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This paper reports on an essential step towards accelerating the development of new, environmentally friendly active protective coatings by structure optimization. The complex microstructure of the pigment particles within a coating have been observed non-destructively in 3D by nano-computed tomography using synchrotron radiation. For the first time, a stochastic geometry model is fitted based on spatial geometric features of the particles observed in the 3D images. The typical cell of a random Gibbs-Laguerre tessellation is used to model the particles' polyhedral shapes as well as the observed joint size and aspect ratio distributions. [Display omitted] • Essential step to simulation and optimization of leaching in active protective coatings • Complex spatial microstructure of pigment particles observed non-destructively in 3D • Stochastic geometry model reproduces variation of sizes, shapes, and their correlation • Model allows to easily alterate the particle distributions starting from the real ones • First step towards a realistic computational model for release of corrosion inhibitors [ABSTRACT FROM AUTHOR]

Surface protective coatings on magnesium alloys have been developed to control the corrosion rate of biomedical magnesium implants under mechano-chemical loadings. Quantifying the effect of coating's microstructural features on the corrosion behaviour of magnesium alloys facilitates the innovative design of biodegradable magnesium implants from the surface to the bulk. The present work is devoted to exploring the applicability of deep learning methods for efficiently predicting the in vitro pitting corrosion behaviour of coated magnesium alloys. To this end, the proposed machining learning method employs different CNN models for predicting the corrosion curve and the evolution of corrosion interfaces. In the proposed deep learning method, phase field simulations with varying coating microstructures are used to generate the required corrosion datasets for training and validating the models. The method is applied to a PEO coated WE43 magnesium alloy to assess its feasibility based on in vitro experiments. Performance analysis shows that the multi-input CNN is superior to the single-input CNN in predicting the corrosion curve. The proposed encoder–decoder architecture can predict the evolution of corrosion interfaces with an average error about 1%. These results demonstrate that the proposed CNN models provide a promising alternative to conventional simulation methods for evaluating the protective performance of coatings. [Display omitted] • Deep learning framework for rapid corrosion prediction of coated magnesium alloys. • The hybrid approach is calibrated with in vitro experiments of a coated magnesium alloy. • The CNN models provide a promising method for evaluating the performance of coatings. • The machine learning approach significantly reduces computational costs. [ABSTRACT FROM AUTHOR]

In 2011, the Great East Japan Earthquake and tsunami caused a hydrogen explosion at the Fukushima Daiichi nuclear power plant, which exposed radioactive materials to the atmosphere and had a very negative impact on the nuclear power industry. Since then, efforts have intensified around the world to make nuclear power safer. Accident-tolerant fuel (ATF) is being developed to prevent the rapid oxidation of zirconium cladding, which directly causes hydrogen explosions. ATF research can be divided into two main approaches: changing the cladding material, or coating the surface of the cladding. Coatings are easier to commercialize and apply to existing nuclear power plants, so most vendors have focused on this approach. Chromium is a popular coating medium because of its superior properties such as a low oxidation rate and excellent adhesion. Therefore, research has been focused on suppressing the rapid oxidation of zirconium cladding in the event of an accident by adding a chromium coating with an appropriate thickness in terms of both economy and effectiveness. Even if the thickness of the coating is fixed, the penetration of oxidizing substances can be further delayed by improving the microstructure of the chromium coating, such as by reducing the grain boundary area. In this study, chromium-coated zirconium cladding tubes were fabricated by the arc ion plating process. The microstructure of the chromium coating was adjusted by varying the negative voltage (0–125 V), which in turn controlled the incident energy at which the chromium ionic particles hit the surface of the cladding tube. Experiments were then performed in 1200 °C steam environment to determine the optimal microstructure for high-temperature oxidation resistance. The development of various material degradation phenomena that occurred during 1200 °C steam oxidation was observed to identify the oxidation mechanism and the main factors of the microstructure that affect the zirconium oxidation rate. [ABSTRACT FROM AUTHOR]

