Results 1 - 10 of 2711
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[en] The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300–360 °C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N2 gas. Lastly, results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.
[en] Three steels were exposed in carburizing sodium at 600 and 650 °C. The kinetics and extent of carburization were characterized. Numerical simulations using the coupled thermodynamic-kinetic modeling software DICTRA were performed. It was introduced that the determined carbon diffusion profiles were induced by the combined diffusion of carbon in the grains and at grain boundaries coupled with the slow formation of carbides. The blocking effect of carbides on the carbon diffusion was observed to evolve as a function of time and microstructure. Acceptable agreement among experimental and simulated intragranular carbon profiles was achieved by optimizing the labyrinth factor and phases.
[en] The kinetic aspects of the competitive reaction of CO and H_2O in the formation of chromia layer on a nickel base alloy at high temperature were studied by thermogravimetry combined to gas phase chromatography. It was shown that competitive adsorption occurred between both molecules and that whatever P(CO)/P(H_2O) ratio, CO mainly reacted in the first instants of oxidation and H_2O became the main long-term oxidant species. After an interfacial and diffusion mixed kinetic regime, the long-term oxidation rate was parabolic and did not depend on the water vapor content in the gas phase. The oxidation kinetics was well described by considering that the rate limiting step was the outwards diffusion of interstitial chromium cations in the oxide layer. (authors)
[en] The high temperature corrosion behavior of two 9Cr and 12Cr ferritic-martensitic steel grades was studied under CO2 pressures varying from 1 to 250 bar for exposure times up to 8000 h. No 'breakaway' oxidation was observed. 9Cr steel grades suffered from fast parabolic uniform oxidation and fast carburization. Increasing CO2 pressure had very little effect on the oxidation rate but increased the carburization rate. The corrosion behavior of both 12Cr steel grades differed and might be influenced by gas composition, minor elements or surface finish. A corrosion mechanism coupling oxidation and carburization is proposed. (authors)
[en] Three titanium alloys were exposed to primary water at 300 degrees C. Oxides of the three alloys consisted of a dense layer and surface crystallites. The dense oxide layer of Ti CP was made of TiO2 rutile whereas it was made of TiO2 anatase for both Ti 64 and Ti10-2-3. Surface crystallites of the three alloys were composed of TiO2 anatase and FeTiO3 ilmenite. Oxide dissolution and precipitation phenomenon were found to play a key role in the corrosion mechanisms. Oxygen vacancies were identified as the main point defect responsible for the growth of the dense oxide layer. (authors)
[en] Under anoxic conditions, the presence of iron is expected to enhance the alteration rate of silicate glass. In order to understand the underlying mechanisms, experiments were performed on a synthetic glass simulating archaeological artifacts to study the effect of metallic iron and siderite in a clay-type groundwater. Characterization of the altered samples at different durations reveals different impacts of iron on glass alteration. In contact with siderite, the sorption of the released silicon maintains temporarily a high alteration rate which eventually drops. With metallic iron, glass is altered near the maximum dissolution rate throughout the experiment because of Fe-silicate precipitation. (authors)
[en] Iron-chromium-aluminium alloys are of interest to the nuclear materials community due to their resistance to high temperature steam oxidation and good mechanical properties under irradiation. The present work investigates oxide formation on Fe-12Cr-6Al-2Mo-0.2Si-0.03Y alloy at temperatures relevant to light water reactor cladding operation following extended aging to assess growth kinetics, chemical composition, and oxide microstructure. Oxide growth follows a logarithmic time dependence. Here, when the oxidization temperature is 400 °C or below, the oxide is amorphous. At 500 °C or above, crystalline α-Al2O3 oxide film develops and the correlated logarithmic rate constant decreases significantly, indicating enhanced oxidation resistance of the formed oxide film.
[en] Oxidation of UC was studied from 873 to 1173 K in air and in 10 Pa oxygen using a High Temperature Environmental SEM (HT-ESEM). Conversion to U3O8 improved when using 873 K as the oxide product was a fine powder. At higher temperatures (973 K to 1173 K) oxidation slowed due to a densification process with formation of coarse fragments. The oxide fragmentation at 973 K and 1073 K and oxide pulverisation at 873 K were observed in situ in a HT-ESEM. Cracking induced fragmentation and pulverisation was linked to stresses generated from the volumetric transformation from UC to U3O8. (authors)
[en] The role of alloying elements on the hydrogen embrittlement (HE) susceptibility of a Fe-18Mn-0.6C alloy was investigated by in situ tensile tests and characterized by the ductility loss associated with intergranular fracture. Under cathodic polarization an improvement of HE resistance is related to the SFE increase with Cu or Al additions reducing the stress-strain and H localization at grain boundaries, which prevents H-induced intergranular cracking. At rest potential, beneficial effects of Cu and Al are related to their influence on hydrogen absorption during the corrosion process. However, residual phosphorus strongly reduces the beneficial effect of aluminum. (authors)
[en] Oxidation of 304L stainless steel was studied in 4 mol/L nitric acid solution at 100 C over a wide potential domain. For different potentials, long-term chronoamperometry experiments coupled with mass loss measurements were performed until steady-state was reached to characterize the corrosion kinetics of the passive and trans-passive domains. With EIS and XPS measurements, the passive domain was characterized by the formation of a thin film, the thickness of which was potential dependent. (authors)