Initiation of Metal-Dusting Pits and a Method to Mitigate Metal-Dusting Corrosion

Initiation of metal dusting was studied by scanning-electron microscopy and Raman spectroscopy. A copper-indicator method was developed to identify locations that are easily attacked by metal dusting. The effect of surface scratches on metal dusting was investigated. Alloy 800 specimens from a hydrogen-reformer plant were analyzed. The alloy developed a nonprotective oxide scale in which the major phase was spinel with a high Fe content. The initiation of metal-dusting pits occurs when channels form through the oxide scale for the transfer of carbon. The channels can be blocked by short exposure of the metal-dusted alloy surface to an oxidizing environment. Metal-dusting corrosion could be mitigated by selection of alloys with long incubation time and by minimizing and/or slowing the pit-growth rate using an intermediate oxidation treatment at an appropriate temperature and in an appropriate environment for a relatively short time.     

Effects of change in growth mechanism due to Yttrium-addition in adhesion of alumina scale formed on Fe3Al alloy: Countercurrent diffusion modification model

The effects of Y-addition on the high-temperature oxidation of Fe₃Al alloy were investigated in air at a temperature range of 800–1100°C. The reactive element enhanced the initial nucleation of the oxide scale and thus formed a fine-grained oxide. The grain refinement of the alumina scale due to the addition of yttrium changed the growth mechanism of the oxide from a countercurrent diffusion of Al and O to a predominantly inward oxygen diffusion, which led to the formation of pegs on the scale/alloy interface, the prevention of the formation of voids in the substrate, and a decrease in growth stress. The beneficial effects of the reactive element on oxide adhesion are explained by “countercurrent diffusion modification model” suggested in this study.     

Deep drawing textures in low carbon steels

Some recent papers published on orientation selection during the static recrystallization of ferritic low carbon steels are reviewed. Both the oriented nucleation and selective growth theories are analyzed critically and classified according to the physical mechanisms underlying these theories. The review concentrates on the progress made by employing techniques of local orientation measurement such aselectron backscattering diffraction (EBSD) andorientation imaging microscopy (OIM). Using the latter technique, the present authors obtained strong evidence for the operation of a selective growth mechanism during the late stages of recrystallization of an ultra low carbon steel that was cold rolled to a reduction of 95%. This article is based on a presentation made in the symposium “ ’99 International Symposium on Textures of Materials”, held at Sunchun National University, Sunchun, April 21–22, 1999 under the auspices of The Korean Institute of Metals and Materials and The Research and Development Center for Automobile’s Parts and Materials.     

Corrosion resistance of Zambian silver coin from the “African Wildlife” series

The surface of Zambian silver coin from the “African Wildlife” series is studied by local X-ray fluorescent analysis, mass-spectrometry, and electrode potential measurements. High purity of the coin metal is pointed out. Faint yellow tarnish at some spots on the surface is caused by local contamination during the coin production or storage. Original Russian Text ? I.G. Erusalimchik, M.N. Filippov, I.V. Murav’eva, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 324–325.     

Surface free energy and surface stress as elastic components of the surface tension of condensed matter

The “surface free energy” and “surface stress” are basic notions in the current theory of the surface tension of solids; they were used online together or separately thousands times, but never “as elastic components of surface tension”. Most of experts highlight that these different notions cannot be mixed or confused since the first one is of the “plastic” and second is of “elastic” nature. Below these opinions are shown to be incorrect. Sufficient evidences, both theoretical and experimental, demonstrate the elastic nature of both the “surface energy” and “surface stress”. In this way, we considered the most convincible models of the metal surface based on the Coulomb interaction and purely elastic surface deformation. The reminiscent of the cantilever-beam-technique data and electrocapillary curves of mercury in combination with the specific adsorption data has logically led to the formulation of the “optimum surface electron density” notion (for the first time in the field of surface tension).     

