ISSN:0947-5117    

DOI:10.1002/maco.19960471219

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19960471220

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractOxide‐dispersed Fe‐28at.% Al‐2%Cr alloys were produced by a powder metallurgy technique followed by hot extrusion. A variety of stable oxides were added to the base alloy to assess the effect of these dopants on the oxidation behavior at 1200°C in air and O2. An Al2O3dispersion flattened the α‐Al2O3scale, but produced none of the other reactive element effects and had an adverse influence on the long‐term oxidation behavior. A Y2O3dispersion improved the alumina scale adhesion relative to a Zr alloy addition at 1200 and 1300°C. However, the Y2O3dispersion was not as effective in improving scale adhesion in Fe3Al as it is in FeCrAl. This inferior performance is attributed to a larger amount of interfacial void formation

ISSN:0947-5117    

DOI:10.1002/maco.19960471202

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19960471203

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe sulfidation behaviour of four nickel aluminium alloys containing 25 to 45 at.% Al was studied over the temperature range of 750 to 950°C in a gas mixture of H2‐H2S (0.1 to 10 vol.%). The sulfidation kinetics were determined using a continous weight gain system. The corrosion products were examined by SEM, EDX and XRD.Sulfidation in H2‐H2S gas mixtures formed bilayered scales consisting of an outer layer of Ni3S2and an inner layer of NiAl3,5S5,5on all alloys regardless of the different aluminium contents. In H2‐H2S gas mixtures the sulfidation kinetic generally followed the parabolic rate law for all alloys. The influence of aluminium content on corrosion rate was relatively low.The influence of low oxygen partial pressure on sulfidation was investigated in H2‐H2S‐H2O mixtures. In these atmospheres the corrosion mechanism is completely different. Severe attack by rapid internal oxidation destroyed all the alloys except Ni25Al (25 at.%Al). The internal oxidation zone consisted of a mixture of γ‐Ni3Al and Al2O3. On the alloys containing 36 and 45 at.% Al local attack occurred, fast growing pocks were observed after an incubation period.Nickel aluminides show this corrosion phenomena only in H2‐H2S‐H2O mixtures. An interruption of the H2S gas flow stops the running internal oxidation. In flowing H2‐H2O atmospheres no internal oxidation was observed. These facts prove that H2S is necessary for starting and maintaining the internal oxidation of th

ISSN:0947-5117    

DOI:10.1002/maco.19960471204

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe high temperature corrosion of different iron aluminides and iron‐aluminium‐chromium alloys containing between 6 and 17 wt% aluminium, 2 and 10 wt% chromium and additions of mischmetal has been investigated in air as well as in carburising, chlorinating and sulphidising environments. It was found that all alloys showed excellent corrosion resistance to both oxidation in air and carburisation in CH4/H2up to at least 1100°C and to sulphidation in SO2/air up to at least 850°C. In these environments the corrosion behaviour is not influenced by the concentrations of aluminium and chromium. In oxygen deficient H2S‐atmospheres, however, the corrosion behaviour depends sensitively on the aluminium and chromium concentration. At least 12 wt% aluminium in chromium‐free alloys or 10 wt% aluminium in alloys containing 10 wt% chromium are required to provide sulphidation resistance at 550°C. The chlorination resistance of iron‐aluminium‐chromium alloys is low due to their formation of volatile alumi

ISSN:0947-5117    

DOI:10.1002/maco.19960471205

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractAn investigation has been carried out into the oxidation‐sulphidation resistance of a series of novel iron aluminides, containing 5 wt% Cr, 0.2 wt% Zr, from 0 to 0.3 wt% Y and from 8 to 16 wt% Al, at 500°C to 700°C. The test environments were H2/H2O/H2S gas mixtures, giving oxygen and sulphur partial pressures in the ranges of 10−24to 10−31atm and 10−9to 10−11atm respectively. The effects of preoxidation on the degradation resistance have also been studied. For comparison, several standard Cr2O3‐forming and Al2O3‐forming alloys were included in the programme.In general, the Al2O3‐forming intermetallics and alloys were much more resistant to degradation than the Cr2O3‐forming alloys while, in all cases, preoxidation increased the time to the onset of breakaway‐type corrosion resulting from the initiation and growth of sulphides. In environments in which the Cr2O3‐forming alloys developed thick sulphide scales, it was found that the iron aluminides developed and retained protective Al2O3‐rich scales more effectively than the conventional Al2O3‐forming alloys. At the relatively low temperatures of these tests, it was more difficult to establish the protective scale than at high temperatures, particularly on the alloys of relatively low aluminium concentration. Thus, an iron aluminide containing 16 wt% Al showed good degradation resistance under all conditions while an aluminide containing 8 wt% Al developed more extensive sulphides at 500°C that at 700°C. Overall, the resistance of the intermetallics to degradation increased with increasing aluminium concentration, although none of them showed excessive sulphidatio

ISSN:0947-5117    

DOI:10.1002/maco.19960471206

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractMetal dusting is a deterioration of metallic materials in strongly carburizing atmospheres under disintegration into a dust of carbon and fine metal particles (coke). The intermetallic compound Fe3Al is also very susceptible to metal dusting and disintegrates under formation of vast amounts of coke. The mechanism corresponds to the metal dusting of iron and steels, Fe3C is formed as an intermediate and the Al is oxidized. With increasing Cr‐addition and with increasing Ni‐content in alloys (Fe,Ni)3Al‐Cr the materials become more resistant, Ni3Al is not attacked by metal du

ISSN:0947-5117    

DOI:10.1002/maco.19960471207

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractIn Molten Carbonate Fuel Cells (MCFC) the separator plates in a stack are exposed to severe conditions. The normal operating temperature of a MCFC is 650°C, while the electrolyte consists of an eutectic mixture of 62/38 Li2CO3/K2CO3. On one side the separator plate material is in contact with a reducing atmosphere and on the other side it is an oxidising atmosphere. Due to the application of a wet seal the material is also in contact with the molten carbonate.A wide range of materials is therefore being investigated to enable a justified materials selection either as base material or as coating.NiAl is one of the investigated materials, which has promising properties, due to the possible formation of a protective oxide LiAlO2layer.A comparison will be made with data available for pure Ni, with special emphasis on the protective character of the oxide layer based on quasi‐stationary polarisation curves, exposure tests at open circuit potential and quenching experiments, incorporating earlier published results obtained on Ni with impedance measurements.All experiments were performed in molten carbonate, while the gas composition over the melt was 64% H2, 16% CO2, and 20% H

ISSN:0947-5117    

DOI:10.1002/maco.19960471208

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19960471209

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY