Effect of surface deposited rare earth oxide gel characteristics on cyclic oxidation behavior of Fe20-Cr alloys

Abstract

Rare earths have been used to increase high temperature oxidation resistance of many chromium dioxide and alumina forming alloys. These rare earths can be added as elements (or as oxide dispersions) to the alloys or applied as an oxide coating to the alloy surface. The sol-gel technique is considered to be very efficient to apply fine oxide particle coatings. Oxide gel coatings of various rare earths such as lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, yttrium, erbium and ytterbium have been applied to an iron-chromium alloy to determine their influence on the cyclic oxidation behavior (RT-900 °C) of the alloy. The morphology and coverage of the rare earth oxide gels varied with the type of rare earth. The cyclic oxidation resistance of the alloy increased with increase in time at temperature required to reach a specific chromium dioxide layer thickness and this in turn was influenced by the rare earth ion radius and characteristics of the rare earth oxide coating such as morphology, stability, coverage, resistance to thermal stresses and consequently adhesion

Cyclic oxidation resistance of rare earth oxide gel coated Fe-20Cr alloys

“…The morphology of the RE oxide gels varied with the nature of the RE and the main morphological features of the different RE oxides are summarized in Table 1 9 .…”

“…The morphology of the different RE oxide gels revealed marked differences 3,9 . Correlations between the morphology of the RE oxide and the COR of coated Fe-20Cr alloy have been reported 9 .…”

“…and Yb 2 O 3 ) on cyclic oxidation behavior of Fe-20Cr alloy specimens 1.0 x 1.0 x 0.5 cm was studied. Details of the procedure used to prepare the sol and the gel coatings can be found elsewhere 9 . The RE oxide gel layers were about 10 µm thick.…”

“…The effect of other rare earth oxides or rare earth oxide concentrates on oxidation behavior of chromia and alumina forming alloys showed the marked effect of rare earth oxides on chromium dioxide growth and this was more than that on alumina growth 7,8 . A direct correlation between the RE ion radius and the extent of protection of chromium dioxide forming alloys at temperatures up to 900 °C has been reported 9 . Certain RE oxide coat characteristics also had a marked effect on oxidation behavior of iron-chromium alloys 9 .…”

“…A direct correlation between the RE ion radius and the extent of protection of chromium dioxide forming alloys at temperatures up to 900 °C has been reported 9 . Certain RE oxide coat characteristics also had a marked effect on oxidation behavior of iron-chromium alloys 9 .…”