Narrow Results

Nano-sized Ni–AlN thin films were prepared by pulse electrodeposition (PE) on A3 steel substrates. The microstructures, surface root-mean-square roughnesses, microhardness values, and corrosion performances of obtained nano-sized Ni–AlN thin films were investigated. Corrosion weight losses of Ni–AlN thin films were predicted by Backward propagation (BP) networks model. The results indicated that average diameters of Ni and AlN embedded in the films were evaluated to 57.9 and 29.2nm, respectively. Also, thin films were observed with uniform and compact surface structures, and Rq value was estimated to only 32.75nm.

In this work, the experimental investigation of the surface integrity and biomechanical properties of the superficial layer obtained by wire electrical discharge machining (W-EDM) of Ti-6Al-4V alloy for biomedical application has been carried out. The surface morphology and elemental composition of the superficial layer have been investigated by field-emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The micro-mechanical behavior in terms of compressive strength and surface hardness was studied using the micro-pillar and nano-indentation technique. The corrosion resistance and in vitro bioactivity have been investigated using electrochemical and immersion test. Morphological analysis showed that surface morphology and superficial layer thickness were affected by peak current, pulse-duration and pulse-interval. The niobium (Nb)-rich layer was developed in superficial layer zone. The low peak current (3–6A), low pulse-duration (5–10$\mu$s) and high pulse-interval ($>45\mu$s) have been recommended for better surface morphology and thin superficial layer (ranging from 4–6$\mu$m) free from surface defects. The micro-pillar and nano-indentation results showed that the superficial layer comprised of a brittle structure that improved the mechanical properties of the layer and the compressive strength was measured to be 1198 MPa. The corrosion resistance analysis revealed that the Nb-rich layer in the superficial layer improved the corrosion resistance and bioactivity. Excellent apatite growth has been found in the W-EDM-processed zone. The W-EDM can be used for the biomedical industry as a potential surface engineering technique.

An aluminized coating for low-carbon steel with good corrosion and wear resistance was first prepared through low-temperature pack aluminization. Then, the low-temperature-aluminized steel substrate was subjected to thermal oxidation in air. The phase composition, surface morphology, roughness, and elemental distribution of the aluminized carbon steel both before and after thermal oxidation were analyzed through X-ray diffraction spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion resistance and wear resistance of the original carbon steel substrate, aluminized carbon steel, and oxidized carbon steel were tested. Results showed that nanowires composed of iron oxide and alumina formed in situ on the top layer of the aluminized carbon steel. The corrosion resistance and wear resistance of the low-carbon steel with the nanowire oxide coating were better than those of the original carbon steel and aluminized carbon steel because the in-situ nanowire oxide film improved the density of the aluminized coating.

Phytic acid (PA) and 3-aminopropyltrimethoxysilane (APTMS) were selected as organic additives and respectively doped into Na₂SiO₃-NaOH electrolyte to prepare ceramic coatings on AZ31B Mg alloys by Plasma Electrolytic Oxidation (PEO) method. The influences of two additives on corrosion resistance of the PEO coatings were compared. The microstructure, composition and corrosion resistance of the PEO coatings were examined by SEM, EDX, XPS, XRD, potentiodynamic polarization test and EIS measurement. The results indicated that each additive increased both the coating thickness and corrosion resistance. However, the PA-doped PEO coating achieves larger thickness but exhibits worse corrosion resistance than the APTMS-doped PEO coating due to larger pore size and looser microstructure.

Aluminum (Al) and its alloys are attractive for a variety of applications due to its advantages like light weight, ease of processing, and high thermal/electrical conductivities. However, it suffers short comings in terms of strength, wear resistance, and corrosion resistance. Thermal spray processes are widely used techniques for the surface property improvement like thermal, wear, and corrosion resistances of aluminum and other light metals. This paper summarizes the recent developments in thermal spraying and related technologies. Plasma spraying, flame spraying, and arc spraying are the chief thermal spraying techniques, whereas the HVOF and D-gun processes are the derivatives of flame spraying process. The cold spraying technique is an emerging coating technique where the particles are heated to a temperature lower than their melting point travel at high velocity and coat on impact with the target material by plastic deformation. Different parameters like heat source characteristics, coating material properties, substrate properties, and spray torch operating circumstances affect the coating microstructure and properties.

