Effect of benzaldehyde on the electrodeposition and corrosion properties of Ni–W alloys

The effect of different concentrations of benzaldehyde on the electrodeposition of Ni–W alloy coatings on a mild steel substrate from a citrate electrolyte was investigated in this study. The electrolytic alkaline bath (pH 8.0) contained stoichiometric amounts of nickel sulfate, sodium tungstate, and trisodium citrate as precursors. The corrosion resistance of the Ni–W-alloy-coated specimens in 0.2 mol/L H₂SO₄ was studied using various electrochemical techniques. Tafel polarization studies reveal that the alloy coatings obtained from the bath containing 50 ppm benzaldehyde exhibit a protection efficiency of 95.33%. The corrosion rate also decreases by 21.5 times compared with that of the blank. A higher charge-transfer resistance of 1159.40 Ω·cm2 and a lower double-layer capacitance of 29.4 μF·cm-2 further confirm the better corrosion resistance of the alloy coating. X-ray diffraction studies reveal that the deposits on the mild steel surface are consisted of nanocrystals. A lower surface roughness value (R_max) of the deposits is confirmed by atomic force microscopy.     

Effect of nano-SiC particles on the corrosion resistance of NiP-SiC composite coatings

NiP-SiC (≈1 1wt% P) composite coatings were electroplated in a Brenner type plating bath. The coatings had amorphous nano-phase composite structure. Direct current and alternating current electrochemical tests were carried out on such coatings in a 3.5wt% solution of NaCl to evaluate their corrosion resistance. The potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) tests, and exposure experiments all show that the corrosion resistance of NiP-SiC coatings first increases and then decreases when the SiC content increases, but the corrosion resistance of NiP-SiC composite coating is better than that of amorphous NiP coatings.     

Microstructure and corrosion resistance of Fe/Mo composite amorphous coatings prepared by air plasma spraying

Fe/Mo composite coatings were prepared by air plasma spraying (APS) using Fe-based and Mo-based amorphous and nanocrystalline mixed powders. Microstructural studies show that the composite coatings present a layered structure with low porosity due to adding the self-bonded Mo-based alloy. Corrosion behaviors of the composite coatings, the Fe-based coatings and the Mo-based coatings were investigated by electrochemical measurements and salt spray tests. Electrochemical results show that the composite coatings exhibit a lower polarization current density and higher corrosion potentials than the Fe-based coating when tested in 3.5wt% NaCl solutions, indicating superior corrosion resistance compared with the Fe-based coating. Also with the increase in addition of the Mo-based alloy, a raised corrosion resistance, inferred by an increase in corrosion potential and a decrease in polarization current density, can be found. The results of salt spray tests again show that the corrosion resistance is enhanced by adding the Mo-based alloy, which helps to reduce the porosity of the composite coatings and enhance the stability of the passive films.     

Microstructural analysis and hot corrosion behavior of HVOF-sprayed Ni–22Cr–10Al–1Y and Ni–22Cr–10Al–1Y–SiC(N) coatings on ASTM-SA213-T22 steel

The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel(HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y(80 wt%; microsized)–silicon carbide(SiC)(20 wt%; nano(N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900°C for 50 cycles in Na_2SO_4–60 wt%V_2O_5 molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction,field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y–20 wt%SiC(N) composite coating was more effective than the Ni–22Cr–10Al–1Y coating against corrosion in the high-temperature fluxing process.     

Influence of chromium on the initial corrosion behavior of low alloy steels in the CO_2–O_2–H_2S–SO_2 wet–dry corrosion environment of cargo oil tankers

The influence of Cr on the initial corrosion behavior of low-alloy steels exposed to a CO2–O2–H2S–SO2 wet–dry corrosion environment was investigated using weight-loss measurements, scanning electron microscopy, N2 adsorption tests, X-ray diffraction analysis, and electrochemical impedance spectroscopy. The results show that the corrosion rate increases with increasing Cr content in samples subjected to corrosion for 21 d. However, the rust grain size decreases, its specific surface area increases, and it becomes more compact and denser with increasing Cr content, which indicates the enhanced protectivity of the rust. The results of charge transfer resistance(Rct) calculations indicate that higher Cr contents can accelerate the corrosion during the first 7 d and promote the formation of the enhanced protective inner rust after 14 d; the formed protective inner rust is responsible for the greater corrosion resistance during long-term exposure.     