Suspension plasma spraying (SPS) as a potential technique to prepare thermal barrier coatings (TBCs) has been attracting more and more attention. However, most reports on SPS were carried out in the atmosphere. Given the unique features of in-flight particles and plasma jets under low pressure, the resulting coatings are expected to be different from those under atmospheric pressure. In this article, yttria-stabilized zirconia (YSZ) thermal barrier coatings were prepared using suspension plasma spraying under different environmental pressures. The results show that as the environmental pressure decreased, the column-like structural coating turned into a vertical crack segmented structure, as well as a dramatic decrease in surface roughness. More nanoparticle agglomerates were formed in the coating under lower environmental pressures. The real porosity of the coating increased with a decrease in environmental pressure. [ABSTRACT FROM AUTHOR]

In conventional thermal spraying processes, it is difficult to employ one type of coating process to economically spray materials having greatly different melting points. In this study, wire electrical explosion spraying(WEES) was applied to prepare refractory Ta10W and non-refractory Ni60A coatings by using a self-designed WEES device. The coating microstructure, deposition efficiency and coating thickness, as well as the adhesive strength of both coatings were investigated. A uniform and dense Ta10W coating with the phase of Ta, Ta 2 N, and FeTaO 4 can be obtained when the energy density was 151.6 J/mm3, while the uniform and dense Ni60A coating made up of FeNi and SiO 2 phase was got at the energy density of 72.7 J/mm3. The maximum deposition efficiency of Ta10W and Ni60A were 53% and 47% respectively. The thickness increment of both coatings decreased with the explosion frequency. The critical load L c in the scratch test can be regarded as a criterion of the adhesive strength, the average critical load of Ta10W was greater than 50 N, while the Ni60A was 38.3 N. Through developing a high-efficient spray device and choosing the appropriate process parameter, especially a suitable energy density, the WEES will be capable to produce the commercially available coatings with greatly different melting points. • A set of high-performance wire electrical explosion spray (WEES) device was developed. • The refractory Ta10W and the non-refractory Ni60A was sprayed by the WEES technology. • The deposition efficiency and coating thickness of both coatings were investigated under continuous multiple sprays. • The adhesive strength of both coatings were characterized by the scratch test. [ABSTRACT FROM AUTHOR]

Abstract This study presents the elaboration of controlled microstructure of yttria stabilized zirconia (8YSZ) coatings by using an axial suspension plasma spraying (SPS) system. Several 8YSZ coatings were fabricated from porous to dense by using same starting feedstock powder via adjustment of the suspension concentration and the deposition distance. The microstructure control is strongly related to the flying droplet size and its momentum in front of the substrate surface. Both aspects significantly determine the droplet flattening behavior, the deposit size, and therefore the final coating microstructure. Graphical abstract Unlabelled Image Highlights • Axial suspension plasma spraying and controlling the coating microstructure • Suspension solid-load content, spraying distance and droplet size • Droplet trajectory, momentum, and impacting on substrate • 8YSZ coatings from porous to dense microstructure by same system [ABSTRACT FROM AUTHOR]

The microstructure of coating layers has important effects on final properties of paper. Eco-friendly bio-latex derived from sustainable starch has being increasingly used in paper coatings to substitute part of the petroleum-based synthetic latex as pigment binder. The influence of starch-based bio-latex on microstructure and surface properties of coatings such as surface composition, surface morphology, void fraction and water absorbency was studied in this paper. X-ray photoelectron spectroscopy (XPS) results showed that bio-latex addition led to a nearly linear decrease in surface carbon content for coatings dried at high temperature. Scanning electron microscope (SEM) images demonstrated that bio-latex addition may cause a lack of binder film at the coating surface that binds pigment particles, which was in agreement with the XPS results. The coatings demonstrated a marginal increase in surface roughness and some decrease in gloss with the addition of bio-latex, as was expected when starch-based binder was used. Unexpectedly, the void fraction of coatings increased slightly, which was contrary to the case in conventional cooked starch. The coatings had a significant decline in water contact angle after bio-latex addition, indicating a considerable increase in water absorbency. The changes in coating microstructure may be attributed to the unique core-shell structure and water-swollen nature of starch-based bio-latex particles. [ABSTRACT FROM AUTHOR]