In this paper, the silane-based sol–gel treatment process was applied to the plasma electrolytic oxidation (PEO) ZM6 Mg-alloy. The microstructural characteristics and corrosion resistance of the PEO/organic composite coatings were studied by means of SEM and XRT in conjunction with electrochemical measurements. The results showed that the microdefects in the PEO coating could be effectively filled with the silane compounds, reducing the porosity of the PEO coating. The treated PEO coating had a hydrophobic property, which may be related to the siloxane network (Si–O–Si) formed on the PEO coating surface. The corrosiveness of the silane agent to the PEO coating and the generation of internal stress in the PEO coating resulted in the damage of microstructures of the PEO coating. The global and local electrochemical measurements showed that the corrosion-resistant performance of the PEO Mg-alloys after the silane-based sol–gel treatment was improved and its service life would be shortened by the balance of micropores without sealing and the damaged microstructure.

In this study, AlCoCrFeNi-TiC_x (x values in molar ratio, x = 0, 0.1, 0.2, 0.3) high-entropy alloy coatings (HEAcs) were prepared on the surface of H13 steel by laser cladding (LC). The microhardness, corrosion resistance, and wear resistance of the HEAcs were analyzed using a microhardness tester, electrochemical workstation, and friction and wear tester, respectively. The results showed that with an increase in the TiC content of the coatings, the interior of the coatings mainly consisted of disordered body-centered cubic (BCC), ordered BCC (B2), and TiC phases, and lattice distortion occurred inside the coatings. TiC was distributed as white particles at the grain boundaries, and the internal microstructure was mainly composed of equiaxed crystals (EC) and petal-like dendrites. The EC were gradually refined owing to the pinning effect. The spinodal decomposition causes a large number of reticulated microstructures inside the grains, and nanoscale TiC precipitation appears in the reticulated microstructures. Owing to lattice distortion and solid solution strengthening, the microhardness of the TiC${}_{0.3}$ coating was up to 966 HV${}_{0.5}$, which was approximately 3.2 times that of the substrate. As the TiC content increases, the friction coefficient and mass loss of the coatings gradually decreased, the self-corrosion current ($I_{\mathrm{\text{corr}}})$ gradually decreased and the self-corrosion potential ($E_{\mathrm{\text{corr}}})$ gradually increased. The coatings exhibited good wear and corrosion resistance.

Proper selection of bath additives is critical to the plating rate, phosphorus content and corrosion resistance of the nickel–phosphorus (Ni–P) alloy deposits. In this work, electroless Ni–P alloy deposition from an acidic bath using sodium hypophosphite as the reducing agent at relatively low temperatures (30°C and 60°C) was carried out in the presence and absence of urea additives. The effects of different concentrations of urea on plating rate and phosphorus content of the Ni–P deposits were studied. The results showed that the plating rate and the phosphorus content of the Ni–P deposits were largely dependent on the concentration of urea in the bath. The corrosion resistance of the Ni–P deposits was evaluated in aerated 3.5 wt.% sodium chloride (NaCl) solution using potentiodynamic polarization curves. It was found that the corrosion resistance of the deposits obtained from the bath solution containing 1 g/L of urea was the highest. In addition, cyclic voltammetry techniques were used to study the mechanism of electroless Ni–P alloy deposition in the bath. The results revealed that the addition of urea to the bath promoted the concentrations of adsorbed atomic hydrogen and sodium hypophosphite on mild steel surface, which markedly increased the phosphorus content of the Ni–P deposits. This work offers a new way that highlights the relation between the urea additives and phosphorus content.

