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1.
The oxidation behaviour of T91 ferritic steel in steam has been studied under isothermal and non-isothermal conditions within a temperature range between 575 and 700 °C. Isothermal treatments resulted in parabolic oxidation kinetics. Three clearly defined oxide layers constituted the oxide scales. The innermost layer was a (Fe,Cr)3O4. The intermediate layer was porous magnetite (Fe3O4) followed by a compact thinner layer of hematite (Fe2O3). Under non-isothermal conditions the oxide scales were irregular and evidently cracked. An increase of the oxidation temperature produces an acceleration of the oxidation process, causing an increase of the oxide scale thickness that depends on the temperature increase and the exposure time. 相似文献
2.
J. Webber 《Corrosion Science》1976,16(8):499-506
A range of FeCr binary alloys containing 2–100%Cr was exposed in O2/3%H2O at 1023–1223K to determine whether the presence of the water had a significant effect on oxidation. Oxidation rates were not significantly different from those in dry oxygen and decreased with increasing time of oxidation. The kinetics of oxidation and the oxide structures both suggested that the early stages of oxidation were controlled by lattice diffusion through layers of FeCr spinel for Fe-2 1/4Cr and Fe-8 1/2Cr, or through (Cr, Fe)2O3 scale for alloys containing 16%Cr or more. 相似文献
3.
A study has been made of the structure of oxide layers formed at different times on abraded Fe oxidized in 1 atm O2 and CO2 at 550°C. A duplex Fe3O4 layer was formed and the inner layer was considered to grow by an oxide dissociation mechanism. The growth of both layers has been explained by a model, which correlates the overall kinetics with oxide grain growth. Derived values of the parabolic rate constant for lattice diffusion have been used to calculate self-diffusion coefficients, which were in good agreement with literature values for Fe diffusion in Fe3O4, but were very much larger than the values for either Fe or O in -Fe2O3. 相似文献
4.
The oxidation behavior in air of Fe-19.6Cr-15.1Mn was studied from 700 to 1000°C. Pseudoparabolic kinetics were followed, giving an activation energy of 80 kcal/mole. The scale structure varied with temperature, although spinel formation occurred at all temperatures. At both 700 and 800°C, a thin outer layer of -Mn2O3 formed. The inner layer at 700°C was (Fe,Cr,Mn)3O4, but at 800°C there was an intermediate layer of Fe2O3 and an inner layer of Cr2O3 + (Fe, Cr,Mn)3O4. Oxidation at 900°C produced an outer layer of Fe3O4 and an inner layer of Cr2O3+(Fe,Cr,Mn)3O4. Oxidation at 1000°C caused some internal oxidation of chromium. In addition, a thin layer of Cr2O3 formed in some regions with an intermediate layer of Fe3O4 and an outer layer of (Fe,Mn)3O4. A comparison of rates for Fe3O4 formation during oxidation of FeO as well as for the oxidation of various stainless steels, which form spinels, gave good agreement and strongly suggests that spinel growth was rate controlling. The oxidation rate of this alloy (high-Cr) was compared with that of an alloy previously studied, Fe-9.5Cr-17.8Mn (low-Cr) and was less by about a factor of 12 at 1000°C and by about a factor of 100 at 800°C. The marked differences can be ascribed to the destabilization of wustite by the higher chromium alloy. No wustite formation occurred in the high-Cr alloy, whereas, extensive wustite formed in the low-Cr alloy. Scale structures are explained by the use of calculated stability diagrams. The mechanism of oxidation is discussed and compared with that of the low-Cr alloy. 相似文献
5.
Bong-Seo Kim Yung-Geol Kim Hee-Woong Lee Won-Sub Chung 《Metals and Materials International》2002,8(4):367-373
The oxidation behavior of Fe-30% Ni-12.5%Co Invar alloy possessing low thermal expansion-high strength has been studied by exposing it in temperature ranges of 1000–1200 in an air atmosphere. The formed oxide scale consisted of two layers, an outer layer and an inner layer, and the oxidation mechanism showed uniform growth for all oxidation conditions. The growth rate of the scale had a parabolic relationship with oxidation time, and the estimated activation energy for the growth of the whole oxide layer was approximately 19.84 kcal/mol. The outer scale consisted of five oxide layers, whose outermost scale consisted of major phase CoFe2O4 containing a particulate Fe2O3 phase. The oxide scale of Fe-30 Ni-12.5% Co had different compositions and phases from the Fe-30%Ni alloy investigated in previous studies. Especaally, when the alloy was exposed for a longer oxidation time and at a higher temperature, the volume fraction ratio of CoFe2O4 to Fe2O3 was found to increase 相似文献
6.
