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In this article, the influence of Nickel (Ni)coating thickness on the interfacial microstructure and mechanical properties of AZ91D/Ti–6Al–4 V bimetal fabricated by compound casting is investigated. In the results, it is shown that the Ni coating and its thickness have a significant effect on the interfacial phase compositions and mechanical properties of AZ91D/Ti–6Al–4 V bimetal. At a Ni‐coating thickness of 6.5–27.3 μm, it transforms into α‐Mg + Mg2Ni eutectic structures + blocky τ‐Ni2Mg3Al ternary compounds at the interface zone. When the Ni‐coating thickness increases to 36.1 μm, part of the Ni coating remains, and the interface layer forms, comprising the Ni solid solution layer, Mg2Ni layer, τ‐Ni2Mg3Al ternary compounds, and α‐Mg + τ‐Ni2Mg3Al particles from Ti–6Al–4 V to AZ91D side in sequence. The microhardness of the interface zone is lower than that of the Ti–6Al–4 V but higher than AZ91D. The bimetal shear strength reaches a maximum value of 87.6 MPa at a Ni‐coating thickness of 19.7 μm enhanced by 78.5% in comparison with that of the bimetal without Ni coating. The results are helpful to further enrich the interface control method of compound casting of Ti/Mg bimetal and determine the ideal interlayer thickness for maximizing interface strength. [ABSTRACT FROM AUTHOR]

In order to fabricate the stable superhydrophobic coatings with antifouling and anticorrosion functions. In this study, a series of nickel-coated superhydrophobic surfaces were designed on carbon steel (CS) using a one-step electrodeposition route. The structures of the prepared superhydrophobic Ni (SN) coatings were identified by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), and the wettability was also tested by contact angle goniometer. The findings displayed that the hierarchical micro-flower structures of the optimal SN coating (0.64 A of circuit density and 9.5 min of deposition time) imparted it excellent superhydrophobic property; the water contact angle (CA) and sliding angle (SA) were 168 ± 1.1° and 4.7 ± 0.6°, respectively. The optimal SN coating was found to have superior mechanical and chemical stabilities, as tested by knife scratching, adhesive tape peeling, sandpaper abrasion, and chemical corrosion resistance. Additionally, the optimal SN coating exhibited outstanding self-cleaning property, anti-corrosion, and superhydrophobic stability. Based on these results, it appears that SN coating prepared by one-step electrodeposition can solve the defect of insufficient long-term durability of electrodepositied superhydrophobic coatings, and has potential industrial application prospects. [ABSTRACT FROM AUTHOR]

The Ni coatings were prepared from nickel metal powder and zirconia ceramic balls by mechanical coating technique. The relationship between rotation speed and coatings thickness was studied, the thickness of the coatings was characterized by the weight increase of the zirconia balls after mechanical coating. The composition and microstructure of the coatings with maximum thickness were analyzed by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray Diffraction (XRD). The results revealed that the formation of coatings consists of thickening from the cold welding between Ni particles and the thinning from the exfoliation of coatings work hardening. The thickness of the coatings reaches the maximum when the above two process progress are close to each other. The results proved that higher speed was favor of the coatings formation, the maximum thickness was obtained at the 15 h for rotation speed of 240 rpm, and microscopic images show that the average thickness was about 20 μm.

