Tensile and in Situ Fibre Properties of 3-D SiC/SiC-Based Composite Tested at Elevated Temperature in Vacuum and Air with and Without an Oxidation Protection System

Abstract

In this study, a 3-D woven SiC/SiC-based composite was manufactured with and without an oxidation protection glass-based sealant and tested in tension up to 1380 oC in vacuum and air. Stress/strain curves showed sealed specimens tested in air to have similar mechanical properties to those of unsealed specimens tested in vacuum at elevated temperature (400 MPa strength and 1.2% strain to failure at 1200 oC) and significantly improved compared to unsealed specimens tested in air. Creep testing of the sealed composite at 1100 oC and 1200 C in air indicated lifetimes significantly greater than those achieved for previous materials. In a similar manner, in situ fibre strength Weibull parameters and fibre/matrix interface shear strength were found to be essentially similar for sealed specimens tested in air and unsealed specimens tested in vacuum. Overall, these results indicated the oxidation protection system utilised to be extremely effective for shortand medium-term exposure up to at least 1200 oC in air. INTRODUCTION Structural materials for applications above 1100 oC are expected to increasingly rely on ceramic matrix composites (CMCs) which utilise continuous fibre reinforcement. Woven multi-directional CMCs are thought to have the best compromise between good mechanical properties and ease of manufacture. Currently envisaged applications for CMCs include afterburner flaps, rocket combustion chamber, turbine disk, and airframe structures for re-entry vehicles. However, operation within aggressive environments is limited by extreme sensitivity of the fibre/matrix interface to oxidation [1] and subsequent deterioration of mechanical properties [2]. One method to protect the fibre/matrix interface against oxidation is through impregnating or sealing the composite surface with a barrier material to reduce oxygen diffusion into the composite. The present work investigates the effectiveness of an oxidation protection system for a 3-D woven SiC/SiC-based composite tested in tension up to 1380 oC in vacuum and air. Ref: I. J. Davies, T. Ishikawa, N. Suzuki, M. Shibuya, T. Hirokawa and J. Gotoh, “Tensile and in situ fibre properties of 3-D SiC/SiC-based composite tested at elevated temperature in vacuum and air with and without an oxidation protection system”, Ceram. Eng. Sci. Proc., 19(3) pp. 275-280 (1998).