The corrosion behavior of amorphous Fe-Cr-Mo-P-C and Fe-Cr-W-P-C alloys in 6 M HCl solution (original) (raw)
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Materials Science and Engineering: A, 1994
The beneficial effect of phosphorus on the corrosion and passivation behavior of amorphous Fe-8Cr-I 3P-7C alloy was studied in 9M H2SO 4 solution at 30 °C. The corrosion loss of the amorphous Fe-8Cr-13P-7C alloy in an initial period of immersion was relatively high but was scarcely changed afterwards. The corrosion potential was initially in the active region of this alloy but was shifted positively up to the passive region within 30 rain. The air-formed film was enriched in chromium but was not protective and dissolved quickly in the initial stage of corrosion. The concentration of chromic ions in the surface film increased with the immersion time. Elemental phosphorus was accumulated on the alloy surface during the initial dissolution. The formation of the elemental phosphorus layer made the open circuit potential more positive as a result of the acceleration of the cathodic hydrogen evolution and by the suppression of the anodic dissolution current. This led to spontaneous passivation as a result of the formation of the chromium-enriched passive film.
XPS investigation of passive films on amorphous Fe Cr alloys
Electrochimica acta, 1992
Abatraet-The passivation of the amorphous alloys Fe,Cr,,X,,C,(X = P, B) was studied combining X-ray photoelectron spectroscopy (XPS) surface analysis and electrochemical measurements. After removing the native (iron oxide) films by mechanical polishing, the alloys form a thin (2 nm), non-protective oxide film with a composition close to the bulk alloy; the corrosion potentials are in the active range. A subsequent anodic passivation in 1 N HsSO, results in passive tihns enriched in chromium oxyhydroxide (7040% of the cations in the film), and phosphates and borates are incorporated into the passive film. Only phosphorus, not boron, is enriched underneath the passive Slm. The presence of an intermediate phosphorus species (identified as elemental P) at the interface film/substrate is revealed after passivation. The role of flhn composition, especially the presence of phosphates, and of the P enrichment underneath the Slm are discussed with respect to the stability of the passive films. It is concluded that the outstanding corrosion resistance and the high repassivation rate of the amorphous alloy with 13% P may be mainly attributed to the enrichment of phosphorus underneath the passive film, reducing to a great extent the ionic conductivity of the interface, and to the incorporation of chromium oxyhydroxide and phosphates in the passive film. A new method that allows simultaneous evaluation of the thickness and composition of surface films on a multicomponent alloy, taking into account the carbon contamination, is presented.
MELT SPUN Fe-Co-Cr-B-Si ALLOYS CORROSION CHARACTERIZATION
scientificbulletin.upb.ro
Această lucrare prezintă rezultatele cercetărilor privind rezistenţa la coroziune a unui nou sistem de aliaje amorfe, Fe-Co-Cr-B-Si. Comportarea la coroziune a aliajelor amorfe, ca de altfel şi a aliajelor cristaline, poate fi determinată atât de factori interni (stuctura şi compoziţia chimică a aliajlului0), cât şi de factori externi (natura mediului agresiv, concentraţie, pH). Lipsa cristalinitaţii şi a defectelor specifice stării cristaline-limite de grăunţi, dislocaţii şi segregaţii, asigură aliajelor amorfe o înaltă rezistenţă la coroziune deşi termomecanic ele sunt metastabile. Cercetările au fost realizate prin metoda gravimetrică pe benzi amorfe din sistemul de aliaje Fe 75-x Co x Cr 1 B 7 Si 17 obţinute prin metoda turnării pe rotitor. Ele au pus în evidenţă influenţa compoziţiei chimice, de exemplu-creşterea continuţului de Co, şi a mediului de lucru: 0.5N HCl, 1N HCl şi 1N H 2 SO 4 , asupra rezistenţei la coroziune. Cele mai bune rezultate s-au obţinut pe aliajul: Fe 65 Co 10 Cr 1 B 7 Si 17. This paper presents the results of the research on the corrosion resistance of a new system of amorphous alloys, i.e. Fe-Co-Cr-B-Si. The corrosion behaviour of amorphous alloys as well as that of any other crystalline alloys may be determined both by internal factors (alloy structure and composition) and by external factors (aggressive medium type, concentration and pH-coefficient). The lack of crystallinity and of defects specific to the crystalline state-grain boundaries, dislocations and segregations ensure a high corrosion resistance to amorphous alloys in spite of being thermodynamically metastable. The research was performed through the gravimetric method on Fe 75-x Co x Cr 1 B 7 Si 17 amorphous alloy ribbons obtained by the melt-spinning technique. This research showed the influence of the alloy chemical composition, i.e. the increase of Co percentage, and working medium: 0.5N HCl, 1N HCl and 1N H 2 SO 4 on corrosion resistance. The best results
Corrosion Resistance of Fe-16%Cr-30%Mo-(C,B,P) Amorphous Coatings Sprayed by HVOF and APS Processes
Two kinds of Fe-16%Cr-30%Mo-(C,B,P) alloy powders having high ability to form an amorphous phase were thermal sprayed onto mild steel substrate using HVOF and APS processes. Perfectly amorphous coating was formed not only by the HVOF process but also by the APS process. The passive current densities of the amorphous coatings sprayed by the HVOF and APS processes were close each other and significantly low compared with that of SUS316L coating in 1 molÁL À1 HCl solution. The coatings of perfectly amorphous phase were little corroded after immersion tests in 1 molÁL À1 HCl solution for one week, though the coatings composed of the mixture of amorphous and crystalline phases corroded markedly.
Preparation of Fe–Cr–P–Co amorphous alloys by electrodeposition
Surface and Coatings Technology, 2005
The effects of bath composition and electroplating conditions on structure, morphology, and composition of amorphous Fe-Cr-P-Co deposits on AISI 1020 steel substrate, priorly plated with a thin Cu deposit, were investigated. The increase of charge density activates the inclusion of Cr in the deposit. However, above specific values of the charge density, which depend on the deposition current density, the Cr content in the deposit decreases. This Cr content decreasing is probably due to the significant hydrogen evolution with the increasing of deposition current and charge density. The effect of charge density on the content of Fe and Co is not clear. However, there is a tendency of increasing of Fe content and decreasing of Co content with the raising of current density. The Co is more easily deposited than the P, and its presence results in a more intense inhibition effect on the Cr deposition than the inhibition effect caused by P presence. Scanning electron microscope (SEM) analysis showed that Co increasing in the Fe-Cr-P-Co alloys analyzed does not promote the susceptibility to microcracks, which led to a good quality deposit. The passive film of the Fe-Cr-P-Co alloy shows a high ability formation and high protective capacity, and the results obtained by current density of corrosion, j cor , show that the deposit with addition of Co, Fe 31 Cr 11 P 28 Co 30 , presents a higher corrosion resistance than the deposit with addition of Ni, Fe 54 Cr 21 P 20 Ni 5 .
Canadian Metallurgical Quarterly, 2010
The aim of this paper was to investigate the effect of increasing cobalt content on the corrosion resistance of the Fe-Co-Cr-B-Si alloys in dilute mineral acids. The corrosion rates in 0.5N HCl, 1N HCl and 1N H 2 SO 4 significantly decrease with an increase in cobalt content. The alloys with a larger amount of cobalt can passivate spontaneously. The high corrosion resistance of the Fe-Co-Cr-B-Si alloys is also due to the formation of chromium-enriched passive film. Generally, the corrosion resistance of chromium-bearing alloy is improved by alloying with various metalloids but it is lowered by addition of boron and silicon. The corrosion behaviour of the amorphous Fe 75-x Co x Cr 1 B 7 Si 17 alloys obtained by the melt-spinning technique was studied using gravimetric method. The best results were obtained with Fe 65 Co 10 Cr 1 B 7 Si 17 alloy. The studied amorphous alloy ribbons exhibit not only excellent physical properties which are useful for many electric and magnetic applications: magnetic sensors, power transformers, high frequency transformers, etc., but also a very good corrosion resistance which extend their application domain.
The role of corrosion-resistant alloying elements in passivity
Corrosion Science, 2007
Passivity of alloys containing corrosion-resistant elements were reviewed. Chromium and valve metals except aluminum form stable oxyhydroxide films even in aggressive hydrochloric acids. Molybdenum forms a passive MoO 2 film in the active region of stainless steels and hence decreases the active dissolution current. In the passive region of transition metals and valve metals, molybdenum is generally in the transpassive state and dissolved. However, if the outer oxyhydroxide film is stable the inner MoO 2 film is protected by the outer oxyhydroxide film and the MoO 2 film acts as the effective barrier against diffusion of matters through the film. Thus the passive current density of 30Cr-2Mo ferritic stainless steel is more than two orders of magnitude lower than that of 30Cr steel without molybdenum in 1 M HCl.