In the present research, the corrosion resistance of Ni–P and Ni–P–Cr coatings on AA7075-T6 aluminum plates under simulated anodic and cathodic conditions of polymer electrolyte membrane fuel cells (PEMFC) has been studied by electrochemical impedance spectroscopy (EIS). Three Ni–P coatings 20 μm, 30 μm, and 40 μm thick applied by electroless deposition were tested. Besides, a two-layer Ni–P–Cr coating 30 μm thick was also analyzed. It was formed by an inner Ni–P layer, and an outer 10 μm thick chromium one added by electroplating. Corrosion tests were combined with interfacial contact resistance (ICR), roughness, contact angle, and SEM-EDX measurements. The best results were obtained for the 20 μm Ni–P and the two-layer Ni–P–Cr coatings, although the latter showed a high ICR value due to the high electrical resistivity of the chromium oxide surface formed. It was verified that coating degradation occurs when the electrolyte penetrates the micro-cracks and the nodular surface interfaces, reaching the base metal and causing the coating delamination. This behavior is associated with a sharp decrease in the polarization resistance (R p) of the equivalent circuit model fitted to the EIS results. • The thickness of Ni–P coatings on Al AA7075-T6 substrates has been optimized. • The best results were obtained for the Ni–P 20 μm thick and the Ni–P–Cr 30 μm coatings. • DRT analysis of the EIS spectra allows to obtain consistent physical models of Ni–P–Cr coatings. • The proposed equivalent circuit model predicts the durability of the coatings. • Coating surface morphology is a very important factor in the corrosion process. [ABSTRACT FROM AUTHOR]

A pure nanostructured Ni coating was directly prepared by continuous cathode plasma electrolytic deposition (CPED) on aluminium alloy 6061. The microstructures and compositions of the as-deposited coatings were studied by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD), followed by hardness and adhesion evaluations. Due to the plasma micro-arc and rapid quench, the Ni coatings prepared by CPED exhibit typically molten morphologies with nanocrystalline structures, which are capable of increasing the hardness values of the coatings. In addition, the adhesion abilities of the as-prepared coatings could be enhanced by metallurgical bonding between the coatings and the substrate. Moreover, the continuous CPED method is a high-efficiency approach to fabricate coatings with large areas. • A pure nanostructured Ni coating was directly prepared by continuous CPED. • The nanostructure of CPED-prepared coating can substantially increase hardness. • The adhesion of the Ni coating is enhanced by metallurgical bonding. • The continuous CPED method is a high-efficiency approach to fabricate coatings. [ABSTRACT FROM AUTHOR]

The effect of ultrasound (US) agitation (at different intensities of US from 0 to 40 Wcm −2 ) on the electrodeposition of Ni-Mo and Ni (as reference) coatings from an aqueous complex citrate–ammonia electrolyte was investigated. Increased US intensity has a meaningful influence on Mo content in Ni-Mo alloys, which vary from about 14.5 wt% to 19.5 wt%. Enrichment of alloys in Mo resulted in the refinement of the microstructure (crystallite size below 10 nm), and the enhancement of coatings' microhardness (from about 720 to 820 HV) and corrosion properties in chloride media (3.5% NaCl). The opposite effect was observed for Ni coatings, where US agitation did not significantly change the efficiency of Ni electrodeposition, phase composition and crystallite size (about 14 nm) of coatings, which led to the same microhardness values (about 700 HV) of the deposits in the whole range of the US intensities. Obtained results confirmed that US agitation applied during electrodeposition mainly acts as an additional factor affecting the hydrodynamic condition of the process, reducing the diffusion layer thickness and influences kinetics of the Mo reduction controlled by diffusion. Thus, increased US intensities in the analysed range (20–40 Wcm −2 ), resulting in increased Mo content in Ni-Mo alloys, directly influences their functional properties. [ABSTRACT FROM AUTHOR]

Flame-sprayed coatings are widely used in the industries attributed to their low cost and simple processing. However, the presence of porosity and poor adhesion with the substrate requires suitable post-processing of the as-sprayed deposits. In the present work, post-processing of the flame-sprayed Ni-based coating has been successfully attempted using microwave hybrid heating. Microwave post-processing of the flame-sprayed coatings was carried out at 2.45 GHz in a 1 kW multimode industrial microwave applicator. The microwave-processed and as-sprayed deposits were characterized for their microstructure, porosity, fracture toughness and surface roughness. The properties of the coatings were correlated with their abrasive wear behavior using a sliding abrasion test on a pin-on-disk tribometer. Microwave post-processing led to healed micropores and microcracks, thus causing homogenization of the microstructure in the coating layer. Therefore, microwave post-processed coating layer exhibits improved mechanical and tribological properties compared to the as-sprayed coating layer. [ABSTRACT FROM AUTHOR]

