Damage Of Thermal Shock, Fatigue And Interaction Fatigue-creep Of 3D-C/SiC In Different Environments

3D-C/SiC is a new kind of promising thermal-structural material in aviation and aerospace field. So far, many studies on general properties of 3D-C/SiC have been carried out, but the study on its interaction fatigue-creep and thermal shock behavior, especially at high temperature, has not been reported. Therefore, a systemic and in-depth study is of significant importance for improving, engineering design and application of 3D-C/SiC on the interaction fatigue-creep and thermal shock properties.Thermal shock behavior and interaction fatigue-creep of 3D-C/SiC had been investigated in the three environments (Argon, dry oxygen, wet oxygen) in the preset work. 3D-C/SiC fabricated with T300 carbon fibers weaved into 3-dimensional and 4-directional structure, was deposited pyrocarbon and SiC matrix at 950-1000 with CVI method. Fiber volume fraction of 3D-C/SiC was 40-45%, composite density was 2.01g/cm3 and porosity was 17%. In addition, the thickness of pyrocarbon interface was 200 nm for interaction fatigue-creep; the interface layer of pyrocarbon for thermal shock had three thickness obtained by controlling deposition time which were 10h, 20h, 30h, respectively.The results indicated that thermal shock curve evaluated by Young's modulus was similar to that by electrical resistance, and they approximately consisted of three stages, that is, the rapid damage stage, the stable damage stage, and then the damage sharply accelerated stage. However, exceptional thermal shock curve expressed by electrical resistance only occurred to drop in the initial stage. Moreover, thermal shock behavior of 3D-C/SiC was distinctly superior to that of recrystallization SiC, and when the deposition time of pyrocarbon was 20h, 3D-C/SiC possessed the longest thermal shock life. In the thermal shock under air medium, a main damage form of 3D-C/SiC was that oxidation of carbon fibers had been caused by peel-back of carborundum coating.For 3D-C/SiC composite, the overall tendency of modulus was diminishing with increased cycle number. The interaction fatigue-creep damage evaluated by electrical resistance possessed three stages, including the decelerated damage stage initiatively, the stable damage stage, and then the sharply accelerated damage stage finally. And in the three mediums (Argon, dry oxygen, wet oxygen), the damage in the wet oxygen was the most severe. And under the three conditions (fatigue, creep and interaction fatigue-creep), the damage caused by the interaction fatigue-creep was the most severe. Several types of damage had been identified, including the matrix microcrack, fiber fracture, debonding and sliding between fiber-bundles, and fiber oxygen involved in the interaction fatigue-creep of 30-C/SiC composites.The expressions of interaction fatigue-creep life and of thermal shock damage evaluated by modulus were obtained by the experimental analysis.