Effect of high temperature oxide scale on steel surface for electroless nickel plating process and characterization of coatings

An attempt has been made for an electroless nickel plating process on two steel substrates (with and without a high temperature oxide scale at the top surface) to identify the role of a high temperature iron oxide scale on coating kinetics. This study investigated if an iron oxide scale on the steel surface acts as a catalyst and promotes faster metal deposition. Coatings were characterized by scanning electron microscopy (SEM), glow discharge oxy emission spectroscopy (GDOES), and X-ray diffraction (XRD) and an iron oxide scale was characterized by Raman spectroscopy. Chemical composition and structure of both the coatings are the same but the coating obtained on a steel substrate having a high temperature oxide scale at the top is two times thicker. The electrochemical performances of both the coated steel substrates were evaluated by Tafel and electrochemical impedance (EIS) tests in an aggressive chloride environment. The coating obtained on a steel substrate containing a high temperature oxide scale at the top exhibits better resistance against chloride attack and charge transfer than the coating obtained on the steel substrate without a high temperature oxide scale at the top. This can be attributed to the highest thickness of this coating, which has the same chemical composition of the other coating, expected to give better resistance against chloride attack and charge transfer.     

Simulation and optimization of complete mechanical behaviour of machine tools

Up to now the consideration of forces between flexible, moved structures, e.g., linear guides on base frame components, depending on different workspace positions wasn’t possible in multi-body simulation. Thereby neither the representation of the complete mechanical behavior nor the optimization of the frame structure depending on different workspace positions is possible. In the context of the Priority Program 1099 of the German Research Foundation “Production Machines with Parallel Kinematics”, methods have been developed, which enable the transmission of forces between flexible bodies multi-body simulation. The existing, flexible MBS-model of the coupler kinematics “Genius 500” is extended by a flexible frame structure and the total deformation is analyzed. Furthermore the present frame structure is replaced by a design space for topology optimization in different workspace positions.     

Structure and crystallographic orientation of aluminum films on n-and p-silicon in the Al-Ti-Si and Al-Ti-SiOx-Si systems

The structure and crystallographic orientation of aluminum films in the Al-Ti-Si and Al-Ti-SiO_x-Si systems is studied with the use of electron microscopic, electron diffraction, and x-ray methods and thermodynamic analysis. The role of barrier layers formed by Ti and by the “Ti-SiO_x low-temperature oxide” composition in the formation and orientation of aluminum grains is determined. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 44–48, July, 2007.     

High-temperature low-cycle fatigue behavior of superalloy MA 760

The high-temperature cyclic behavior of oxide dispersion-strengthened superalloy MA 760 was studied at different temperatures and specimen orientations. The cyclic hardening curves at different strain am-plitudes were determined at 650, 900, and 950 °C, and the stress-strain response of the material was sub-stantiated by detailed fractographical scanning electron microscopy (SEM) and microstructuralJoptical microscopy, STEM) observations. During cycling, MA 760 did not exhibit marked hardening or soften-ing, and also the final fracture occurred very rapidly without a significant decrease in the cyclic strength of the material. The “brittle” nature of deformation behavior of MA 760, especially at lower test tempera-tures, as well as oxidation-induced secondary cracking along grain boundaries, was clearly revealed by microscopical studies of the fracture surfaces. At 650 °C, evidence of dislocation cutting of γ was ob-served in transmission micrographs, but at higher temperatures, dislocation climb and by-passing of γ particles were found to become more prominent features. At all test temperatures, dislocation climb over yttria particles, as well as the departure side pinning effect of dislocations at nonshearable particles, was frequently observed.     

Nickel and chromium cycles: Stocks and flows project part IV

Nickel and chromium are essential ingredients in alloys increasingly important for energy-efficient, environmentally friendly modern technology. Quantitative assessment of the flows of these metals through the world economy from resource extraction to final disposal informs resource policy, energy planning, environmental science, and waste management. This article summarizes the worldwide technological cycles of nickel and chromium in 2000. Stainless steel is the major use of these metals, but they serve numerous other special needs, as in superalloys for high-temperature service, as plating materials, and in coinage. Because they are used primarily in alloys, novel recycling issues arise as their use becomes more widespread. “... the great New York and St. Louis double track, nickel plated railroad...” — Norwalk, Ohio, Chronicle 10 March 1881 announces arrival of surveyors for the future Nickel Plate Railway “Later [1911] I formed an alloy of Iron and Chromium, which showed remarkable resistance to rust and tarnish ... [It was] rediscovered by an Englishman named Brearley, in 1914.” —Elwood Haynes to Stephen F. Roberts, 17 January 1925     

Carbon Transfer in Sodium System Under Thermal Cycling-Possibility of “Metal Dusting”