Corrosion of metals in contact with molten salts used for thermal energy storage and heat transport at high temperatures is a serious impediment to the development of next-generation concentrating solar thermal systems. Toward addressing this limitation, novel multiscale fractal-textured Ni coatings on a variety of substrate alloys are presented in this study for exceptional corrosion mitigation in molten carbonate salts at a high temperature. Strongly adherent, durable, single-layer, and double-layer multiscale fractal coatings were fabricated using the electrodeposition method. Corrosion performance of the coatings on SS310, SS316, SS347, and In800H was studied in molten carbonate salt (32% Li 2 CO 3 +33% Na 2 CO 3 +35% K 2 CO 3) at 750 °C. Single-layer coatings are stable up to 300 h immersion, whereas double-layer coatings are stable beyond 750 h. The corrosion rate of double-layer Ni coatings on ferrous alloys was reduced by as much as 60% from that of uncoated surfaces and was about 18% below that of higher cost, high Ni content Ha230. The study represents the first-ever report of corrosion characteristics of alloys in carbonate salts at 750 °C and the first demonstration of a means of dramatically reducing corrosion in carbonate salts at a high temperature. The article is significant in that it provides a viable approach for low-cost structural alloys to be corrosion-resistant to molten carbonate heat transfer fluids and storage media in high-temperature concentrating solar thermal applications. The corrosion-resistant coatings provide opportunities for the use of low-cost, ferritic alloys instead of the expensive nickel-based alloys in practice. • Strongly adherent fractal-textured Ni coatings were fabricated using electrodeposition. • Corrosion characteristics of optimized coatings were studied in molten carbonate salt at 750 °C. • Single-layer Ni coatings showed corrosion resistance up to 300 h. • Double-layer Ni coatings reduced corrosion rate by 60% and were stable over long durations >750 h. • Double-layer Ni coated ferrous alloys exhibited ∼18% lower corrosion rate than Ha230. [ABSTRACT FROM AUTHOR]

The present work investigates the possibility of bias introduced in grazing-incidence-angle X-ray diffraction techniques applied to residual stress measurements. In these studies, monotextured nanocrystalline nickel coatings obtained by electrodeposition were examined as the model reference samples. Selected Ni coatings exhibited well developed and simple gradient-free residual stress states that were visible using conventional sin2ψ measurements with varying X-ray penetration depths. These results were verified against the stress state picture obtained by two variants of grazing-incidence X-ray methods: multi-reflection (different hkl) and constant angle of incidence (single hkl). The outcome of both grazing techniques consistently excluded stress gradients in the samples, which agreed with conventional sin2ψ measurement results. However, only the results of the constant angle of incidence technique agreed with those obtained by the sin2ψ method in terms of calculated residual stress level, suggesting this approach could be applied in further studies of graded material coatings. All analysed coatings yielded uniformly distributed tensile residual stress related to gradual structure development in electrodeposited Ni coatings studied by electron microscopy techniques. [ABSTRACT FROM AUTHOR]

