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1.
The composition and structure of passive films formed on a series of iron—chromium alloys in de-aerated 1M H2SO4 were quantitatively studied by XPS. The chromium content of passive film increased drastically at ca. 13 %Cr of the bulk alloy composition, whereas no composition change was found in the surface of the substrate alloy immediately under the passive film. The high corrosion resistance of iron—chromium alloys with high chromium content is attributed to the protective nature of hydrated chromium oxy-hydroxide, which is the main constituent of passive films on the alloys containing chromium of 12.5 at. % or more. 相似文献
2.
The increase in molybdenum content in amorphous FeMoPC alloys facilitates the passivation in 1 N HCl in contrast to crystalline iron base alloys without chromium. An attempt was made to clarify the effect of molybdenum through the composition of surface film analyzed by XPS. The passive film consists mainly of ferric oxy-hydroxide, while a large amount of hexavalent molybdenum species is found in the surface film formed in the active region. The effect of molybdenum is interpreted as follows: the active dissolution necessary for proceeding the passive film formation leads to the precipitation of hexavalent molybdenum species on the alloy surface and as a result, the active dissolution is stifled. This fact leads to the passivation with the aid of iron ions which are already accumulated in the alloy/solution interface during the active dissolution. 相似文献
3.
The effect of ion implantation on the corrosion behaviour of pure iron—II. Chromium ion implantation
As part of a programme to investigate the effect of ion implantation on the corrosion behaviour of iron, pure iron specimens have been implanted with doses of 5 × 1014 and 2 × 1015 chromium ions/mm2. Using a three-sweep potentiokinetic polarization technique the corrosion behaviour of these surface alloy layers has been compared with that of conventional binary FeCr alloys containing from 0.8 to 12.5 wt%Cr. It was found that apart from a slight thickening of the air-formed oxide film induced by the ion implantation process, the polarization behaviour of conventional alloys and of alloys produced by ion implantation was qualitatively very similar. Quantitatively the low dose chromium implanted specimens corresponded to a conventional Fe-4.9%Cr alloy while the high dose chromium implanted specimens resembled conventional alloys containing x12.5%Cr. These data provide a sound basis for the interpretation of the potentiokinetic polarization and corrosion behaviour of the novel surface alloy layers which can be produced by ion implantation. 相似文献
4.
《Corrosion Science》1986,26(7):547-559
AES depth profiling and XPS have been used for the characterization of thin oxide layers thermally grown in situ in the UHV-analysis chamber on pure iron, chromium and the alloys Fe24Cr and Fe24Cr11Mo at a temperature of 384°C. The apparent oxide film thickness and the film composition were monitored as a function of oxygen exposure. The oxidation rate of the Fe24Cr alloy was found to lie in between that of pure iron and chromium. The films formed have a duplex structure, the outer part being iron oxide, the inner part mostly chromium oxide. Alloying with molybdenum decreases the rate of oxidation by a mechanism involving the formation of a barrier layer rich in molybdenum at the oxide-metal interface. No molybdenum is found in the outer part of the oxide film. 相似文献
5.
The amorphous FeCrPC alloy was compared with the crystallized alloy having the same composition in potentiodynamic polarization curves and with an 18Cr8Ni stainless steel in current decay after abrading the specimens under anodic polarization. Through these results along with the previous ESCA study, the extremely high corrosion-rseistance of the amorphous iron alloys containing 8 at.% or more chromium has been interpreted in terms of the rapid formation of thick, uniform, highly corrosion-resistant passive film due to the characteristics of the amorphous alloys. 相似文献
6.