In this study, the AlTiCrN coatings with different Cr contents were deposited from AlTi and Cr targets using a hybrid coating process that combines high power impulse magnetron sputtering with DC magnetron sputtering. The microstructure and mechanical properties of the AlTiCrN coatings were investigated using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and nano-indentation. The tribological behaviors of the AlTiCrN coatings were evaluated by pin-on-disk tribo-tests at 400 °C, 600 °C and 800 °C, respectively. The results indicated that all the AlTiCrN coatings exhibited (Al,Ti,Cr)N solid solution phases with FCC NaCl-type structure. With increase in Cr target power, the Cr content increased from 0 to 25 at. %, tailoring changes in coating microstructure and properties. Firstly, the preferred orientation shifted from (111) to (200). Secondly, the hardness and elastic modulus of the AlTiCrN coatings increased from 31.4 ± 1.4 GPa and 448.8 ± 9.3 GPa at 0 at.% Cr to 33.7 ± 1.4 GPa and 469.5 ± 8.2 GPa at 8.9 at.% Cr, and then decreased with further increase in Cr content. Thirdly, the friction coefficient and wear rates of the coatings against Al 2 O 3 balls also exhibited some relationship with the coating compositions and test temperatures. The inherent mechanism was analyzed and discussed. [ABSTRACT FROM AUTHOR]

Heavy steel automotive parts have been replaced with aluminum-based lightweight materials worldwide. In particular, grey cast iron engine blocks, which are very heavy components in vehicles, have been replaced by aluminum-silicon hypoeutectic alloys in order to reduce emissions and fuel consumption. However, aluminum alloys are not able to withstand severe engine cylinder conditions due to their poor mechanical properties. In this study, a Mo blended ferrous coating was fabricated using atmospheric plasma spraying to replace the grey cast iron liner in the automotive cylinder bore. Five fractions of Mo, 0, 5, 10, 15, and 20 wt%, with ferrous powder were prepared to investigate the effect of Mo on the microstructure and mechanical properties of coatings. All of the Mo-added coating layers showed significantly improved mechanical properties, such as hardness and wear resistance compared to that of grey cast iron. However, as Mo content exceeded 10 wt% of the blend, the tribological properties gradually degraded due to brittle fracture of Mo. As a result, 10 wt% Mo blended with ferrous powder provided optimized mechanical properties and can be substitute for grey cast iron liners in the automotive industry. [ABSTRACT FROM AUTHOR]

Ni–40% WC composite coatings were prepared on 40Cr surfaces by high frequency induction cladding and then were treated by electrical contact strengthening (ECS) to further improve the coating properties. The effects of ECS on the coating microstructure, microhardness, phase transformation and wear behaviour were investigated using optical microscopy, field emission scanning electron microscopy, Vickers hardness measurements, X-ray diffraction and rolling contact wear tests. As the contact current increased, the porosity and grain size of the resulting composite coating decreased, and its cohesion increased. The hard phase in the coatings also diffused further. After ECS treatment, the average hardness of the Ni–40% WC composite coatings ranged from 652 HV 0.1 up to 906 HV 0.1 . As demonstrated by the results of the rolling contact wear tests, the composite coatings treated by ECS exhibited improved wear resistance. [ABSTRACT FROM AUTHOR]

Metallic coatings were processed on a 35CrMo4 substrate using a thermal flame spray technique. The deposited metal was a high carbon steel, low alloyed with Cr, Mn and Si. In those coatings FeO and Fe 3 O 4 oxides were found, as well as stable α-ferrite phase and some γ-austenite phase. γ-Austenite phase is metastable and transforms into stable α-ferrite during annealing treatment at 300 °C. This γ to α-phase transformation, as well as the evolution of the oxides during the annealing post-treatment, has some influence on the mechanical properties of the coating: hardness, tribological properties, Young's modulus and adhesion on the 35CrMo4 substrate. [ABSTRACT FROM AUTHOR]

