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Corrosion is a major problem for high strength aluminium alloys. Thickening of the naturally formed oxide layer through anodizing is one of the main approaches to improve the corrosion resistance of these materials. Chromate anodizing is extremely efficient to produce anodized layers with good corrosion resistance and painting adhesion, however chromate based surface treatments must be banished from industrial use. The corrosion resistance of aluminium alloy 2524 (AA2524) anodized in tartaric/sulphuric acid (TSA) bath and protected with a hybrid sol-gel coating was evaluated by means of electrochemical impedance spectroscopy (EIS) and salt-spray tests. The morphologies of the obtained layers were characterized by SEM-FEG while the chemical in depth distribution of the hybrid layers was evaluated by means of Rf-GDOES. The effect of anodizing voltage on the sol-gel impregnation and the protection afforded by the layers was evaluated. Electrical equivalent circuit fitting of the EIS data has shown that the anodized layer thickness plays an important role in the protection mechanism of the sol-gel layer. Salt-spray tests highlighted the significant contribution of the sol-gel distribution in the anodized layer. [ABSTRACT FROM AUTHOR]

In order to improve the oxidation and corrosion resistance of metallic bonding layer, the in situ function gradient coating possessing the oxidation and corrosion resistance structure was fabricated on the surface of Al-Si coating by laser melt injection nano-CeO 2 . The micrograph, characteristic parameters of morphology and microdefect, microstructure of melten pool of modified Al-Si coating were investigated. The results show that the modified Al-Si coating can be prepared successfully. Optimum laser power, scanning speed and laser beam diameter was 150 W, 1500 mm·min − 1 and 2 mm, respectively. The microscopic morphology and the characteristic parameters of molten zone were directly related to the conducting direction of the input energy. The plastic change of melten pool was the main reason for the total crack length at different levels. Increasing laser power properly was benefit for reducing the emergement of the crack. The method of introducing fine particles by laser melt injection almost brought no pore defects. The effect of the inner diffusion barrier was enhanced, and the outer layer was rich in rare earth and fine grains. [ABSTRACT FROM AUTHOR]

Development of corrosion resistant materials in biomass fired power plants demands specific attention since the condensation of deposits rich in KCl on heat exchanger surfaces induces severe corrosion attack, which is different from corrosion in traditional coal fired plants. Therefore, the ability of preoxidized layers formed on a commercial Cr-Ti-Al-containing Ni-based alloy (Nimonic 80A) to withstand biomass-induced corrosion was investigated. Preoxidation treatments at 900 °C in O 2 and O 2 + 10 vol% H 2 O, respectively, were conducted before samples were exposed to conditions that mimicked biomass firing. Complementary characterization methods were employed to study samples after preoxidation as well as after corrosion exposure. The oxides obtained by the preoxidation treatments protected the alloy during corrosion exposure at 560 °C for a period of 168 h. In contrast, non-preoxidized samples suffered corrosion attack and formed porous non-protective oxides containing the alloying elements, Ni, Cr, Ti and Al. The influence of the preoxidation layers on the corrosion mechanism is discussed. [ABSTRACT FROM AUTHOR]

In this study, effect of Na 2 SiO 3 ·5H 2 O (Na 2 SiO 3 ) concentration on the two-step peo coating was investigated. The specimens were primarily processed in a solution composed of (NaOH + Na 2 SiF 6 + Na 2 SiO 3 ·5H 2 O) for 900 s. The pre-coated specimens were then immersed into secondary solutions containing various Na 2 SiO 3 concentrations and processed for a constant time of 900 s. Scanning electronic microscope (SEM), was used to investigate the structural properties of the coatings while XRD and EDS were used to analyze the elemental and phase composition of the coatings. SEM results revealed that the coatings formed for Na 2 SiO 3 ~ 9 g/L have highly compact layers and least surface porosity ~ 1.18%. From the FWHM and high intensity peak ratios of Mg 2 SiO 4 (112) and Mg (101) phases, it was found that coatings formed in Na 2 SiO 3 ~ 9 g/L solution are highly crystalline and rich in Mg 2 SiO 4 which was further supported by the maximum content of Si in the EDS analysis. From the hardness measurement it was found that the outer layer of the coating have the highest values of hardness and follow increasing trend with Na 2 SiO 3 concentration. However, coating prepared for Na 2 SiO 3 ~ 9 g/L was found to have least difference in hardness values with respect to coating thickness. Finally corrosion analysis of coating was carried out using potentiodynamic polarization in 3.5 wt% NaCl solution which revealed increase in the corrosion current for secondary coatings prepared for 6 g/L and 12 g/L of Na 2 SiO 3 , however the coating prepared for 9 g/L of Na 2 SiO 3 was found to have the highest corrosion resistance ~ 627.9 kΩ and corrosion potential ~− 0.19 V. [ABSTRACT FROM AUTHOR]

The corrosion properties of Ni-Mo alloy coatings with different molybdenum content (11–32 wt%) were investigated in the course of exposure to 0.5 M NaCl solution. Polarization resistance and impedance measurements showed that after contact with corrosive media, the formation of passive film on the coating surface, determines the corrosion resistance of Ni-Mo alloys. XPS analysis revealed that, the passive film growth was enhanced by the presence of higher amounts (26–28 wt%) of Mo in the coating. It was found, that after exposure to corrosive solution, Mo oxides occurred at the passive film/metal interface, while Ni hydroxide dominated in the bulk of the passive film. [ABSTRACT FROM AUTHOR]

Pure chromium coatings can act as decorative or corrosion-resistant coating, but they present poor tribological properties. Even electroplated hard chrome coatings present some problems, as micro-cracks that reduce their corrosion protection and induce fatigue failure. In addition, Cr plating and its dangerous process with Cr VI baths has been banished in several countries. Physical or chemical post-coating treatments can be applied onto coatings in order to enhance their surface properties, as high temperature oxidation, chemical baths or ion implantation. Plasma immersion ion implantation process was carried on PVD chromium coatings as a post-coating treatment and nitrogen ions were implanted on the surface of deposited chromium thin films, by means of two different plasma sources for ion implantation. Both configurations for plasma sources led to the formation of nitride compounds on the surface of the films. The treated films presented low coefficient of friction, high hardness and better adhesion when compared to the untreated film. [ABSTRACT FROM AUTHOR]

