Coatings tailored to corrosion protection of metallic substrates are of the utmost relevance to ensure reliability and long-term performance of coated parts as well as the product value of the coated materials. Presently, there is a strong emphasis on the development of advanced functional and smart coatings for corrosion protection in different technological applications. On the one hand, there is a need for more advanced coatings for conventional applications and, on the other hand, there is a need to answer the requirements of several new Hi-Tech applications. Thus, this review highlights the most recent trends in the field of functional coatings for corrosion protection of metallic materials in a wide range of technical applications. Emphasis is given to self-healing coatings and smart coatings combining multiple functionalities for increased corrosion protection. Recent developments on the introduction of functionalities based on encapsulation of corrosion inhibitors, anti-fouling agents and superhydrophobic additives or modification of organic and hybrid matrices chemical manipulation are reviewed. Special attention is dedicated to functional coatings for corrosion protection of bioresorbable metallic implants that have an important impact in biomedical applications.
The article reports on the enhanced hardness of nanocomposite coatings, their thermal stability, protection of the substrate against oxidation at temperatures above 1000 °C, X-ray amorphous coatings thermally stable above 1000 °C and new advanced hard nanocomposite coatings with enhanced toughness which exhibit (i) low values of the effective Young's modulus E satisfying the condition H/E > 0.1, (ii) high elastic recovery W ≥ 60%, (iii) strongly improved tribological properties, and (iv) enhanced resistance to cracking; here E = E(1−ν ), E is the Young's modulus and ν is the Poison's ratio. At the end trends of next development of hard nanocomposite coatings are briefly outlined. ► Enhanced hardness and thermal stability of nanocomposites ► X-ray amorphous coatings thermally stable above 1000 °C ► Protection of the substrate by coating against oxidation up to ~ 1500 °C ► Hard coatings composed of nanograins dispersed in an amorphous matrix ► Hard coatings with enhanced toughness and enhanced resistance to cracking
During the last decade a number of ceramic materials, mostly oxides have been suggested as new thermal barrier coating (TBC) materials. These new compositions have to compete with the state-of-the-art TBC material yttria stabilized zirconia (YSZ) which turns out to be difficult due to its unique properties. On the other hand YSZ has certain shortcomings especially its limited temperature capability above 1200 °C which necessitates its substitution in advanced gas turbines. In the paper an overview is tried on different new materials covering especially doped zirconia, pyrochlores, perovskites, and aluminates. Literature results and also results from our own investigations will be presented and compared to the requirements. Finally, the double-layer concept, a method to overcome the limited toughness of new TBC materials, will be discussed.
Diamond-like carbon (DLC) films combine several excellent properties like high hardness, low friction coefficients and chemical inertness. The DLC coating material can be further classified in two main groups, the hydrogenated amorphous carbon (a-C:H, ta-C:H) and the hydrogen free amorphous carbon (a-C, ta-C). By adding other elements like metals (a-C:H:Me) or non-metal elements like silicon, oxygen, fluorine or others (a-C:H:X), several modifications of the properties can be adjusted according to application requirements. First reports on hard amorphous carbon films were published in the 1950s and about 20 years later there began worldwide intensive research activities on DLC. In the following years the number of publications increased continuously and the importance for industrial applications became more and more evident. Several deposition techniques were applied to prepare a-C:H, ta-C, metal containing a-C:H:Me and non-metal containing a-C:H:X coatings. In parallel the structure and deposition mechanisms of DLC coatings were extensively studied. An essential obstacle for a broad industrial application was the high compressive stress level in a-C:H films causing delamination and limiting the film thicknesses. With metal based intermediate layer systems most adhesion problems could be solved satisfactorily and thus from the mid-1990s the pre-conditions for a broad application especially in the automotive industry were given. With modified a-C:H:X and a-C:X coatings a considerable friction reduction or surface energy adjustments could be achieved.
