Corrosion and Electrochemical Behavior of β-W CVD Coatings in NaCl Solution

Protection of Metals and Physical Chemistry of Surfaces - The paper presents the results of a study of the corrosion-electrochemical behavior of coatings based on the metastable phase of tungsten...     

Effect of Microstructure on Corrosion Behavior of Mg–Sr Alloy in Hank's Solution

Mg–Sr alloy has been studied as a potential biodegradable material with excellent bioactivity to promote the bone formation. However, its degradation behavior needs to be well controlled to avoid the negative effect, which is important for future application. Therefore in this study, the microstructure and its effect on corrosion behavior of an Mg–1.5 Sr alloy were investigated. The microstructures of the alloy under different processing procedures were characterized by both optical and scanning electron microscopes. The corrosion performance was studied in Hank's solution using immersion,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests. The results showed that the grain size and the amount and distribution of b-Mg_(17)Sr_2 had obvious effects on the corrosion behavior of Mg–Sr alloy. The smaller the grain size was, the more the protective surface layer formed on Mg–Sr alloy, and the higher the corrosion resistance was. For the as-cast Mg–Sr alloy, the network-like second phases precipitated along the grain boundaries could not hinder the corrosion due to their own corrosion cracking accelerating the intergranular corrosion. However, the refinement of second phases increased the corrosion resistance of the as-extruded alloy. After solution treatment at 450 °C for 5 h, the grains in the alloy did not grow much and b-Mg_(17)Sr_2 phases homogenously distributed in the alloy, resulting in the increase in corrosion resistance. However, after aging treatment, large amount of precipitated second phases increased the galvanic corrosion of the alloy, accelerating the development of corrosion.     

Preparation of High Corrosion Resistance Ni-Fe-Sm Alloy Films in Reline SystemEI北大核心CSCD

针对在传统水溶液电解质中制备的 Ni-Fe 合金存在表面粗糙且耐腐蚀性能差的问题,在氯化胆碱-尿素离子液体体系 (Reline)中,加入稀土元素 Sm 对 Ni-Fe 合金进行改性,制备 Ni-Fe-Sm 三元合金膜。采用循环伏安测试、塔菲尔测试、扫描电镜、X 射线能谱仪研究金属离子在 Reline 离子液体中的电化学行为、合金膜表面形貌及其耐腐蚀性能。结果表明,Ni(Ⅱ)、 Fe(Ⅱ)为一步不可逆还原过程,Ni-Fe-Sm 合金在 Reline 体系中成核机制为三维瞬时成核。合金膜表面各金属元素分布均匀, 微观结构呈瘤状球形颗粒,合金膜表面细致,裂纹少,排布整齐。在 3.5 wt.%NaCl 和 10 wt.%HCl 溶液中,加入稀土元素 Sm, 合金膜的耐腐蚀性能显著提高,当沉积电位为?1.22 V,沉积时间为 20 min 时,自腐蚀电流密度最小,腐蚀速度最低,自腐蚀电位最正,耐腐蚀性能最高。进一步丰富了在 Reline 体系中添加稀土元素提高合金耐腐蚀性能的认识,使其在防护、存储等领域有较好的应用前景。     

High Temperature Corrosion Behavior of Cold Spray Ni-20Cr Coating on Boiler Steel in Molten Salt Environment at 900 °C

Cold spray is an emerging technology that produces high density metallic coatings with low oxide contents and high thermal conductivity, which makes them ideal for high temperature corrosion resistance. In the current investigation, Ni-20Cr alloy powder was deposited on SA 516 boiler steel (0.19C-1.07Mn-0.020S-0.25P-0.010Si-balance Fe) by cold spray process. Oxidation kinetics was established for the uncoated and cold spray Ni-20Cr coated boiler steel in an aggressive environment of Na₂SO₄-60%V₂O₅ at 900 °C for 50 cycles by the weight change technique. X-ray diffraction, FE-SEM/EDAX, and x-ray mapping techniques were used to analyze the oxidation products. Uncoated steel suffered corrosion in the form of intense spalling and peeling of its oxide scale, which may be due to the formation of unprotective Fe₂O₃ oxides. The Ni-20Cr coating was successful in reducing the weight gain of the steel by 87.2% which may be due to the formation of oxides of nickel and chromium.     