Surface modification of biodegradable magnesium implants to improve the surface-related properties and longevity is of crucial importance. This paper compares the corrosion behavior of hydroxyapatite (HAp) coated WE43 Mg alloy, developed using two different coating techniques viz. electrophoretic deposition (EPD) and pulsed laser deposition (PLD). The coated samples were tested for their corrosion behavior in Hank's balanced salt solution (HBSS) at 37 ± 2 °C. The higher adhesion of HAp obtained using PLD technique reduced the diffusion through coating and provided enhanced corrosion resistance to the bulk WE43 alloy. The corrosion rate was observed to be 0.073 mm/yr for HAp coated using PLD whereas, the coating developed by EPD and bare substrate had a corrosion rate of 0.194 and 0.97 mm/yr respectively. The electrochemical impedance spectroscopy (EIS) results obtained in the form of Nyquist and Bode plot further substantiated the results obtained using potentiodynamic polarization curve. The resistance offered by the solution was 51.5% lesser and the coating resistance was 96.87% higher for PLD coating than EPD coated sample. The SEM images of the HAp coated samples before and after corrosion clearly revealed that the degradation of HAp coated using EPD was higher compared to PLD. Hence, WE43 alloy coated with HAp by two different coating processes proves to have slower degradation rate in comparison with uncoated substrate and amongst the two coating processes PLD can be employed to develop successful coatings for application of Mg alloys in the field of orthopedics. [ABSTRACT FROM AUTHOR]

Molten calcium-magnesium-alumino-silicate (CMAS) corrosion is the most dangerous failure mode for thermal barrier coatings (TBCs). The real-time monitoring and mode discrimination of the corrosion failure process are desirable to understand the corrosion failure mechanism of TBCs. In this paper, the failure mechanism of the TBCs subjected to molten CMAS attack is investigated with acoustic emission (AE). Based on the number and amplitude, and compared to the substrate and the TBCs without CMAS, more serious damage is found to occur in the TBCs attacked by the molten CMAS. Possible failure modes are discriminated by wavelet analysis, and the results indicate that there are four distinct frequency bands corresponding to surface vertical cracks, sliding interface cracks, opening interface cracks, and substrate deformation in the TBCs suffered high temperature molten CMAS corrosion. In fact, the frequency band of sliding interface crack is associated with two crack types, including the crack at the YSZ/BC interface and the parallel crack in the ceramic coating induced by the compressive stress. These two cracks dominate the whole failure process, and ultimately result in the spallation of coatings. [ABSTRACT FROM AUTHOR]

In this work, a hybrid dual layer surface coating consisting of a silicon (Si) underlayer and poly(ε-caprolactone) (PCL) overlayer was investigated that was designed to reduce the corrosion rates of magnesium-based biomaterials. The Si underlayer was 1.2 μm thick and composed of spherical nanoparticles. The overlayer of PCL was 75.2 μm thick and comprised network of pores. Corrosion-induced reduction of the compressive strength of a Si/PCL-coated Mg–Ca–Bi alloy was lower than that of the uncoated or Si layer-coated alloys. However, the bonding strength of the Si coating (24.6 MPa) was significantly higher than that of the Si/PCL-coated samples (6.8 MPa). The Si/PCL coating dramatically enhances the charge transfer resistance of the Mg alloy (2.11 kΩ cm 2 ) in simulated body fluid when compared with a Si-coated sample (2265.12 kΩ cm 2 ). Si/PCL coatings are considered a promising route to control the corrosion rate and mechanical properties of Mg-based biomaterials. [ABSTRACT FROM AUTHOR]

Polychlorotrifluoroethylene (PCTFE) particles were co-deposited with nickel–tungsten (Ni–W) coatings through electro-deposition process. The nanocomposite coatings have been prepared in four different concentrations (0, 4, 8 and 20 g/l). Corrosion performance of the coatings was examined using potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). Surface morphology and composition of the composite coatings were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDAX) measurements and X-ray Diffraction (XRD) analysis. The tribological properties of a surface have been investigated in ambient condition by Atomic Force Microscopy (AFM). Results show that, there is a significant shift in corrosion potential towards the noble direction, decrease in corrosion current density, and increase in charge transfer resistance and decrease in double-layer capacitance values with the incorporation of PCTFE particles in the Ni–W matrix. Higher PCTFE contents, however, negatively affected the corrosion behavior of the coatings. Co-deposition of the PCTFE particles into the Ni–W coating changed the structure and morphology of the deposited coating and decreased the nodules and crystalline size. By increasing the PCTFE concentration of coatings, microhardness decreased and the elastic behavior of coating, increased. The coatings with 4 and 8 g l − 1 PCTFE shows the low friction force in comparison with other samples. [ABSTRACT FROM AUTHOR]

Co-Ni alloy coatings were produced by two different electrodeposition techniques, i.e., supercritical carbon dioxide (Sc-CO 2 ) assisted electrodeposition and conventional electrodeposition in air. Effect of the two electrodeposition techniques on surface morphology, grain size, crystalline texture, microhardness, wear and corrosion resistance of the resulting Co-Ni alloy coatings were investigated. The results show that the Co-Ni alloy coating electroplated with the aid of Sc-CO 2 fluid exhibits brighter surface appearance, lower surface roughness and smaller grain size. The preferred orientation plane of (1 0 0) for the coating prepared in air is changed to be close-packed (1 1 1) facets for the coating produced in emulsified Sc-CO 2 bath. The microhardness of the Co-Ni alloy coating deposited in emulsified Sc-CO 2 bath is much higher than that of the one produced by the traditional electrodeposition. Moreover, the Co-Ni alloy coating produced in emulsified Sc-CO 2 bath possesses better wear and corrosion resistance, which wear and corrosion rate are respectively about one fourth and half of the one deposited by the conventional electrodeposition. This work offers an attractive strategy for fabricating Co-Ni alloy coating as protective layers to increase the lifetime of components exposed to corrosion and wear condition. [ABSTRACT FROM AUTHOR]

An investigation on the corrosion resistance and antibacterial properties of polyelectrolytes and polysiloxane coatings on magnesium alloy with gentamicin was made. The microstructure and composition of the multilayer coatings were characterized by using Fourier transform infrared spectroscopy, X-ray diffractometer and scanning electron microscopy. The analysis of electrochemical measurement in HBSS suggested that the composite coatings improved the corrosion resistance of AZ31 alloy. Finally, the result of plate-counting method demonstrates the effective antibacterial properties of the functionalized substrates. Thus, it can be concluded that the multilayer-treatment reported here is a versatile approach to develop antibacterial and anticorrosion coatings on magnesium implants. [ABSTRACT FROM AUTHOR]

