# Ceramic Matrix Composites for Aero Engine Applications--A Review
## 7 Manufacturing Processes for CMCs
### Matrix Deposition/Infiltration from a Gas Phase  
Chemical vapor infiltration (CVI) is considered one of the most attractive manufacturing processes for creating fiber-reinforced CMCs [198]. In this process, the porous preform is added in a surrounding of a reactive gas mixture, which decomposes and yields a solid deposit that is concentrated in the pores of the preform when the mixture is thermally activated. This process allows for the creation of preform complex net shape components, at low temperatures, without occurring any damage to the textile structure, which results in controlling and modifying the microstructure of the final matrix [198]. CMCs such as SiC/SiC and C/C composites are fabricated using this process, allowing for excellent high temperature, strength, modulus of elasticity, creep, and corrosion resistance properties, in comparison with other unreinforced SiC composites [199].  
There are several different CVI techniques developed for different composites, with the most well-known one being the isothermal one (I-CVI), used for non-oxide CMCs beginning with Cf/C and moving to SiCf/SiC composites. This process was initially created for the densification of refractory composites [109]. In recent decades, it has been used for the densification of Cf/C for aircraft brakes and SiCf/SiC for aerospace components [200]. Some of the most fabricated matrices with CVI are SiC, C, Si3N4, BN, Al2O3, B4C, TiC, and ZrO2.  
I-CVI is introduced as thermal-gradient CVI (modified CVI) and is used for the manufacturing of large individual parts, such as rocket nozzles [201]. In this method, the preform is heated more uniformly due to the increase in thermal conductivity of the infiltrated preform [202; 203]. The thermal gradient F-CVI deposition has been introduced as a replacement for the I-CVI while working on SiC and Si3N4 matrices with different porous preforms, where the mass transfers occurred by forced convection due to a pressure gradient [199]. [PERSON] et al. researched the practicality of the manufacturing of SiC/SiC components by using the F-CVI process [204]. Furthermore, it has been researched that the infiltration times of the F-CVI process, reporting that the SiC matrix fabrication times were reduced even though the preforms were 2.5 mm thick [205].  
Another alternative technique, called microwave-heated CVI (MW-CVI), is used for controlling the inverse temperature profile of a ceramic fiber preform while heating [205]. It can produce a controllable temperature profile inside a preform [206]. It allows the creation of a temperature gradient from the center of the preform to the outside layers, meaning that the deposition of the ceramic matrix occurs from the inside to the outside, without connecting to the sealing of the outer pores of the preform, that might cause any structural problems [207]. Research on scaling up this process and designing a pilot-scale reactor has been recently published [208].  
Further research shows the evolution of an improved film boiling CVI process for manufacturing large-size Cf/C CMCs by using kerosene as a precursor. The result of this process was a composite produced with rapid CVI with a homogeneous microstructure and density that allowed for good feasibility of the film boiling CVI procedure for large components [209]. Rapid-CVI is particularly applied to C/C composites and is considered to have two different types of fabrication methods. The first method is called boiling film, in which the porous fiber preform is absorbed inside the liquid state precursors [210]. The second method is rapid vapor-phase densification, in which the porous preform is added to a furnace and is isothermally heated by a graphite tool, offering a forced flow to the precursor gas that exists beside the preform and the graphite tool [210].