三联冶炼GH4169合金研究进展EI北大核心CSCD

三联冶炼技术的突破促进了我国GH4169合金盘锻件全流程制备技术的优化。本文综述了GH4169合金的化学成分、三联冶炼技术、开坯技术、锻造技术、残余应力控制、质量控制体系等方面的研究进展。三联冶炼技术的突破提高了GH4169合金的纯净度,降低了冶金缺陷概率;镦拔+径锻联合开坯提高了GH4169合金棒材组织均匀性和成材率;残余应力控制技术降低了GH4169合金盘件加工和服役过程中的变形量。此外,本文讨论了GH4169合金在超高强度、超大尺寸、高耐蚀性能和抗氢脆等研究中存在的难题,并对未来工作方向进行了展望。     

Corrosion Protection of Aluminum Alloy AA7020 in NaCl Solution by Hybrid Sol–Gel Coatings

Protection of Metals and Physical Chemistry of Surfaces - In this study, two different hybrid sols as tetraethyl orthosilicate/(3-Glycidyloxypropyl) trimethoxysilane (TEOS/GPTMS) and tetrapropyl...     

Hot Corrosion Behavior of Some Superalloys in a Simulated Incinerator Environment at 900 °C

Incinerators are being used to burn solid waste of all types. This burning of waste creates a very aggressive environment at extremely high temperature. This environment attacks the various components of the incinerators. Some studies have been reported regarding behavior of steels in simulated incinerator environment at 550 °C. In present work superalloys Superco 605, Superni 600, and Superni 718 have been subjected to cyclic oxidation in 40 wt.% K₂SO₄ + 40 wt.% Na₂SO₄ + 10 wt.% KCl + 10 wt.% NaCl environment at 900 °C under cyclic condition. Weight change measurements have been done and weight change has been plotted against the numbers of cycles. The oxide scales formed on the surface of the corroded superalloys have been characterize by FESEM, EDS, XRD, cross-sectional analysis, and x-ray mapping. The nickel-based superalloys Superni 600 and Superni 718 indicated better resistance to corrosion in the above environment whereas Superco 605 lead to massive weight gain.     

Electrochemical Corrosion Behavior of Magnetron-Sputtered Al-Mo Gradient-Coated Steel in 3.5 wt.% NaCl Solution

A gradient three-layer Al-Mo coating was deposited on steel using magnetron sputtering method. The corrosion properties of the coating were studied in 3.5 wt.% NaCl solution using electrochemical techniques, whereas the hydrogen-induced cracking (HIC) resistance was examined by constant-load tests using notched tensile specimens. These results were compared with conventional electroplated cadmium-coated steel. The results show that the gradient Al-Mo coating exhibits better corrosion and HIC resistance when compared to electroplated cadmium. This was due to the excellent corrosion resistance of the bottom aluminum-rich layer, while the top Mo-rich layer provided good lubrication properties.     

The Corrosion Behavior of Carbon Steel in Sulfide Aqueous Media at 30°C

In this paper, we studied the effect of sulfide ions on the corrosion behavior of carbon steel to simulate the geological disposal of high-level radioactive waste. In geological storage conditions, sulfidogenic environment was sustained by sulfate-reducing bacteria. Corrosion tests were conducted in systems in a controlled atmosphere of 5% H₂/N₂. Batch experiments were conducted at 30°C for 1 month with steel coupons immersed in Na₂S solutions. The structural characterization of the corrosion products was investigated by scanning electron microscope/energy dispersive x-ray spectroscopy, confocal micro-Raman spectrometry, and x-ray diffraction. In the absence of sulfide ion, a magnetite (Fe₃O₄) corrosion product layer was formed on steel surface while in the presence of sulfide ions we observed the formation of a poorly crystallized irons sulfide at low-sulfide concentration (1 mg/L) and a solid adherent pyrrhotite layer at higher sulfide concentration (5-15 mg/L). The strong drop in steel corrosion rate with sulfide concentration was revealed and related to the formation of well-crystallized pyrrhotite.     