A sputtered coating of a low-Cr alloy without Si was deposited on the cast alloy with the same composition. The short term (100 h) oxidation behavior of the sputtered coating and the cast alloy was evaluated in air at 800 °C. The results indicated that the sputtered coating exhibited a higher oxidation resistance than the cast alloy. It was found that the mass gain of the cast alloy increased continuously with oxidation time and was higher than that of the sputtered coating, which demonstrated only a slight increase in mass gain with oxidation time after 5 h thermal exposure. During the initial thermal exposure of 0.5 h, the oxide scale formed on the cast alloy consisted of Fe2O3 and (Fe,Co,Cr)3O4 spinel with a small amount of Cr. However, (Fe,Co,Cr)3O4 spinel and Fe2O3 were thermally grown on the sputtered coating. After oxidation for 100 h, the oxide scale formed on the cast alloy consisted of Co3O4 and (Fe,Co)3O4 with internal oxide of Cr, while a double-layer oxide consisting of an outer (Fe,Co,Cr)3O4 spinel layer and an inner Cr2O3 layer was developed on the sputtered coating. 相似文献
7.
The influence of surface pretreatment and metal orientation on the oxidation of coarse-grained polycrystalline Fe has been studied at 240 to 320°C in 5×10–3 Torr O2 using electron diffraction, electron microscopy, and Mössbauer spectroscopy to complement kinetic data. Consistent with previous studies on Fe single crystals, differences in oxidation kinetics for surfaces covered with an electropolish film from those with a similar thickness prior oxide formed by dry oxidation at room temperature are interpreted in terms of differing densities of leakage paths in the oxide layers. The more complex kinetics for electropolished polycrystalline Fe are a result of the leakage path density, the degree of oxide separation, and the extent of -Fe2O3 formation varying with substrate orientation. Where adherent Fe3O4 layers are formed on polycrystalline and single-crystal Fe surfaces, the parabolic rate constants give an activation energy which is consistent with a previous value of 32 kcal · mole–1, suggesting that at these low temperatures the transport mechanism for magnetite growth is cation diffusion via easy diffusion paths in the oxide. 相似文献
8.
Fe-21.5 wt. %Cr-5.6 wt. %Al oxidation, at 1000°C, in dry or wet oxygen shows that steam has an influence on the oxide-scale growth mechanism. Steam modifies the kinetics of early-stage oxidation. In dry oxygen, an initial fast linear regime is observed during one hour. Under wet conditions, weight-gain curves follow the same parabolic regime over the entire oxidation test. The scale structure strongly depends on the presence of steam in the gaseous environment. With dry oxygen, the scale is composed mainly of-Al2O3 after the initial formation of-Al2O3 identified by ESCA and RHEED. The kinetics transient stage corresponds to the necessary time for the internal part of the initial-Al2O3 scale to transform into a continuous-Al2O3 diffusion barrier. Under wet oxygen conditions, transient oxides are identified as (Mg, Fe) (Cr, Al)2O4, MgAl2O4 (orthorhombic), Al2O3 (hexagonal), these oxides transform into MgAl2O4 (cubic), Cr3O4, Fe2O3,-Al2O3, with time. When water vapor does not change drastically oxidation kinetics, the induced presence of iron and chromium in the oxide scale could be responsible for weakening the protectiveness of alumina scales. 相似文献
9.
