# Ceramic Matrix Composites for Aero Engine Applications--A Review
## 7 Manufacturing Processes for CMCs  
As highlighted in Section 6, CMCs exhibit mechanical and thermal properties comparable with, and in some cases, even better than, the conventional superalloys used in aero-engines. However, their adoption relies on other variables as well, such as the cost of development, industrialization, manufacturing, and the availability of manufacturing technologies and systems. In this section, the manufacturing capabilities and technologies associated with the fabrication of CMCs will be discussed.  
Figure 14: Comparison of (**left**) maximum service temperature and (**right**) thermal shock resistance of CMCs.  
Figure 13: Comparison of maximum service temperature vs. thermal shock resistance of available CMCs.  
Until recently, there has been a small number of manufactured CMC materials which mostly include carbon fibers embedded in a silicon carbide matrix fabricated with chemical vapor infiltration and some oxide-oxide aluminosilicate matrices combined with sintering and sol-gel infiltration process. As a result, there is a high demand for the fabrication of a variety of CMC components fabricated with efficient processes allowing for lower processing times, cost, and greater mechanical and thermal attributes. This is achieved with the embodiment of a wider range of ceramic materials apart from C/SiC or C/C composites, which can also be pre-impregnated with carbon/carbon materials and pre-ceramic polymer, processed with the already existing manufacturing processes. Research also indicates that no special interface is needed to fabricate low-cost CMC structures or implement prepreg when a separated fiber/matrix interphase is not required. These combinations of materials can include amorphous variations of Si-O-N-C, HfC, SiC, HfC, etc. Ceramic components are produced mainly from polymer infiltration pyrolysis (PIP), melt infiltration (MI), sintering processes, and chemical vapor infiltration (CVI) [183]. The typical methods used for CMC fabrication are summarized in Figure 15.  
The processing can be grouped in a three-step series, which every CMC material goes through to achieve the needed mechanical, thermal, and physical properties [184]. The first step consists of a lay-up and fixation of the fibers, formed according to the required component geometry. The second step consists of the infiltration of the matrix material. This step includes five different procedures, which are needed to fill the ceramic matrix in between the fibers and the pre-form. These infiltration procedures are sintering at a significantly low temperature (1000-1200 \({}^{\circ}\)C), pyrolysis of a pre-ceramic polymer, chemical reaction of elements, deposition retrieved from a gas mixture, and finally, electrophoretic deposition of a ceramic powder [184; 109; 185].  
Non-oxide CMCs are manufactured with deposition out of a gas mixture, pyrolysis of a preceramic polymer, or chemical reaction of elements. Oxide CMCs are manufactured by sintering or electrophoretic deposition of a ceramic powder [185; 186]. The third and final step consists of machining and, if required, coating or impregnation of the intrinsic porosity [185]. In the following paragraphs, the most frequently used manufacturing processes will be reviewed.