Structural and mechanical properties of a high-performance BN fibre

Abstract : The relationship between the structure, microtexture and mechanical properties of a high-performance polyborazine-based BN fibre has been studied in detail. Techniques such as Raman and IRTF spectroscopies, X-ray diffraction, scanning and transmission electron microscopies and microtraction tests were used. It has been shown that the longitudinal mechanical properties of the fibre directly depend on the microtextural and structural properties. In particular, the Young's modulus in the fibre-axis (E=440 GPa) is directly controlled by the fibre structure: the fibre presents a high degree of alignment of the (002) planes compared with the fibre axis (τ=0.90) and the high value of the elastic modulus in the fibre-axis is attributed to the strong covalent bonds in the basal planes. On the other hand, the ultimate tensile strength (σR=2000 MPa) and the low density (d=1.85 g cm−3) of the fibre are limited by the external defects and the porosity in the volume of the fibre.