OXIDATION OF HIGH-TEMPERATURE ALLOYS (SUPERALLOYS) AT ELEVATED-TEMPERATURES IN AIR .1.

Four commercial alloys-Hastelloy C-4, alloy 1.4306S (SS 304L), Incoloy 800H, and Incoloy 825-were studied for their oxidation behavior at el evated temperatures. Specimens were exposed to air from 600 to 1200-de grees-C for 1 to 400 hr. Reaction kinetics of oxidation were determine d, and the morphology of the surface-oxide scales was investigated Has telloy C-4 showed better resistance to oxidation for exposure temperat ures up to 1000-degrees-C in comparison with the other three alloys. I n this temperature range, it follows a cubic rate law of oxidation due to formation of uniform, protective, and adherent oxide scales. The l atter three alloys obeyed the parabolic rate law at 1000-degrees-C and 1200-degrees-C, but for lower temperatures a mixed behavior was shown . The oxide layer developed on the alloy 1.4306S was always in the for m of stratified nodules/warts. For longer exposures the nodules joined each other to form continuous but discrete layers. Incoloy 800H and I ncoloy 825 behaved in an almost identical manner, their reaction kinet ics being governed by the parabolic rate law throughout the temperatur e range. Oxide spalling was observed at all temperatures. In contrast to Incoloy 800H the Incoloy 825 was totally oxidized for longer exposu res at 1200-degrees-C.