Corrosion behavior of high Al- and Fe-bronze Cu-15Al-xFe in NaCl solution北大核心CSCD

Sub-rapidly solidified Cu-15Al-xFe (x=10, 12, 15) alloy bars were prepared by copper mould casting. The corrosion behavior of the bronzes in 3.5%NaCl solution was investigated by means of potential dynamic polarization measurement and static immersing corrosion test. The microstructure of the bronzes before and after corrosion test was characterized with scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), and then the relevant corrosion mechanism and the effect of Fe content on the corrosion resistance were discussed in detail. The results showed that the corrosion resistance of Cu-15Al-12Fe alloy is the best in 3.5%NaCl solution. The three bronzes Cu-15Al-xFe (x=10, 12, 15) all suffered from selective corrosion, which was resulted from the dealuminization and deferrization of the phase reach in Fe and Al. © 2016, Corrosion Science and Protection Technology. All rights reserved.     

Galvanic Series of Metals and Effect of Alloy Compositions on Corrosion Resistance in Sanya SeawaterEI北大核心CSCD

With the development of ocean engineering, various metallic materials have been applied to the marine environment. It is an urgent requirement to study the galvanic series and alloy composition optimization of metallic materials in the tropical marine environment. In this work, open circuit potentials (OCP) and galvanic series of 36 kinds of metallic materials in Sanya seawater were studied. By considering the response of OCP to tidal changes, the anti-corrosion effects of alloying elements were also ana lyzed. The results show that the OCP of metallic materials in Sanya seawater has a large range. The galvanic series order of metallic materials from high to low in Sanya seawater is: nickel alloy, duplex stainless steel, austenitic stainless steel and pure copper, ferritic stainless steel, martensitic stainless steel, copper alloy, low alloy steel, carbon steel, cast iron, aluminum alloy and aluminum anode. Low-carbon high-alloy content carbon steel and high Cr, Ni contents stainless steel have higher OCP. The potential fluctuations of carbon steel with tidal changes involves two phases: (1) under the dynamics control, the OCP of carbon steel is more negative at high tide; (2) under the diffusion control, the OCP is more positive at high tide. The potential fluctuations of metallic materials reflect the effect of the corrosion product film on the change of ionization balance, and metals with less potential fluctuations have better inhibition on ion diffusion. In Sanya seawater, the carbon steel, which has more alloying content and less carbon content, has less potential fluctuations with the tidal changes and has good oxygen diffusion resistance. The potential fluctuations of austenitic stainless steel with tidal changes are less than that of ferritic stainless steel and martensitic stainless steel. After 2700 h immersion, austenitic stainless steel and martensitic stainless steel, which have a higher content of Mo, have more stable OCP. In other words, the corrosion film gets a better corrosion resistance. The OCP of aluminum anode in Sanya seawater environment increases when the oxygen content is brought up. The OCP of Zn-containing or Ga-containing aluminum anode remains relatively stable. Al bronze and T2 copper have less potential fluctuations with tidal changes, and perform good corrosion resistance in Sanya seawater.     

Corrosion Resistance Behavior of Cr–Cu Alloyed Thermo-Mechanically Treated Reinforced Bars in 3.5% NaCl Solution

Protection of Metals and Physical Chemistry of Surfaces - The corrosion resistance of reinforcing steels are of interest to the building and construction industry as it decides the durability of...     

Effect of Constituent Elements on the Corrosion Resistance of Single-Phase CoCrFeNi High-Entropy Alloys in NaCl SolutionEI北大核心CSCD

