Effects of Temperature and Steam Environment on Fatigue Behavior of Three SIC/SIC Ceramic Matrix Composites; Master's thesis

摘要

The fatigue behavior of two woven SiC-SiNC ceramic matrix composites (CMCs) was investigated at 1300 deg C in laboratory air and in steam. The first composite (C1) consists of a PIP SiNC matrix reinforced with Sylramic (Syl) fibers woven in a five-harness satin weave fabric and coated with a proprietary dual-layer interface. The second composite (C2) consists of a modified PIP SiNC matrix reinforced with Sylramic-iBN (Syl-iBN) fibers woven in a five-harness satin weave fabric and coated with a proprietary dual-layer interface. The tensile stress-strain behavior was investigated and the tensile properties measured at 1300 deg C. Tension-tension fatigue behavior was studied for fatigue stresses ranging from 100 to 180 MPa at 1300 deg C in air and in steam. The presence of steam caused noticeable degradation in fatigue performance of both composites at 1300 deg C. The fatigue limit of the composite C1 (based on a run-out condition of 2 x 105 cycles) was 100 MPa (53% UTS at 1300 deg C) in both air and steam. The fatigue limit of the composite C2 was 160 MPa (66% UTS) in air and 140 MPa (58% UTS) in steam. The retained strength and modulus of all specimens that achieved run-out were characterized. Specimens of both composites tested in air retained 100% of their tensile strength, while the specimens of both composites tested in steam retained only about 90% of their tensile strength.