Corrosion Behavior of Ni–20Cr–18W–1Mo Superalloy in Supercritical Water

The corrosion behavior of Ni–20Cr–18 W–1Mo superalloy in supercritical water 500 °C/25 MPa for 200 h is investigated using gravimetry, SEM/EDS, XPS, and TEM. The oxide films show a layered structure with Ni rich in the outer layer, and Cr rich in the inner layer, consisting of an outer Ni(OH)2and NiO layer, including some Cr(OH)3, and an inner Cr2O3, Ni Cr2O4, and WO3 layer. Mo elements are not oxidized. The oxide films grow via a mixed mechanism,namely metal dissolution/oxide precipitation mechanism and solid-state growth mechanism. The effects of secondary and primary carbides on the weight-gain trend and oxide formation are discussed.     

Electrodeposition of Ni–Co alloy films onto titanium substrate

Binary bright Ni–Co alloy films were electrodeposited on titanium in the chloride–sulfate electrolytes.The influences of Co2?concentration, current density, and temperature on the Ni–Co alloy films electrodeposition were investigated. The films were analyzed by scanning electron microscope(SEM), energy dispersive spectroscopy(EDS), and X-ray diffraction(XRD). Cathodic polarization for Ni–Co codeposition was performed on Ti working electrodes. With the increase of Co2?concentration, the Ni content in the films decreases and the current efficiency increases slightly. The Ni content increases with the increase of temperature, while it decreases with the increase of current density to a minimum and then increases. The cathodic reduction peak potential is measured to be-1.34 V. Anomalous deposition is found to occur in the Ni–Co codeposition. The SEM of Ni–Co alloy films shows that hydroxide particles are not present on the surface and fine grain, compact, smooth, and bright Ni–Co alloy films are obtained. The XRD result indicates that the deposited Ni–Co alloy film is Ni-solid solution with a facecentered cubic in structure.     

Influence of Rust Layers on the Corrosion Behavior of Ultra-High Strength Steel 300M Subjected to Wet–Dry cyclic Environment with Chloride and Low Humidity

The influence of rust layers on the corrosion behavior of ultra-high strength steel 300 M subjected to a simulated coastal atmosphere was investigated by corrosion weight loss, surface analysis techniques, and electrochemical methods.The results exhibit the presence of a large proportion of c-Fe OOH and a-Fe OOH and a small amount of Fe3O4 in the outer rust layer. During the wet–dry cyclic process, the bonding performance and the density of outer rust layer deteriorate with the thickness of outer rust. The inner rust layer plays a main role on protectiveness, which can be attributed to the formation of an ultra-dense and adherent rust film with major constituent of a-Fe OOH and a-Fe2O3 on the steel.     

XPS Analysis of the Passive Film Formed on 825 Nickel Based Alloy Lined Pipe

The compositions and structures of the passive films formed on 825 nickel base alloy lined pipe serving for one year in an actual corrosion environment including 2.0 MPa H2S and 1.5 MPa CO2 at a temperature of 55℃were investigated by X-ray photoelectron spectroscopy(XPS).The results show that the passive films formed on 825 nickel base alloy is not destroyed even thicker than air-formed one and the films are composed of multilayer with different composition in each layer:an external part composed of a mixture of Cr and Ni oxide(more Ni included)and an inner part composed of a mixture of Cr and Ni oxide(Cr-rich layer).     

Studies of Composition and Structure of CO2 Corrosion Film of X56 Steel in the Medium of CO2 and Salt Water

The X56 steel samples was corroded in the medium of salt water solution at the conditions of CO2 partial pressure Pco2 0.5 to 2.0 MPa. temperature 80℃ and flow rate 1.4m/s. Corrosion weigh loss, composition and strutcture, morphology and phase of corrosion films of the samples were investigate by SEM, EDS, XRD and XPS. The results indicated that the corrosion degree was accelerated with increasing Pco2. The intense localised corrosion occurred on the surface of samples. The corrosion films mainly comprised of FeCO3 and complex phase products (Fe. Ca,...)CO3. There exists serious pitting on the metal substrates under the corrosion film. The theoretic and experimental analyses indicate this is caused by existed micropores or micro holes in films, which have the function of mass transportation.     