W. Kai W. L. Jang R. T. Huang C. C. Lee H. H. Hsieh C. F. Du 《Oxidation of Metals》2005,63(3-4):169-192
The oxidation behavior of FeCoNi, FeCoNiCr, and FeCoNiCrCu equi-molar alloys was studied over the temperature range 800–1000 °C in dry air. The ternary and quaternary alloys were single-phase, while the quinary alloy was two-phase. In general, the oxidation kinetics of the ternary and quinary alloys followed the two-stage parabolic rate law, with rate constants generally increasing with temperature. Conversely, three-stage parabolic kinetics were observed for the quaternary alloy at T 900°C. The additions of Cr and Cu enhanced the oxidation resistance to a certain extent. The scales formed on all the alloys were triplex and strongly dependent on the alloy composition. In particular, on the ternary alloy, they consist of an outer-layer of CoO, an intermediate layer of Fe3O4, and an inner-layer of CoNiO2 and Fe3O4. Internal oxidation with formation of FeO precipitates was also observed for this alloy, which had a thickness increasing with temperature. The scales formed on the quaternary alloy consisted of an outer layer of Fe3O4 and CoCr2O4, an intermediate layer of FeCr2O4 and NiCr2O4, and an inner layer of Cr2O3. Finally, the scales formed on the quinary alloy are all heterophasic, consisting of an outer layer of CuO, an intermediate-layer of CuO and Fe3O4, and an inner-layer of Fe3O4, FeCr2O4, and CuCrO2. The formation of Cr2O3 on the quaternary alloy and possibly that of CuCrO2 on the quinary alloy was responsible for the reduction of the oxidation rates as compared to the ternary alloy. 相似文献
10.
The oxidation of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (Incoloy 909 type alloy), was investigated at temperatures between 1000 K and 1400 K in Ar-(1, 10%)H20 atmosphere using metallographic, electron probe microanalysis, and X-ray diffraction techniques. The oxide scales consist of an external scale and an internal scale which has an intergranular scale (above 1200 K) and an intergranular scale. The oxide phases in each scale are identified as-Fe2,O3 (below 1200 K) or FeO (above 1300 K) and CoO · Fe2O3 and FeO · Nb2O5, respectively. The morphologies, the oxide phases and the oxidation rates do not depend on the partial pressure of H2O in the range between one and ten percent in Ar gas. The rate constants for the intergranular-scale formation in this alloy are about one-tenth as large as those in Fe-36%Ni alloy reported previously. At all the temperatures the scales grow according to a parabolic rate law and the apparent activation energies for the processes are estimated. 相似文献
11.
The oxidation behavior of Ti36Al, Ti35Al-0.1C, Ti35Al-1.4V-0.1C, and Ti35 Al-5Nb-0.1C (mass-%) in air and oxygen has been studied between 700 and 1000°C with the major emphasis at 900°C. Generally an oxide scale consisting of two layers, an outward- and an inward-growing layer, formed. The outward-growing part of the scale consisted mainly of TiO2 (rutile), while the inward-growing part is composed of a mixture of TiO2 and -Al2O3. A barrier layer of Al2O3 on TiAl between the inner and the outer part of the scale was visible for up to 300 hr. Under certain conditions, the Al2O3 barrier dissolved and re-precipitated in the outer TiO2 layer. This shift leads to an effect similar to breakaway oxidation. Only the alloy containing Nb formed a longlasting, protective Al2O3 layer, which was established at the metal/scale interface after an incubation period of 80–100 hr. During this time, Nb was enriched in the subsurface zone up to approximately 20 w/o. The growth of the oxide scale on TiAl-V obeyed a parabolic law, because no Al2O3 barrier layer formed; large Al2O3 particles were part of the outward-growing layer. A brittle 2-Ti3Al-layer rich in O formed beneath the oxide scale as a result of preferential Al oxidation particularly when oxidized in oxygen. Oxidation in air can lead also to formation of nitrides beneath the oxide scale. The nitridation can vary between the formation of isolated nitride particles and of a metal/Ti2AlN/ TiN/oxide, scale-layer system. Under certain conditions, nitride-layer formation seemed to favor protective Al2O23 formation at the metal/scale interface, however, in general nitridation was detrimental with the consequence that oxidation was generally more rapid in air than in oxygen. 相似文献
12.