High entropy alloys (HEAs) origin from a new alloy design concept with multi-principal elements, which have attracted significant interests in the past decade. The high configurational entropy in HEAs results in simple solid solutions with fcc and bcc structures. Especially, the single solid solution CoCrFeNi alloy exhibits excellent properties in many aspects, such as mechanical properties, thermal stability, radiation resistance and corrosion resistance. The excellent corrosion resistance of CoCrFeNi alloy is ascribed to the single-phase structure and uniform element distribution coupled with much higher Cr content than stainless steel. The single-phase structure and uniform element distribution can prevent the occurrence of localized corrosion, and higher Cr content can protect the alloy surface better with the form of oxidation film. Moreover, the corrosion resistance of CoCrFeNi-based HEAs, such as CoCrFeNiAlx, CoCrFeNiCux, CoCrFeNiTix, have also been extensively investigated. In most CoCrFeNi-based HEAs, the elements of Co, Cr, Fe and Ni are with equal-atomic ratio. However, the equal-atomic ratio is not necessary to obtain satisfactory properties and to ensure the single fcc structure in Co-Cr-Fe-Ni system. Accordingly, it is essential to further consider the effect of alloying elements on the corrosion resistance in Co-Cr-Fe-Ni HEA. In this work, the effect of Co, Fe and Ni elements on the corrosion resistance of single fcc Co-Cr-Fe-Ni system with concentrated constitution but different atomic ratios in 3.5% NaCl solution are investigated by using LSCM and EIS. The potentiodynamic polarization results indicate that the increase of Fe and the decrease of Ni will decrease the passivation current density of the alloys when the Co and Cr contents are equal. With the increase of Co and the decrease of Ni, the alloys show smaller passivation current density and better corrosion resistance when the Fe and Cr contents are equal. With the decrease of Co and the increase of Fe and Ni, the alloys show higher corrosion potential and smaller corrosion tendency when the Cr content is constant. These results will be helpful for the design of corrosion resistant HEAs in NaCl aqueous solution.     

Modeling and Simulation of Hydrogen Behavior in TungstenEI北大核心CSCD

Based on national strategic needs for fusion energy, our group have investigated the behavior of H isotopes including dissolution, diffusion, accumulation and bubble formation in W using a first-principles method in combination with molecular dynamic method. It is found that the dissolution and nucleation of H in defects follow an "optimal charge density" rule, and a vacancy trapping mechanism for H bubble formation in W has been revealed. An anisotropic strain enhanced effect of H solubility due to H accumulation in W has been found, and a cascading effect of H bubble growth has been proposed. Noble gases/alloying elements doping in W has been proposed to suppress H bubble formation, because these dopants can change the distribution of charge density in defects and block the formation and nucleation of H-2 molecule. These works are reviewed in this paper. Our calculations will provide a good reference for the design, preparation and application of W-PFM under a fusion environment.     

Micro-Superplastic Behavior of Copper Oxide in AgCuO CompositesEI北大核心CSCD

In the investigation of AgCuO composites, we have found a type of copper oxide particles with a superplastic deformability behavior, which is similar to that of metals. To find the reason of the deformability of the copper oxide particles. SEM, STEM and TEM were used to analyze their crystal structures in AgCuO composites, The results show that the copper oxide particles with micro-superplasticity in the composites have cubic crystal structure, and their maximum elongation can be up to 300%, The copper oxide particles with no micro-superplasticity in the composites have monoclinic crystal structure. But the micro-superplastic behavior and mechanism of the copper oxides with the cubic crystal structure are not clear for the time being, the further investigation could be needed.     

Corrosion of titanium in phosphoric acid at 250 °C

Corrosion studies of a commercially pure titanium in phosphoric acid solutions at 250 °C were carried out by immersion test in an autoclave. At lower phosphoric acid concentration (0.1 mol/L), the corrosion was mild. At higher phosphoric concentration (1.0 mol/L) corrosion, a 25 μm-thick white corrosion products layer was formed on the samples after 24 h immersion. XRD analysis shows that the white layer consists mainly of titanium oxide phosphate hydrate (π-Ti₂O(PO₄)₂·2H₂O). The corrosion product shows the morphology of fiber bundles. A thermodynamic analysis of the formation of the corrosion product is presented.     

