Novel C <sub>sf</sub>/SiBCN composites prepared by densifying C <sub>sf</sub>/MA-SiBCN with the PIP process: Oxidation behavior and damage mechanism
Wenhao Dou, Daxin Li, Bingzhu Wang, Zhihua Yang, Jun Chen, Dechang Jia, Ralf Riedel, Yu Zhou
Abstract
For the purpose of improving oxidation resistance of short carbon fiber (C<sub>sf</sub>) reinforced mechanically alloyed SiBCN (MA-SiBCN) composites (C<sub>sf</sub>/MA-SiBCN), the dense amorphous C<sub>sf</sub>/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<sub>sf</sub>/MA-SiBCN composites at 1100 ℃, and the oxidation behavior and damage mechanism of the as-prepared C<sub>sf</sub>/SiBCN at 1300~1600 ℃ were compared and discussed with C<sub>sf</sub>/MA-SiBCN. The C<sub>sf</sub>/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<sub>sf</sub>/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.