High power pulsed magnetron sputtering (HPPMS) is an emerging technology that has gained substantial interest among academics and industrials alike. HPPMS, also known as HIPIMS (high power impulse magnetron sputtering), is a physical vapor deposition technique in which the power is applied to the target in pulses of low duty cycle (< 10%) and frequency (< 10 kHz) leading to pulse target power densities of several kW cm . This mode of operation results in generation of ultra-dense plasmas with unique properties, such as a high degree of ionization of the sputtered atoms and an off-normal transport of ionized species, with respect to the target. These features make possible the deposition of dense and smooth coatings on complex-shaped substrates, and provide new and added parameters to control the deposition process, tailor the properties and optimize the performance of elemental and compound films.
Diamond-like carbon (DLC) films deposited by cathodic vacuum arc evaporation (CVAE) have attracted worldwide interest from research groups and industry since the beginning of the 1990s. Hydrogen-free amorphous carbon (a-C) coatings were first deposited by CVAE about two decades after the first description of hydrogenated a-C coatings (a-C:H) deposited by glow-discharge techniques. This paper highlights the development and broad potential of hard a-C coatings deposited by direct (DCVAE) and filtered (FCVAE) cathodic arc evaporation, including pulsed arc. DLC films offer a wide range of exceptional physical (optical, electrical), chemical (interaction with media), mechanical (hardness, elastic modulus), biomedical and tribological properties. Monolithic tetrahedrally-bonded hydrogen-free coatings (ta-C) provide the highest hardness, while various softer a-C coatings are also useful in some applications. Many film properties such as electrical conductivity and surface energy can be modified by alloying with elements such as H, N, Si, B, F, P and metals. Recent research and industrial solutions for generating DLC coatings by CVAE of carbon-based cathodes are described, and hybrid methods using metal cathodes and gas-phase sources are discussed. Coatings containing additional elements and having complex architectures are also discussed, and selected properties for various coating types are presented. The number of industrial applications of ta-C and a-C coatings continues to increase, mainly for tribological coatings to reduce wear and friction. Various applications of coatings deposited by CVAE are described, including data hard disks, engine parts, razor blades, valve seals, decorative coatings, cutting and forming tools, biomedical products and others.
Plasma electrolytic oxidation (PEO) processing for light metals is known for decades and has been established as a well-known industrial surface treatment offering a reasonable wear and corrosion protection. However, long-term protection is compromised by the intrinsic porosity and limited range of composition in the PEO layer. A novel approach is to introduce particles to the electrolyte, aiming at their in-situ incorporation into PEO coatings during growth. The idea is that with the help of particles the defects can be sealed, and the composition range and the functionalities of produced coatings can be enhanced. So far, multifunctional coatings with anticorrosion, self-lubrication, anti-wear, bioactive and photocatalytic properties were produced with the aid of particle addition. The properties of particle itself, together with electrical and electrolyte parameters during PEO processing determine the way and efficiency of particle uptake and incorporation into the coatings. Normally incorporation of the particles into the coating can range from fully inert to fully reactive. This paper reviews recent progress on particle-containing PEO coatings formed on Mg, Al and Ti alloy substrates. The main focus is given to the uptake mechanism of particle into PEO layers and the introduced microstructural and functional changes.
Diamond-like carbon (DLC) films deposited by cathodic vacuum arc evaporation (CVAE) have attracted worldwide interest from research groups and industry since the beginning of the 1990s. Hydrogen-free amorphous carbon (a-C) coatings were first deposited by CVAE about two decades after the first description of hydrogenated a-C coatings (a-C:H) deposited by glow-discharge techniques. This paper highlights the development and broad potential of hard a-C coatings deposited by direct (DCVAE) and filtered (FCVAE) cathodic arc evaporation, including pulsed arc. DLC films offer a wide range of exceptional physical (optical, electrical), chemical (interaction with media), mechanical (hardness, elastic modulus), biomedical and tribological properties. Monolithic tetrahedrally-bonded hydrogen-free coatings (ta-C) provide the highest hardness, while various softer a-C coatings are also useful in some applications. Many film properties such as electrical conductivity and surface energy can be modified by alloying with elements such as H, N, Si, B, F, P and metals. Recent research and industrial solutions for generating DLC coatings by CVAE of carbon-based cathodes are described, and hybrid methods using metal cathodes and gas-phase sources are discussed. Coatings containing additional elements and having complex architectures are also discussed, and selected properties for various coating types are presented. The number of industrial applications of ta-C and a-C coatings continues to increase, mainly for tribological coatings to reduce wear and friction. Various applications of coatings deposited by CVAE are described, including data hard disks, engine parts, razor blades, valve seals, decorative coatings, cutting and forming tools, biomedical products and others. (C) 2014 Elsevier B.V. All rights reserved.
