Tension-Compression Fatigue of a SiC/SiC Ceramic Matrix Composite at Elevated Temperature

Abstract

Tension-compression fatigue behavior of a nonoxide ceramic composite with a multilayered matrix was investigated at 1200 °C in laboratory air. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in an eight-harness-satin weave (8HSW). Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Tension-compression fatigue behavior was studied for fatigue stresses ranging from 80 to 200 MPa at a frequency of 1.0 Hz. The R ratio (minimum stress to maximum stress) was −1.0. Fatigue run-out was defined as 2 × 105 cycles. Fatigue limit was 80 MPa. Specimens that achieved fatigue run-out were subjected to tensile tests to failure to characterize the retained tensile properties. The material retained 100% of its tensile strength. Reductions in tensile modulus and in compressive modulus were negligible. Composite microstructure, as well as damage and failure mechanisms were investigated.