ISSN:0947-5117    

DOI:10.1002/maco.19950460423

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19950460424

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19950460425

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19950460426

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19950460428

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

ISSN:0947-5117    

DOI:10.1002/maco.19950460402

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThree austenitic FeNiCr steels, G 4848, G 4852 and 36 XM, have been corroded in CH4+ H2mixtures at 850, 900 and 1000°C. Under these conditions a new metal dusting phenomenon has been observed where closed cavities near the exposed surfaces of the alloys are filled with a powdery mixture of graphite, iron metal, chromium carbide and also in cases SiO2. It is tentatively concluded that the powder is formed through the decomposition of (Cr, Fe)7C3

ISSN:0947-5117    

DOI:10.1002/maco.19950460403

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe rapid, destructive low‐temperature oxidation (pesting) of MoSi2is an important limitation to its practical use. The growth of molybdenum silicide diffusion coatings by a halide‐activated pack cementation method results in an adherent superficial, salt by‐product, whose composition depends on the halide activator used to grow the coating. As a consequence of the residual salt deposit, coatings grown by a NaF‐activated pack did not pest after 2500 hours of isothermal oxidation or after cyclic oxidation for 600 1 hour cycles in air at 500°C. An additional minor improvement in the pesting resistance was observed for the germanium‐doped MoSi2Coatings.The growth kinetics for a three‐layer Ge‐doped Mo(Si, Ge)2/Mo5(Si, Ge)3/Mo3(Si, Ge) coating are compared with rates calculated for the diffusion‐controlled growth of an undoped three‐layer silicide and for three‐layer germanide coatings. The activation energy for the solid‐state diffusional growth of MoSi2is the same as that for Mo(Si, Ge)2, but the growth rates for Mo(Si, Ge)2are faster. The activation energies for the solid state diffusional growth of the inner Mo5(Si, Ge)3and Mo3(Si, Ge) layers are similar to Mo5Ge3and Mo3Ge, but the rates are slower. The chemical demixing of Mo(Si, Ge)2under a chemical potential gradient creates a maximum in the Ge concentration at the Mo(Si, Ge)2/Mo5(Si, Ge)3interface, which produces unusual growth kinetics for the Mo5(Si, Ge)3

ISSN:0947-5117    

DOI:10.1002/maco.19950460404

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractConventional electron microscopy, analytical electron microscopy, high resolution electron microscopy and high resolution SIMS have been used to investigate the effect of the reactive elements, Yand Zr, on the oxide scale formation on NiAl. Polycrystalline NiAl samples, doped with either 0. 1 wt% Yor 0.2 wt% Zr, were oxidized in air at 1200°C.18O tracer experiments in conjunction with high resolution SIMS suggest that the reactive elements reduce the outward diffusion of cations. Energy dispersive X‐ray spectroscopy on a dedicated STEM showed that the reactive elements segregate to the grain boundaries in the oxide scale and to the metal/oxide interface. The amount at the oxide scale grain boundaries was calculated to be 0.2 monolayers for both Zr and Y doped NiAl. The amounts of segregation were calculated to be 0.15 monolayers (Zr‐doped) and 0.07 monolayers (Y‐doped) at the metal/oxide interface. The presence of sulfur was detected in Y‐rich particles in the NiAl close to the i

ISSN:0947-5117    

DOI:10.1002/maco.19950460405

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe corrosion of two Fe‐Nb alloys containing 15 and 30 wt% Nb has been studied at 600–800°C under 1 atm of pure oxygen. The reaction followed the parabolic rate law to a reasonable approximation with rate constants much lower than for the oxidation of pure iron under the same conditions. Internal oxidation and depletion of niobium in the alloy have never been observed. The external scales were composed of a matrix of Fe2O3containing a dispersion of double Fe‐Nb oxide, while FeO and Fe3O4were not observed. The oxidation behavior of these alloys is interpreted with reference to an approximate phase diagram of the ternary system FeNbO, taking into account the effects of the low solubility of niobium in the base metals and of the presence of two metal phases in

ISSN:0947-5117    

DOI:10.1002/maco.19950460406

出版商:WILEY‐VCH Verlag GmbH    

年代:1995

数据来源: WILEY