Despite great corrosion and tribological properties of Cr (VI), the utilization chromium (VI) is extremely restricted due to its hazards for environment. Therefore, the objective of this study was to replace Cr (VI) with less hazardous coating such as Cr (III) and Ni (II). In this study, Ni–Cr alloy coatings were electrodeposited in Cr (III)–Ni (II) bath using various current densities. The effects of current density on deposition rate, morphology and chemical composition of the coatings were investigated. Potentiodynamic polarization and EIS (electrochemical impedance spectroscopy) tests in 3.5% NaCl solution were used to evaluate corrosion properties of the coatings. Tribological behaviors of the coatings were also studied by means of ball-on-disk method. The results showed an optimum range of current densities, in which the deposition rate was low. Ni–Cr alloy surface roughness along with Cr content was optimized by increasing the current density. The alloy coating containing 39.8 wt.% Cr, had the best corrosion and wear resistance among all the samples. The corrosion current density and volume loss of this coating were about 9 and 52 times lower than those of the steel substrate, respectively. [ABSTRACT FROM AUTHOR]

The amorphous Ni–P layer of high phosphorus content was deposited on 3003 aluminum alloy sheet either without interlayer or over an interlayer of sprayed Al–Ce coating. Their surface morphology, microstructure and chemical composition distribution were analyzed using scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD). Their corrosion resistance was characterized by potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and immersion corrosion test. The results showed that the corrosion resistance of Ni–P coating with sprayed Al–Ce interlayer was superior to that of conventional electroless Ni–P coating. The corrosion current density and corrosion rate of Ni–P coating with sprayed Al–Ce interlayer decreased greatly compared with conventional electroless Ni–P coating. [ABSTRACT FROM AUTHOR]

The corrosion of AA2024-T3 with a trivalent Cr process (TCP) conversion coating and Pr-based primer was investigated through the application of novel sample preparation and high-magnification scanning transmission electron microscopy (STEM) techniques. Electrochemical impedance spectroscopy was utilized to determine water uptake properties of the coating system. A method to extract thin foil samples of substrate/coating interfaces was demonstrated using a focused ion beam approach. Thin foils were prepared from locations around a blister that formed at a scribe edge after a 13-day exposure in ASTM B117. Imaging and chemical analysis were performed on each thin foil using STEM and energy dispersive spectroscopy. An unexposed region of the same sample type was also studied. Active corrosion inhibitors (Pr and Cr) were not detected in the scribe after exposure. Mg was enriched on the substrate surface and in the TCP region of exposed and unexposed samples, likely an artifact of the coating preparation process. Additionally, chloride was found deeper in the primer and TCP regions at locations closer to the blister. Furthermore, there was no detectable corrosion under an intact coating after exposure for this coating system, with the caveat that each thin foil represented an extremely localized interfacial region. [ABSTRACT FROM AUTHOR]

This study is one part of a series of efforts to optimize the microstructure and tribological properties of the Ti–Si–C–N coatings for a wide range of industrial applications. In this study, Ti–6Al–4V samples were coated with thick Ti–Si–C–N coatings (25–35 μm) using a plasma enhanced magnetron sputtering (PEMS) process, in which Ti was sputtered from two magnetrons at fixed power of 4 kW for each magnetron in a reactive environment of Ar, N 2 and trimethylsilane (TMS). The substrate power density (ion bombardment power density) was varied by varying the bias voltage and the ion flux, which was varied by changing the electron emission current in the PEMS process. After the depositions, scanning electron microscopy (SEM) and X-ray diffractometry (XRD) were used to study the microstructure and morphology of these coatings. Nano-indentation was performed to study the surface hardness H and modulus of elasticity E , from which the ratios of H / E * and H 3 / E * 2 were calculated, where E * = E / (1 − ν 2 ) and ν is the Poisson's ratio. The solid particle erosion (SPE) resistance of the coatings was evaluated using a sand blaster with 50 μm alumina particles at two incident angles of 30° and 90°. Finally, an electrochemical test was conducted to determine the coating corrosion resistance. It was found that all coatings had a nanocomposite microstructure. But the coatings produced at the higher substrate power densities (0.13–0.20 W/cm 2 ) had a smaller crystallite size (5.2–5.8 nm) with a better morphological quality, i.e. free from columnar structure, defects or delamination. The substrate power density has a strong influence on the surface hardness and the ratios of H / E * and H 3 / E * 2 . The higher the substrate power density, the higher these values. The solid particle erosion resistance and corrosion resistance of the coatings also correlated well with the substrate power density. Coatings deposited at higher power densities of ion bombardment exhibited better erosion resistance and corrosion resistance than those deposited at lower substrate power densities. [ABSTRACT FROM AUTHOR]

In this study, nano-silicon (Si) thin films were deposited on biodegradable Mg–6Zn–0.8Mn–3Ca substrates by physical vapor deposition (PVD) method. Subsequently, nano-hydroxyapatite (HA) was coated as a second layer on the nano-Si film using electrochemical deposition (ED). The surface morphology and the corrosion behavior of the composite coatings were evaluated using scanning electron microscope, X-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, potentiodynamic polarization tests and immersion tests. The Si/HA nano-composite coating, with an average particle size of 72 nm, represented a uniform and dense film consisting of HA as the outer layer (8–10 μm) and Si as the inner layer (1.5–2 μm). However, some micropores and microflaws were observed in the Si thin film. The polarization test indicated that Si/HA coating could efficiently reduce the corrosion rate of Mg alloy in simulated body fluid from 2.57 to 0.12 mm/year. However, only moderate reduction in corrosion rate was observed in the case of single layer nano-Si coating. Hydrogen evolution studies showed greater reduction in degradation rate of Si/HA and Si coated samples, compared to uncoated alloy. Immersion test showed the formation of apatite layer on the surface of Si/HA film after immersion in SBF that resulted in noticeable improvement of bioactivity. [ABSTRACT FROM AUTHOR]

The effects of high-energy electropulsing treatment (EPT) on the microhardness and corrosion behavior of the surface gradient oxide coating on the titanium alloy matrix were investigated using infrared thermoscope, micro-hardness, three-dimensional optical microscope, electrochemical work station, scanning electron microscope equipped with electron backscatter diffraction, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetry analyzer. Results showed that the surface modification brings in surface strengthening effect and improved surface corrosion resistance performance (in the fluoridated acidified artificial saliva) of titanium alloy strips with outstanding bonding-strength oxide coating through EPT transition zone. Rapid recrystallization, grain growth and texture evolution of surface matrix alloy are present with increasing DAFA (distance from the anode) of EPT. In this process, microstructure/texture evolution influences the oxidation layer thickness and the oxidation rate with the relationship between these two parameters fitting the approximate positive linear equation and the turning trend located at 120 mm DAFA. Compared with TG-traditional furnace heating process, the growth rate of oxidation under EPT is noticeably enhanced by two orders of magnitudes and surface oxide coating experiences a crystal transformation from anatase-TiO 2 to rutile-TiO 2 . Ionization and acceleration of oxygen by EPT are put forward to discuss the accelerated growth and crystal transformation kinetics of the oxidation process. Therefore, improved surface wear resistance and anti-corrosion performance with a strong adherent gradient oxide coating on the titanium alloy strips surface can be achieved by highly-efficient EPT process which can be applied in biomedical applications. [ABSTRACT FROM AUTHOR]

To improve the corrosion resistance and cytocompatibility of magnesium alloy (Mg alloy), an anticorrosive and bioactive composite coating was triumphantly prepared on Mg alloy surface. First, Mg alloy substrates were treated by cathodic plasma electrolytic deposition (CPED). Then, bioactive carboxymethyl chitosan (CMCS) was covalently immobilized on CPED-treated Mg alloy via polydopamine as intermediate layer. X-ray photoelectron spectroscopy and scanning electronic microscopy were employed to detect the change of chemical composition and surface morphology of Mg alloy substrate at various stages of surface modification. Results of water contact angle measurement showed that the hydrophilicity of the surface has improved significantly after surface modification. Potentiodynamic polarization data and hydrogen evolution test demonstrated that corrosion resistance of modified Mg alloy significantly increased compared with that of pristine sample. Cytotoxicity test and cell morphology analysis confirmed that adhesion and proliferation of osteoblasts on CMCS-modified Mg alloy surface were improved remarkably. The approach presented here would be attractive for surface modification of biomaterials. [ABSTRACT FROM AUTHOR]

Corrosion resistant and superhydrophobic cerium (Ce) coating is fabricated by a one-step electrodeposition process. The Ce coating deposited at 50 V for 10 min displays superhydrophobicity with a contact angle of 162° and a sliding angle less than 4°, which is attributed to its micro-nano flower-like structure and the cerium myristate produced on its surface. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests show that the as-prepared superhydrophobic coating has excellent corrosion resistance that can provide effective protection for the substrate. The corrosion resistance of the superhydrophobic surface is closely related to their wettability. Moreover, the superhydrophobic Ce coating has good chemical stability because it exhibits low corrosion current density in various corrosive solutions except the solution with strong alkalinity. Finally, it is confirmed that the as-prepared superhydrophobic surface has low surface energy and self-cleaning ability. It is believed that the facile and low-cost method offers an effective strategy and promising industrial applications for fabricating superhydrophobic surfaces consisting of rare earth element. [ABSTRACT FROM AUTHOR]

In this paper tribological and corrosion behavior of CrN coatings obtained through magnetron sputtering (MS) and cathodic arc evaporation (CAE) deposition techniques were studied. The effect of interfaces and defects like droplets or porosities detected with scanning electron microscope analysis, both on coating surface and cross sections, was stressed and interpreted in terms of different behavior during the electrochemical polarization tests carried out in NaCl solution or wear tests executed using a pin-on-disk tribometer. Nanoindentation measurements and scratch tests were also executed to characterize the coatings. The effect of different substrate hardness obtained changing the chemical composition of the steel bulk material was also considered, and its effect on the wear mechanisms of damaging was investigated. Regardless of the presence and distribution of the defects and the number of layers, a value of high hardness for the substrate is crucial for the long term pin-on-disk test because it can prevent the delamination of the coating. A different type of defect corresponds to a different corrosion current but, regardless of the deposition technique, the presence of a double layer ensures a better resistance to corrosion and excludes a preferential path for the localized corrosion in small areas of the steel substrate. [ABSTRACT FROM AUTHOR]

The cobalt–chromium–molybdenum (Co–Cr–Mo) alloys are widely used for the total substitution of the human hip and knee joints, because of their good mechanical properties. However, they induce human tissue reactions and inflammation, because of wear and corrosion phenomena; the debris, arising from metal wear and related ions, are toxic and hazardous for the patient health and reduce implant's life. In this work, a high carbon content Co–Cr–Mo alloy has been coated to improve both wear resistance and biocompatibility. The coating, formed on the alloy surface by means of a thermal treatment in molten salts, consists of a multilayer of tantalum carbides (TaC and Ta 2 C) or a single carbide layer (TaC). Structural, morphological, mechanical and wear properties of the untreated and coated materials were studied. Furthermore, the effect of a surface pre-treatment with deposition of a carbon layer has been investigated. As for the wear properties, tribological tests were carried out on samples reproducing three of the typical coupling systems of artificial joints, i.e. metal on polyethylene (MoP), ceramic on metal (CoM) and metal on metal (MoM). The friction coefficient and wear behavior are influenced by the presence of the coatings; the multilayer coating exhibits higher wear resistance and adhesion to the substrate compared to the single carbide layer. The pre-treatment with carbon enhances surface reactivity and adhesion to the substrate. [ABSTRACT FROM AUTHOR]

Compressor blades used in gas turbine engines for marine applications must work in harsh environment such as erosion and corrosion. Multilayer nitride coatings produced by physical vapour deposition (PVD) have exhibited promising potential in improving the corrosion resistance. In this paper, three types of Ti/TiN multilayer coatings with different thickness ratios (M1: 10 nm/40 nm, M2: 20 nm/80 nm, M3: 30 nm/80 nm) were deposited onto 1Cr11Ni2W2MoV stainless steel substrates by plasma activated electron beam physical vapour deposition (EB-PVD). The microstructure, hardness and corrosion behaviour of the Ti/TiN multilayer coatings and TiN single layer coating were comparatively studied. The columnar grain growth of the TiN single layer coating was suppressed by the introduction of the Ti metallic sublayers. With the increase of the Ti sublayer thickness, the characteristics of the layered microstructure became more apparent. The substrates coated with Ti/TiN multilayer coatings exhibited better corrosion resistance (maximum 87% protection efficiency for M3) and higher hardness value (maximum 34.1 GPa for M1) than those coated with TiN single layer. [ABSTRACT FROM AUTHOR]

Mg–Al-layered double hydroxide (LDH) coatings were fabricated by a combined co-precipitation method and hydrothermal process on an AZ31 alloy substrate. The characteristics of the coatings were investigated using SEM, XRD, FT-IR and EDS. The corrosion resistance of the LDH coatings was studied using potentiodynamic polarization and electrochemical impedance spectrum. The results demonstrated that the LDH coatings, characterized by nanoplates stacked vertically to the substrate surface and ion-exchange ability, possess excellent corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract: Wire-brushing was applied under varying conditions to surfaces of AZ31B Mg alloy sheets for the purpose of grain refinement. The microstructure, mechanical properties and corrosion resistance of the wire-brushed Mg sheets were investigated. The thickness of the maximum deformed areas from the wire-brushed surfaces were about 20μm, and the deformed areas near the surfaces each consists of nanocrystals and ultrafine grains. A nanocrystalline surface layer consisted of equiaxed nanocrystals smaller than 100nm, with the smallest mean grain size being 68.2nm. The mean grain size in the nanocrystalline layer depended on the feed speed rather than the pressing load of the wire-brushing. Powdery Mg debris, which were produced at the surface of the sheet during wire-brushing, moved several millimeters during the wire-brushing. The 0.2% proof stress and tensile strength slightly increased after the wire-brushing, although the elongation decreased. The corrosion resistance of the wire-brushed sheet was approximately 4 times higher than that of the starting sheet. [Copyright &y& Elsevier]

