Boron carbide products have a unique combination of properties: high hardness, high modulus of elasticity, high thermal conductivity, resistance to aggressive environments. The covalent nature of the chemical bond makes boron carbide a difficult-to-compact material and requires the use of sintering temperatures of 0.9-0.95 T melting point. Use such sintering methods as hot pressing, SPS, which involve the simultaneous application of pressure with high temperature. These methods significantly limit the size and shape of the obtained products, have low productivity and are very energy intensive. As a result, the high cost of boron carbide products significantly limits its use. It is important to look for methods of obtaining reinforced ceramic materials based on boron carbide with relatively low consolidation temperatures than in the methods of hot pressing and SPS. The dissertation work is devoted to the decision of the actual scientific and technical problem - creation of the reinforced ceramic materials based on B4C for work in extreme conditions of operation with high physical and mechanical properties.
In order to create reinforced ceramics based on B4C, the paper considers the possibility of obtaining ceramic composites of the B4C-Si-Cf system using the method of infiltration of porous samples with B4C by silicon melt. The infiltration method allows to reduce the temperature of high-density ceramics B4C with high mechanical properties.
The influence of technological parameters on the microstructure, phase composition and mechanical properties of B4C ceramics was studied on infiltrated samples with different initial porosity and carbon-containing binder. Microstructure studies have shown that a decrease in the initial porosity leads to a decrease in the size of the secondary B4C grains due to the dissolution and interaction of the starting particles with the silicon melt. The morphology of SiC particles changes from elongated to multifaceted, irregular shape. The reduction of the initial porosity affects the phase composition of the ceramic: the number of phases B4C and SiC decreases, and the residual silicon increases.
In order to determine the effect of carbon fiber reinforcement on the structure, phase composition and physical and mechanical characteristics of B4C-based ceramics, infiltrated samples with different contents (0, 5, 10, 15 and 20%) of carbon fiber (BB) to the original B4C powder were investigated. It is established that the increase in the content of carbon fibers contributes to the increase of the formed phase of SiC with a simultaneous decrease in the amount of residual silicon. Metallographic studies have shown that in the process of interaction of silicon melt with carbon fibers, composite fibers with the structure "core (C) -shell (SiC)" are formed. The maximum value of flexural strength (510 ± 27 MPa) of the obtained B4C ceramics is achieved by adding 10% of carbon fibers to the original B4C powders. The highest value of the Young's modulus (380 GPa) is achieved at an explosive content of 20 %. A study of the physical properties (electrical conductivity and CTE) of B4C ceramics found that with increasing concentration of carbon fibers, the electrical conductivity increases and CTE decreases.
In order to establish the influence of treatment in the field of controlled temperature gradient (CTG) on the structure, phase composition and mechanical properties of B4C-based ceramics, pre-infiltrated B4C samples with different particle size distribution obtained by zone melting were studied. Metallographic studies have shown that the use of B4C infiltrated ceramics in CTG leads to recrystallization of B4C through silicon melt, followed by the formation of composites with a strong framework of small B4C grains. At the same time, it is possible to control the content of silicon carbide in the infiltrated composite by changing the particle size distribution of the original powder B4C. It was found that the use of CTG treatment leads to a decrease in the amount of residual silicon in B4C-based ceramics due to the growth of SiC grains that are in B4C ceramics after infiltration. The application of treatment in CTG leads to an increase in the hardness of B4C ceramics due to the significant content of phases with high hardness. Increasing the processing speed in CTG from 5 to 10 mm/s leads to an increase in the value of tensile strength of composites from 138±8 MPa to 169±10 MPa due to grinding of the ceramic structure and the formation of lamellar particles β-SiC.
According to the obtained scientific and experimental results, reinforced composite materials based on B4C were obtained by the method of infiltration of silicon melt. The use of carbon fiber reinforcement can increase the mechanical properties of infiltrated ceramics. Ceramic plates were obtained from infiltrated reinforced samples for use as components of the edges of the glider of unmanned aerial vehicles.
