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Corrosion resistance of nanocrystalline Fe_73.5Si_13.5B₉Nb₃Cu₁ alloy was investigated and compared to its amorphous counterpart. Low-temperature crystallization occurred during the annealing of amorphous tapes was used to obtain a nanocrystalline structure. The influence of annealing condition on the structure and corrosion resistance of the alloy in NaCl and H₂SO₄ solutions was investigated. Based on the testing results, it was found that nanocrystalline tapes have higher corrosion resistance than amorphous counterpart and H₂SO₄ can promote the occurrence of corrosion compared with NaCl.

In this paper, corrosion behavior of an AISI 304 stainless steel modified by niobium or niobium nitride (denoted as niobized 304 SS and Nb-N 304 SS, respectively) is investigated in simulated solid polymer fuel cell (SPFC) operating conditions. Potentiodynamic polarizations show that the corrosion potentials of surface modified 304 SS shift to positive direction while the corrosion current densities decrease greatly comparing with the bare 304 SS in simulated anodic SPFC environments. The order of corrosive resistance in corrosive potential, corrosive current density and pitting potential is: Nb-N 304 SS > niobized 304 SS > bare 304 SS. In the methanol-fueled SPFC operating conditions, the results show that the corrosion resistance of bare and niobized 304 SS increases with the methanol concentration increasing in the test solutions.

To improve the corrosion resistance of an electro-galvanized steel sheet, we deposited magnesium film on it using a vacuum evaporation method and annealed the films at 250–330°C. The zinc–magnesium alloy is consequently formed by diffusion of magnesium into the zinc coating. From the anodic polarization test in 3% NaCl solution, the films annealed at 270–290°C showed better corrosion resistance than others. In X-ray diffraction analysis, ZnMg₂ was detected throughout the temperature range, whereas Mg₂Zn₁₁ and FeZn₁₃ were detected only in the film annealed at 310°C. The depth composition profile showed that the compositions of Mg at 270–290°C are evenly and deeply distributed in the film surface layer. These results demonstrate that 270–290°C is a proper temperature range to produce a layer of MgZn₂ intermetallic compound to act as a homogenous passive layer.

Thermal spray coating method has been known to be an attractive technique due to its relatively high coating speed. However, a high corrosion resistance of the coating film deposited by thermal spray method should be improved to prolong its lifetime. In this study, four types of coated films (DFT: 400 μm), that is, pure zinc, pure aluminum and two Al – Zn alloy (Al:Zn = 85:15 and Al:Zn = 95:5) films were coated onto a carbon steel (SS401) with arc spraying, and the corrosion behaviors of these samples were investigated using the electrochemical method. The pure aluminum sample had the best corrosion resistance in seawater solution and alloy (Al:Zn = 85:15) film, so called galvalume followed the pure aluminum sample, moreover, the alloy (Al:Zn = 95:5) sample exhibited the worst corrosion resistance.

An optimum repair welding for the piston crown which is one of the engine parts exposed to the combustion chamber is considered to be very important to prolong the engine lifetime from an economical point of view. In this study, two types of filler metals such as 1.25Cr–0.5Mo, 0.5Mo were welded with SMAW method and the other two types of filler metals such as Inconel 625 and 718 were welded with GTAW method, respectively, and the used base metals were the cast and forged steels of the piston crown material. The weld metal zones welded with Inconel 625 and 718 filler metals exhibited higher corrosion resistance compared to 1.25Cr–0.5Mo and 0.5Mo filler metals. In particular, the weld metal zone welded with Inconel 718 and 0.5Mo, filler metals indicated the best and worst corrosion resistance, respectively. Consequently, it is suggested that the corrosion resistance of the weld metal zone surely depends on the chemical components of each filler metal and welding method irrespective of the types of piston crown material.

The main purpose of this work is to optimize the mechanical properties of tungsten–copper (W–Cu) nanocomposite fabricated by the sintering process. For this purpose, the parameters of sintering temperature, sintering time and weight percentage of copper were selected to optimize the compression strength, impact strength, hardness and corrosion resistance of the W–Cu nanocomposite using the desirability function procedure and response surface method. The analyses of transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were also performed to examine the microstructure of W–Cu nanocomposite. The results exhibited that a rise in the sintering temperature from 1000^∘C to 1150^∘C significantly enhanced the impact strength of W–Cu nanocomposite, while a rise in the sintering temperature from 1150^∘C to 1300^∘C deteriorated the impact strength. Moreover, the compression strength and hardness of the W–Cu nanocomposite continuously improved by elevation of sintering temperature from 1000^∘C to 1300^∘C. A rise in the amount of Cu from 20wt.% to 40wt.% led to a reduction in the hardness of the W–Cu nanocomposite, while a rise of Cu content improved the impact and compression strengths. The results also indicated that the mechanical properties of W–Cu nanocomposite enhanced simultaneously by using 27wt.% Cu at sintering temperature of 1197^∘C and sintering time of 2.7h. The samples sintered at the optimal conditions indicated a higher corrosion resistance than that sintered at the initial conditions.