In recent years, nanoparticles are increasingly used in scientific research and have attracted the attention of many scholars. In this paper, ceramic coatings were prepared on the surface of magnesium and its alloys using the plasma electrolytic oxidation (PEO) technique. We investigated different nanoparticles added to the electrolyte and explored the mechanism of nanoparticle effects on the formation and protection mechanism, morphology and structure, thickness and roughness, and electrochemical corrosion behavior of the coatings. The results show that the coating morphology changes significantly and the surface is more uniform and dense due to the addition of nanoparticles in the electrolyte. The addition of nanoparticles increases the thickness of the coating to some extent, but as its addition to the electrolyte increases, the coating thickness decreases. Since the prepared coatings inevitably produce micropores and microcracks, which may have an impact on the corrosion resistance of the coatings, how to improve the corrosion resistance of the coatings has become a common concern. Nanoparticles can participate in the growth of the coating and will enter the micropores under discharge conditions. On the one hand, they can play a role in closing the porous layer, and on the other hand, they will form some special structures on the surface, thus improving the corrosion resistance of the coating. Finally, we outlook the problems and challenges of the PEO technique in practical applications.

This work addressed the effect of CMT-GMAW multi-control welding of Inconel 617 alloy with different wire feed rates (8.9, 9.4, and 9.9 m/min) on the microstructure, hardness, and electrochemical properties. The weld joints are composed of columnar dendritic structure with cellular crystals. Electron backscattered diffraction (EBSD) study showed equiaxed dendrite at the center of weld metal with growth direction perpendicular to the fusion boundary. The weldments showed diffraction peaks at $43.53^{\circ }$, $50.12^{\circ }$, and $74.82^{\circ }$, and these peaks mainly represent gamma ($\gamma$) and gamma prime ($\gamma$’) phases along with the carbide peaks of Ti (C, N), M${}_{23}$C₆ and M₆C. The Base metal (BM) had a lower hardness (232 ± 10 HV${}_{0.2}$) and lower corrosion rate (0.212 mpy) than the weld joints. The increase in wire feed rate (WFR) results in the decrease of microhardness (267 ± 5 − 251 ± 6 HV${}_{0.2}$) and increase in corrosion rate (1.833-28.140 mpy). The base metal exhibited higher potential ($E$${}_{\text{corr}}$) and lower current density ($I$${}_{\text{corr}}$) than the weld joints. As wire feed rate (WFR) increases, heat input increases; solidification time increases, grain boundaries coarsen, resulting in a lower grain boundary (GB) density, and hence increased carbide precipitation and segregation in weld zone leading to higher stable anodic current density, which caused corrosion resistance to deteriorating. The BM was more corrosion resistant than the weld joints. The metallurgical and physical changes caused by the welding process affect the corrosion resistance of the weld joints. This leads to the weld metal corroding faster than the base metal.

Conventional electroless Ni–B–Mo (ENB–Mo) deposits are formed using hazardous lead or thallium-containing solutions, which must be removed. In this study, ENB–Mo deposits were developed in a bath free of stabilizers and harmful heavy metals. This study estimates the effect of variation of coating bath temperature on tribological performance of ENB–Mo coating developed over AISI 1040 steel. The chosen bath temperatures were $85^{\circ }$C, $90^{\circ }$C, and $95^{\circ }$C to achieve ENB–Mo coating with varying B and Mo content. The 12–15 $\mu$m thick coating was uniform. In comparison to steel substrate, all of the coatings show enhanced corrosion resistance. In the as-deposited state, coatings were mixed amorphous and nanocrystalline with peak of Fe overlapping with Ni. Moreover, TGA results revealed that inclusion of molybdenum enhanced coatings thermal stability. The worn specimens at $300^{\circ }$C reveal development of shielding tribo-oxide coatings and existence of microstructural changes. At high working temperatures ($300^{\circ }$C), wear debris also has a major impact on tribological mechanisms of coatings. Correlation between microstructure, tribological behavior, and corrosion resistance have also been conducted for ENB–Mo coatings.