Despite the large industrial use of pack aluminizing processes for the protection of parts (e.g. cooling channels) of gas turbine blades, systematic studies relating the formation mechanisms and the chemical composition of pack aluminized layers to important process parameters, including the nature of the base alloy and the temperature, are scarce. In this study, 4 different alloys (pure Ni, Ni–20Cr, Inconel 738 and directionally solidified CM247LC) were subjected to a pack aluminizing process at three different temperatures (950°C, 1000°C, 1040°C), using a pack mix containing a fluorine-based activator; the results were compared to those obtained with a chemical vapor deposition (CVD) aluminizing process performed at 1040°C with the same fluorine-based gaseous precursor. The microstructural characterization, performed by SEM+quantitative EDX analysis, XRD and nanoindentation testing, shows that, during the heating stage of the pack aluminizing process, Al is transported to the sample surface at temperatures too low to allow significant simultaneous diffusion of Ni; therefore, a δ-Ni2Al3 outer layer is formed by inward Al diffusion below the alloy surface, and its growth then continues during the isothermal stage as well. As a result, the chosen isothermal treatment temperature does not affect growth mechanisms, although it modifies the overall thickness of the aluminized layer. δ-Ni2Al3 is converted to β-NiAl after a subsequent vacuum heat treatment at 1120°C. In a CVD process, where gaseous precursor are introduced only after attaining the isothermal treatment stage, Al and Ni diffuse simultaneously from the very beginning of the aluminizing process and β-NiAl is directly developed. Less mobile species (heavy atoms, such as W) in the alloy composition hinder all diffusion phenomena, both during pack aluminizing and during subsequent vacuum heat treatment: after aluminizing, precipitates are developed within the δ-Ni2Al3 outer layer and, after vacuum heat treatment, the resulting β-NiAl layer exhibits a compositional gradient. [ABSTRACT FROM AUTHOR]

Abstract: Over the past decade, researchers have demonstrated much interest in laser cladded metal matrix composite coatings for its good wear resistance, corrosion resistance and high temperature properties. The effects of RE on the microstructure and properties of laser coatings have also got more and more attention. In this paper, in situ Fe-NbC composite coatings with different CeO2 addition were produced on die steel by laser cladding. The formation mechanism of NbC particles was analyzed. The effects of RE on microstructure and micro-hardness of coatings were investigated. It was revealed that larger NbC particles with hard edges formed around Nb particles, and smaller flocculent NbC particles formed by the chemical reaction of Nb and solid graphite in the molten pool. CeO2 plays important roles in reducing micro-porosities, refining grains, and improving the precipitation of NbC. Therefore, the average micro-hardness and its smoothness from the top to the bottom of the coating were improved after adding CeO2. [Copyright &y& Elsevier]

Abstract: The mechanical properties and structural integrity of mullite (3Al2O3·2SiO2) environmental barrier coatings (EBCs) are key factors towards the implementation of these systems in real applications. By using chemical vapor deposition, the chemical composition of mullite in these coatings may be tailored to obtain high Al/Si ratios in the outer surface, for an optimum corrosion protection in gas turbine environments. In this work, the influence of such Al/Si ratio on the mechanical properties and structural integrity of different Al-rich mullite coatings is evaluated by means of nanoindentation and nanoscratch tests. It is found that hardness and elastic modulus of the coating increases as the Al/Si ratio raises. On the other hand, an inverse trend is discerned for the apparent fracture toughness, although this is stated to be an indirect consequence of the resulting residual stress state, without any relevant effect on the intrinsic toughness of the mullite coatings. Regarding structural integrity, an increasingly brittle response to the sliding contact is evidenced as chemical composition moves towards higher Al/Si ratios. However, within the load range studied, brittle-like damage at the coating surface did not translate into critical decohesion at the coating/substrate interface. It sustains the effective protective role of the studied layers as EBCs. Therefore, all the studied coatings are found to exhibit a suitable structural integrity for their potential use as EBCs. [Copyright &y& Elsevier]

Abstract: Fe-based metallic glasses can be potential structural materials owing to their combined superior strength, excellent corrosion and wear resistance properties. In this study, synthesis of Fe–Cr–Mo–W–Mn–C–Si–B metallic glass composite with a large fraction of amorphous phase is accomplished using laser direct deposition. X-ray diffraction (XRD) and transmission electron microscopy investigations reveal the existence of amorphous structure. Microstructure analyses by optical microscopy and scanning electron microscopy (SEM) indicate the periodically repeated microstructures of amorphous and crystalline phases. Partially crystallized structure brought by laser reheating and remelting during subsequent laser scans aggregated in the overlapping area between each scan. XRD analysis showed that the crystalline particle embedded in the amorphous matrix was Cr1.07Fe18.93 phase. The periodically repeated amorphous/crystalline composite microstructure remained the same from the first to the last layer. Microhardness of the amorphous phase (HV0.2 1591) showed a much higher value than that of the crystalline phase (HV0.2 947). Similar values of wall macrohardness and phase microhardnesses indicated that the amorphous phase is the main contributor to the average hardness of laser deposited metallic glass. Wear resistance property of deposited layers showed a significant improvement with the increased fraction of amorphous phase. [Copyright &y& Elsevier]

Abstract: An improved corrosion resistance of aluminized press hardened steel Usibor® AlSi compared to untreated 22MnB5 steel is observed in cyclic corrosion tests even though cracks are present in the coating after the hot stamping resulting in the simultaneous corrosion of the coating and the steel beneath. The coating shows a poorer performance in continuous salt spray test than in cyclic corrosion test. Electrochemical measurements and in situ measurement of the elemental dissolution rates combined with the characterization of the corroded surface are used to argue in favor of an anticorrosion mechanism related to the barrier protection by corrosion products formed. Al and Fe oxides were formed in continuous test and aluminosilicates and a mixture of hydroxides after the cyclic test. The formation of specific corrosion products is assumed to be due to a specific surface pH evolution during corrosion testing. [Copyright &y& Elsevier]

