Ways of Increasing Thermal Stress Resistance of Ceramic Materials

Improvement of the mechanical characteristics of the ceramics possessing limited plasticity in a wide temperature band should be made in view of its operational parameter [365]. For tool materials working in temperature range of brittle failure, the aspiration for rising strength and fracture toughness is ardently expressed and it is related, first of all, to reduction of unsoundness of the materials and creation of structural conditions which increase energy consumptions by fracture [11]. For increasing of thermal stress resistance in this area of temperatures, the methods used, basically, are connected with elimination of structural defects by optimization of modes of compaction and sintering, curing defects, thermal-mechanical programmed hardening, modifi- cation of a stressed state of a surface and introduction of a metal binding [352].

For increase of long-term thermal stress resistant characteristics in the temperature area where macro-plastic strain becomes possible, all methods used, as a rule, are applicable for metal materials. Thus in the field of temperatures, where the process of deformation is supervised by movement of dislocations [351], the methods are applied which aspire to complicate dislocation mobility by substructural hardening, doping resulting in formation of stronger chemical bonds in compounds and doping with formation of the second phases. In conditions of loading, where the dominating mechanism of deformation is grain boundary slip at high-temperature creep, an effective method of increase is recrystallization, allowing significantly to reduce the extent of borders due to increase of the grain size. It is necessary to consider using methods of hardening, so that the structural changes directed on increase of mechanical characteristics at high temperatures should not worsen the mechanical characteristics at temperatures T<T_bp.