High temperature sodium systems encounter thermal cycling during operation. Under this condition, the behavior of carbon dissolved in sodium needs special attention. Carbon chemistry of sodium is very complex because of the existence of multiple carbon-bearing species. In addition, carbon exists both in the dissolved (“active”) and undissolved (“inactive”) forms. Under thermal cycling conditions, as the temperature is lowered, carbon may precipitate as sodium acetylide. The equilibrium carbon activity imparted by this species is high enough to cause the precipitation of iron carbide (Fe₃C) in ferrous alloys. The Fe₃C may be destabilized at lower activities of carbon in the environment (when the temperature is increased) and may decompose to a fine dispersion of metal and graphite. This phenomenon of “metal dusting” is extremely detrimental to the components of sodium systems. The article analyses the possibility of “metal dusting” in an operating sodium system.     

The growth of oxide platelets on nickel in pure oxygen. II. Surface analyses and growth mechanism

The structural properties of NiO platelets emerging from a primary oxide layer by oxidation of pretreated nickels in pure oxygen between 650 and 800° C have been investigated in relation with the initial metallic layers and the primary oxide. Surface composition and segregation of impurities were also studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy. Textural properties and structural orientation of both the primary oxide layer and the platelets were analyzed by X-ray diffraction and transmission electron microscopy. Platelets grew along {111} planes, leading to elliptical or semicircular bicrystals. The driving force for the present type of growth originates from the stresses accumulated in the thin, primary oxide layer. Impurities do not directly interact with this growth, but enable a specific grain structure to be developed thereby favoring platelet growth.     

Corrosion behavior of Hastelloy C-276 in supercritical water

The corrosion behavior of a nickel-based alloy Hastelloy C-276 exposed in supercritical water at 500–600 °C/25 MPa was investigated by means of gravimetry, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. An oxide scale with dual-layer structure, mainly consisting of an outer NiO layer and an inner Cr₂O₃/NiCr₂O₄-mixed layer, developed on C-276 after 1000 h exposure. Higher temperature promoted oxidation, resulting in thicker oxide scale, larger weight gain and stronger tendency of oxide spallation. The oxide growth mechanism in SCW seems to be similar to that in high temperature water vapor, namely solid-state growth mechanism.     

Cyclic Oxidation of P91 by Thermogravimetry and Investigation of Integrity of Scale by “Transient-Mass-Gain” Method

The growth and degradation of the oxide scale on modified 9Cr–1Mo ferritic steel was studied at 1123 K using a thermogravimetric balance by employing the “transient-mass-gain method” in conjunction with the adaptation of a cyclic-oxidation procedure. The total duration of the oxidation was 1000 h. The experiment revealed that the cracking of the scale was initiated when the average thickness was 72 μm. Spallation occurred when the average thickness was 75 μm. The rate of spallation was found to be enhanced as the scale thickens and attained a higher rate after 90 μm. The rate constants for the different stages of oxidation were found to be different. The specimen was examined by SEM, EDS and XRD. The scale morphology revealed outwardly protruded growth, a uniform adherent oxide layer and a spalled region. Four oxide phases were identified; Cr₂O₃, Fe₂O₃, (FeCr)₂O₃ and FeCr₂O₄. The spall contained more (FeCr)₂O₃ whereas the adherent scale was more FeCr₂O₄.     

Mechanisms of plastic deformation in microcrystalline and nanocrystalline TiNi-based alloys

Mechanisms of plastic deformation of a high-temperature B2 phase that act upon tension, compression, and high-pressure torsion in TiNi-based single crystals have been studied depending on the crystal orientation. For the crystals with orientations located near the [$ \bar 1 $ \bar 1 11] and [$ \bar 1 $ \bar 1 12] poles in the standard stereographic triangle, multiple dislocation slip prevails upon both compression and tension. In “hard” crystals with the deformation axis close to the [001] direction, in which the Schmid factors for dislocation slip are close to zero, the main deformation mechanisms are the mechanical twinning in the B2 phase and the stress-assisted B2 → B19′ martensitic transformation. All the above listed mechanisms take part in the formation of the {111}〈hkl〉 texture. The mechanism of the change in the orientation of “hard” polycrystalline grains upon the formation of a nanocrystalline and amorphous-crystalline state has been demonstrated on the example of the evolution of the structure of [001] crystals upon severe plastic deformation in a Bridgman cell.     