《Corrosion Science》1999,41(2):213-227
The anodic oxidation of dilute Al–Cr alloys, containing 0.8 and 1.7 at% Cr, has been investigated in order to understand the oxidation behaviour of the alloying element and its influences on the film composition and morphology. The alloys reveal two stages of oxidation: an initial stage, in which only aluminium atoms are oxidized to form a chromium-free anodic alumina film, and a subsequent stage, in which both aluminium and chromium are oxidized, in their approximate alloy proportions, with generation of a chromium-contaminated anodic alumina film. In the first stage, chromium is enriched in a thin layer of alloy, immediately beneath the anodic film, to an amount corresponding to a layer of average thickness 1.5 nm and of average composition, Al–20 at% Cr. Following the oxidation of chromium, oxygen is produced electrochemically within the film at or near the alloy/film interface, probably associated with the development of chromium-rich clusters in the enriched alloy layer and, subsequently, formation of semiconducting chromium-rich oxide. Thus, the film material formed at the alloy/film interface by inward migration of O2- ions contains many oxygen-filled bubbles with associated high pressures. The chromium species present in the film migrate outward more slowly than Al3+ ions. Hence, a layer of chromium-free anodic alumina, which thickens as the film grows, is maintained adjacent to the film/electrolyte interface. 相似文献
7.
A study of the localized pitting attack of 20% Cr/25%Ni stainless steel and a similar alloy containing a dispersion of titanium nitride particles has been made over the temperature range 1023 to 1173 K. Pitting is initiated when localized spoiling of the protective chromic oxide film occurs. Rapid oxidation of the chromium-depleted substrate then proceeds with the formation of an iron-rich oxide mound on the alloy surface and spinels containing nickel, chromium, and iron within the pit itself. A silica layer which, in general, remains on the alloy surface acts as a diffusion barrier during this stage of the reaction. With increasing depth of attack the local chromium concentration in the alloy at the base of the pit attains a critical value (16%) for a protective chromium oxide film to reform; the pitting attack then effectively ceases, although a a subsequent slow rate of growth continues through the protective film at the base. The observed maximum depth of pitting as a function of time is consistent with the parabolic variation predicted by the proposed mechanism. There is no significant difference in the kinetics of attack between the alloys examined. 相似文献
8.
X-ray photo-electron spectroscopy has been used to investigate the correlation between the compositions of a surface film and the underlying alloy and the beneficial effects of alloying elements. The addition of alloying elements less noble than iron increases the corrosion resistance in the active region by improving the protective quality of the corrosion product film in which the cations of alloying elements are significantly concentrated. Even if the passivity of alloying elements is not stable in the passive region of alloys, the alloying asists the formation of passive hydrated iron oxy-hydroxide film by decreasing the dissolution rate of alloys prior to the passive film formation. The improvement of corrosion resistance by alloying with the elements more noble than iron has been interpreted in terms of the decrease in the anodic activity of alloys. 相似文献
9.
X-ray photo-electron spectroscopy has been used to investigate the correlation between the compositions of a surface film and the underlying alloy and the beneficial effects of alloying elements. The addition of alloying elements less noble than iron increases the corrosion resistance in the active region by improving the protective quality of the corrosion product film in which the cations of alloying elements are significantly concentrated. Even if the passivity of alloying elements is not stable in the passive region of alloys, the alloying asists the formation of passive hydrated iron oxy-hydroxide film by decreasing the dissolution rate of alloys prior to the passive film formation. The improvement of corrosion resistance by alloying with the elements more noble than iron has been interpreted in terms of the decrease in the anodic activity of alloys. 相似文献
10.
11.
Using an XPS technique, the composition and thickness of the surface film and the composition of the underlying alloy surface on Fe-Cr, Fe-Co and Fe-Ni alloys were studied after polishing with silicon carbide paper in trichloro-ethylene and cyclohexane. The compositions of the underlying alloy surface after polishing were almost the same as those of the bulk alloys but the film compositions depended on the alloying addition and environment during polishing. The cationic fractions in the surface films on the Fc-Cr alloys polished in both solvents were almost the same as the corresponding atomic fractions of the bulk alloys. In contrast, iron ions were apt to be concentrated in the surface films on the Fe-Co and Fe-Ni alloys, and the weights of nickel ions were different in the surface films on the Fe-Ni alloys polished in different solvents. Chloride ions were found in the surface films due to the reaction of the metal surface with trichloro-ethylene. The amount of chloride ions was particularly large in the surface films on the Fe-Ni alloys. Heating the alloy specimens under the vacuum of the spectrometer resulted in almost complete reduction of the surface films on the Fe-Co and Fe-Ni alloys, and in the change in the compositions of all alloy surfaces. 相似文献
12.