Corrosion resistance properties of AZ31 magnesium alloy after Ti ion implantation

Magnesium alloys have a wide range of applications in industry; however, their corrosion resistance, wear resistance, and hardness are rather poor, which limit their applications. Ti ion was implanted into the AZ31 magnesium alloy surface by metal vapor vacuum arc (MEVVA) implanter. This metal arc ion source has a broad beam and high current capabilities. The implantation energy was fixed at 45 keV and the dose was at 9 × 1017 cm?2. Through ion implantation, Ti ion implantation layer with approximately 900 nm in thickness was directly formed on the surface of AZ31 magnesium alloy, by which its surface property greatly improved. The chemical states of some typical elements of the ion implantation layer were analyzed by means of X-ray photoelectron spectroscopy (XPS), while the cross sectional morphology of the ion im-plantation layer and the phase structure were observed by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The property of corrosion resistance of the Ti ion implanted layer was studied by the CS300P electrochemistry corrosion workstation in 3.5% NaCl solution. The results showed that the property of corrosion resistance was enhanced remarkably, while the corrosion velocity was obviously slowed down.     

Influence of DC Current on Corrosion Behaviour of Copper–Aluminium Composite Plates

In this study, neutral salt spray accelerated corrosion test of copper–aluminium composite under 0–125 A DC current was carried out under 5% concentration. The effect of corrosion behaviour on copper–aluminium composite by DC current was carried out by a scanning electron microscope(SEM) with energy-dispersive spectroscopy(EDS), X-ray diffraction(XRD) patterns, X-ray photoelectron spectroscopy(XPS), weight-loss method and electrochemical analysis. The results show that the current can accelerate the corrosion rate. Meanwhile, the current temperature effect can reduce the corrosion rate. The current caused directional migration of ions resulting in different corrosion products on positive and negative poles of specimen, and the corrosion degree on the positive pole was more serious. The galvanic corrosion mechanism at the copper–aluminium interface is different from the pitting corrosion mechanism far away from the interface, and the latter is more affected by DC current.     

Dendritic Boundary Corrosion of AA2198 Weld Using Fiber Laser Welding with Al–Cu Filler Wire

The microstructures and corrosion behaviors of AA2198–T851 alloy and weld were analyzed under corrosive conditions.Weld was formed using an innovative fiber laser welding process with AA2319 Al–Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaCl solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical components and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al–Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heataffected zone with a compact protective film.     

Magnetic properties of sputtered anisotropic Pr–Fe–B thin films with different structures and antiferromagnetic materials

Anisotropic Pr–Fe–B films with soft-magnetic layer(Fe) and/or antiferromagnetic layer(Mn, Fe Mn or Mn O) were prepared by direct-current(DC) magnetron sputtering on Si(100) substrates heated at 650 °C. The influence of four types' different structures on the magnetic properties of Pr–Fe–B films was investigated.The phase and magnetic properties were characterized by means of X-ray diffraction(XRD) and superconducting quantum interference device(SQUID). Addition of antiferromagnetic layer enhances both the coercivity and the remanence ratios of Pr–Fe–B films with suitable structures. The interface number increases and the antiferromagnetic–ferromagnetic exchange interaction is likely to become stronger, which affect the improvement of magnetic properties. To further understand the influence of structures with soft-magnetic Fe layer and/or antiferromagnetic Fe Mn layer on the magnetic properties of Pr–Fe–B hard-magnetic films, the thickness of Pr–Fe–B layer was designed to decrease from 600 to 50 nm. The improvement of magnetic properties becomes obvious in Mo(50 nm)/Pr–Fe–B(25 nm)Mo(2 nm)Fe Mn(20 nm)Mo(2 nm)Pr–Fe–B(25 nm)/Mo(50 nm) film.     

Corrosion Behavior of the Ni-Cr-Fe Base Superalloy GH984G in a Synthetic Coal Ash and Flue Gas Environment

The corrosion behavior of the new Ni–Cr–Fe base superalloy GH984 G in a synthetic coal ash and flue gas environments was studied at 700℃. The results showed that the corrosion rate was slow during the initial corrosion stage,then followed by a stage of faster mass loss. During the corrosion test, the scale trended to spall slightly, resulting in the formation of corrosion pits on the sample surfaces. The main corrosion products were identified as Ni Fe CrO_4 and a small amount of Cr_2O_3. The scale microstructure involved the presence of three corrosion layers. The outer layer contained Cr,Ni, Fe, O and a small amount of S. Many micro-cracks were detected in the Cr-rich intermediate oxide layer. The inner corrosion layer was thin and rich in S. Internal sulfidation and internal oxidation occurred in the substrate. Because of its relatively high Cr content, the GH984 G superalloy exhibited a good corrosion resistance under the test conditions.     

70Cu—30Ni合金海水腐蚀产物膜形成过程

本文研究了７０Ｃｕ－３０Ｎｉ合金海水暴露不同时间腐蚀产物膜特征和成分变化。研究表明，该合金腐蚀产物膜内存在的一个富Ｎｉ区随着暴露时间延长而变宽且Ｎｉ的富集程度增加，富Ｎｉ腐蚀产物膜充当阳极，从而保护基体，长期暴露所形成的腐蚀产物膜出现裂纹或沟，这是由于膜下基体在这些位置存在结构或成分的变化使膜的生长速度减慢或者内应力导致膜的破裂，随着外层膜的溶角与脱落，原裂纹或沟成为凸出条纹，凸出条纹中Ｎｉ与Ｃｕ     

Seawater corrosion of 70Cu‐30Ni alloy of incomplete recrystallization of intermittent and full immersion

The corrosion of 70Cu‐30Ni alloy of incomplete recrystallization was investigated by electrochemical technique, intermittent and full immersion in natural seawater, SEM and AES. Exposed to seawater for a short time, 70Cu‐30Ni alloy formed uniform and compact corrosion product films, which were rich in nickel, oxygen and seawater species for intermittent immersion; while the alloy fully immersed displayed loose and thick films, which were of denickelification and intergranular corrosion occurred to the underlying substrate. It was found that some regular crystals situated at the intersection of boundaries or the outer layer of the film and the crystals are ascribed to the reduction of cuprous ions to compensate the deficiency of oxygen for the cathodic process. Intergranular corrosion was observed in the underlying substrate for intermittent immersion after a long‐term exposure. Intermittent immersion can, to some degree, slow down the corrosion but not prevent the alloy of incomplete recrystallization from intergranular corrosion. Consequently, the corrosion mechanism of 70Cu‐30Ni alloy is proposed to be determined by its microstructure, independent of exposure conditions.     

Characteristics and formation of corrosion product films of 70Cu-30Ni alloy in seawater

The corrosion product films of 70Cu-30Ni alloy, composed of recrystallized grains or deformed and recrystallized grains, were investigated in 3.5% NaCl and natural seawater by electrochemical techniques, SEM, EDX and AES. The recrystallized alloy displayed a steady increase in the polarization resistance while the alloy of incomplete recrystallization kept its polarization resistance at a low level as increasing the immersion time in 3.5% NaCl. The films formed on the recrystallized alloy in seawater were thin, uniform and rich in nickel. After long-term immersion, the films, still thin and protective, consisted of convex lines and smooth zones between the lines. The convex lines were richer in nickel and contained more seawater species than the zones, so this led the lines to preferentially dissolve and new lines to appear where the film grew slower. Immersed in seawater, the alloy of incomplete recrystallization showed thick, loose and porous films, of which the inner layer was denickelified and the outer layer contained a great amount of seawater species, and of which the underlying substrate was found with severe intergranular corrosion. The tube specimens of incomplete recrystallization for four-year immersion were perforated by intergranular corrosion.     

Relationship of corrosion product films and recrystallization of 70Cu‐30Ni alloy

The corrosion and microstructure of 70Cu‐30Ni alloy plates and commercial tubes were investigated by processing, electrochemical technique and seawater exposure as well as optical microscopy, SEM, EDX and AES. The alloy plate with incomplete recrystallization, consisting of deformed and recrystallized grains, demonstrates loose and porous outer layers and denickelification in the inner layers for its corrosion product films, whereas the recrystallized alloy plate forms smooth and compact corrosion product films rich in nickel after immersion in seawater for 3 and 6 months. The incompletely recrystallized alloy tube keeps an active state and the recrystallized tube has a passive zone in the anodic polarization curve in 3.5% sodium chloride. Furthermore, the former shows loose and thick corrosion product films, which are of denickelification in the inner layer and contain a significant amount of seawater species in the outer layer, and on the surface of the latter are thin uniform and compact corrosion product films containing a Ni enrichment zone which becomes richer in Ni and wider with increasing immersion time. It is found that intergranular corrosion proceeds along the boundaries of deformed and recrystallized grains, and it is ascribed to electrochemical cells built for the reason of potential difference between the two kinds of grains.     

Surface characterization and immersion tests of TiNi alloy coated with Ta

The surface chemical composition and chemical state of Ti–50.6 at.% Ni alloy samples coated with tantalum by an arc ion plating method were investigated by X-ray photoelectron spectroscopy (XPS). The results of XPS survey and high resolution spectra show that a thin oxide film with Ta₂O₅ in the outmost layer and tantalum suboxides in the inner layer are formed on the tantalum coating as a result of natural passivation of Ta in the atmosphere. The Ni ion release with time from uncoated and coated samples immersed in 0.9%NaCl solution was also investigated by atomic absorption spectrometry (AAS). Compared to the coated samples, the uncoated samples show a higher release rate that decreases slightly with time. The degree of dissolution for the coated sample is reduced from 0.28 to 0.74 μg/cm² after 49 days, implying the coating has a beneficial effect on the inhabitation of Ni ion release from the TiNi substrate. The atomic force microscope (AFM) images and section analysis show that the root mean square (RMS) roughness increases from 10.349 to 65.587 nm, and the maximum roughness (R_max) increases from 36.027 to 278.22 nm, confirming that immersion in the NaCl solution results in roughening of the coating surface.     

