shown that the electrolyte pH increase from 4 to 6 leads to a decrease in the phosphorus content and to an increase in the molybdenum concentration in the electrodeposits. A direct correlation between the microhardness and the wear resistance of electrodeposits and the phosphorus content in coatings is shown. [ABSTRACT FROM AUTHOR]

The tribological behaviour of cobalt–tungsten alloy coatings electrodeposited under direct or pulse current mode from a cobalt sulphate–sodium tungstate bath was investigated. At a low average current density of 05 A dm–2 the coatings contain a low amount of tungsten that leads to a milky appearance of the coatings. These coatings have a high roughness, a low hardness, and exhibit a high coefficient of friction and a high wear in sliding tests against corundum. In contrast, cobalt–tungsten coatings deposited at a higher average current density of 1 A dm–2 also have a milky appearance but exhibit tribological properties comparable to the ones of electrodeposited hard chromium and physical vapour deposited TiN. [ABSTRACT FROM AUTHOR]

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Nanostructured WC–Co based coatings were investigated. The main focus was given to the effect of Al and Cr addition on their tribological behaviour. These coatings were successfully deposited from engineered nanosized powders using high velocity oxy fuel (HVOF) and atmospheric plasma spraying (APS). Porosity level was <3%. Crystal sizes of around 20–30 nm determined by TEM in such coatings, confirm the retention of a nanosize after thermal spraying. The nanostructured coatings were tested for their tribological characteristics and compared to industrial micrometre sized WC–Co coatings and common wear resistant engineering materials. It was found that decarburisation of the coating constituents is a critical issue and has a large impact on the tribological behaviour of the coatings. Proper selection of spraying technique, spraying parameters and distribution of phases are shown to be key factors for achieving nanostructured coatings with high wear resistance. [ABSTRACT FROM AUTHOR]

The electrochemical behaviour of electropolished and anodised aluminium was studied by electrochemical impedance spectroscopy (EIS). Freshly electropolished aluminium behaves as a pure capacitor exhibiting Warburg impedance at low frequencies. Storage of the electropolished aluminium, even in an air-tight bottle, results in the reconstruction of a uniform compact barrier layer. The impedance response of a stored electropolished aluminium as well as anodised aluminium after oxide removal, done by chemical etching, exhibits only a capacitive loop in the complex plane. The effect of the oxide layer thickness on the impedance data was investigated for layers formed during anodising at a cell potential of 15 or 23 V. Impedance measurements carried out over a wide range of frequencies gave useful information on the efficiency of the thinning of the barrier layer at the bottom of porous aluminium oxide layers. The rate of thinning of the barrier layer was estimated for samples anodised at different voltage. [ABSTRACT FROM AUTHOR]