In order to enhance the corrosion resistance of calcium-based phosphate coating, the molybdenum-modified coating was successfully prepared by adding Na₂MoO₄ in a phosphate bath. The prepared composite film layers were studied by EDS, XRD and SEM. The corrosion resistance performances of the films were investigated by electrochemical measurements. The results showed the main composition of molybdenum-modified film was MoO₂, MoP₂, and MoP₄, the diameter of cracks on the surface of the coating was significantly reduced, which provided better protection to the substrate. In addition, the potentiodynamic polarization curves of the molybdenum-modified film show that the corrosion potential was positively shifted by 0.068 V compared to the calcium-based phosphate coating and the corrosion current was reduced to 2.556 × 10${}^{-5}$ A · cm${}^{-2}$, indicating improved corrosion resistance.

After micro-arc oxidation, the surface properties of AZ31 magnesium alloy have been improved. However, micro-arc oxidation treatment leads to high insulation, which limits its application in electronic devices. To increase conductivity, a conductive coating was developed by adding multi-walled carbon nanotubes (MWCNTs) to the epoxy resin. The microstructure and performance of the coating were tested by SEM, thermogravimetric analyzer, four-probe conductivity meter, high-temperature friction and wear tester, and electrochemical workstation. The results indicate that the optimal conductivity with a resistivity of 303$\mathrm{\Omega }\cdot$m is obtained when the MWCNT content is at 4wt%. In addition, MWCNTs are filled with a network structure of epoxy resin, which increases the density of the coating and enhances their wear and corrosion resistance.

Different anodized coatings are prepared on the surface of 2024 aluminum alloy from different solutions by pulse anodizing to improve corrosion resistance and hardness. The thickness, roughness, structure, hardness, surface morphology, and corrosion resistance of different anodized coatings are studied. It is found that the anodized coating is composed of a porous layer on the surface and a nonporous barrier layer inside, showing the structure of $\gamma$-Al₂O₃ and $\alpha$-Al₂O₃. The anodized coating prepared from sulfuric acid solution mixed with oxalic acid and glycerol has a larger thickness and higher hardness. The surface morphology of the anodized coatings is porous. The thickness of the anodized coating prepared from oxalic acid solution is small and the pore distribution is not uniform. However, the anodized coating obtained from sulfuric acid solution mixed with oxalic acid and glycerol has the smallest average pore size of 6.38nm and ordered pore distribution, resulting in the best corrosion resistance.

The ultrasonic is applied during the electrodeposition process of CoMo/Al₂O₃ composite coating on 10# steel to enhance its corrosion resistance in simulated sewage water. The influence of ultrasonic power on the thickness, roughness, chemical composition, surface morphology, and corrosion resistance of the composite coating is investigated. In an aqueous solution, a co-deposition of cobalt and molybdenum can be induced to form CoMo alloy coating. The Al₂O₃ nanoparticles are incorporated into CoMo alloy to form CoMo/Al₂O₃ composite coating. When the ultrasonic power increases from 0W to 100 W, the electrodeposition rate of the composite coating increases from 63.25mg/h to 153.73mg/h, and the thickness of the composite coating also increases from 15.6$\mu$m to 28.1$\mu$m. The surface roughness of composite coating electrodeposited without ultrasonic is about 0.436$\mu$m. The CoMo/Al₂O₃ composite coating electrodeposited at 100W ultrasonic power exhibits the smallest surface roughness of 0.193$\mu$m and presents a denser surface morphology composed of 74.4% Co, 10.3% Mo, and 15.3% Al, resulting in better corrosion resistance with the smallest corrosion current density of only 9.7$\mu$A/cm². However, when the ultrasonic power is 150W, the intense hydrogen evolution on the surface of the cathode reduces the density of the coating surface, which leads to the deterioration of corrosion resistance.

