Erkut CORA, BSc. Student
Metallurgical and Materials Engineering
Yıldız Technical University
Development of B4C-CaB6-TiB2 Ceramic Matrix Composites
Co-Supervisors: Emirhan Karadağlı, Oğuz Karaahmet, Assoc Prof. Dr. Buğra Çiçek
Boron carbide is commonly used in material science due to its advanced properties. Generally, its advanced properties are low density (2.52 g/cm3), high hardness (HV = 29.1 GPa) and its high melting temperature (2450 ˚C). It is also very stable against chemicals and abrasion –. These unique and superior properties provide boron carbide to be able to use in the areas where extreme conditions are applied. These properties are highly related with its strong covalent bonds between boron and carbon atoms. Boron carbide stoichiometrically based solid that contains 9-20% carbon. The carbon content can be up to 10% depending on the temperature, In the systems containing less than 9% the melting point decreases with excess boron. In systems that contain more than 20% carbon, the melting point decreases since graphite formation occurs. There is a visible decrease in mechanical properties due to this formation , .
These strong covalent bonds that actually lead to superior properties of the material also make this material to be hardly sintered and brittle. Monolithic boron carbide needs very high temperatures (1800-2200 ˚C) and high pressures (20-50 MPa)* to be sintered for obtaining high densities. These difficulties concerning high sintering temperature and pressure can be reduced by introducing additives to the green body. These additives can have infinitesimal numbers of types.
Addition of these additive materials will end up with the decrease in the properties of monolithic boron carbide. TiB2 is one of these additives, in the presence of this material to boron carbide system, sintering temperature reduces significantly and crack propagation can be highly controlled and consequently higher fracture toughness values can be achieved.
There are a few studies on the composites that Calcium Hexaboride is as an additive to Boron Carbide. Apart from other additives, due to the similar physical and chemical properties of Calcium Hexaboride to Boron Carbide, sintering is easier and reduction in mechanical properties are low.  Additionally, when CaCO3 used as a source of CaB6 during reactive sintering at high temperature decreases the costs of the production. 
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 DEVELOPMENT OF BORON CARBIDE - CALCIUM HEXABORIDE CERAMIC COMPOSITES Yasin Bozkurt YILMAZ, MASTER THESIS
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