Influence of clusters in melt on the subsequent glass-formation and crystallization of Fe–Si–B metallic glasses

The liquid structure of seven representative Fe–Si–B alloys has been investigated by ab initio molecular dynamics simulation focusing on the role of clusters in terms of glass-forming ability(GFA) and crystallization. It is demonstrated that the type of primary phase precipitated from amorphous state under heat treatment is determined by the relative fraction and role of various clusters in melt. The alloy melt shows higher stability and resultantly larger GFA when there is no dominant cluster or several clusters coexist, which explains the different GFAs and crystallization processes at various ratios of Si and B in the Fe–Si–B system. The close correlation among clusters, crystalline phase and GFA is also studied.     

Corrosion behavior of Ni–P/nano-TiC composite coating prepared in electroless baths containing different types of surfactant

In current research, in order to enhance the incorporation of nano-sized TiC particles into electroless Ni–P (EN) coating, different types of surfactant (cationic, anionic, and polymeric) were added to the plating bath. The effects of addition of the surfactants on surface morphology, deposition rate, TiC and P contents of the prepared coatings were investigated. The surface morphology was evaluated by scanning electron microscopy (SEM). It was demonstrated that in the presence of the anionic, polymeric and somehow cationic surfactants, TiC nano-particles were embedded in the matrix which influenced the surface morphology. The effect of surfactant types on the corrosion properties of Ni–P/TiC coated steel was also studied. Corrosion behavior of the coated steel was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) which affected by the incorporation of TiC particles into the Ni–P matrix. The level of corrosion resistance improvement depended largely on the phosphorous and TiC concentration of the applied coating.     

Reusing oxide-based pulverised fly ash and medical waste particles to develop electroless nickel composite coatings(Ni–P/fly ash and Ni–P/SiO_2–Al_2O_3)

Recycling and reusing materials from waste have become a nexus in the development of sustainable materials, leading to more balanced technologies. In this study, we developed a composite coating by co-depositing recycled ceramic particles, pulverised fly ash(PFA) and medical ceramics(MC), into a nickel–phosphorus matrix using a typical electroless plating process. Scanning electron microscopy(SEM) images indicated well-dispersed particles in the Ni–P matrix. However, compared with the MC particles, the PFA particles were distributed scantily with a lower content in the matrix, which could be due to the less impingement effect during the co-deposition. A modified microstructure with refined grains was obtained for the PFA-incorporated composite coating, as seen in the SEM micrograph. The X-ray diffraction result of the MC-incorporated composite coating showed the formation of Nix Siy phases in addition to the typical Ni3 P phases for the heattreated electroless Ni–P coatings. Upon heat treatment, the PFA-reinforced composite coating, due to a modified microstructure, exhibited a higher microhardness up to HK0.05 818, which is comparable to that of the traditional SiC particle-embedded composite coating(HK0.05 825).The findings can potentially open up a new strategy to further advance the green approach for industrial surface engineering.     

Preparation of electroless Ni–P composite coatings containing nano-scattered alumina in presence of polymeric surfactant

Ni–P electroless coating was applied on low carbon steel with the incorporation of different amounts of nano Al2O3 powder (ranging from 3 g/l to 30 g/l) in electroless bath. Corrosion properties and microstructures of the coating were studied. The dispersion stability of alumina colloidal particles stabilized by polymeric (non-ionic) surfactants in an electroless bath was also investigated. The surface morphology and the relevant structure were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of the coated steel was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques. The results showed that increasing alumina concentration not only changed the surface morphology, but also promoted the corrosion resistance. Addition of surfactants has an indirect effect on the amount of the incorporated particles. Meanwhile, in the presence of surfactant, corrosion resistance of Ni–P coating containing even a small quantity of alumina was improved since a stabilized bath was obtained.     