pH值对碳钢在高含硫油田水中腐蚀行为的影响

采用电化学测试方法和动态腐蚀失重实验并结合扫描电镜和能谱分析, 研究不同pH值下J55钢在高含硫油田水中的腐蚀行为。结果表明, 随着溶液pH值升高, J55钢阴极去极化作用减弱, 腐蚀速率下降。当pH值在5.6~7.2时, 腐蚀产物主要是疏松且易脱落的粗晶粒四方硫铁矿FeS_1-x, 无法在碳钢表面形成保护膜, 形成大量腐蚀坑, 使碳钢表面腐蚀较严重;当pH值在8.7~11.0时, 腐蚀产物主要是氧化铁, 在碳钢表面形成了致密的保护膜, 阳极有明显的钝化现象, 碳钢表面腐蚀轻微。     

On the formation of magnetite coatings on low-carbon steel in ammonium nitrate solution

Initial stages of the formation of magnetite coating (MC) on low-carbon steel in ammonium nitrate solution at a temperature of 98°C is studied by atomic force microscopy. Analyzing the results obtained by flicker-noise spectroscopy allows the degree of continuity and structuring of MC to be estimated. It is shown that the formation of magnetite nuclei in the course of direct electrochemical reaction may take place in the first minutes of oxidation; continuous coating is formed in 10–15 min. Original Russian Text ? D.B. Vershok, P.I. Misurkin, V.A. Timofeeva, A.B. Solov’eva, Yu.I. Kuznetsov, S.F. Timashev, 2008, published in Korroziya: Materialy, Zashchita, 2007, No. 10, pp. 28–35. This work was supported in part by the program “New Approaches to Corrosion and Radiation Resistance of Materials, Radioecological Safety” of the Department of Chemistry and Materials Science, Russian Academy of Sciences, and by the subprogram “Creating New Constructional and Functional Materials based on Nanotechnologies” of the Presidium of the Russian Academy of Sciences program “Developing Methods for Obtaining Chemical Substances and Creating of New Materials”.     

Achieving Carbon Neutrality in the Global Aluminum Industry

In the 21st century, sustainability is widely regarded as the new corporate culture, and leading manufacturing companies (Toyota, GE, and Alcoa) and service companies (Google and Federal Express) are striving towards carbon neutrality. The current carbon footprint of the global aluminum industry is estimated at 500 million metric tonnes carbon dioxide equivalent (CO_2eq), representing about 1.7% of global emissions from all sources. For the global aluminum industry, carbon neutrality is defined as a state where the total “in-use” CO_2eq saved from all products in current use, including incremental process efficiency improvements, recycling, and urban mining activities, equals the CO_2eq expended to produce the global output of aluminum. This paper outlines an integrated and quantifiable plan for achieving “carbon neutrality” in the global aluminum industry by advocating five actionable steps: (1) increase use of “green” electrical energy grid by 8%, (2) reduce process energy needs by 16%, (3) deploy 35% of products in “in-use” energy saving applications, (4) divert 6.1 million metric tonnes/year from landfills, and (5) mine 4.5 million metric tonnes/year from aluminum-rich “urban mines.” Since it takes 20 times more energy to make aluminum from bauxite ore than to recycle it from scrap, the global aluminum industry could set a reasonable, self-imposed energy/carbon neutrality goal to incrementally increase the supply of recycled aluminum by at least 1.05 metric tonnes for every tonne of incremental production via primary aluminum smelter capacity. Furthermore, the aluminum industry can and should take a global leadership position by actively developing internationally accepted and approved carbon footprint credit protocols.     

Role of promoting oxide morphology dictating the activity of Au/SiO2 catalyst in CO oxidation

The interfacial interaction of gold nanoparticles deposited on either model SiO₂/Si(100) or high surface area amorphous or mesoporous silica with minute amounts of promoter oxide like “active” FeO_x, TiO₂ and CeO₂ has been discussed. The role of the active oxide, its contribution to the perimeter along the gold nanoparticles has been interpreted. The oxide may invoke electronic interaction and simultaneously the defect structure of oxides likely has a key issue in the formation and stabilization of very small Au particles. The activity of the Au/oxide perimeter depends not only on the size of the Au particles, but also on the size and morphology of the oxide component (likely amorphous structure) regardless of whether it is supporting Au nanoparticles or decorating them. The activity in CO oxidation over Au catalysts is strongly affected by the length of the Au/“active” oxide perimeter which is regarded as the “active interface”. The longer length of the perimeter is evidenced by the enhanced CO oxidation activity.