B. Pujilaksono T. Jonsson H. Heidari M. Halvarsson J.-E. Svensson L.-G. Johansson 《Oxidation of Metals》2011,75(3-4):183-207
The oxidation behaviour of the binary alloys Fe?C2.25Cr, Fe?C10Cr, Fe?C18Cr and Fe?C25Cr (wt%) in dry and wet O2 at 600???C is investigated by isothermal exposures of carefully polished samples for up to 168?h. The oxidized samples are investigated gravimetrically and the oxides formed are studied by X-ray diffraction. X-ray photoelectron spectroscopy is used for depth profiling of the thin oxides. The scale surface is imaged by SEM. Cross-sections through the scale are analyzed by SEM/EDX for imaging and for measuring the chemical composition. The oxidation behavior of the four FeCr alloys is intermediate between those of iron and chromium. Fe?C2.25Cr oxidizes in a way similar to iron in both environments, forming a poorly protective scale consisting of FeCr spinel at the bottom, magnetite in the middle and a hematite cap layer. In dry O2, Fe?C10Cr, Fe?C18Cr and Fe?C25Cr form a thin and protective (Fe,Cr)2O3 oxide similar to the chromia film formed on pure chromium. In wet O2, Fe?C10Cr, Fe?C18Cr and Fe?C25Cr initially form the same kind of protective oxide film as in dry conditions. After an incubation time that depends on alloy chromium content, all three alloys go into breakaway oxidation and form thick, poorly protective scales similar to those formed on Fe?C2.25Cr. Breakaway oxidation in wet O2 is triggered by the evaporation of CrO2(OH)2 from the protective (Fe,Cr)2O3 oxide. 相似文献
13.
The amount of each oxide phase developed upon thermal oxidation of a γ‐Ni‐27Cr‐9Al (at.%) alloy at 1353 K and 1443 K and a partial oxygen pressure of 20 kPa is determined with in‐situ high temperature X‐ray Diffractometry (XRD). The XRD results are compared with microstructural observations from Scanning Electron Microscope (SEM) backscattered electron images, and model calculations using a coupled thermodynamic‐kinetic oxidation model. It is shown that for short oxidation times, the oxide scale consists of an outer layer of NiO on top of an intermediate layer of Cr2O3 and an inner zone of isolated α‐Al2O3 precipitates in the alloy. The amounts of Cr2O3 and NiO in the oxide scale attain their maximum values when successively continuous Cr2O3 and α‐Al2O3 layers are formed. Then a transition from very fast to slow parabolic growth kinetics occurs. During the slow parabolic growth, the total amount of non‐protective oxide phases (i.e. all oxide phases excluding α‐Al2O3) in the oxide scale maintain at an approximately constant value. The formation of NiCr2O4 and subsequently NiAl2O4 happens as a result of solid‐state reactions between the oxide phases within the oxide scale. 相似文献
14.
The influence of chromium on the mechanical properties of the aluminides Fe3Al and Ni3Al has been studied extensively. In order to evaluate the role of Cr during the early stages of oxidation, Fe3Al and Ni3Al containing 2 and 4 at.% Cr were oxidized in dry air at 500°C for 6, 50, and 100 hr. The oxide scale on Fe3Al consists of a layer of Fe2O3 mixed with FeAl2O4 on top of a continuous layer of (Al, Cr)2O3. Ni3Al is covered with a mixed layer of (Al, Cr)2O3 and NiO/NiAl2O4 underneath a layer of NiO/NiAl2O4. Moreover, Cr induces the nucleation and growth of Fe2O3 and NiO particles at the oxide surface of Fe3Al and Ni3Al, respectively. This is due to enhanced cationic diffusion through the Cr-modified oxides. As a conclusion, additions of Cr up to 4 at.% are detrimental to the oxidation behavior of both aluminides at 500°C. 相似文献
15.
Microstructure characterization of corrosion behavior of an alumina forming austenitic (AFA) steel exposed to supercritical carbon dioxide was conducted at 450–650 °C and 20 MPa. At low temperature and short exposure times, the oxidation kinetics were parabolic and the oxide scales were mainly composed of protective and continuous Al2O3 and (Cr, Mn)-rich oxide layers. As the temperature and exposure time increased, the AFA steel gradually suffered breakaway oxidation and its oxide scales showed a multilayer structure mainly composed of Fe3O4, (Cr, Fe)3O4, NiFe/FeCr2O4/Cr2O3/Al2O3, FeCr2O4/Al2O3, and NiFe/Cr2O3/Al2O3, in sequence. The corrosion mechanism based on the microstructure evolution is discussed in detail. 相似文献
16.
