TEM Investigation of the Microstructure of the Scale Formed on a FeCrAlRE Alloy at 900 A degrees C: The Effect of Y-rich RE Particles
Journal article, 2010
Three oxide features: the thin and smooth protective oxide, reactive element (Ti-, Zr- or Y-rich) particles, and patches of thick oxide surrounding the Y-rich reactive element particles, were observed on a commercial FeCrAlRE alloy, Kanthal AF, exposed at 900 A degrees C. The microstructural development of the patches of thick oxide was investigated on samples exposed for 24 or 168 h in either dry O-2 or O-2 + 40% H2O. Analytical transmission electron microscopy in combination with site-precision TEM sample preparation by FIB/SEM was used. In all patches a thin but continuous inward growing alpha-Al2O3 layer was formed under a thick outward growing alumina layer, which initially consisted only of gamma-Al2O3. In dry O-2, transformation of gamma-Al2O3 (in the outer layer) to alpha-Al2O3 had started during 24 h and a considerable amount of gamma-Al2O3 had transformed after 168 h. The transformation originated immediately above the inward growing alpha-Al2O3. No such transformation occurred in O-2 + H2O. The possible effects of the Y-rich RE particles, as well as the effects of water vapour, on the oxidation were discussed.
reactive element
FIB/SEM
oxidation resistance
oxide scales
Phase transformation
dry
alumina scales
Water vapour
temperature oxidation
o-2
kanthal af
RE
FeCrAl alloy
Microstructure
40-percent
High
adherence
transient oxidation
h2o
EDX
TEM
Al2O3
minor additions
Y
Author
Fang Liu
Chalmers, Applied Physics, Microscopy and Microanalysis
Helena Götlind
Environmental Inorganic Chemistry 1
Jan-Erik Svensson
Chalmers, Chemical and Biological Engineering, Environmental Inorganic Chemistry
Lars-Gunnar Johansson
Chalmers, Chemical and Biological Engineering, Environmental Inorganic Chemistry
Mats Halvarsson
Chalmers, Applied Physics, Microscopy and Microanalysis
Oxidation of Metals
0030-770X (ISSN) 1573-4889 (eISSN)
Vol. 74 1-2 11-32Subject Categories
Chemical Engineering
DOI
10.1007/s11085-010-9195-5