High Termperature Oxidation Behavior And Mechanism Of Mechanical-alloyed(MA) SiBCN Ceramic

SiBCN ceramic has excellent phase stability, creep resistance and oxidation resis-tance in high temperature that draws many researchers’ attention. However, neither e-nough researches of bulk SiBCN ceramic was investigated nor researches of the relation-ship between the microstructure and the oxidation resistance. In this paper, oxidationbehavior and kinetics of SiBCN ceramic under1100°C to1500°C, the contribution ofBN(C) and the diffuison of oxygen during oxidation proces were studied.Bulk MA SiBCN, MA SiC and MA SiC-BN ceramics were prepared by mechanicalalloying and hot pressing route. The evolution of surface and intersection morphologywith time ranging from1h to20h at1100°C,1300°C and1500°C were studied by SEM.Amorphous SiO2and critobalite were found in the oxidation scale of MA SiBCN. Severbubble formation was found in MA SiBCN ceramic after1300°C20h or1500°C10h,while bubble formed after1300°C1h in MA SiC-BN. The oxidation scale of MA SiBCNhas a good cohesion with matrix and is pore-free from1100°C to1500°C up to20h. Smallpores were found in the interface between oxidation scale and matrix in MA SiC ceramicat1500°C. Oxidation scale of MA SiBCN is dense and uniform at1100°C to1500°C, butthat of MA SiC-BN become porous when temperature above1300°Cand the oxidaitontime increase.XPS analysis shows that the C-B-N bond content relative to all bonds of boron in-creased after oxidation in the surface of MA SiBCN ceramic under1100°C to1500°C,which proofs that C-B-N bond has higher chemical stability at high temperature oxidation.Decarbon phenomenon during oxidation is due to the prior oxidation of graphite-carbonby the assitance of oxygen. The isotope oxidation shows that the oxygen diffusion methodin the oxidation scale of MA SiBCN ceramic is mainly the lattice substitutional diffusionrather than molecular interstitial diffusion found in MA SiC. The estimated diffusion co-efficient of oxygen in the oxidation scale of MA SiBCN ceramic is larger than that ofcristobalite. TEM analysis shows single-layer-structure of oxidation scale with good co-hesion. The parabolic constants of MA SiBCN ceramic at1100°C,1300°C and1500°Care0.410μm2/h，0.827μm2/h and11.7μm2/h, respectively.