Novel C_sf/SiBCN composites prepared by densifying C_sf/MA-SiBCN with the PIP process: Oxidation behavior and damage mechanism

For the purpose of improving oxidation resistance of short carbon fiber (C_sf) reinforced mechanically alloyed SiBCN (MA-SiBCN) composites (C_sf/MA-SiBCN), the dense amorphous C_sf/SiBCN composites containing both MA-SiBCN and polymer-derived SiBCN (PDCs-SiBCN) matrices were prepared by repeated polymer infiltration and pyrolysis (PIP) process of layered C_sf/MA-SiBCN composites at 1100 ℃, and the oxidation behavior and damage mechanism of the as-prepared C_sf/SiBCN at 1300~1600 ℃ were compared and discussed with C_sf/MA-SiBCN. The C_sf/MA-SiBCN composites resist oxidation attack up to 1400 ℃ but fails at 1500 ℃ due to the collapse of the porous framework, while the PIP densified C_sf/SiBCN composites are resistant to statistic air up to 1600 ℃. During oxidation, oxygen diffuses through pre-existing pores and the pores left by oxidation of carbon fibers and pyrolytic carbon (PyC) to the interior of the matrix. Owning to the oxidative coupling effect of MA-SiBCN and PDCs-SiBCN matrices, a relatively continuous and dense oxide layer is formed on the sample surface, and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains amorphous glassy structure mainly consisting of Si and O and incomplete oxidized but partially crystallized matrix which is primarily responsible for the improvement of the oxidation resistance.