Doping inorganic ions to regulate bioactivity of Ca –P coating on bioabsorbable high purity magnesium

Performance of biomaterials was strongly affected by their surface properties and could be designed artificially to meet specific biomedical requirements. In this study, F(F), Si O2 4(Si), or HCO 3(C)-doped Ca–P coatings were fabricated by biomimetic deposition on the surface of biodegradable high-purity magnesium(HP Mg). The crystalline phases, morphologies and compositions of Ca–P coatings had been characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy-dispersive spectroscopy(EDS). The biomineralization and corrosion resistance of doped Ca–P coatings had also been investigated. The results showed that the Ca–P coating with or without doped elements mainly contained the plate-like dicalcium phosphate dehydrate(DCPD) phase. The doped F, Si, or C changed the surface morphology of Ca–P coatings after mineralization. Doped F enhanced the mineralization of Ca–P coating, and doped Si retarded the mineralization of Ca–P coating.However, H2 evolution of HP Mg discs with different Ca–P coatings was close to 0.4–0.7 ml/cm2 after two-week immersion. That meant that the corrosion resistance of the Ca–P coatings with different or without doped elements did not change significantly.     

Electroplating of Ni/Co–pumice multilayer nanocomposite coatings: Effect of current density on crystal texture transformations and corrosion behavior

The present paper aims to investigate the influence of the current density in the electroplating process on the microstructure, crystal texture transformations, and corrosion behavior of Ni/Co-pumice multilayer nanocomposite coatings. The Ni/Co-pumice composite coatings were prepared by deposition of Ni, followed by the simultaneous deposition of pumice nanoparticles (NPs) in a Co matrix via an electroplating process at various current densities. Afterward, the morphology, size, topography, and crystal texture of the obtained samples were investigated. Furthermore, electrochemical methods were used to investigate the corrosion behavior of the produced coatings in a solution of 3.5wt% NaCl. The results indicated that increasing the plating current density changed the mechanism of coating growth from the cell state to the column state, increased the coating thickness, roughness, and texture coefficient (TC) of the Co (203) plane, and reduced the amount of pumice NPs incorporated into the Ni/Co-pumice composite. The electrochemical results also indicated that increasing the current density enhanced the corrosion resistance of the Ni/Co-pumice composite.     

利用氧化基粉煤灰粉和医疗废弃物颗粒开发无电镀镍基复合涂层 (Ni–P/粉煤灰和Ni-P/Ni–P/SiO2–Al2O3)

Recycling and reusing materials from waste have become a nexus in the development of sustainable materials, leading to more balanced technologies. In this study, we developed a composite coating by co-depositing recycled ceramic particles, pulverised fly ash (PFA) and medical ceramics (MC), into a nickel–phosphorus matrix using a typical electroless plating process. Scanning electron microscopy (SEM) images indicated well-dispersed particles in the Ni–P matrix. However, compared with the MC particles, the PFA particles were distributed scantily with a lower content in the matrix, which could be due to the less impingement effect during the co-deposition. A modified microstructure with refined grains was obtained for the PFA-incorporated composite coating, as seen in the SEM micrograph. The X-ray diffraction result of the MC-incorporated composite coating showed the formation of Ni_xSi_y phases in addition to the typical Ni₃P phases for the heat-treated electroless Ni–P coatings. Upon heat treatment, the PFA-reinforced composite coating, due to a modified microstructure, exhibited a higher microhardness up to HK_0.05 818, which is comparable to that of the traditional SiC particle-embedded composite coating (HK_0.05 825). The findings can potentially open up a new strategy to further advance the green approach for industrial surface engineering.     

