ISSN:
1573-4889
Keywords:
Co-Mn alloys
;
high-temperature oxidation
;
multilayer structures
;
cation concentration profiles
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The oxidation behavior of Co alloys containing up to 23.0 % Mn was investigated at temperatures of 1273–1473 K in an oxygen pressure range of 10–105 Pa using thermogravimetry, electron-probe microanalysis, and optical microscopy. Oxidation followed a parabolic rate law, except in the early reaction stage. For the growth of the (Co, Mn)O scale, parabolic rate constants increased with increasing manganese content, whereas with further additions of manganese the rate constants decreased due to an intermediate layer of (Co, Mn)3O4. This critical manganese content increased with increasing temperature. The scale structures were classified into three groups: group I, a single-layer scale; group II, an inner-outer double layer; and group III, an inner-intermediate-outer triple layer. The inner layer consisted of (Co, Mn)O; the outer layer was a mixture of (Co, Mn)O and (Co, Mn)3O4; the intermediate layer was composed of (Co, Mn)3O4. Cation concentration profiles were measured across the external scales with single- or multilayer structures. Diffusional analysis indicated that manganese moved 1.25 times faster than did cobalt in the (Co, Mn)O scale. Activation energies for oxidation are 118–126 kJ/moles for groups I and II, and for the alloys in group III they are 290–367 kJ/moles. Parabolic rate constants and scale structures are discussed on the basis of the Co-Mn-O phase diagram.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00659271
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