Distinctive Features of the Rheosynthesis of Ceramic and Cermet Materials under Self-Propagating High-Temperature Synthesis Extrusion Conditions

This paper presents current ideas and original research results in a new area of self-propagating high-temperature synthesis (SHS): rheosynthesis of articles from ceramic and cermet materials under conditions combining combustion processes and high-temperature shear deformation. A scientific basis of the production of articles with the use of these processes is information about stimulated or spontaneous post-processes in synthesis products as a result of targeted mechanical and thermal influences on a viscoplastic medium. Characteristic features of the rheological behavior of various synthesis products are discussed in relation to specific high-temperature shear deformation conditions. Subjects of investigation are presented and the key condition determining the moldability and extrudability of synthesis products is formulated. We identified various mechanisms influence of shear deformation and pressure on structure formation in SHS processes. There were demonstrated that, owing to the observed features of the structure formation and phase composition of synthesis products obtained under the effect of pressure and shear deformation (deformation texture formation, alignment of pore systems in the external force direction, etc.) and rheological structural effects (thixotropy, viscosity superanomaly, and superplasticity), there are optimal temperature and time ranges where a controlled transition of synthesis products to macroscopic flow can be ensured. As a consequence, it is possible to directly produce multifunctional articles from powders of refractory inorganic compounds in a single processing step using a single apparatus in tens of seconds.