Joining of Ceramic Matrix Composites for steelmaking industry applications

This thesis focuses on the development of a joining process for Ceramic Matrix Composites (CMCs) for applications in the steelmaking industry. It is divided into two parts: a bibliographic research in which the materials involved are described in detail, and a second part which includes the experimental activity carried out at the Department of Applied Science and Technology of the Politecnico di Torino within the Glance (Glasses Ceramics and Composites) Group. The main advantages of CMCs over other materials are their high heat resistance, hardness, corrosion resistance and low density. Over the years, CMCs have gained significant importance in industrial applications over single-phase ceramic materials and other materials due to their unique physical properties. They are high-temperature and corrosive-resistant materials able to maintain excellent thermo-mechanical properties in extreme production conditions, i.e., in steelmaking environment. One of the main problems of CMC materials is that their use depends on their ability to be joined, since the manufacturing of CMC large components is complex and expensive. To achieve the set purpose, TiBraze200Nb and TiBraze1450 high-entropy alloys were used to join both oxide- and non-oxide-based CMCs. The latter were also joined using YAS (Y2O3-Al2O3-SiO2) glass-ceramics because of their exceptional compositional and structural stability at high temperatures. Subsequently, the prepared specimens were characterized by scanning electron microscopy and mechanical tests. The challenge of this thesis is to combine the proper process parameters with the appropriate joining method using the most suitable materials TiBraze200Nb alloy containing a binder content lower than 16 wt.% is used as brazing material for oxide-based CMC joints; good results were achieved using a 17-hours air drying and a thermal process which implies a brazing temperature of 1050°C and a post-braze diffusion at 900°C. The non-oxide-based CMC joined with TiBraze1450 alloy with Molybdenum interlayer were manufactured using a brazing temperature of 1440°C and without post-braze diffusion step; they showed improved outcomes if compared to joints obtained using the only high-entropy alloy as brazing material. Satisfactory results were also obtained with non-oxide-based CMCs joined with YAS using a process temperature of 1400°C and a dwelling at 1105°C.