Oxidation behavior of Cr2AlC ceramics at 1,100 and 1,250 C

The isothermal oxidation behavior of Cr2AlC ceramics oxidized in air at 1,100 and 1,250 C for 20 h was studied. The phase compositions and microstructure of the oxidized surface were identified and observed by XRD and electron probe microanalysis (EMPA), respectively, while the cross sections of oxidized samples were also examined by EMPA equipped with energy dispersive spectrum capabilities. The results indicated that the oxidation of Cr2AlC samples was carried out by the outward diffusion of Al, together with small amounts of Cr, and the inward diffusion of O to form a surface layer of a-Al2O3, while carbides (Cr7C3 and Cr3C2), rather than oxides (Cr2O3), were formed in a layer under the surface. The mass gain per unit surface area of oxidized Cr2AlC followed a parabolic relation with oxidation time, and the parabolic rates, kp, for oxidation at 1,100 and 1,250 C were 1.1 9 10-12 and 7.1 9 10-10 kg2 m4 s-1, respectively