Abstract: Yttria-stabilized zirconia (3YSZ) coatings were successfully obtained by suspension plasma spraying. The coatings present generally two-zones-microstructure comprising nanostructured zones contributed by unmolten, partially sintered nanoparticles surrounded by lamellar splats formed from molten and agglomerated in-flight fine solids. In addition, different types of cracks inside the coating microstructure were classified and quantified by image analysis such as e.g. inner microcracks and segmentation cracks associated with quenching process as well as horizontal interlamellar cracks. Thermophysical properties of sprayed coatings were tested with a thermal diffusivity set up basing onto light flash principle. Subsequently, the thermal conductivity was determined with the use of literature data of density and specific heat. The calculations showed very low thermal conductivities values. The values did not correlate with coatings porosity data. Consequently, the analysis of variance (ANOVA) test allowed evaluating the possible impact of the various types of cracks on thermal conductivity. By this analysis, a good correlation between vertical cracks, which include microcracks and segmentation cracks, and thermal conductivity was found. The findings also confirmed the increase of thermal conductivity associated with this type of cracks. [Copyright &y& Elsevier]

Abstract: The microplasma synthesis of the surface layers on aluminum alloy 2024 was studied by optical emission spectroscopy in situ. The evolutions of atomic line intensities in emission spectra and the properties of obtained coatings are discussed. The evolution in the chemical composition of plasma microdischarges and coatings layer structure in the light of previously obtained data on the dynamics of phase transformation by EPR and semi-quantitative X-ray analysis were compared. In the early stages of the synthesis of the plasma consists mainly of the substrate components, but with coating thickness increasing the electrolyte components become dominant. The formation of a dense layer enriched with α-Al2O3 requires specific conditions, which can be found from the changes in the emission spectra of microdischarges radiation. [Copyright &y& Elsevier]

Abstract: This work explored the microstructure of continuous hot-dip galvanized zinc coating on two dual phase steels, focusing on the sample preparation methods for cross-sectional microstructure and Fe–Al intermetallic compound observation. Based on the microstructure revealed by proper method, we established a relationship between the annealing atmosphere and coating microstructure. The experimental results showed that the coating thickness and Fe–Al intermetallic compound''s size are relevant to the annealing atmosphere. And the coexistence of Fe–Al intermetallic compound and Fe–Zn phase has proved indirectly that the aluminothermic reduction is working during hot-dip galvanizing. [Copyright &y& Elsevier]

Abstract: The purpose of this work is to identify the influence of zinc bath temperature on the morphology and the thickness of reactive steel (Fe–0.1 wt.%Si alloy) coatings. The Fe–0.1 wt.%Si samples were galvanized for 3 min at temperatures in the range of 450–530 °C in steps of 10 °C. The coatings were characterized by using scanning electron microscopy/energy dispersive X-rays analysis. It was found that the coating thickness reaches the maximum at 470 °C and the minimum at 500 °C, respectively. When the reactive steel is galvanized at temperatures in the range of 450–490 °C, the coatings have a loose ζ layer on the top of a compact δ layer. With the increase of the galvanizing temperature, the ζ layer becomes looser. When the temperature is at 500 °C, the ζ phase disappears. With the increase of temperature, the coatings change to be a diffuse-Δ layer (δ+ liquid zinc). [Copyright &y& Elsevier]

