Characterization and Microstructural Evolution of Continuous BN Ceramic Fibers Containing Amorphous Silicon Nitride

Boron nitride (BN) ceramic fibers containing amounts of silicon nitride (Si(3)N(4)) were prepared using hybrid precursors of poly(tri(methylamino)borazine) (PBN) and polycarbosilane (PCS) via melt-spinning, curing, decarburization under NH(3) to 1000 °C and pyrolysis up to 1600 °C under N(2). The effect of Si(3)N(4) contents on the microstructure of the BN/Si(3)N(4) composite ceramics was investigated. Series of the BN/Si(3)N(4) composite fibers containing various amounts of Si(3)N(4) from 5 wt% to 25 wt% were fabricated. It was found that the crystallization of Si(3)N(4) could be totally restrained when its content was below 25 wt% in the BN/Si(3)N(4) composite ceramics at 1600 °C, and the amorphous BN/Si(3)N(4) composite ceramic could be obtained with a certain ratio. The mean tensile strength and Young’s modulus of the composite fibers correlated positively with the Si(3)N(4) mass content, while an obvious BN (shell)/Si(3)N(4) (core) was formed only when the Si(3)N(4) content reached 25 wt%.