A three-dimensional model has been developed for modelling the selective dissolution and passivation of alloys. The model has been used to simulate the passivation of iron-chromium alloys. The real structure of the alloy is taken into account (bcc in the present case), as well as the structure of the initial surface. The passivation is modelled in considering the formation of “oxide” nuclei, resulting from the presence of local chromium-rich clusters. During the dynamic evolution of the model, based on the Monte Carlo method, surface diffusion and dissolution of atoms occur according to probabilities dependent on the nature of the atom (Cr or Fe) and on its chemical environment. The conditions of simulation can be changed through a set of parameters defining the rules for surface diffusion, selective dissolution and number of Cr atoms in the Cr clusters required to initiate locally the passivation. The effects of these parameters on the simulation have been tested for an alloy containing 22 at.% Cr and compared with experimental data. The results show that the diffusion of Fe has little influence on the course of passivation while the diffusion of Cr has a marked effect. When the number of surface chromium atoms required to form a nucleus of passive film increases, the passivation becomes less rapid, with a marked effect on the composition of the passivated layer. The extent of the chromium enrichment in the passivated surface obtained in the model for the initial stages of passivation is not as high as the one measured experimentally in the stationary state of passivity.Other simulations have then been performed with various chromium contents in the alloy. The results show the existence of a transition, which is not sharp but progressive, between alloys that cannot be passivated to alloys that are passivated. 相似文献
13.
Gang Chen Zhongyi Wang Hui Wang Xiaolin Zhao Jiang Hu Shaohai Wang Shaofeng Zhang 《Surface & coatings technology》2012
The dental cobalt–chromium alloys are an important biomaterial used in making artificial dentures. Bacterial adhesion to cobalt–chromium alloys usually results in severe complications such as periodontal infection, secondary caries, and denture stomatitis, which have severe adverse impacts on human health. Therefore, an effective method is needed to reduce the bacterial adhesion to dental cobalt–chromium alloys. The aim of this study was to investigate the effects of ta-C films deposited on a dental cobalt–chromium alloy on the adhesion of Streptococcus mutans (ATCC175), Actinomyces viscosus (ATCC19246) and Candida albicans (ATCC76615). A filtered cathodic vacuum arc (FCVA) technique was used to coat the cobalt–chromium alloy with a ta-C film. Atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface characteristics of the coating. Surface roughness was detected. Surface free energy and its components were calculated by measuring the contact angle. The results showed that the maximum sp3 fraction was achieved at 200 V substrate bias voltage. Compared with uncoated specimens, the ta-C film coated specimens had a lower surface roughness, a higher surface energy and a higher hydrophilicity. Most importantly, the adhesion of the three tested bacterial strains to the ta-C film coated cobalt–chromium alloy was significantly decreased. These results showed that ta-C film surface treatment could significantly reduce the bacterial adhesion to dental cobalt–chromium alloys, suggesting the potential of ta-C film surface treatment in artificial denture applications. 相似文献
14.
The oxidation kinetics of two metallic glasses have been studied by ellipsometry and Auger Electron spectroscopy. The presence of chromium in Fe-based alloys has a marked influence on the corrosion film formed and on the kinetics of film formation. The chromium-free alloy shows piecemeal parabolic oxide growth; this is transformed into a logarithmic growth law for the chromium concentration studied. The influence of moisture on the kinetics of film formation has also been studied. 相似文献
15.
The effect of heat treatment on the corrosion behavior of sputter-deposited aluminum–chromium alloys
《Corrosion Science》1999,41(3):477-499
The effect of heat treatment on the corrosion resistance of sputter-deposited aluminum–chromium alloys containing 16–51 at% chromium has been studied in 0.1 and 0.5 M HCl. Structural relaxation decreases the corrosion rate of Al–16Cr alloy on which the passive film cannot be formed, since the corrosion rate is controlled by the reactivity of the alloy surface. The corrosion rate of spontaneously passive Al–35Cr alloy increases by crystallization. The chromium enrichment of the matrix, as a result of precipitation of a nanocrystalline aluminum-rich phase, results in enhancement of the corrosion resistance. However, if the size of the less corrosion-resistant aluminum-rich grains exceeds a critical limit of ∼20 nm, the corrosion resistance decreases. 相似文献
16.