This paper presented a new research perspective about the MAO coating on Al–Mg-Sc alloy, which based on the main alloying element Mg. From this perspective, the paper firstly analyzed the spatial distribution, phase structure and chemical states of the alloying element Mg in the near surface layer of MAO coating by SEM, EDS, XRD and XPS. SEM observations suggested that the surface porosity and Mg content of the MAO coating was reduced with the increase of Na 2 SiO 3 concentration. EDS analysis revealed that Mg was deposited at the bottom of the discharge channel and the Mg content in the MAO coating gradually increased along the thickness direction. XRD analysis manifested the formation of MgAl 2 O 4 and MgO in the near surface layer of MAO coating, which was detected similarly by XPS spectra. ARXPS detection proved that MgO was distributed at the surface and MgAl 2 O 4 was distributed at deeper regions, which was attributed to the fact that further oxidation promoted the transformation of MgO into MgAl 2 O 4 due to instantaneous high temperature and high pressure. Finally, MgAl 2 O 4 gradually became the main magnesium oxide in the near surface layer of MAO coating with the process of MAO reaction. • A new research perspective about the MAO coating was based on element Mg. • The first study of the spatial distribution, phase structure and chemical states of Mg were conducted. • Evolution mechanism of elements Mg in near surface layer of MAO coating was analyzed. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, graphite grains of different sizes were added into the electrolyte to prepare ceramic coatings on aluminum by plasma electrolytic oxidation (PEO). Scanning electron microscopy (SEM) coupled with an energy dispersive X-ray analysis system (EDX), Raman spectroscopy and X-ray diffractometer (XRD) were used to characterize the coatings. A three-electrode system was used to evaluate the corrosion performances of the coatings in a 3.5wt.% NaCl solution. It was found that the morphology and corrosion performance of the coatings were significantly influenced by the size of the graphite grains. Compared with bigger graphite grains, finer ones were involved in the oxidation process and embedded within the ceramic coatings, which made the coatings less porous and more compact. Thus, the corrosion resistance of the coatings with embedded graphite grains was greatly improved. [Copyright &y& Elsevier]

Abstract: In plasma spray process, the arc root lifetime at the anode wall is limited and new arc roots are continuously created according to restrike, takeover or mixed modes. It results in voltage fluctuations at frequencies in the few thousands hertz range. Such phenomena play a key role in the spray process through the fluctuations of particle trajectories and correspondingly their velocity and temperature time-variations at impact. They have been intensively studied for Ar–H2 plasmas produced by Sulzer-Metco PTF4 and Praxair plasma torch. However, the arc movement depends on several parameters such as the plasma spray parameters, the plasma gas mixture composition, the electrode geometry and the plasma forming gas injector design. In this paper, two commercial plasma torches, PTF4 and 3MB, running both with argon–hydrogen gas mixtures, have been studied. This research work shows the geometry effect and the cold boundary layer thickness on the arc voltage fluctuations, as well as the particle thermal treatment and the resulting coating properties. [Copyright &y& Elsevier]

Abstract: The recharging technique by thermal spraying offers the opportunity of renovating the worn surface parts of a machine element to give it again a new technical life despite its previous degradation in service. This process has consequently interesting economic impacts. In order to improve the adherence between 100Cr6 steel deposits and the substrate material (left worn crankshafts), company SNC ATRA of Béjaïa uses at present a composite formed by (100Cr6 steel/molybdenum bond coat of 0.2mm thick/crankshaft substrate). As a matter of fact, it is shown in the present work that the molybdenum bond coat is not appropriate since, for the 0.2mm thickness, lateral cracks are observed in the middle of the bond coat. On the other hand, our experiment is that a deposit of 100Cr6 steel projected directly on the substrate seems more promising since no gaps or cracks were detected at the “deposit/substrate” interface of this two-material composite. Lastly, phase analysis using X-ray diffraction confirmed that during spraying process, a stable α-phase (bcc) of 100Cr6 wire was transformed to a new phase of γ-phase (fcc). The coatings exhibited the higher microhardness which would contribute to increase wear resistance. [Copyright &y& Elsevier]

Abstract: Impacting behavior and deposition formation of Ni–Ti–Zr–Si–Sn bulk metallic glass during kinetic spraying were investigated in this study. Bulk metallic glass particle deposition was primarily dependent on the impacting particle velocity. Secondly, the impacting particle temperature could transfer the deposition mode from fracture-induced local melting to severe viscous flow, especially for the splat on previously deposited splat. It is suggested that the deposition behavior of bulk metallic glass particles is determined by the competition between fracture and deformation. Fracture and deformation are controlled by adiabatic shear instability at the faying interface during impacting, with causal factors including temperature-dependent superplasticity of the bulk metallic glass and an abnormally high strain rate of the individual particle impact during kinetic spraying. [Copyright &y& Elsevier]