Electrochemical impedance spectroscopy (EIS) is one of the electrochemical techniques used in materials science. The present measurements are used to evaluate the corrosion resistance of new types of coated steel rebar used in reinforced concrete. In this study, Si-based coating materials are used and evaluated, because adding Si to metals and alloys, including steel, generally increases their corrosion, oxidation, and erosion resistance. The result suggests that electrochemical impedance spectroscopy may be useful for monitoring corrosion activity on coated steel rebars. Based upon impedance changes, it appears that the silicon powder coating bonds well to the steel, and that the coating has a good performance.

A manganese oxide contained coating was prepared on biodegradable AZ31B magnesium alloy to control the degradation of AZ31B and improve its biocompatibility. Morphology, composition, and corrosion resistance of the coating were studied. The SEM observations showed that the coating was approximately 4–6 μm in thickness with net-like microcracks. The XPS analysis indicated that the coating was mainly composed of MgO, Mg(OH)₂, MnO₂, Mn₂O₃, and Mn₃O₄. It was found that AZ31B with such coating showed better corrosion resistance in simulated blood plasma through electrochemical and immersion tests. The hemolytic assay indicated that the treated AZ31B had no hemolytic effect.

Different aluminide coatings were prepared on oil casing steel N80 at a relatively lower temperature of 530°C for 2 h by pack powder modified with different content of zinc (Zn). The cross-sectional microstructure, element distribution and properties of as-aluminized oil casing steel N80 were investigated by SEM, EDS, micro-hardness test and electrochemical corrosion measurement. Results show that aluminide coating with around 50 μm in thickness can be successfully achieved by a low-temperature pack aluminizing processing with the addition of Zn. Zn in the pack powder can enhance the uniformity and continuity of the coating layer, while it has little effect on the thickness of as-packed coating with the increasing content of Zn from 38.8 wt.% to 84.4 wt.%. As the content of Zn is over 58.8 wt.%, two layer coating consisting of pure Zn layer and Fe–Al aluminide layer can be formed on oil casing steel N80 substrate. Furthermore, oil casing steel N80 with aluminizing coating shows a higher microhardness than that of original one except in the depth range of pure Zn layer, but the microhardness of oil casing steel substrate does not decrease after aluminizing which can be inferred that low-temperature aluminizing processing reported here will not bring any damages on the mechanical properties of oil casing steel N80. Additionally, a lower self-corrosion current density of oil casing steel N80 with aluminizing coating also indicates that low-temperature aluminizing processing is helpful to the corrosion resistance of oil casing steel N80.

Influence of surfactants on the corrosion properties of chromium-free electroless nickel deposit were investigated on AZ91D magnesium alloy. The corrosion tests were carried out by immersion test (1 M HCl) and electrochemical polarization test (3.5 wt% NaCl). The surfactants in the electroless nickel bath increases the corrosion resistance properties of the deposit on the magnesium alloy. In addition, smoothness and amorphous plus nano-crystalline phase were increased and accounted for the significant corrosion resistance. As a consequence, the corrosion potential moved towards the positive direction and the corrosion current density decreased. The immersion tests also provided the same trend as that of electrochemical polarization test. On the whole, the study concluded that corrosion resistance was enhanced by including a surfactant in the electroless deposits on magnesium alloy.

Reactive plasma sprayed coatings were prepared on carbon steel substrates with Ti and B₄C as starting materials. Two kinds of gases (Ar and N₂) were used as feeding gases for powders, respectively. 10 wt.% Cr was added in the powders as binder to increase the bond strength of the coating. The phases, microstructure, micro-hardness and corrosion polarization behavior in 3.5 wt.% NaCl solution of the two coatings were studied. The results show that TiN-TiB₂ coatings were prepared under both conditions. The two coatings have typically laminated structure. However, the coating prepared with Ar as feeding gas has higher porosity and some unmelted Cr particles. It also contains certain content of titanium oxides. The microhardness of coating prepared with Ar as feeding gas is lower due to its higher porosity, unmelted Cr particles and some amounts of TiO₂. The corrosion resistance of TiN-TiB₂ coating prepared with Ar as feeding gas in 3.5 wt.% NaCl solution is worse than that of the coating prepared with N₂ as feeding gas. Yet the corrosion resistance of reactive plasma sprayed TiN-TiB₂ coating is improved greatly compared with that of carbon steel. The thermodynamic analysis of reactive plasma spraying process is also discussed.

