• computed tomography
• filament winding
• chemical vapour infiltration
• ceramic matrix composite

Ceramic Matrix composite (CMCs) are a class of composite materials obtained by combining a reinforcing ceramic phase with a ceramic matrix showing a high toughness, compared to other monolithic ceramics, along with high-temperature stability, low density, high thermal shock resistance, high hardness, and high corrosion resistance, thus making them potential candidate to replace conventional alloys employed in high-temperature applications.
Many high-temperature processes will gain benefits from the use of this class of composites, thanks to their high performance in demanding and harsh conditions. The main drawbacks are mostly linked to the current applied manufacturing processes which require expensive batch processes at high temperatures and in controlled atmosphere thus leading to a final cost for a CMC component from some hundred to some thousands of euro/kilogram and limiting their usage. Therefore, several studies on CMCs have focused on the development of cheaper, more efficient and cleaner fabrication methods. The latter is one of the main objectives of the European CEM-WAVE project (GA n°958170), in which the purpose is to develop an innovative CMC production process with higher energy efficiency, reduced CO2 emissions and production costs. In according with those principles, this master degree work aims to make a little step ahead facing some of the previously discussed challenges by proposing the usage of a Microwave-assisted Chemical Vapour Infiltration (MW-CVI) technology as a clean, economic and efficient solution for a widened usage of CMCs.
The application of a microwave-assisted heating is an attractive alternative, being a clean and more efficient source of thermal energy thanks to its peculiarity of obtaining an inverse temperature profile in the sample. The volumetric heating mechanism coupled with surface heat losses results in higher temperatures in the centre of the material. That allows for the MW-CVI process to start from the heart of the preform continuing towards the surface as the density of the sample increases. The premature occlusion of the pores can thus be completely avoided overcoming one of the fundamental technological problems of conventional CVI with considerable reduction in processing times and costs. Nevertheless, the use of a MW heating generally leads to additional problems and challenges for the effective processing of materials. One of the crucial aspects deals with the manufacturing of CMC preforms characterized by good dielectric properties and a reinforcing architecture allowing the passage of the reactive gases throughout the material.
Therefore, this work has investigated the manufacturing process of a SiC/SiC composite based on Microwave-assisted Chemical Vapour Infiltration technologies. Here, the non-destructive micro computed tomography (µCT) has been employed to investigate the internal microstructures of the fibrous preforms, which correspond to the CMC composed by the only fibres in the initial part of the process. These samples have been produced by a filament winding (FW) technique and the result of that operation has been examined by the µCT. The fibrous preform had two possible geometries, a hollow tube with a circular section and a hollow tube with a rounded-square section, allowing an investigation of the FW performance for an axisymmetric structure and a non-axisymmetric structure. Then, the MW-CVI process has been performed on a fibrous preform to densify the SiC fibre reinforced preform with the SiC matrix. Combining the data from the infiltration and the data from the (µCT), the influence of the filament winding process on the MW-CVI densification of the SiC/SiC composites have been evaluated optimizing the preform manufacturing steps in order to improve the matrix infiltration process.