Abstract: A CoNiCrAlY coating was thermal-spray projected using different procedures (plasma, HVOF and HFPD) onto stainless steel specimens. Thermal fatigue tests were conducted in an experimental combustion chamber under a similar atmosphere to power plant service conditions. The microstructure of the coatings depend on the projection method. The oxide content depends on both the maximum temperature attained and the interaction time between powders and air that occurs during the spraying. Porosity is also related to the spraying procedure by way of the particle size, average temperature and velocity attained by the particles when they impact with the cold substrate. The substrate-coating adherence of plasma and HVOF procedures are very high and are not significantly affected by thermal fatigue. On the contrary, the adherence of HFPD spraying is significantly lower, as well as being reduced by thermal fatigue. [Copyright &y& Elsevier]

Abstract: A hybrid (deterministic/stochastic) fundamental model is proposed for the major physico-chemical processes involved in an industrial HVOF thermal spray process (Diamond Jet hybrid gun, Sulzer Metco, Westbury, NY, USA). The model includes continuum type differential equations that describe the evolution of gas and particle temperature and velocity, and a rule-based stochastic simulator that predicts the evolution of the coating microstructure. Regarding gas/particle dynamics, the Reynolds- and Favre-averaged Navier–Stokes equations and the energy balance equations are solved with the renormalization group (RNG) k– turbulence model, and the particle trajectories, temperature histories and melting degrees are determined using the fourth-order Runge–Kutta method. On the microscopic particle deposition process, the formation of coating microstructure is captured by the Madejski deformation model and several rules that govern splat formation, solidification and coating growth. Based on the proposed model, a detailed comprehensive parametric analysis is carried out to study the relationship between the key process parameters and the particle in-flight behavior as well as the resulting coating properties. [Copyright &y& Elsevier]

Abstract: A blended NiCr–Cr2O3–Ag–CaF2/BaF2 feedstock was sprayed using an atmospheric plasma spray process. Physical and thermophysical properties of each constituent phase are quite different and resulting interactions of each constituent with the plasma jet can be expected to be different. Thus, attempts to change the plasma jet characteristics by changing the hydrogen gas flow rate in view of the thermophysical properties of the plasma jet were tried. Phase compositions and microstructures were evaluated as a function at hydrogen gas flow rate. The effects of phase composition and microstructure on the Vickers microhardness and bond strength were also evaluated. For empirically tracing each constituent particle trajectory, spot spraying bead was produced. Finally, particle temperature and velocity as a function of the hydrogen gas flow rate was measured using alumina–titania particle instead of the blended feedstock. [Copyright &y& Elsevier]

Titanium coatings were deposited on stainless steel and glass substrates by electron beam evaporation in vacuum (4×10−4 Pa) and at different neon and argon gas pressures (from 0.33 to 2.00 Pa). The effect of background gas pressure and type on film microstructure was evaluated by scanning electron microscopy (SEM). Since it was not feasible to maintain a constant evaporation rate for all runs, the ‘deposition efficacy’, a parameter defined as the ratio between coating thickness and mass of material evaporated, was statistically modelled using non-linear regression analysis to determine the effects of gas scattering. The results revealed that neon and argon promote similar scattering of the titanium vapour and this may point to a lower likelihood of gas-phase metal cluster formation in neon. The coating microstructure was found to change from a tapered grain structure, obtained under vacuum conditions, to a faceted one at low gas pressure (0.33 Pa), becoming more porous as gas pressure increased. For a given gas pressure, no significant differences could be observed in coating microstructure between the use of argon or neon. These findings may be significant when considering the use of neon as an alternative gas to argon, for improving reactive gas ionisation (through Penning mechanisms) in Plasma-Assisted Physical Vapour Deposition. [Copyright &y& Elsevier]