Abstract: Pure magnesium and/or its alloys (AZ31E, AZ91E) are the optimum shell materials for electronic products that contact the hands of the users, and are corroded by the sweat solution (0.1% urea, 0.5% NaCl and 0.5% lactic acid). The corrosion behavior of the tested electrodes was investigated in artificial sweat solution as function of immersion time. In the electrochemical cell Mg or its alloy acts as the anode and NaCl in sweat solution is the corrosive medium. Results showed that the most corroded electrode was pure magnesium while the least corroded was AZ91E alloy. Chitosan was used as coating with different concentrations for AZ91E alloy to protect it against corrosion. The results were carried out using various electrochemical techniques such as potentiodynamic polarization, electrochemical impedance (EIS) and surface examination via scanning electron microscope (SEM). After coating AZ91E alloy with 5% chitosan the formed film was thicker than that formed on the uncoated one and its thickness increased with increasing chitosan concentration. The micrographs showed that the coated AZ91E alloy has superior corrosion resistance properties as compared to the uncoated alloy and that corrosion decreases with increasing the polymer concentration. EIS and polarization results were confirmed by SEM micrographs. [Copyright &y& Elsevier]

Abstract: In this work, a series of low temperature zinc phosphate conversion coatings formed on mild steel. The surface treatment was carried out at different pHs in the phosphate solutions containing Mn2+. An epoxy/polyamide coating was then applied on the phosphated substrates. Potentiostatic polarization test was carried out in order to evaluate the corrosion protection properties of the phosphated samples in 3.5wt.% NaCl solution. The microstructure and morphology of the coatings were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopic (AFM). The adhesion strengths of the epoxy coatings applied on the surface treated samples were measured before and after 30days of immersion in 3.5wt.% NaCl solution by a pull-off test. Results showed that the corrosion resistance of the phosphate coating was significantly enhanced using Mn2+ (especially at 7g/L). A less porous and more compact phosphate coating formed on the metal surface in the presence of Mn2+ compared with the one without additive. Adhesion properties were enhanced by addition of Mn2+ to the phosphate coating composition. [Copyright &y& Elsevier]

Abstract: Chromium-free conversion coatings were deposited from a bath containing potassium hexafluorotitanate(IV). The substrate was electrogalvanized carbon steel. The obtained coatings had a microspheroidal structure and were homogenous. An XPS analysis showed that the coatings were composed of: oxides, hydroxides, phosphates, carbonates and fluorocompounds. As part of this study, the influence of coating deposition time on the surface morphology, chemical composition and physicomechanical properties of the samples was examined. DC polarization measurements, electrochemical impedance spectroscopy and neutral salt spray tests showed that the investigated Cr-free coatings markedly increase the corrosion resistance of electrogalvanized steel in a chloride environment. [Copyright &y& Elsevier]

Abstract: Titanium carbide coatings have a broad range of biomedical applications because of their high hardness, low friction, excellent corrosion resistance, and good biocompatibility. NiTi alloys are also widely used in surgical implants in orthodontics and orthopedics. In order to improve the surface properties, nanostructured titanium carbide coatings are deposited on NiTi by plasma immersion ion implantation and deposition after a titanium interlayer has been fabricated on the NiTi substrate. The structure and corrosion behavior which impact the biological properties are investigated systematically by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, atomic force microscopy, and electrochemical impedance spectroscopy in simulated body fluids at 37°C. The TiC thin films with a C/Ti ratio of 1.087 have the (220) orientation. The EIS results demonstrate that the Ti/TiC multilayer provides significantly better corrosion resistance and stability compared to the uncoated NiTi substrate. [Copyright &y& Elsevier]

Abstract: 4140 steel substrates were coated with hafnium nitride/vanadium nitride multilayered with the objective of improving their corrosion resistance. The multilayered coatings were grown via a reactive r.f. magnetron sputtering technique by systematically varying the bilayer period (Λ) and the bilayer number (n) while maintaining constant the total coating thickness (~1.2μm). The coatings were characterized by X-ray diffraction (XRD), electron and transmission microscopy. The electrochemical properties were studied by Electrochemical Impedance Spectroscopy and Tafel curves. XRD results showed preferential growth in the face-centered cubic (111) crystal structure for [HfN/VN]n multilayered coatings. The best enhancement of the mechanical behavior was obtained when the bilayer period (Λ) 15nm (n=80) which yielded the highest hardness (37GPa) and elastic modulus (351GPa). The values for the hardness and elastic modulus are: 1.48 and 1.32 times greater than the coating with n=1, respectively. The maximum corrosion resistance was obtained for coatings with (Λ) equal to 15nm, corresponding to bilayer n=80. Polarization resistance and corrosion rate was around 112.19kΩcm2 and 0.094∗10−3 mmy respectively, these values were 172.6 and 0.007 times better than those shown by the uncoated 4140 steel substrate (0.65kΩcm2 and 0.014mmy, respectively). [Copyright &y& Elsevier]

Abstract: Although stainless steel is a widely used material for biomedical applications, its surface properties for long term application are still a serious concern. Here, chemical surface treatment by electropolishing and acid dipping is used for improving surface properties of 316L stainless steel to provide a homogenous, smooth and corrosion resistant surface with high biocompatibility profile. X-ray photoelectron spectroscopy (XPS) was performed to trace surface chemical composition before and after chemical treatment. Surface enrichment of corrosion resistant compounds was shown by XPS. Corrosion behavior of the treated samples was evaluated by electrochemical analysis. Surface energy was also studied through contact angle measurements. The roughness of the surface was traced by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques. The lowest roughness (Sa: 0.96±0.29nm) was observed for the highest acid dipping duration (1800s). The surface energy was remarkably subsided by acid dipping duration. MTT assay and cell adhesion studies were conducted to evaluate in vitro biocompatibility showing high cell viability percentage with proper cell adhesion on the surface-treated samples. [Copyright &y& Elsevier]

Abstract: In the present study Ti(C, N) ceramic layer was synthesized on the surface of Ti–6Al–4V alloy by pack nitro-carburizing method to improve surface properties of this alloy. Rectangular blocks were placed in a carbon contained graphite cup and heat treated in a nitrogen atmosphere at different temperatures and soaking times. Phase analysis results indicated that higher treatment temperatures led to increase carbon concentration in Ti(C, N) phase. Almost uniform layer with very high hardness compared to the base material was synthesized and the thickness of the layer increased with increasing treatment time and temperature. Also, corrosion resistance of the alloy was improved dramatically after pack nitro-carburizing process. In some samples, separation of a layer from base material was observed and a suggested mechanism for this phenomenon was declared. [Copyright &y& Elsevier]

