Investigations on microstructure and mechanical properties of boron nitride fiber using experimental and numerical methods

Boron nitride (BN) fiber has attracted increasing attentions in the aerospace and other engineering fields due to its outstanding thermal, mechanical and electromagnetic properties. In this paper, the relationship between the microstructure and mechanical properties of BN fiber is investigated using the experimental and numerical methods. The microstructure of BN fiber is characterized by XRD, SEM, and TEM, subsequently a representative model is established via classical molecular dynamics (MD) for revealing the relationship between the mechanical properties and the structures of grain size, grain orientation, and crystallinity. Experimental observations show that the BN fiber is composed of amorphous boron nitride ( a -BN), turbostratic boron nitride ( t -BN) and hexagonal boron nitride ( h -BN), where the h -BN grains with the AB stacking sequences are embedded in a -BN or t -BN. Molecular dynamics (MD) simulation results show that the BN fiber which h -BN grains arranged along the fiber axis has higher Young's modulus and fracture strength. With the increase of crystallinity, the Young's modulus increases and the fracture strength decreases for all the simulation results. In terms of the grain size, there should be a trade-off between the high modulus and high strength of BN fiber, i.e., the former requires larger size of h- BN grains, and the latter needs smaller ones. These findings could not only bridge the microstructure and mechanical properties but also be useful for the synthesis of high-performance BN fiber.