• Colloidal silica is used as substitute of TEOS in 45S5 glass coatings development • Colloidal silica feedstocks show adequate properties to be used in plasma spraying • The rate of glass formation in the plasma plume is affected by the silica source • The element's distribution and phase nature are not affected by the silica source 45S5 bioactive glass coatings were deposited by plasma spraying from liquid feedstocks. In these feedstocks, the SiO 2 needed to achieve the 45S5 bioactive glass composition has been provided either as tetraethyl orthosilicate (typical precursor of glasses by sol–gel), or as colloidal silica suspension or mixtures of both sources. The synthesised materials were analysed in terms of rheology and sedimentation tests, and subsequently deposited onto metallic substrates under two different spraying distances. The resulting coatings were characterised on the basis of microstructure and phase nature. All feedstocks developed preserved the composition of the 45S5 bioactive glass and showed adequate viscosity and stability to be transported and injected into the plasma plume. However, different coating microstructures were achieved when using tetraethyl orthosilicate or colloidal silica suspensions. Besides, regardless the source of silica an improvement of the coatings microstructure and phase nature have also been observed when the spraying distance was significantly reduced. [ABSTRACT FROM AUTHOR]

• Different anodizing conditions were systematically studied on AA1050 alloy. • Anodic coatings without hillocks were obtained at lower anodizing current density. • Coatings formed at lower temperature have higher hardness. • Al 2 O 3 and PTFE particle addition to the anodic coating improves its wear resistance. In the present study, porous anodic aluminium oxide (AAO) coatings with and without particles of Al 2 O 3 (aluminium oxide) and polytetrafluorethylene (PTFE) were produced on AA1050 aluminium alloy via galvanostatic anodizing in acidic electrolyte. The effects of anodizing conditions (i.e. temperature, current density and composition of electrolyte) on the morphology, thickness, and microhardness were studied via scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and Vickers hardness tester. The results showed that the decrease of electrolyte temperature from 24 to 10 °C and the addition of 20 g/L oxalic acid to 15% H 2 SO 4 electrolyte led to the formation of thicker (34 µm) and harder porous AAO coating with hillocks. Furthermore, the decrease of applied current density from 3 to 1 A/dm2 resulted in the formation of thinner coating (10 µm) without hillocks. The intermetallic phases based on Al-Fe and Al-Fe-Si compounds present in AA1050 alloy were not preferably dissoluted during the anodizing process at 10 °C of electrolyte. The tribological properties of the anodic coatings were investigated by the dry friction test. The results showed that the addition of Al 2 O 3 and PTFE particles to sulfuric-oxalic acid electrolyte resulted in hard anodic composite coatings with enhanced wear resistance. [ABSTRACT FROM AUTHOR]

Micro-arc oxidation (MAO) coating was produced on the surface of Al-Ti double-layer composite plate. Different concentrations of 0–8 g/L Na 2 WO 4 were added into the MAO electrolyte and its effects on the MAO behavior and coating microstructure were investigated. The results showed that the addition of Na 2 WO 4 enhanced the MAO reaction intensity on the part of Al alloy (P-Al) in the Al-Ti composite plate and correspondingly increased the coating thickness, while the reaction intensity and coating thickness on the part of Ti alloy (P-Ti) was decreased. XRD analysis confirmed a formation of WO 3 in both side coatings of the composite plate, and W6+ was detected similarly by XPS spectra. SEM observations indicated that the surface porosity and thickness of the P-Ti coating was reduced, while those of the P-Al coating was increased with the increase of Na 2 WO 4 concentration. TEM analysis verified that corresponding oxide phases and WO 3 were formed in the different MAO coatings on the P-Al or the P-Ti and the addition of Na 2 WO 4 enhanced the coating compactness of the transition zone. EDX detection proved that W concentration in the P-Ti coating was higher than that in the P-Al coating. The nano-indentation tests showed that the hardness and Young's modulus of both side coatings were improved with adding Na 2 WO 4. A competitive mechanism was proposed for the MAO process with the addition of Na 2 WO 4 , and the distribution of electrical energy was found to be balanced in both sides of composite plate. Unlabelled Image • The electrical energy distribution during the MAO process of Al-Ti double-layer composite plate was analyzed. • The distribution of electrical energy on the Al-Ti double-layer composite plate surface was improved with adding the Na 2 WO 4. • The addition of Na 2 WO 4 could improve the structure of MAO coating. • The influence mechanism of Na 2 WO 4 on the MAO behavior was summarized. [ABSTRACT FROM AUTHOR]

