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

To improve the oxidation resistance of short carbon fiber (Csf)-reinforced mechanically alloyed SiBCN (MA-SiBCN) (Csf/MA-SiBCN) composites, dense amorphous Csf/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN (PDCs-SiBCN) were prepared by repeated polymer infiltration and pyrolysis (PIP) of layered Csf/MA-SiBCN composites at 1100 °C, and the oxidation behavior and damage mechanism of the as-prepared Csf/SiBCN at 1300–1600 °C were compared and discussed with those of Csf/MA-SiBCN. The Csf/MA-SiBCN composites resist oxidation attack up to 1400 °C but fail at 1500 °C due to the collapse of the porous framework, while the PIP-densified Csf/SiBCN composites are resistant to static air up to 1600 °C. During oxidation, oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon (PyC) to the interior of the matrix. Owing to the oxidative coupling effect of the 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 an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix, which is primarily responsible for improving the oxidation resistance.