ISSN:
1573-4889
Keywords:
Oxidation
;
Co-Cr alloys
;
diffusion
;
18O
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Kinetics of oxidation of Co-Cr alloys containing 0.4%–15% Cr was studied as a function of temperature (1273–1573 K) and oxygen pressure (4 × 102–105Pa). The oxidation process was found to be approximately parabolic and faster than that for pure cobalt. The scales are double-layered and consist of a compact outer CoO layer and a porous inner layer containing CoO slightly doped by chromium and spinel CoCr2O4. The oxidation mechanism was investigated by means of platinum markers and the18O isotope. The scale on the alloys containing less than 1% Cr grows exclusively by outward diffusion of cobalt, while that on the alloys containing more chromium—with a significant contribution of inward oxygen transport from atmosphere. This transport is not a lattice diffusion, but proceeds presumably through microfissures resulting from the secondary process of perforating dissociation of the outer scale layer.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00738387
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