Physicochemical principles for creating composite ceramics based on refractory compounds

Sintered ceramics based on refractory compounds help to solve many problems in modern technology. The range of demands placed on new materials is very wide, and so without refractory substances that combine important properties, it is difficult to make technical progress. Heat-treatment substances include the transition metals (MeIV-VIII), metal-like compounds (borides, carbides, nitrides, and silicides), covalent compounds (B4C, BN, SiC, Si3N4, CaB6, AlN), and refractory ionic-covalent oxides. Some of the substances from these classes are used in technology, including those in the form of alloys and sintered ceramics. However, the variety of known properties for design materials makes it essential to develop composite materials, including ceramics. A feature of the latter is the essential high-temperature processing as a stage in the shaping of the prescribed structure, predetermining the desired combination of working properties, including those that are required for use of the materials at high temperatures. Both the formation of the stated structure and ensuring its maximum stability in composites during service are determined by the stability of the phase constituents and their compatibility in a wide temperature range. Information about the compatibility of the phases can be obtained form the corresponding n-component phase diagrams or evaluative thermodynamic calculations. Important information has been collected on the phase equilibria, and the structure of phase diagrams for systems that develop various classes of refractory compounds. 15 refs., 3 figs., 1 tab