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

摘要

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 α-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, k _p, for oxidation at 1,100 and 1,250 °C were 1.1 × 10−12 and 7.1 × 10−10 kg2 m4 s−1, respectively.