High-Temperature Corrosion Behaviour of Aluminized-Coated and Uncoated Alloy 718 Under Cyclic Oxidation and Corrosion in NaCl Vapour at 750 °C

To evaluate the suitability of HR3C and 22Cr–25Ni–2.5Al AFA steels as the heat-resistant alloys, the oxidation behavior of them was investigated in air at 700, 800, 900 and 1000 °C. The evolution of oxide layer on the surface and subsurface was investigated using a combination of compositional/elemental (SEM, EDS) and structural (XRD, GDOES) techniques. A dense and continuous Cr₂O₃ healing layer on the HR3C was formed at the temperature of 700 or 800 °C, but the Cr₂O₃ oxide film on HR3C was unstable and partly converted into a less protective MnCr₂O₄ with the increase in temperature to 900 or 1000 °C. The composition and structure of oxide film of 22Cr–25Ni–2.5Al AFA steels are significantly different to the HR3C alloys. The outer layer oxides transformed from Cr₂O₃ to Al-containing oxides, leading to a better oxidation resistance at 700 or 800 °C compared to HR3C. Further, the oxide films consist of internal Al₂O₃ and AlN underneath the outer loose layer after 22Cr–25Ni–2.5Al AFA oxidized at 900 or 1000 °C. It can be proved that the internal oxidation and nitrogen would make 22Cr–25Ni–2.5Al AFA steels have worse oxidation resistance than HR3C alloys at 900 or 1000 °C.     

In-Situ Electrochemical Corrosion Behavior of Nickel-Base 718 Alloy Under Various CO<Subscript>2</Subscript> Partial Pressures at 150 and 205 °C in NaCl Solution

The electrochemical corrosion behavior of nickel-base alloy 718 was investigated using electrochemical impedance spectroscopy and potentiodynamic polarization techniques at various partial pressures of CO₂ (\(P_{{{\text{CO}}_{2} }}\)s) in a 25 wt% NaCl solution at 150 and 205 °C. The passive films composed of FeCO₃ exhibit good corrosion resistance with a feature of Warburg impedance, Tafel plots show a complete passivation and the anodic reactions was dominated by a diffusion process at low \(P_{{{\text{CO}}_{2} }}\)s (1.8–9.8 MPa) at 150 °C. While numerous dented corrosion areas appeared on the sample surface for the \(P_{{{\text{CO}}_{2} }}\) of 11.6 MPa at 205 °C, the Tafel plot with three anodic peaks and the Nyquist diagram with an atrophied impedance arc were present. This dented corrosion attribute to the synergistic effects of stress, temperature, \(P_{{{\text{CO}}_{2} }}\) and Cl^?, the temperature and stress could play crucial roles on the corrosion of the alloy 718.     

Investigation of Corrosion Behavior of Welded Joint of X70 Pipeline Steel for Deep SeaEI北大核心CSCD

X70 pipeline steel with thick specifications (40.5 mm) for 3500 m deep sea reached the international advanced level in the wall thickness and service depth. Due to the high heat input during the welding process, the corrosion resistance of inside welding and outside welding would vary depending on the microstructure differences. The corrosion resistance of the welded joints of X70 pipeline for deep sea was studied by the immersion test, the weight loss test, the electrochemical test in this work. The components of the passive film were analyzed by XRD and the microstructure was observed by SEM. The results show that the corrosion resistance of the weld metal is the best. The corrosion resistance of the heat affected zone follows. The corrosion resistance of the base metal is the worst. And for the same area, the corrosion resistance of the inside welding is better than that of the outside welding. The formation of dense Fe3O4 passivation film can effectively slow down the progress of the reaction, and the corrosion products of Fe2O3, FeOOH and Fe(OH)(3) which are loose in the outer layer, have no protective effect on the matrix. The microstructure of the weld metal with the best corrosion resistance is mostly the intragranular nucleation ferrite and martensite-austenite (M-A) constituent is fine and uniform. The microstructure gradient of the heat affected zone is the largest, the M-A constituent is coarse and the corrosion resistance is inferior to the weld metal. The base metal consists of ferrite and bainite, the bainite is island-like distribution and the corrosion resistance is the worst. Microstructure of the inside welding is more refined, owing to the influence of outside welding thermal cycle, and the volume fraction of M-A constituent in inside welding is higher than that of the outside welding, so the corrosion resistance is better than that of the outside welding.