Biodegradability is a big advantage of magnesium-based materials in biomedical applications such as bone fixation, cardiovascular stents, and even stomach trauma repair. Different from other metals such as stainless steels and Ti alloys, the interface between the Mg-based implants and biological environment is dynamic. In order to improve the surface properties to allow better and more expeditious adaptation to the physiological surroundings, it is imperative to design and construct a surface to satisfy multiple clinical requirements such as mechanical strength, biocompatibility, and degradation rate. This paper reviews recent work pertaining to surface modification of Mg-based biomaterials with emphasis on surface coatings and ion implantation. The biodegradation behavior and related mechanism in the physiological environment after surface modification are also described. Surface modification is a promising means to elevate the performance of Mg-based biomaterials and expected to be extensively applied to surface design of biomaterials. ► Surface modification of Mg-based biomaterials is reviewed. ► Emphasis is on surface coatings and ion implantation. ► The biodegradation behavior in the physiological environment is described.
Solvent-based epoxy resins are often used for the anti-corrosion purpose but their cured process fabricating plentiful micro-pore via solvent evaporation is an intrinsic shortcoming and it is thus necessary to obstacle their micro-pore for enhancement antiseptic property. With the purpose of the enhancement, we synthesized TiO –GO sheet hybrids using titanium dioxide loading on graphene oxide sheets with the help of 3-aminopropyltriethoxysilane, and dispersing the sheets into epoxy resin at a low weight fraction of 2%. The electrochemical impedance spectroscopy (EIS) test and monitoring coatings' morphology in corrosion process reveal that the corrosion resistant performance is significantly enhanced by the addition of TiO –GO hybrids to epoxy. Comparisons with other nanofillers including TiO and graphene oxide (GO) indicate that TiO –GO hybrids exhibit an obvious superiority in enhancing the corrosion resistant of epoxy coatings at the same contents. The superiority of the TiO –GO hybrids is related to their exfoliation, dispersion and excellent plugging micro-pore property arising from their laminated structure. Furthermore, the corrosion resistant mechanisms were tentatively proposed for the TiO –GO/epoxy coatings.
Surface texturing is a surface modification approach, resulting in an improvement in tribological performance such as friction and wear resistance. Surface texturing can be performed either as a protruded or recessed asperity, with the latter being more popular due to advantages in terms of micro-lubrication and ease of manufacturing. There are a number of ways of material preparation for surface texturing, with the laser surface texturing being the most popular because of its flexibility and high accuracy. The performance of textured surface depends on the geometrical characteristics of the surface texture and the operating condition of the bearing components. In hydrodynamic and mixed lubrication, microcavity in negative surface texture acts as a reservoir for fluid lubricant, while in boundary lubrication, it traps wear particles to reduce further abrasion. In the past, tremendous amount of research effort has been put into the study of surface texturing, with an aim to investigate the underlying effect of surface texturing on tribological performance. This paper presents a critical review of research and development on surface texturing over the past decades, highlighting design, optimization and fabrication of surface texture, and their effects on tribological performance in terms of friction and load bearing capacity under different lubrication regimes. Numerical modelling approaches involving Reynolds and Navier–Stokes equations employed to understand and determine the tribological behaviour are discussed and compared with respect to experimental investigations. Thin film coatings on textured surface have been found to be a promising means to further reduce friction and increase wear life.
