Stress engineering of SiCf/SiC composites: Interfacial stress adjustment and its effects on tensile behaviors of UD SiCf/SiC composites fabricated by hybrid CVI and PIP methods

Abstract

Internal stress is usually generated during the preparation of the SiCf/SiC composites and is generally considered to be uncontrollable and detrimental to SiCf/SiC composite's mechanical properties. However, in this study, internal stress is proposed for the first time as a tool to regulate the interfacial bonding properties of the SiCf/SiC composites. And the interfacial compressive stress was successfully controlled by hybrid CVI and PIP methods. The results of Raman analysis show that the interfacial compressive stress increases with the increase of the PIP SiC content. The interfacial shear strength (τi) and interfacial dynamic friction strength (τf) was determined by micro-shear tests. Both τi and τf increase with the increase of interfacial compressive stress. With different interfacial bonding strength, the SiCf/SiC composites show different tensile behaviors. A high τi can lead to a high tensile modulus and proportional limit stress (PLS) and a high τf can lead to the disappearance of the second linear stage and low fracture strain. The axial residual stress of matrix also was tested, and the results indicate that it does not have a dominant influence on the mechanical properties. Finally, the SiCf/SiC composites achieve the superhigh PLS of 729.8 ± 9.2 MPa and modulus of 288.0 ± 7.9 GPa when the BN thickness is 100 nm and the interfacial compressive stress is 1127.7 MPa. This strategy of interfacial stress engineering may provide a new and valuable design idea for improving the mechanical properties of the SiCf/SiC composite and other composites. This strategy is also of great significance for broadening the design criteria and enriching the preparation methods and internal stress regulation methods of high-performance composites.