G. Latha N. Rajendran S. Rajeswari 《Journal of Materials Engineering and Performance》1997,6(6):743-748
The nitrogen-bearing alloys (alloy 33 and alloy 24) and stainless steel type 316L were used in this investigation in order
to study the effect of alloying elements on electrochemical behavior and on the nature of passive film in seawater. Scanning
electron microscopic studies were carried out to identify the pit morphology of the alloys. Surface analysis of the alloys
by x-ray photoelectron spectroscopy after passivation showed that nitrogen and chromium are enriched at the surface of the
passive film. 相似文献
17.
The pitting potential Epit of 18/8 CrNi stainless steels with different sulfur content (0.003, 0.017 and 0.29%) has been determined from potentiodynamic polarization curves in deaerated neutral solutions (0.1 M NaCl and 1 M Na2SO4 + 0.1 M NaCl) with nominally identical chloride content. Epit decreased with increasing sulfur content of the alloy and was about 0.2 V more negative in pure 0.1 M NaCl solution. The chemical composition of the passive film and the adsorbed chloride content have been determined by XPS surface analysis on mechanically polished samples passivated for one hour at potentials below the pitting potential. XPS results show that the surface films are composed in all cases of mixed iron‐chromium oxi‐hydroxides with a higher chromium content than the bulk composition. The average passive film composition (ca. 40% chromium oxi‐hydroxide) and the film thickness (2.3 ± 0.2 nm) were similar for all 18/8 CrNi steels regardless the different sulfur content. The amount of chlorides in the passive film is about twice as high on steels exposed to pure 0.1 N NaCl solution compared to the mixed 1 M Na2SO4 + 0.1 M NaCl solution. Thus the lower pitting potential measured in pure 0.1 N NaCl solution correlates with the higher amount of chloride ions on the passive film surface. 相似文献
18.
The oxidation and carburization of two 20 Cr 30 Ni alloys with nominally 0 and 0.5 wt % Si have been investigated by cyclic exposure to carbon monoxide and carbon dioxide at 1000°C. In carbon monoxide a chromium oxide film is formed which inhibits further carbon deposition. In carbon dioxide an iron chromium oxide of the spinel type is formed which during subsequent exposure to carbon monoxide acts as a catalyst for carbon deposition. In some areas a breakthrough of the initially formed chromium oxide layer occurs during carbon dioxide treatment. Extensive carbon penetration takes place in these breakthrough areas. The spinel formation and the breakthrough is retarded in the silicon-containing steel owing to the formation of a thin continuous silica layer at the metal-chromium oxide interface. This has a beneficial effect on the carburization resistance. The results also imply that it is possible to lower the catalytic effect of the tube material on carbon deposition or even on coke formation by controlling the surface oxide composition and structure. 相似文献
19.
S. Mato G. Alcala G. E. Thompson P. Skeldon K. Shimizu H. Habazaki T. Quance M. J. Graham D. Masheder 《Corrosion Science》2003,45(12):2881-2892
The behaviour of iron during anodizing of sputter-deposited Ta/Fe alloys in ammonium pentaborate electrolyte has been examined by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Anodic films on Ta/1.5 at.% Fe, Ta/3 at.% Fe and Ta/7 at.% Fe alloys are amorphous and featureless and develop at high current efficiency with respective formation ratios of 1.67, 1.60 and 1.55 nm V−1. Anodic oxidation of the alloys proceeds without significant enrichment of iron in the alloy in the vicinity of the alloy/film interface and without oxygen generation during film growth, unlike the behaviour of Al/Fe alloys containing similar concentrations of iron. The higher migration rate of iron species relative to that of tantalum ions leads to the formation of an outer iron-rich layer at the film surface. 相似文献