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

**Yang Li 1,2, Min Ge 1,2, Shouquan Yu 1,3, Huifeng Zhang 1,3, Chuanbing Huang 1,3, Weijia Kong <sup>1</sup> , Zhiguang Wang 1,2 and Weigang Zhang 1,2,3,\***


**Abstract:** Boron nitride (BN) ceramic fibers containing amounts of silicon nitride (Si3N<sup>4</sup> ) were prepared using hybrid precursors of poly(tri(methylamino)borazine) (PBN) and polycarbosilane (PCS) via melt-spinning, curing, decarburization under NH<sup>3</sup> to 1000 ◦C and pyrolysis up to 1600 ◦C under N<sup>2</sup> . The effect of Si3N<sup>4</sup> contents on the microstructure of the BN/Si3N<sup>4</sup> composite ceramics was investigated. Series of the BN/Si3N<sup>4</sup> composite fibers containing various amounts of Si3N<sup>4</sup> from 5 wt% to 25 wt% were fabricated. It was found that the crystallization of Si3N<sup>4</sup> could be totally restrained when its content was below 25 wt% in the BN/Si3N<sup>4</sup> composite ceramics at 1600 ◦C, and the amorphous BN/Si3N<sup>4</sup> 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 Si3N<sup>4</sup> mass content, while an obvious BN (shell)/Si3N<sup>4</sup> (core) was formed only when the Si3N<sup>4</sup> content reached 25 wt%.

**Keywords:** composite ceramic fibers; boron nitride; silicon nitride
