# Ceramic Matrix Composites for Aero Engine Applications--A Review
## 5 Non-Oxide CMCs
### Silicon Carbide Matrix CMCs  
Silicon carbide fibers have high tensile strength, high elastic modulus, and very good thermal stability, making them one of the best candidates for reinforcement [129; 132]. Silicon carbide ceramic matrix composites include a silicon carbide matrix phase and a fiber phase, fabricated with various manufacturing processes. The SiC fiber preform is infiltrated and densified with a SiC matrix, enhancing the final composite with improved mechanical and thermal properties. Monolithic SiC ceramics have very low fracture toughness and cannot withstand very high temperatures, issues that are addressed by SiC/SiC CMCs [129; 133].  
Silicon carbide CMCs are one of the most popular composites used for high-performance applications. This is due to having lower density, higher toughness, higher damage tolerance, and better creep and wear resistance than other carbon fibers and ox ide/oxide CMCs or monolithic ceramics [129; 134]. SiC/SiC CMCs have higher temperature capability, lower thermal expansion, and better thermal conductivity than most metallic superalloys and CMCs, as well as monolithic ceramics [135; 129; 136].  
It has been found that SiC fibers manufactured with polymer pyrolysis serve a finer and more flexible diameter form rather than those produced with CVD or sintering processes [136]. On the other hand, SiC/SiC CMCs are used in aircraft applications such as turbine engine hot section components [137]. In recent years melt infiltration (MI) of SiC/SiC CMCs succeeded at a temperature limit of 1316 \({}^{\circ}\)C due to the existence of silicon in the matrix [138]. MI process increases maximum porosity levels, allowing for lower thermal conductivity and lowering the thermal shock resistance [138]. The correct fabrication of the fiber/matrix interphase allows deflecting matrix cracks and prevents early failure of the fibrous reinforcement [139; 140; 141].  
Research also indicates that SiC/SiC CMC systems, made from up to 45% of the volume fraction of woven and quasi-isotropic laminate silicon carbide fibers, can withstand temperatures up to 1300 \({}^{\circ}\)C, which are well above the temperature resistance capability of any metallic alloy [142]. By using this type of CMC material, the MI step for filling pores in the SiC matrix can be eliminated [143]. After testing the mechanical and thermal properties of the SiC/SiC, it was also shown that this type of CMC fabricated with the CVI processes offered greater tensile strength and strain, as well as better thermal shock resistance [144]. Furthermore, studies proved that the creep and fatigue behavior could be increased through the chemical vapor infiltration-processed SiC matrices that were reinforced with low modulus SiC fibers such as Hi-Nicalon in a range of 1000-1300 \({}^{\circ}\)C [145].  
Results showed that woven laminates were able to withstand high temperatures without microcracking, but in lower temperatures, results showed that creep and fatigue occurred in the composites after a few hours [146]. This allows them to be used as components in gas turbine applications, thruster nozzles, and heat exchanger applications.