Laser-Assisted Joining of SiC/SiC Composites for Energy Applications

The objective of this Master thesis is to join SiC/SiC ceramic matrix composites by using an Infrared diode laser as a heating method. Currently, operational temperatures in the energy sector are constantly rising, posing significant challenges for materials. In this context, ceramic matrix composites are becoming increasingly important due to their ability to withstand high temperatures, to their “quasi-ductility”, and their low density. Therefore, it is essential to study effective methods for creating joints between these materials. Since SiC/SiC do not melt, the joint will be made using a third material, the joining material. This Master thesis will focus on two different joining materials: SAY (Silica-Alumina-Yttria based glass-ceramic) and YAG (Yttrium-Aluminum Garnet). The methods for applying SAY and YAG powders to the samples will be analyzed, along with the processes and tests conducted to identify the optimized laser parameters to achieve the melting of these materials without damaging the composite. For SAY as joining material, an optimal set of laser parameters was identified, and sound joints were obtained in air, in a few seconds laser joining process. Additionally, the results of the ad-hoc mechanical tests performed on the obtained samples will be presented, done by using a specifically designed compression test, aimed to detach a laser joined SiC/SiC end-plug from the SiC/SiC tube. Under the optimized laser joining conditions, nearly all samples joined by SAY achieved a considerable strength during the mechanical test, in some cases leading to the SiC/SiC tubes fracture. Laser parameters for YAG as joining material still must be optimized to achieve the complete melting of YAG without compromising the integrity of the ceramic matrix composite.