Magnesium and its alloys are potential biodegradable implant materials due to their attractive biological properties. But the use of magnesium is still hampered by its poor corrosion resistance in physiological fluids. In this study, a HA-containing coating was fabricated by micro-arc oxidation (MAO). The active plasma species of micro-discharge was studied by optical emission spectroscopy (OES). The microstructure and composition were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion behavior and apatite-forming ability were studied by electrochemical tests and immersed samples in simulated body fluids (SBF). The results show that the microdischarge channel model is gas discharges and oxide layer discharges. The elements from the substrate and electrolyte take part in the formation of the coating. The MAO coating significantly improves the corrosion resistance of AZ31 magnesium alloy and enhances the apatite formation ability.

In this paper, we discuss the formation of ceramic coatings by a combined processing of low-temperature pack aluminizing and oxidation treatment on the surface of X80 pipeline steel substrates in order to improve the corrosion resistance ability of X80 pipeline steel. First, Fe-Al coating consisting of FeAl₃ and Fe₂Al₅ was prepared by a low-temperature pack aluminizing at 803 K which was fulfilled by adding zinc in the pack powder. Pre-treatment of X80 pipeline steel was carried out through surface mechanical attrition treatment (SMAT). Further oxidation treatment of as-aluminized sample was carried out in the CVD reactor at 833 K under oxygen containing atmosphere. After 1 h duration in these conditions, ceramic coating consisting of α-Al₂O₃ was formed by in situ oxidation reaction of Fe-Al coating. Those coatings have been characterized by different techniques including X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscope (EDS), respectively. Ceramic coating shows a dense and uniform microstructure, and exhibits good coherences with X80 pipeline steel substrates. By electrochemical corrosion test, the self-corrosion current density of X80 pipeline steel with as-obtained ceramics coating in 3.5% NaCl solution shows an obvious decrease. The formation of α-Al₂O₃ ceramic coating is considered as the main reason for the corrosion resistance improvement of X80 pipeline steel.

Nd–Fe–B permanent magnets possess excellent properties. However, they are highly sensitive to the attack of corrosive environment. The aim of this work is to improve the corrosion resistance of the magnets by phosphatization, silanization, and electrostatic spraying with organic resin composite coatings. Field emission scanning electron microscope (FE-SEM) and energy dispersive spectrometer (EDS) tests showed that uniform phosphate conversion coatings and spray layers were formed on the surface of the Nd–Fe–B magnets. Neutral salt spray tests exhibited that, after treated by either phosphating, silanization or electrostatic spraying, the protectiveness of Nd–Fe–B alloys was apparently increased. And corrosion performance of magnets treated with silane only was slightly inferior to those of phosphatized ones. However, significant improvement in corrosion protection was achieved after two-step treatments, i.e. by top-coating spray layer with phosphate or silane films underneath. Grid test indicated that the phosphate and silane coating were strongly attached to the substrate while silane film was slightly weaker than the phosphate-treated ones. Magnetic property analysis revealed phosphatization, silanization, and electrostatic spraying caused decrease in magnetism, but silanization had the relatively smaller effect.

The influence of Mn²⁺/Ni²⁺ mole ratio in electrolytes on the Ni–Mn alloy deposits was studied. The electrodeposition mechanism of Mn with Ni is analyzed by the cyclic voltammogram (CV) and an "induced co-deposition" mechanism is proposed for Ni–Mn alloy electrodeposition. The results show that the Mn content in Ni–Mn alloy deposit and the hardness increased with the increase of Mn²⁺/Ni²⁺ mole ratio in electrolytes. When the Mn²⁺/Ni²⁺ mole ratio in bath was 2/1, the corrosion current density of the deposit coating was the lowest and the corresponding corrosion potential was higher, and under these conditions the coating with a Mn content of 1.20 wt.% showed good corrosion resistance. The scanning electron microscopy (SEM) of the alloy coatings exhibited that the morphology of Ni–Mn alloy coatings were different from Pure Ni coating, and when Mn²⁺/Ni²⁺ was 2/1, the surface was compact and homogeneous.