Oxidation and corrosion resistant hydrophobic graphene oxide-polymer composite (GOPC) coating was fabricated on the copper by electrophoretic deposition (EPD). The GOPC coatings were characterized by scanning, and transmission electron microscope (SEM, TEM), thermogravimetric (TGA) and electrochemical impedance spectroscopy (EIS). At optimal EPD conditions of operating voltage 10 V and deposition time 30s, uniform crack free deposit with thickness 45 nm was achieved. Potentiodynamic polarization and EIS investigation demonstrated the efficacy of GOPC coating in shielding copper from corrosion under stringent environment condition. The electrochemical degradation of GOPC coating is more than three orders of magnitude lower than the bare copper substrate. This was due to the impermeability of GOPC coatings to ion diffusion of oxidizing gas and corrosive liquid solution. The procedure employed is fairly facile, inexpensive and less time consuming.
This study investigated the effects of incorporation of two different shapes functionalization fullerene C60 (FC60) and functionalization graphene (FG), into the polymer matrix on the tribological and anti-corrosion performances of epoxy coating. The structural and morphological characterization was examined using Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy and scanning electron microscopy. It was found that the functional groups had been grafted on the surface of C60 and G. The tribological and anti-corrosion results indicated that composite coatings showed a lower friction coefficient, wear traces area and higher anti-corrosion in comparison with neat epoxy, owing to the balance of reinforcement, lubrication and barrier properties of nanofillers and cracks generated by them, and optimal additive concentration of FC60 and FG both were 0.5 wt.%. Furthermore, this work opens up that FC60/EP coatings exhibited better tribological performance but worse corrosion resistance ability compared with FG/EP coatings due to the different shapes of nanofillers. Different tribological and anti-corrosion mechanisms were analyzed in details. Schematic of EP composite coating reinforcement with different shape FC60 and FG (a) and (b) during corrosion process, (c) and (d) during tribological process under dry sliding and seawater lubrication.
The review is focused on the latest achievements in the field of plasma-assisted fabrication of biocompatible CaP-based coatings for medical implants with the emphasis on the coatings composition, structure, mechanical and biological performance. The discussed properties of biocompatible CaP coatings have been recently prepared using the most frequently applied plasma-assisted techniques such as plasma spraying (PS), radio-frequency (RF) magnetron sputtering, pulsed laser deposition (PLD), and ion beam-assisted deposition (IBAD). The review shows that plasma-assisted fabrication allows us to prepare dense, homogeneous, pore-free and high adherent biocompatible coatings able to prevent the leaching of toxic ions from metal to the surrounding tissues or rough and porous coatings capable of stimulating osteogenesis of a new bone. The main advantages and limitations of the described techniques of CaP-based coatings fabrication are presented as well as the most important challenges and critical issues are highlighted. ► The latest achievements in the field of plasma-assisted fabrication of CaP-based coatings are discussed. ► Advantages of the most frequently used plasma-assisted techniques are presented. ► Amorphous or crystalline coatings with the different Ca/P ratio are prepared. ► Porous or dense coatings with high adhesion strength are deposited. ► Challenges and crucial issues are highlighted.
This review provides an overview of recent advances in the application of superhydrophobic surfaces to act as corrosion barriers. The adverse consequences of corrosion are a serious and widespread problem resulting in industrial plant shutdowns, waste of valuable resources, reduction in efficiency, loss or contamination of products, and damage to the environment. Superhydrophobic surfaces, inspired by nature, can be considered as an alternative means for improving the protection of metals against corrosion. Due to the possibility of minimizing the contact area between liquids and a surface, superhydrophobic surfaces can offer great resistance to corrosion. Artificial superhydrophobic surfaces have been developed with the potential of being applied in numerous settings including self-cleaning, anti-icing, oil-water separation, and especially anti-corrosion applications. In this paper, we review the concept of superhydrophobicity through presentation of different theoretical models. The fabrication and application of superhydrophobic surfaces are presented, and we then discuss the use of superhydrophobic coatings as barriers against the corrosion of metals.