Abstract: A nontraditional electrodeposition technique carried out in an electrolyte vacuum boiling environment was introduced, and nickel deposits with a favorably good surface quality were prepared at a considerably high growth rate of up to 0.307μm/s. The studies of influences of cathode current density on the microstructure, microhardness and corrosion resistance of deposits showed that, in comparison to the deposit obtained at 9A/dm2, the one electrodeposited at 63A/dm2 exhibited finer grains (about 100nm) and a denser structure in the absence of additives, and the preferred orientation degree of (400) decreased while (220) increased correspondingly; with the current density increasing from 3A/dm2 to 81A/dm2, the microhardness, as a whole, increased up to 605.5HV, and the corrosion rate also increased, from 5.2% to 19.2% in 10wt.% HCl solution and from 3.5% to 14.6% in 10wt.% H2SO4 solution. In addition, the preferred orientation crystal plane was not affected by the additives, while the corrosion resistance of the deposits prepared with a sodium dodecyl sulfate additives was enhanced. These variations are mainly due to multiple effects of vacuum environment including boiling-motion effect of the electrolyte immediately close to the cathode surface or deposited films, vacuum degassing effect and purification effect. Compared with the nickel deposits from an atmosphere electrodeposition bath, the ones prepared by electrolyte vacuum boiling electrodeposition presented different texture, higher microhardness as well as better corrosion resistance. [Copyright &y& Elsevier]

Abstract: To improve the corrosion resistance, a superhydrophobic silica film on Mg–3.0Nd–0.2Zn–0.4Zr (wt.%, NZ30K) magnesium alloy was successfully prepared by the combination of micro-arc oxidation (MAO) and sol–gel method using tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) as precursors. The MAO layer with highly porous surface was formed as an intermediate layer to ensure the excellent adhesion of superhydrophobic silica film to the substrate. The parameters of the sol–gel process such as molar ratios of TEOS/C2H5OH and MTES/TEOS had significant effects on the surface morphologies and water-repellent properties of the silica films. A superhydrophobic silica film with static contact angle of 151° was obtained as the molar ratios of TEOS/C2H5OH and MTES/TEOS were 1/30 and 1/2 respectively. It is shown that the superhydrophobic silica film can significantly improve the corrosion resistance of NZ30K magnesium alloy by nearly three orders of magnitude by analysis of the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in 3.5wt.% NaCl solution. 168h immersion test further demonstrates that the superhydrophobic silica film can effectively provide long-term corrosion protection for NZ30K magnesium alloy. In addition, the superior corrosion protection performance of the superhydrophobic silica film compared with that of the pure silica film without the addition of MTES can be attributed to the good coverage of hydrophobic methyl groups on its surface, which could effectively decrease the direct contact surface to corrosive medium. [Copyright &y& Elsevier]

Abstract: Current efforts of recent implant technology have been aimed principally at the improvement of corrosion resistance and biocompatibility. The present study demonstrates that the electro polymerisation of pyrrole and incorporation of zirconia (ZrO2) nanoparticles can be successfully combined to produce bioactive polypyrrole nanocomposite coatings for orthopaedic implants. Polypyrrole/ZrO2 nanocomposite coatings were electrochemically synthesised by cyclic votametric technique on 316L stainless steel (SS) in aqueous solution of oxalic acid. The existence of ZrO2 nanoparticles in polypyrrole (PPy) matrix was confirmed by Fourier Transform Infrared (FT-IR) spectroscopy and X ray diffraction (XRD) analysis. The surface morphology of coated 316L SS substrates was observed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). Micro hardness of coated 316L SS was examined using Vickers hardness method. The electrochemical studies were carried out using cyclic polarisation and electrochemical impedance spectroscopy (EIS) measurements. In order to describe the biocompatibility, contact angle measurements and in vitro characterisation were carried out in simulated body fluid (SBF) solution. The results showed that the nanocomposite coatings exhibit superior biocompatibility and enhanced corrosion protection performance over 316L SS due to their hydrophilic, smooth, compact and less porous surface morphology than that of pure polypyrrole coatings. [Copyright &y& Elsevier]

Abstract: This paper reports an investigation on the characteristics of a novel quaternary protective coating to be used in biomedical applications, namely ZrNbCN, with Nb as alloying element. The coatings were prepared by the reactive magnetron sputtering method. Different film compositions were obtained by varying the total reactive gas (CH4 +N2) flow rate, while maintaining constant the CH4/N2 flow ratio. ZrCN films were also prepared as reference coatings. The coatings, with two different non-metal/metal ratios, were comparatively investigated in terms of the elemental composition, chemical bonds, corrosion resistance, and biological properties. The results indicated that the corrosion resistance and biocompatibility of the films depend on the composition. Improved corrosion behavior and biocompatibility were found by adding alloying elements (Nb) to the basic ZrCN structure. A better corrosion resistance and higher cell viability were observed for an increase in non-metal/metal ratio in ZrNbCN coatings. [Copyright &y& Elsevier]

Abstract: An ultrafine-grained (UFG) surface layer was produced on Zr–1%Nb alloy using severe plastic deformation process induced by ultrasonic impact peening (UIP). XRD analysis and TEM observations allow establishing the links between the microstructure formed at different extents of the effective strain ē and superficial microhardness and corrosion resistance. In the topmost surface layer about 10μm thick, average grain size diminishes down to approx. 100nm after the UIP process for 4min (ē ≈0.86). The mechanism of the grain subdivision is discussed on the basis of TEM observations of microstructure in surface layer at different strain extents with taking into account the dynamic recrystallization process facilitated by deformation induced heating. XRD analysis reveals high compressive residual stresses and strong basal texture. Two features of the surface layer formed after the UIP process, viz. UFG structure and strong basal texture, are considered to play the major roles in essential increase in microhardness (from 1 to 2.35GPa) and corrosion resistance of the Zr-1%Nb alloy in saline solution. Decreased surface roughness and large compressive residual stresses also promote higher corrosion resistance. [Copyright &y& Elsevier]

Abstract: The effect of nano-silica particles on the protective properties of polyurethane (PU) coatings has been investigated. Current PU clear coats have shown promising scratch, abrasion and UV resistance properties, however their corrosion resistance has not been much investigated. This study focuses on the effect of non-polar nano-silica particles on electrochemical properties of 2-pack polyurethane matrix. Nano silica was incorporated at different levels into acrylic polyol/HDI polyisocyanate polyurethane matrix and cured at three different temperatures (20°C, 70°C and 110°C). DC resistance technique and Electrochemical Impedance Spectroscopy (EIS) have been employed to evaluate protective properties. Free films were prepared to determine the water-uptake using coating capacitance function measured in the early stages of exposure. Also the effect of nanoparticles on cross-linking density and glass transition temperature (Tg) was investigated by Dynamical Mechanical Thermal Analysis (DMTA) technique. Abrasion resistance was evaluated using Taber abrasion tester by measuring the weight loss from a coated panel. Electrochemical results showed a positive effect on the permeability properties for PU coatings with 5% of embedded nano-silica particles. Also coatings cured at higher temperatures showed improved protective properties. The Tg also increased with elevated curing temperature which was attributed to an increase in cross-linking density. The Taber abrasion test indicates that both, nano-silica particles and higher curing temperatures enhance abrasion resistance. [Copyright &y& Elsevier]

