THE EFFECT OF Y AND TI ON FECRAL OXIDATION AT 1400-DEGREES-C

Inco alloy MA956 (Fe-20wt%Cr-4.5%Al-0.35%Ti + 3vol% Y2O3-Al2O3) was oxidized in 1 atm of dry, flowing O2 at 1400-degrees-C. Good scale-metal adhesion was observed. Some spalling occurred upon cooling, but it remained within the oxide, not through to the bare metal. Cyclic experiments showed good scale adherence. Y was found to segregate to the oxide grain boundaries and by implication to have modified oxidation behavior through a reactive element effect. However, while at lower temperatures Ti was also found to segregate, at 1400-degrees-C very little segregation was detected. Instead, almost-equal-to 0.5 mum TiN(x) particles were observed in the scale. These particles appear to have cracked the surrounding oxide during cooldown. It is postulated that the spallation observed was due to these particles. MA956 was compared to Kanthal alloy APM (Fe-20%Cr-5.5%Al-0.03%Ti + almost-equal-to 2vol%ZrO2-Al2O3) and a conventionally-cast Fe-20%Cr-10%Al alloy, in order to study the effect of Y and Ti.