ISSN:
1573-4889
Keywords:
nucleation
;
carburization
;
transient oxidation
;
surface pretreatment
;
surfacesensitive analytical techniques
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The initial corrosion reactions on a number of Fe-Cr-Ni and Cr-Ni alloys when exposed in a H2-CH4 gas mixture ofa c =0.8 and $$p_{O_2 } $$ ≈ 10−30 bar at1098 K have been investigated. All alloys were studied with surfaces in boththe cold-worked and electropolished conditions. The experiments, in whichexposure times up to 400 rain were used, were carried out in a conventionalcorrosion rig and also in a small reaction chamber contained within an X-rayphotoelectron spectrometer. The use of XPS, SEM, and TEM showed thattransient α-Cr2O3 layers formed on all alloy surfaces during the heat-up period.On the electropolished surfaces, the oxide layers developed nonuniformly withrespect to microstructure and thickness, whereas homogeneous, compact, andfine-grained α-Cr2O3 layers formed on the cold-worked specimens. Followingan incubation period, M7C3 carbides nucleated on the surfaces; they grew byconsuming the less stable α-Cr2O3 and also through diffusion of metal fromthe alloy substrate. The mode of nucleation of the M7C3 and its rate of growthwere strongly dependent on the character of the transient α-Cr2O3 layers. Afterremoval of α-Cr2O3, carbon ingressed into the substrate where M23C6 wasformed internally. These results are broadly in line with the thermodynamicstability predictions and are discussed in terms of simple models.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00659597
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