Environments containing water vapour are common in many industrial processes, such as power generation systems. Hence, long-term oxidation (1000 h) of P-91 and AISI 430 was studied at 650 and 800 °C, in 100% H2O atmosphere. The oxidation resistance of the AISI 430 is better than that of the P-91, due to the formation of protective phases on the surface. At 650 °C, a scale composed of Fe3O4, Fe2O3 and (Fe,Cr)3O4 is formed on P-91, although at 800 °C the scale is mainly composed of Fe3O4 and (Fe,Cr)3O4. On the other hand, on AISI 430 the scale is composed mainly of (Fe,Cr)2O3 at 650 °C, and at 800 °C a layer of Cr2O3 is formed and remains owing to the higher diffusion rate of Cr at this temperature than at 650 °C, the latter of which compensates the Cr depletion by the degradation of the chromia scale. 相似文献
17.
Valentin Badin Entela Diamanti Pierre Forêt Evelyne Darque-Ceretti 《Oxidation of Metals》2014,82(5-6):347-357
This study focuses on the characterization of the oxide scales formed after different exposure times in the range of 2.5–20 min. A commercially available ferritic steel grade AISI 441 was exposed to wet argon at 1100 °C with 5, 9 and 13% H2O. Raman microspectroscopy, XRD, EDS and XPS were used to fully characterize the oxide scale. For all samples exposed for over 4 min, the scale was constituted of three layers in this order: a thin top layer of spinel phases (Fe,Cr,Mn)3O4 with local outgrowths; a second and main layer of Cr2O3 + (Mn,Cr)3O4; and finally a bottom layer of SiO2. The uncommon presence of Fe in the top layer was also observed. 相似文献
18.
H. Hooshyar T. Jonsson J. Hall J.-E. Svensson L. G. Johansson J. Liske 《Oxidation of Metals》2016,85(3-4):321-342
The effect of p(H2O) and p(H2) on the oxidation of 304L stainless steel at 600 °C has been investigated in the present study. The samples were analysed by means of X-ray diffraction, Auger spectroscopy, and scanning electron microscopy equipped with energy dispersive spectroscopy. The results showed that at fixed p(H2), the corrosion rate increased considerably with increasing p(H2O). At fixed p(H2O), the corrosion rate decreased slightly with increasing p(H2). Duplex oxide scales formed during the exposure in all environments. The outer and inner layer consisted of Fe3O4 and (Fe, Cr)3O4, respectively. The latter was mainly in the form of internal oxidation. The Cr-rich oxide formation was observed at the initial oxidation process before oxide breakdown. The Auger analysis also suggested the presence of Cr-rich oxide layer just after the breakaway oxidation. The results indicated that the rate-determining step in the corrosion attack is surface controlled or diffusion controlled through an oxide layer with fixed thickness over time. 相似文献
19.
The phase constituent, morphologies, layer structures of the scale of 12Cr–W–Mo–Co heat resistant steel (HRS) formed in dry air and air with 10% vapour were systematically investigated. The interface between the scale and ferritic/martensitic matrix of this HRS was also studied. For the scale formed in air, single particle- and sheet-shaped oxide layer, which are composed of (Fe, Co, Cr)2O3, were formed. The scale combines with steel matrix via coherent or semi-coherent structure. For the scale formed in air with 10% vapour, the oxides take the shape of particulate. Layering phenomenon has been observed, i.e. the external layer is composed of (Fe, Co)2O3/(Fe, Co)3O4, the internal layer with spinel (Fe, Co, Cr)3O4 and the transition layer with Cr rich and Cr poor regions. The interface between the transition layer and the matrix is tight and steady, but the region linking the internal scale and transition layer is shaky and brittle. Both the oxidation processes in air and air with 10% vapour are considered to be controlled by diffusion mechanism. 相似文献
20.
1. | Raising the cobalt concentration from 0 to 40% improves the oxidation resistance of Ni–20Cr alloys, since the amount of Cr2O3 in the scale increases. The oxidation resistance is highest for the alloy with 40% Co. Larger amounts of Co up to 70% lead to the formation of CoO in the scale and smaller amounts of chromium oxide, which has a negative effect on the oxidation resistance of Ni–Cr alloys. |
2. | The addition of up to 25% Fe to Ni–20Cr–Co alloys reduces the amount of Cr2O3 in the scale and lowers the oxidation resistance. With larger amounts of Fe the amount of Cr2O3 in the scale again increases, the oxidation resistance increasing correspondingly. Alloys with 45% Fe have the same oxidation resistance as alloys without Fe. |