Long-term oxidation performance of SiCf/SiC composites at 1200°C in air atmosphere manufactured by PIP and hybrid CVI/PIP techniques

Abstract

In this paper the long-term oxidation resistance of SiCf/SiC composites manufactured by a single PIP technique and a hybrid CVI-PIP technique at 1200 °C in a static air has been systematically studied. It has been found that after oxidation at 1200 °C for 200 h, SiCf/SiC composites by the hybrid CVI-PIP technique can retain flexural strength as high as 76% and still exhibit a typical quasi-plastic fracture. In contrast, after oxidation for 100 h, SiCf/SiC composites produced by the single PIP technique can only keep 31.8% of their initial flexural strength and demonstrate a typical brittle fracture. An insertion of a dense and crystalline CVI derived SiC layer between fibers/interphase and PIP derived matrix makes the difference. To be specific, for those single PIP derived composites, i.e. without this CVI SiC layer, the fibers/interphase are totally exposed to oxidative environments due to the nature of PIP derived matrix that is porous and full of micro-cracks. Worse still, the oxidized products of PIP derived matrix, viscous and sticky SiO2, tends to tightly wrap up fibers, forming a strong fiber/matrix bond. On the contrary, for those hybrid CVI-PIP derived composites, the dense CVI SiC layer serves as an oxidation barrier, not only blocking the inward flowing of oxygen to invade interphase/fibers, but also precluding the viscous and sticky SiO2 reach fiber surface. The superior properties of SiCf/SiC composites produced by hybrid CVI-PIP technique suggest it be a desirable manufacture technique for industrial applications.