HOVF喷涂Ni–22Cr–10Al–1Y 和Ni–22Cr–10Al–1Y–SiC (N)涂层对ASTM-SA213-T22钢组织和热腐蚀行为的影响

The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel (HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y (80wt%; micro-sized)–silicon carbide (SiC) (20wt%; nano (N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900°C for 50 cycles in Na₂SO₄–60wt%V₂O₅ molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction, field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than 2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y–20wt%SiC (N) composite coating was more effective than the Ni–22Cr–10Al–1Y coating against corrosion in the high-temperature fluxing process.     

水热法合成Zn–Mg基层状双氢氧化物涂层用于铜在氯化物和氢氧化物介质中的腐蚀防护

Layered double hydroxides (LDHs) hinder corrosive elements by forming a double layer and locking them between its layers. Hence, LDHs are interesting materials in corrosion inhibition. In this work, Zn–Mg-based LDHs are grown over a copper substrate by using a hydrothermal method. Two types of Zn–Mg-based LDH coating are prepared based on hydrothermal reaction time. Both types are characterized through Fourier transform infrared spectroscopy, Raman spectroscopy, high-resolution scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy, and X-ray diffraction. Results show that the two types of LDH coating are successfully grown on copper; however, they differ in thickness and structural configuration. Corrosion testing of the LDH coatings is executed in 0.1 M NaCl and 0.1 M NaOH through alternating current impedance measurements and Tafel polarization curves. Results show that L48 gives more than 90% protection to copper, which is higher than the protection provided by L24. However, both LDH coatings (L24 and L48) are more effective corrosion inhibitors in NaCl than in NaOH, suggesting that the LDH coatings can more efficiently exchange Cl ions than OH ions.     

Effect of Al2O3 and Y2O3 on the corrosion behavior of ZrO2-benzotriazole nanostructured coatings applied on AA2024 via a sol-gel method

zirconia-based nanostructured coatings were deposited on AA2024 to improve the corrosion resistance properties. Three different nanostructured coatings, namely, zirconia-benzotriazole, zirconia-alumina-benzotriazole, and zirconia-yttria-benzotriazole, were applied on AA2024 via a sol-gel method using the dip-coating technique. Next, the coatings were annealed at 150℃ after each dipping period. The phases and morphologies of the coatings were investigated using grazing incidence X-ray diffraction (GIXRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). The corrosion properties were evaluated using electrochemical methods, including polarization and electrochemical impedance techniques in 3.5wt% NaCl solution. The obtained results confirm the formation of homogeneous and crack free zirconia-benzotriazole-based nanostructured coatings. The average roughness values for zirconia-benzotriazole, zirconia-alumina-benzotriazole, and zirconia-yttria-benzotriazole nanostructured coatings were 30, 8, and 6 nm, respectively. The presence of alumina as a stabilizer on zirconia coating was found to have a beneficial impact on the stability of the corrosion resistance for different immersion times. In fact, the addition of alumina resulted in the dominance of the healing behavior in competition with the corrosion process of zirconia-benzotriazole nanostructured coating.     

Influence of microstructure on the corrosion resistance of Fe–44Ni thin films

An Fe–44Ni nanocrystalline (NC) alloy thin film was prepared through electrodeposition. The relation between the microstructure and corrosion behavior of the NC film was investigated using electrochemical methods and chemical analysis approaches. The results show that the NC film is composed of a face-centered cubic phase (γ-(Fe,Ni)) and a body-centered cubic phase (α-(Fe,Ni)) when it is annealed at temperatures less than 400℃. The corrosion resistance increases with the increase in grain size, and the corresponding corrosion process is controlled by oxygen reduction. The NC films annealed at 500℃ and 600℃ do not exhibit the same pattern, although their grain sizes are considerably large. This result is attributed to the existence of an anodic phase, Fe_0.947Ni_0.054, in these films. Under this condition, the related corrosion process is synthetically controlled by anodic dissolution and depolarization.     