Unlike the traditional direct current deposition, a novel method of ultrasonic-assisted double pulse current deposition was developed to fabricate nanocrystalline Ni coatings on the surface of pure Titanium (TA2) substrate. In order to make surface modification of TA2 substrate for better electrodeposition of Ni coatings with strong interfacial adhesion, an effectively activating solution of a dilute HF-containing solution contained of DMF, TiCl 3 , and Ce(NO 3 ) 3 additives was applied. Attentively, different ultrasonic frequencies (i.e., 0, 45, and 80 kHz) produced by ultrasonic field were employed for comparing their effects on managing textural evolution of Ni growth. Besides an optimization of periodic variation for ultrasonic frequency (UF) was innovatively designed as a novel approach to prepare nanostructured Ni coatings with better densification. In addition, several electrochemical measurements of electrochemical impedance spectroscopy (EIS) and polarization curves were devoted to making a comparative study of corrosion behaviors for electrodeposited Ni coatings under different ultrasonic frequencies. Survey results showed that a fully denser structure of nanocrystalline Ni coating was achieved by adding ultrasonic oscillations into the electroplating processes. So it exhibited superior corrosion resistance for Ni coatings prepared at 45 + 80 kHz (PV), followed by 45, 0, and 80 kHz in Hank's solution at 36.5 °C. Considering combined effects from both ultrasonic oscillations and double-pulsed current on structural evolution of electrodeposited Ni coating, an analytical modeling was illustrated for evaluating their mechanisms on modifications of concentration polarization and cathodic overpotential for more dynamic recrystallization and better structural densification of Ni grains. [ABSTRACT FROM AUTHOR]

• (Cr, Ni)-codoped 4 H silicon carbide SiC, electronic/optical properties are calculated. • For this system a ferromagnetic (FM) order is detected. • Doping Ni at Si sites should not destroy the effective coupling of the spins induced by Cr. • Metallic character of (Ni, Cr)-codoped 4H–SiC allow using it in microwave circuits. • The strong FM coupling originates from p-d hybridization interaction. For (Cr, Ni)-codoped 4 H silicon carbide SiC, electronic/optical properties are calculated, and a ferromagnetic (FM) order is detected. Doping Ni at Si sites should not destroy the effective coupling of the spins induced by Cr, could enormously boost the quality of absorbing electromagnetic waves, and acts as resist coatings for Cr-doped 4 H -SiC. The metallic character shown by (Ni, Cr)-codoped 4H–SiC allow us using it in microwave circuits. Its FM order is mainly due to Cr impurities, so that the strong FM coupling originates from p-d hybridization interaction. Our results show that substituting Al for Ni either in (Al, Cr) or (Al, Cr)-doped 4H-SiC may improve the magnetism of 4H–SiCand enhance its microwave absorbing properties in the mm-wave band. [ABSTRACT FROM AUTHOR]

An alternative to nickel coatings obtained from a Watts bath could be offered by coatings deposited from solutions based on environmentally-friendly citric acid and its salts. It was found that proper selection of the citrate solution concentration (0.3 M), the cathodic current density (5 A/dm2) and hydrodynamic conditions (600 rpm) allows homogeneous nanocrystalline coatings to be obtained, with high current efficiency and characterised by high microhardness (above 600 HV 0.05). Furthermore, the properties of nickel coatings deposited in optimal conditions were compared with the characteristics of nickel coatings deposited from the commercially used low-concentrated Watts bath. Based on analysis using scanning and transmission electron microscopy, as well as X-ray diffraction, significant differences in the microstructure of the compared coatings, which determine their functional properties, were shown. Both coatings were homogeneous and adhered well to the steel substrate. However, significant differences can be observed in their surface morphology and structure. Nickel coatings deposited from citrate baths had a compact, globular surface and nanocrystalline microstructure. For coatings obtained from a Watts bath, a surface with visible pyramid-shaped structures was observed. Grains/clusters of grains were visible as a columnar-shape structure, with an average length of about 500–630 nm and a width of about 130–165 nm. In consequence, the microhardness of the nickel coatings obtained from citrate bath (about 618 HV 0.05) was more than twice as high as the value for the coatings deposited from a Watts bath (about 261 HV 0.05). • Citrate-based bath as an alternative to commercially used Watts solution was tested. • Plating conditions for obtaining superior nanocrystalline Ni coatings were developed. • Citrate salts in the platting bath causes the significant crystallite size reduction. • The resulting Ni coatings are characterised by high hardness ∼618 HV (Watts bath ∼261 HV). [ABSTRACT FROM AUTHOR]