Corrosion resistant Fe–Al/Al₂O₃ duplex coating for pipeline steel X80 was prepared by a combined treatment of low-temperature aluminizing and micro-arc oxidation (MAO). Phase composition and microstructure of mono-layer Fe–Al coating and Fe–Al/Al₂O₃ duplex coating were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) with energy dispersive spectrometer (EDS). Corrosion resistance of the coated pipeline steel X80 in a simulated oil and gas well condition was also investigated. Mono-layer Fe–Al coating consists of Fe₂Al₅ and FeAl, which is a suitable transitional layer for the preparation of ceramic coating by MAO on the surface of pipeline steel X80. Under the same corrosion condition at 373 K for 168 h with 1 MPa CO₂ and 0.1 MPa H₂S, corrosion weight loss rate of pipeline steel X80 with Fe–Al/Al₂O₃ duplex coating decreased to 23% of original pipeline steel X80, which improved by 10% than that of pipeline steel X80 with mono-layer Fe–Al coating. It cannot find obvious cracks and pits on the corrosion surface of pipeline steel X80 with Fe–Al/Al₂O₃ duplex coating.

Different electroless Ni–P coatings were deposited on open-cell aluminum foams at various bath pH. The effect of bath pH on the morphology, structure, components, phases and corrosion resistance of the Ni–P coating was studied by scanning electron microscopy (SEM), confocal laser scanning microscope (CLSM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), immersion test and electrochemical polarization measurement, respectively. The experimental results show that the bath pH not only changed the reactivity of the bath, but also had a influence on the microstructure and anticorrosive property of electroless Ni–P coating. The high pH bath raises the thickness of Ni–P coating but decreases the content of phosphorus element in the Ni–P coating. The corrosion resistance of the coated aluminum foams increases when the bath pH rises.

Samples of AISI 201 austenitic stainless steel were produced by plasma nitriding at 350${}^{\circ }$C, 390${}^{\circ }$C, 420${}^{\circ }$C, 450${}^{\circ }$C and 480${}^{\circ }$C for 5h. Systematic characterization of the nitrided layer was carried out in terms of micrograph observations, phase identification, chemical composition depth profiling, surface microhardness measurements and electrochemical corrosion tests. The results show that the surface hardness and the layer thickness increased with increasing temperature. XRD indicated that a single S-phase layer was formed during low temperature ($\le$420${}^{\circ }$C), while Cr₂N or CrN phase was formed besides S-phase when nitrided at 450${}^{\circ }$C and 480${}^{\circ }$C. The specimen treated at 390${}^{\circ }$C presents a much enhanced corrosion resistance compared to the untreated substrate. The corrosion resistance deteriorated for samples treated above 450${}^{\circ }$C due to the formation of chromium nitrides.

The electrodeposition of Ni–nano-Cr₂O₃ composite coatings was studied in electrolyte containing different contents of Cr₂O₃ nanoparticles (Cr₂O₃ NPs) on mild steel surfaces. Some techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness, the potentiodynamic polarization curves (Tafel) and electrochemical impedance spectroscopy (EIS) were used to compare pure Ni coatings and Ni–nano-Cr₂O₃ composite coatings. The results show that the incorporation of Cr₂O₃ NPs resulted in an increase of hardness and corrosion resistance, and the maximum microhardness of Ni-nano-Cr₂O₃ composite coatings reaches about 495 HV. The coatings exhibit an active-passive transition and relatively large impedance values. Moreover, the effect of Cr₂O₃ NPs on Ni electrocrystallization is also investigated by cyclic voltammetry (CV) and EIS spectroscopy, which demonstrates that the nature of Ni-based composite coatings changes attributes to Cr₂O₃ NPs by offering more nucleation sites and less charge transfer resistance.

The plasma electrolytic borocarbonitriding (PEB/C/N) process on pure iron was carried out in 25% borax solution with glycerine and carbamide additives under different discharge time at 360V. The morphology and structure of PEB/C/N hardened layers were analyzed by SEM and XRD. The hardness profiles of hardened layers were measured by microhardness test. Corrosion behavior of PEB/C/N layers was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Their wear performance was carried out using a pin-disc friction and wear tester under dry sliding test. The PEB/C/N samples mainly consisted of $\alpha$-Fe, Fe₂B, Fe₃C, FeN, FeB, Fe₂O₃ and Fe₄N phases, and the Fe₂B phase was the dominant phase in the boride layer. It was found that the thickness of boride layer increased with the discharge time and reached 14$\mu$m after 60min treatment. The microhardness of the boride layer was up to 2100HV, which was much higher than that of the bare pure iron (about 150HV). After PEB/C/N treatment, the corrosion resistance of pure iron was slightly improved. The friction coefficient of PEB/C/N treated pure iron decreased to 0.129 from 0.556 of pure iron substrate. The wear rate of the PEB/C/N layer after 60min under dry sliding against ZrO₂ ball was only 1/10 of that of the bare pure iron. The PEB/C/N treatment is an effective way to improve the wear behavior of pure iron.