Peculiarities of Burning and Structurization of Ceramic Materials in the System Cr–Al–Si–B

Abstract

The work was devoted to investigation of kinetics of SHS-process, staging of chemical transformations and structure formation of ceramic materials in multicomponent Cr–Al–Si–B system. An influence of reactionary mixture composition and initial temperature of the SHS-process on the combustion tem- perature and rate was investigated. The values of that parameters decreases during increasing of Al concentration. Increasing of the initial temperature of SHS-process leads to directly proportional growth of said indices, suggesting the single combustion mechanism for each composition, when staging of chemical reaction of synthesis products formation is not change. Besides, increase of Al content leads to increase of portion of Al–Si eutectic melt, and dissolving of Cr particles in this melt becomes a limiting stage of the combustion process, which leads to decrease of effective activation energy values from 291 to 109 kJ/mole. The staging of chemical transformations in the combustion wave was investigated and an assumption about mechanism of struc- ture formation was made. Initially, in the preheating zone a contact melting of Al–Si eutectic occurs with subsequent formation of the reactionary sur- face by spreading of the melt on the surface of Cr and B particles. Then the melt is saturated with these elementss with further crystallization of CrB and Cr(Si,Al) 2 grains. In the areas enriched by Cr and B and depleted by melt the formation of CrB may occur by a mechanism of solid-phase interaction invol- ving gas-transport reactions. Sequenced formation of monoboride CrB, and then silicide Cr 5 Si 3 or alumosilicide of Cr Cr(Si,Al) 2 was established by means of dynamic diffraction method. Ceramic targets for magnetron deposition of multicomponent coatings were produced by forced SHS pressing technology.