Effect of reaction sintering modes on the structure and properties of carbide ceramics

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Experimental studies of the structure, phase composition, physical and mechanical properties of the reaction-sintered ceramics based on silicon carbide and boron obtained by reaction sintering have been performed. It has been shown that the properties of the reaction-sintered ceramics based on carbides are largely determined by the quality of impregnation of the porous carbide frame with silicon, which depends on the total and open porosity, shape and size of the pores of the compact, the composition of the charge from the carbide powder. High-temperature sintering, followed by impregnation of the carbide frame with silicon and its interaction with the carbon constituent of the frame, largely determines the properties of the material. The main task in the implementation of this process is to create conditions that ensure the full filling of pores in the initial compact during impregnation with silicon melt and, secondly, maximum activation of chemical interaction between the melt of silicon, carbon and other components that compose the charge. A complex of studies on the effect of compacting pressure and annealing temperature of the charge based on silicon carbide and boron powders with the addition of graphite on the pore structure of the compact and the quality of its impregnation with a silicon melt has been carried out in this work. It has been shown that the density, bending strength, hardness of ceramics based on silicon carbide and boron carbide obtained by reaction sintering are increased with a rise in compacting pressure of carbide frames. The optimum porosity of the carbide frame is 25–30 %; the pore size is 1.0–1.5 μm. It has been also demonstrated that ceramics based on boron carbide and boron carbide with 50 % silicon carbide impregnated with silicon at high-temperature sintering has higher strength and hardness values than those based on silicon carbide due to higher adhesion strength at the interface of boron carbide particles and binder, caused by the dissolution of boron carbide in the silicon melt and the formation of complex carbide particles on the surface.