Theoretical investigation on structure, mechanical performance and oxidation resistance of the boron-doped PyC interphase in SiCf/SiC composites

Abstract

Pyrolytic carbon (PyC) is widely used as the interphase in SiCf/SiC composites because of the crack deflection capability originating from its weakly bonded layered structure. However, the poor oxidation resistance limits its application in SiCf/SiC. Boron doping can improve oxidation resistance due to the crack-healing effects of boron oxide. To explore the optimal boron doping content in PyC interphase, structure characters and mechanical properties of C128−xBx (x = 8, 20, 32, 44, 64) were simulated by ab-initio molecular dynamics. Modeling results suggest a transition of C128−xBx from layered to amorphous accompanied by a change of its elasticity tensor from strongly anisotropic to nearly isotropic. The predicted optimal boron content is near 34 at%, at which the B-doped PyC maintains a layered structure with a high crack deflection potential according to the Cook & Gordon model while having a high crack-healing capability with a large volume expansion factor.