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

摘要

The bicrystals of both an Fe-36 percent Ni alloy and Incoloy alloy 909 were oxidized 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. In oxidized Fe-36 percent Ni bicrystals, leading cellular oxide nodules formed in intragranular subscale and a tensile stress promoted intergranular oxidation and the formation of cavities at the grain boundary. In oxidized Incoloy alloy 909 bicrystals, intergranular subscale only slightly led the internal subscale. However, intergranular oxidation was obvious in equiaxed specimens of this alloy. The external scale was stratified in Fe-36 percent Ni alloy, but it exhibited cellular or pocket-like structure in Incoloy alloy 909. The latter alloy possessed a much better resistance to oxidation than the Fe-36 percent Ni alloy.