形变对70Cu—30Ni合金腐蚀行为的影响

研究了７０Ｃｕ－３０Ｎｉ合金固溶处理后不同程度形变及其在ＮａＣｌ溶液浸泡和海水暴露中的腐蚀行为。结果表明，随着形变量增加，７０Ｃｕ－３０Ｎｉ合金腐蚀电位和极化电阻随时间下降速度增加，其腐蚀产物膜中镍含量增加，氯离子浓度减小，所形成的海水腐蚀产物薄膜。     

退火工艺对Cu-30Ni合金管耐海水腐蚀性能的影响

    通过电化学测试方法研究了不同参数退火后Cu-30Ni合金管在静止人工海水中的腐蚀行为.结果表明,海水腐蚀初期,富Ni表面膜对Cu3-0Ni合金管耐海水腐蚀性能的影响起主要作用,其相对于基体成为阳极性保护,且随着退火温度升高,保温时间延长,Cu3-0Ni合金管抗蚀能力越好;随着海水浸泡时间的延长,退火后Cu-30Ni合金管的显微组织结构对海水腐蚀性能影响占优,细小的富Ni颗粒成为微电池的阳极,优先被腐蚀;720℃×30 min热处理后试样抗腐蚀性能较好,腐蚀40天后,没有发现点蚀坑.     

The oxidation behaviour of 304 stainless steel in oxygenated high temperature water

Characteristics of the oxide films formed on 304 stainless steel immersed in 290 °C oxygenated water for different duration time were examined. The results show that the oxide film is mainly composed of outer irregularly shaped α-(Fe, Cr)₂O₃ and minor spinel in the inner layer. The morphology and chemical composition of the oxide film evolve with increasing immersion time. The surface layer is first enriched in Cr and then enriched in Fe. It is proposed that the oxide nucleated by solid-state reactions with the selective dissolution of Fe and Ni, and grew up through precipitation of extraneous metallic ions from solution.     

A method for calculating the extent of galvanic corrosion and cathodic protection in metal tubes assuming unidirectional current flow

A simple procedure for calculating how galvanic corrosion and cathodic protection effects are distributed within metallic tubular systems carrying electrolytes is described. The procedure involves the use of equations which are analytical solutions and, in some instances, equations which require numerical solutions which can easily be effected using microcomputers. The equations arc based on an assumption of unidirectional flow of electric current which is shown to be valid for appreciably conducting electrolytes, such as seawater. Various combinations of linear polarisation kinetics, Tafel law polarisation kinetics and totally diffusion-controlled kinetics can be used. Experimental verification of the procedure has been obtained using synthetic seawater for titanium and Cu-30Ni tubes in galvanic contact and for cathodically protected Cu-30Ni tube. It is proposed that the procedure could find useful application at the design stage of plant involving two or three different metals, or of cathodically protected pipework, when any necessary preventative measures indicated by an analysis could be adopted. Plant containing two or three metals can be, for example, in the form of heat-exchangers, pipe to plate combinations or pipework systems connected by plastic sections. Useful design data relating to cathodically-protected pipework can be obtained for systems based on either sacrificial protection or impressed current.     

低碳钢在海水中的阴极电化学行为

采用电化学技术结合XRD分析, 研究了A3碳钢在海水中的阴极电化学行为, 探讨了锈层在阴极过程中的作用. 碳钢表面生成的锈层由内锈层和外锈层组成, 内锈层主要组成相为γ-FeOOH, α-FeOOH, β-FeOOH以及Fe₃O₄与γ-Fe₂O₃的混合物. 浸泡126 d时, 外锈层主要由γ-FeOOH组成; 浸泡364 d由γ-FeOOH, α-FeOOH, Fe₃O₄和 γ-Fe₂O₃组成. 不同锈层在阴极过程中所起的作用不同. 外锈层主要作用是阻碍溶解氧到达金属表面, 内锈层除此之外还可以参与还原反应, 加速阴极反应. 提出了一个评价锈层参与还原反应程度的参数α, 在浸泡不同时期锈层参与还原反应的比例不同, 浸泡前7 d, α值上升比较明显, 随后增加比较缓慢, 浸泡168 d后基本稳定. 探讨了内、外锈层组分的变化以及锈层各组分间的相互作用.