Cold Spraying of high strength materials, i.e., Inconel 718 is still challenging due to the limited deformability of the material restricting the quality of deposits. Thus, process parameters must be tuned for reaching higher particle impact velocities and temperatures to allow for maximum amounts of well-bonded particle-substrate and particle-particle interfaces. In the present study, Inconel 718 powder was cold sprayed under varied process gas temperatures for a systematic study of the influence on the quality of thick deposits. In addition, one set of samples of each batch was exposed to post heat treatment procedures by hot isostatic pressing, thermal soft annealing, and aging for attaining hard bulk material properties. Deposits microstructure, porosity, electrical conductivity, hardness, and residual stress were analyzed in as-sprayed and as-heat treated conditions. Results are discussed in terms of the " coating quality parameter ", defined as the ratio between particle impact velocity and critical velocity. As-sprayed deposits exhibit microstructures with highly deformed particles and well bonded internal interfaces. X-ray diffraction reveals that powder and deposits present a γ-solid-solution phase, allowing to assume conventional softening behavior for estimating critical conditions for bonding. Increasing the process gas temperature leads to lower coating porosity and higher electrical conductivity. Deposits showed similarly high microhardness and compressive residual stresses, both caused by work hardening during cold spraying. Subsequent heat treatments improved the quality of internal interfaces, mostly for deposits with high values of " coating quality parameters ". By distinguishing influences on several coating properties, these results contribute to gain basic knowledge for successful manufacturing of Inconel 718 thick deposits by cold spraying, particularly concerning needed coating quality parameters for adjusting desired properties. • High quality IN718 thick deposits were successfully produced by cold spray. • Deposit properties show a correlation with the estimated "coating quality parameters". • Process gas temperatures were selected to maximize the deposit properties. • Enhanced thick deposit properties were achieved by heat treatment. [ABSTRACT FROM AUTHOR]

TiMgN coatings with three different Mg contents (10, 20 and 35 at.%) were prepared by reactive magnetron co-sputtering. Three different coating microstructures have been studied by using i) polished and ii) sand-blasted sample surfaces and iii) by employing the Glancing angle deposition (GLAD) technique on polished substrates. The chemical composition was analyzed by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry or by glow discharge optical emission spectrometry and coating morphology was characterized by SEM on focused ion beam sliced samples. To determine the Mg release from the TiMgN samples two techniques measuring the open circuit potential were employed: a) an in-situ technique by using a scanning flow cell coupled to an inductively coupled plasma mass spectrometer and b) an ex-situ technique, namely inductively coupled plasma optical emission spectroscopy. The results (measured Mg release) from these two analysis techniques are compared and discussed with respect to results obtained from corrosion studies performed in neutral salt spray tests. It was found that the lowest Mg release has been determined for polished and the highest for GLAD samples. A correlation between the amount and duration of Mg release with the corrosion behavior of the samples could be established and formerly proposed corrosion protection mechanisms could be confirmed. • Corrosion protection of steel is improved by increasing Mg content in TiMgN. • Coatings on polished and sand-blasted substrates and GLAD films were studied. • In-situ ICP-MS and ex-situ ICP-OES measurements of the Mg release have been analyzed. • Mg released from coatings depends on Mg content and very much on coatings morphology. [ABSTRACT FROM AUTHOR]