Kn. Lee et Wl. Worrell, HIGH-TEMPERATURE OXIDATION BEHAVIOR OF IRIDIUM-BASED ALUMINA-FORMING TERNARY INTERMETALLICS, Oxidation of metals, 41(1-2), 1994, pp. 37-63
The oxidation behavior of iridium-based intermetallics in the ternary
iridium-aluminum-silicon system has been investigated. Additions of up
to 20at.% silicon to, iridium-aluminum binary alloys reduce the alumi
num concentration necessary for the formation of a protective alumina
scale from greater than 55 at.% in the absence of silicon to as low as
20 at.% when 20 at.% silicon, is present. Ternary iridium-aluminum-si
licon alloys with 30-50at.% aluminum and 8-10at.% silicon exhibit para
bolic oxidation behavior, and the rate constants are in good agreement
with those previously determined for binary iridium-aluminum alloys.
The oxidation rate of ternary iridium-aluminum-silicon alloys with 10a
t.% silicon and 30-40 at.% aluminum deviates from the parabolic-oxidat
ion behavior for alumina scale growth in the later oxidation stage, pr
esumably due to the formation of a silica inner layer. Thermal cycling
of the Ir-50 Al-8Si and Ir-60-Al samples does not result in scale spa
llation due to the coefficient of thermal expansion match between the
alumina scale and intermetallic substrate.