Homogeneous epoxy coatings containing nanoparticles of SiO , Zn, Fe O and halloysite clay were successfully synthesized on steel substrates by room-temperature curing of a fully mixed epoxy slurry diluted by acetone. The surface morphology and mechanical properties of these coatings were characterized by scanning electron microscopy and atomic force microscopy, respectively. The effect of incorporating various nanoparticles on the corrosion resistance of epoxy-coated steel was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The electrochemical monitoring of the coated steel over 28 days of immersion in both 0.3 wt.% and 3 wt.% NaCl solutions suggested the beneficial role of nanoparticles in significantly improving the corrosion resistance of the coated steel, with the Fe O and halloysite clay nanoparticles being the best. The SiO nanoparticles were found to significantly improve the microstructure of the coating matrix and thus enhanced both the anticorrosive performance and Young's modulus of the epoxy coating. In addition to enhancing the coating barrier performance, at least another mechanism was at work to account for the role of the nanoparticles in improving the anticorrosive performance of these epoxy coatings.
High power impulse magnetron sputtering (HiPIMS) has been at the center of attention over the last years as it is an emerging physical vapor deposition (PVD) technology that combines advantages of magnetron sputtering with various forms of energetic deposition of films such as ion plating and cathodic arc plasma deposition. It should not come as a surprise that many extension and variations of HiPIMS make use, intentionally or unintentionally, of previously discovered approaches to film processing such as substrate surface preparation by metal ion sputtering and phased biasing for film texture and stress control. Therefore, in this review, an overview is given on some historical developments and features of cathodic arc and HiPIMS plasmas, showing commonalities and differences. To limit the scope, emphasis is put on plasma properties, as opposed to surveying the vast literature on specific film materials and their properties.
This article attempts to give an overview of the literature on the treatment of textiles with non-thermal plasmas. Because of the enormous amount of potential uses of non-thermal plasmas for the modification of textile products, categorizing the applications is difficult, and therefore a review is given on plasma treatment effects or results rather than on the textile applications that benefit from the treatment.
Ceramic coatings were created on the surface of 6061 aluminum alloy using a plasma electrolytic oxidation (PEO) process employing a pulsed direct current (DC) power mode in an alkaline electrolyte. The effect of electrical parameters including frequency and duty cycle on the microdischarge behavior and coating growth was investigated at constant current. Surface features of coatings were studied using scanning electron microscopy. Energy dispersive spectroscopy was employed to investigate elemental distribution on the coating surfaces and cross-sections. Applying lower duty cycles was found to result in increased breakdown voltages and microdischarges with higher spatial density and lower intensity. Further, applying a lower duty cycle was also found to promote the uniformity of silicon distribution in the coating. Based on these new findings, a new conceptual model is proposed to explain the concentration distribution of Si on the surface of coatings prepared at different duty cycles.
Epoxy coatings containing graphene oxide (GO) and amino-silane modified GO (A-GO) with various weight fractions (0.05, 0.1, 0.3, and 0.5 wt%) are prepared to investigate the effect of silane modified GO on performance of nanocomposite coatings. (3-Aminopropyl) triethoxysilane (APTES) is used as organosilane for A-GO synthesis. A-GO is characterized by FTIR, XRD, FE-SEM, and EDS. The dispersion quality of nanosheets in epoxy coating is examined by FE-SEM, revealing the interfacial interaction of GO in coating has improved via silane modification. Besides, the pull-off adhesion strength of epoxy coating to substrate increases by about two times via adding A-GO. The results of electrochemical impedance spectroscopy show that epoxy/A-GO coatings can provide superior corrosion protection performance and maximum corrosion resistance is achieved via adding 0.1 wt% A-GO. By increasing the loading of A-GO, the barrier properties decrease due to agglomeration of nanosheets in polymer matrix.