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The effect of certain reactive elements on the oxidation behaviour of chromia‐ and aluminaforming alloys
Author(s) -
Mrowec St.,
Gil A.,
Jedliński J.
Publication year - 1987
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19870381004
Subject(s) - chromia , oxidizing agent , lanthanum , materials science , yttrium , substrate (aquarium) , diffusion , metallurgy , isothermal process , chemical engineering , temperature cycling , reactive material , chromium , inorganic chemistry , chemistry , oxide , thermal , thermodynamics , oceanography , physics , organic chemistry , engineering , geology
The influence of implanted yttrium and lanthanum on the oxidation behaviour of Co‐45Cr and Co‐25Cr‐1Al chromia formers as well as of β‐NiAl and Co‐25Cr‐9Al alumina formers has been studied in isothermal and thermal cycling conditions in the temperature range 1273–1573 K. It has been found that protective properties of Cr 2 O 3 ‐scale and its adherence to the substrate are greatly improved by both reactive element additions. This beneficial effect results from the promotion of fine grained scale formation and consequently the elimination of outward diffusion of chromium. The influence of implanted yttrium (but not lanthanum) on the growth rate and adherence of alumina scale is analogous. In this case, however, both these effects result from elimination by reactive element addition of the inward diffusion of oxygen. It may be then concluded that the influence of implanted reactive elements on the oxidation behaviour of both chromia and alumina formers consists mainly in changing the mechanism of scale growth and not in various interfacial phenomena. It has been found also that the protective properties of alumina scale are considerably improved by elimination of grain boundaries from the substrate, this effect being stronger than that resulting from reactive element addition. Beneficial influence of implanted reactive elements should be expected only when the protective scale layer is formed from the very beginning of the reaction, directly on the initial surface of the material exposed to the oxidizing atmosphere.