Nanochannel Diffusion-Controlled Nitridation of Polycarbosilanes for Diversified SiCN Fibers with Interfacial Gradient-SiC_xN_y Phase and Enhanced High-Temperature Stability

Diversified SiCN fibers with gradient-SiCxNy phase in the interfacial regions between the major phases of carbon-rich SiC phase and Si3N4 phase were prepared via nanochannel diffusion-controlled nitridation of polycarbosilane fibers under different NH3 flow rates. The obtained fibers with excellent mechanical properties showed a different nanostructure and improved high-temperature behavior compared with polysilazane- and polysilylcarbodiimide-derived SiCN ceramics. The enhanced high-temperature properties could be contributed to the inhibition of carbothermal reduction of the Si3N4 phase by the gradient-SiCxNy phase in the interfacial region between the Si3N4 phase and carbon-rich SiC phase. Meanwhile, a suitable amount of interfacial SiCxNy phase as well as the fine distributed microstructure can be helpful to inhibit the high-temperature crystallization of both the SiC phase and Si3N4 phase. Additionally, a nanostructural model has been proposed to understand the effect of interfacial gradient-SiCxNy phase and compositional-dependent high-temperature behavior of obtained SiCN fibers. Our findings provide a novel strategy to prepare SiCN-based ceramic materials with excellent high-temperature stabilities, which we expect to possess great potential in structural and (multi)functional applications at high temperatures and under harsh environments.