High temperature oxidation of the bicrystals of Incoloy alloy 909 and an Fe-36% Ni alloy in air under tensile stress

The bicrystals of both an Fe-36% Ni alloy and Incoloy alloy 909 were oxidiz ed at 1200 and 1250 K in air respectively with a tensile stress of 2.5, 4.9 , or 14.7 MPa. The thickness of external scale, inter granular subscale and intragranular subscale all exhibited linear relationships with the square root of oxidation time, indicating that oxidation followed parabolic law. I n oxidized Fe-36% Ni bicrystals, leading cellular oxide nodules formed in i ntragranular subscale and a tensile stress promoted intergranular oxidation and the formation of cavities at the grain boundary. In oxidized Incoloy a lloy 909 bicrystals, intergranular subscale only slightly led the internal subscale. However, intergranular oxidation was obvious in equiaxed specimen s of this alloy. The external scale was stratified in Fe-36% Ni alloy, but it exhibited cellular or pocket-like structure in Incoloy alloy 909. The la tter alloy possessed a much better resistance to oxidation than the Fe-36% Ni alloy.