In previous studies, the microstructure, mechanical properties and corrosion resistance of Hastelloy X fabricated by selective laser melting (SLM) have been investigated; however, it is hoped that heat treatment will effect on its properties. Therefore, this study is to discuss heat treatment effect on Hastelloy X fabricated by SLM. It is interestingly found that fracture strain greatly increases with heat treatment, and the yield ratio decreases, which demonstrates the material is more reliable. High temperature tensile behavior is discussed; it is worth mentioning that not only fracture strain of the HT sample increases greatly at 550^∘C in comparison with SLM sample, but also ultimate tensile strength increases from 632 MPa to 639 MPa; the results show that the mechanical property can be improved at medium and high temperature by heat treatment. The corrosion resistance of HT sample deteriorates slightly, which can be explained by Cr-rich precipitates. In conclusion, the material after heat treatment is suitable for applications requiring high mechanical reliability and medium and high temperature occasions, but it is not befitting for corrosive environments.

This paper presents an analysis of the properties of sintered steels in terms of their practical use for production of interconnectors in fuel cells. The study covers measurements of mechanical properties, microstructural examinations and analysis of surface profile in the sintered samples. The porosity and contact resistance between interconnectors and gas diffusion layer are also examined. The main criterion adopted for choosing a particular material for the components in fuel cells is their corrosion resistance under operating conditions of hydrogen fuel cells. In order to determine resistance to corrosion in the environment of operation of fuel cells, potentiokinetic curves are registered for synthetic solution 0.1 M H₂SO₄ + 2 ppmF^- at 80°C.

Nanostructured hybrid silica/epoxy films containing boehmite nanoparticles were investigated in the present work as pretreatments for AA2024 alloy. To produce the nanocomposite sol-gel films, boehmite nanoparticles prepared from hydrolysis/condensation of aluminum isopropoxide (AlI) were doped into another hybrid organosiloxane sol. The produced oxide nanoparticles have the capability to act as nanoreservoirs of corrosion inhibitors, releasing them controllably to protect the metallic substrate from corrosion. For this purpose the corrosion inhibitor, cerium nitrate, was introduced into the sol-gel system via loading the nanoparticles. The morphology and the structure of the hybrid sol-gel films were studied by Scanning Electron Microscopy (SEM). The corrosion protection properties of the films were investigated by Potentiodynamic Scanning (PDS) and Electrochemical Impedance Spectroscopy (EIS). The results show that the presence of boehmite nanoparticles highly improved the corrosion protection performance of the silica/epoxy coatings. Moreover, they can act as nanoreservoirs of corrosion inhibitors and provide prolonged release of cerium ions, offering a self-healing property to the film.

Electron Beam-Physical Vapor Deposition (EB-PVD) is being used in coating component for many applications such as electronic industry for producing nanostructures and ICs coatings. In this work, nanostructured copper was deposited on glass using EB-PVD technique. Surface and elemental characteristics of EB-PVD coatings investigated and evidenced corrosion resistance of nanostructured coatings produced by this technique are higher than Cu sheet in chloride media.

The process of electroless plating Ni-P and Ni-P/nano-SiO₂ on API-5L X65 carbon steels was improved. The Ni-P/nano-SiO₂ composite coatings were prepared from the bathes containing different concentrations of nano-SiO₂ particles. The coatings surface and morphologies were observed via scanning electron microscopy (SEM). The chemical compositions were analyzed by EDAX. The corrosion behaviors were evaluated by electrochemical impedance spectroscopy tests. The experimental results indicated that SiO₂ nano-particles co-deposited but some agglomeration occurred. Micro-hardness of electroless Ni-P-SiO₂ composite coatings increased due to the existence of nano-particles. Corrosion tests showed that both electroless Ni-P and Ni-P/nano-SiO₂ composite coatings demonstrated significant improvement of corrosion resistance of substrate in salty atmosphere and latter coating type appeared to offer a better corrosion protection.