Fatigue of Advanced SiC/SiC Ceramic Matrix Composites at Elevated Temperature in Air and in Steam

Abstract

High-temperature mechanical properties and tension-tension fatigue of three SiC/SiC ceramic composites are discussed. Effects of steam on high-temperature fatigue are evaluated. The three composites consist of a SiC matrix reinforced with SiC (Hi-Nicalon™) fibers. Composite 1 was processed by chemical vapor infiltration (CVI) of SiC into fiber preforms coated with BN. Composite 2 had an oxidation inhibited matrix consisting of alternating SiC and B4C layers and was processed by CVI. Fiber preforms were coated with pyrolytic carbon with B4C overlay. Composite 3 had a melt-infiltrated (MI) matrix consolidated by combining CVI-SiC with SiC particulate slurry and molten Si infiltration. Fiber preforms were coated with BN. Tension-tension fatigue was investigated at 1200°C in air and in steam. Steam significantly degraded the fatigue performance of composites 1 and 3, but had little influence on the fatigue performance of composite 2. Composite microstructure, as well as damage and failure mechanisms were investigated.