Abstract: A comparative study was carried out on the deposition mechanism, microstructure, and corrosion resistance of Cu films electrodeposited from the base electrolyte of CuCl2·2H2O in a choline chloride–ethylene glycol eutectic solvent with absence and presence of the additive of ethylene diamine (EDA). The base electrolyte is unstable and produces rough Cu films with columnar grains. Upon the introduction of EDA, the modified electrolyte becomes stable and the nucleation of Cu deposits is strongly inhibited, thus producing a smooth and compact surface with finer grains. Uniform corrosion and decreased corrosion current density are recognized in the fine grained Cu films. [Copyright &y& Elsevier]

Abstract: Adhesive strength of Al coatings electrodeposited on AZ91D in aluminum chloride/1-ethyl-3-methylimidazolium chloride was improved by the development of a zincate pretreatment and optimized current pulse electrodeposition method. A dense Zn layer was deposited on both the α- and β-phase surfaces of AZ91D substrate pre-treated in a Cu2+ added activation bath prior to the zincate process. On this zincated substrate an Al coating was electrodeposited by bipolar current pulse polarization and the adhesive strength of the Al coating to the substrate was better than 11MPa. The Al coating obtained under the optimal condition also showed good corrosion resistance in 3.5wt.% NaCl solutions. [Copyright &y& Elsevier]

Abstract: IBAD-Al monolayers and amorphous Al2O3 monolayers were alternately deposited on sintered NdFeB magnets. IBAD-Al layers were prepared by direct current (DC) magnetron sputtering with ion-beam-assisted deposition (IBAD). Structure of the IBAD-Al/Al2O3 multilayers and their corresponding corrosion resistance and mechanical properties were investigated. Columnar structure is less visible in the IBAD-Al layers. Corrosion behaviour was investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation and neutral salt spray (NSS) test. The IBAD-Al/Al2O3 bilayer and multilayers present very low corrosion current densities in potentiodynamic polarisation tests (~10−11 Acm2). The top Al2O3 layers are critical to improve the corrosion resistance of Al based coatings. Furthermore, the hardness of multilayers is improved as the period decreases. [Copyright &y& Elsevier]

Abstract: The present work deals with the process of electroless deposition and electrochemical corrosion behavior of nickel-polychlorotrifluoroethylene-phosphorous (Ni-PCTFE-P) nanocomposite coatings. The process of autocatalytic-catalytic reduction of Ni in nickel sulfate and sodium hypophosphate solution with PCTFE suspended particles has been employed for the formation of the electroless Ni-PCTFE-P composite coatings. Surface morphology and composition of the composite coatings are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) measurements and X-ray diffraction (XRD) analysis. Corrosion behavior of coatings is evaluated using open-circuit potential (E OCP) measurements, electrochemical impedance spectroscopy (EIS) and polarization techniques in 3.5wt.% NaCl solution. The study reveals significant shift in corrosion potential towards the noble direction, decrease in corrosion current density, increase in charge transfer resistance and decrease in double‐layer capacitance values with the incorporation of PCTFE particles in the Ni-P matrix. The significant improvement in corrosion resistance observed for Ni-PCTFE-P nanocomposite coatings (25.3kΩ cm2) compared to Ni-P (16kΩ cm2) could have resulted from the microstructural differences of pure Ni-P with Ni-PCTFE-P nanocomposite coatings. [Copyright &y& Elsevier]

Abstract: Titanium oxide coatings were prepared on NiTi alloys by MAO treatment in concentrated H2SO4 electrolyte using DC power supply. The surface of the coating exhibited a typical MAO porous and rough structure. XPS analysis indicated that the coatings were mainly consisted of O, Ti, and a trace amount of Ni, and the concentration of Ni was greatly reduced compared to that of the NiTi substrate. The curves of potentiodynamic polarization indicated that the corrosion resistance of NiTi alloy was significantly improved by micro-arc oxidation. The coatings were tightly adhesive to the substrates with the bonding strength higher than 45MPa. The SBF soaking test result showed that a kind of bone-like apatite was observed on the MAO coating after soaking for 28days, suggesting that MAO treatment in concentrated sulfuric acid electrolyte was an effective way to improve the bioactivity of NiTi alloys. [Copyright &y& Elsevier]

Abstract: A smart vanadia protective coating of self-repairing functionality that has proven to provide superior corrosion resistance for several magnesium and aluminum alloys has successfully been designed by our group. A newly developed series of magnesium alloys, namely ZE41 alloy, has recently been proposed for automotive, electronics and aerospace applications. The advanced ZE41 alloy possesses very low density, high specific strength, and good castability and weldability characteristics compared to aluminum and steel based alloys. However, the corrosion resistance of ZE41 alloy in the presence of corrosive chloride environment is relatively low. The possibility of utilizing such coatings to add self-repairing functionalities to ZE41 alloy was discussed in this paper. The electrochemical corrosion behavior of the vanadia coatings over ZE41 alloy was investigated in 3.5% NaCl solution using EIS, linear polarization and cyclic voltammetry techniques. The optimum conditions for obtaining protective vanadia coatings of self-repairing abilities and improved localized corrosion resistance were determined. Surface examination of the coatings was investigated using SEM-EDS and macroscopic imaging. [Copyright &y& Elsevier]

Abstract: Al–Cu–Mg (Grade 2024) aluminum alloy was plated with nickel–boron coatings by the electroless deposition method. Some of the coatings were submitted to a hardening heat treatment specifically designed for electroless nickel coated aluminum alloys, with the following conditions: 180°C — 4h; in an atmosphere containing 95% Ar and 5% H2. Uncoated aluminum, treated and untreated samples were submitted to the Taber abrasion test to assess their wear resistance. The wear track was then examined by SEM and roughness measurement. The wear resistance of the coated samples was quite good, with a Taber Wear Index of 28.5 before heat treatment and 24 after (obtained with CS-17 wheels). The corrosion resistance of the samples was investigated by the way of polarization and electrochemical impedance spectroscopy (EIS) and the influence of the heat treatment was observed. Corrosion resistance of the system is good, with a corrosion potential close to −250mV, and heat treatment improves it slightly. Taber abrasion tests were used to simulate erosion of the coatings during use. Worn coatings were then submitted to electrochemical tests to assess conservation of corrosion resistance during use of coated samples. Only a slight decrease of the corrosion resistance was observed. [Copyright &y& Elsevier]