The effect of platinum additions on the oxidation of directionally-solidified Ni-Cr-Al-Y-Cr3C2 alloys at 1,100 and 1,200 degrees C

Citation
Fh. Stott et al., The effect of platinum additions on the oxidation of directionally-solidified Ni-Cr-Al-Y-Cr3C2 alloys at 1,100 and 1,200 degrees C, MATER HIGH, 16(1), 1999, pp. 15-26
Citations number
37
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Material Science & Engineering
Journal title
MATERIALS AT HIGH TEMPERATURES
ISSN journal
0960-3409 → ACNP
Volume
16
Issue
1
Year of publication
1999
Pages
15 - 26
Database
ISI
SICI code
0960-3409(1999)16:1<15:TEOPAO>2.0.ZU;2-Y
Abstract
The effects of 2wt% platinum addition on the oxidation behaviour of directi onally-solidified, yttrium-containing Ni-Cr-Al-Cr3C2 alloys (Ni-12.3Cr-6.9A l-1.8C-0.2Y in wt%) at 1,100 degrees and 1,200 degrees C in oxygen have bee n investigated under isothermal and thermal cycling conditions. Owing to th e presence of yttrium, aluminium oxidized externally rather than internally at both temperatures. At 1,100 degrees C, the addition of platinum apparen tly favoured the formation of a continuous Al2O3 scale over primary carbide s intersecting the alloy surface. The scale remained substantially adherent after isothermal oxidation, but lifted and cracked on thermal cycling, tho ugh it did not spall significantly. Overdoping with yttrium (0.7 wt%Y) had a detrimental effect on the scale adherence, probably because it altered th e homogeneity of the platinum distribution by forming Pt-Y intermetallics. At 1,200 degrees C, an external Al2O3 scale formed initially, but spalled e xtensively after short times under both isothermal and thermal cycling cond itions. During cyclic oxidation, re-formation of an aluminium scale was pos sible until a critical level of aluminium depletion in the alloy was reache d, with the less protective oxides forming during the subsequent oxidation cycles. The inherent lack of ductility of the Al2O3 scale over the carbide particles, coupled with the CrO3 vaporization at high temperatures, could a ccount for the observations.