Evaluation of plasma sprayed YSZ thermal barrier coating with the CMAS deposits infiltrati on using impedance spectroscopy

The yttria-stabilized zirconi a (YSZ) thermal barri er coatings (TBCs) prepared by atmo-sp heric plasma spraying with different heat treatment period at the temperature of 1250°C were studied in the present investig ation. Electrochemical impedance spectroscopy (EIS) was employed to non-destructively examine the impedance and capaitance behavior of free standi ng YSZ coatings deposited by plasma spray with CMAS (calcium–magnesium–alumino-silicate) infiltration. Equivalent circuit was established on the basis of the biomodal structure in coatings. The sintering behavior of the coatings can be reflected by the changes of resistance and capacitance of the coating . By EIS , the microstructure evolution of the coating with CMAS deposits was discussed in detail.     

Microstructure of Ni–Al powder and Ni–Al composite coatings prepared by twin-wire arc spraying

Ni–Al powder and Ni–Al composite coatings were fabricated by twin-wire arc spraying (TWAS). The microstructures of Ni-5wt%Al powder and Ni-20wt%Al powder were characterized by scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the obtained particle size ranged from 5 to 50 μm. The morphology of the Ni–Al powder showed that molten particles were composed of Ni solid solution, NiAl, Ni₃Al, Al₂O₃, and NiO. The Ni–Al phase and a small amount of Al₂O₃ particles changed the composition of the coating. The microstructures of the twin-wire-arc-sprayed Ni–Al composite coatings were characterized by SEM, EDS, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that the main phase of the Ni-5wt%Al coating consisted of Ni solid solution and NiAl in addition to a small amount of Al₂O₃. The main phase of the Ni-20wt%Al coating mainly consisted of Ni solid solution, NiAl, and Ni₃Al in addition to a small amount of Al and Al₂O₃, and NiAl and Ni₃Al intermetallic compounds effectively further improved the final wear property of the coatings. TEM analysis indicated that fine spherical NiAl₃ precipitates and a Ni–Al–O amorphous phase formed in the matrix of the Ni solid solution in the original state.     

Corrosion behavior of low alloy steels in a wet–dry acid humid environment

The corrosion behavior of corrosion resistant steel (CRS) in a simulated wet–dry acid humid environment was investigated and compared with carbon steel (CS) using corrosion loss, polarization curves, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), N₂ adsorption, and X-ray photoelectron spectroscopy (XPS). The results show that the corrosion kinetics of both steels were closely related to the composition and compactness of the rust, and the electrochemical properties of rusted steel. Small amounts of Cu, Cr, and Ni in CRS increased the amount of amorphous phases and decreased the content of γ-FeOOH in the rust, resulting in higher compactness and electrochemical stability of the CRS rust. The elements Cu, Cr, and Ni were uniformly distributed in the CRS rust and formed CuFeO₂, Cu₂O, CrOOH, NiFe₂O₄, and Ni₂O₃, which enhanced the corrosion resistance of CRS in the wet–dry acid humid environment.     

Erosion–corrosion behavior of austenitic cast iron in an acidic slurry medium

A series of austenitic cast iron samples with different compositions were cast and a part of nickel in the samples was replaced by manganese for economic reason. Erosion–corrosion tests were conducted under 2wt% sulfuric acid and 15wt% quartz sand. The results show that the matrix of cast irons remains austenite after a portion of nickel is replaced with manganese.(Fe,Cr)3C is a common phase in the cast irons, and nickel is the main alloying element in high-nickel cast iron; whereas,(Fe,Mn)3C is observed with the increased manganese content in low-nickel cast iron. Under erosion–corrosion tests, the weight-loss rates of the cast irons increase with increasing time. Wear plays a more important role than corrosion in determining the weight loss. It is indicated that the processes of weight loss for the cast irons with high and low nickel contents are different. The erosion resistance of the cast iron containing 7.29wt% nickel and 6.94wt% manganese is equivalent to that of the cast iron containing 13.29wt% nickel.