Kaidash O. Scientific fundamentals of formation of structure and properties during sintering from submicron refractory carbides and nitrides of advanced ceramics for the mechanical engineering

Thesis for Doctor of Science (Engineering) degree in the 05.02.01 Specialty - Materials Science - V. M. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kyiv, 2018. The thesis is devoted to the solution of the scientific and technical problem of the creation of advanced ceramics based on refractory carbides and nitrides with increased mechanical, chemical and functional characteristics, able to operate in conditions of rigid abrasion wear, corrosive media, increased thermal and mechanical loads in products and equipment for various branches of mechanical engineering. The problem was solved by establishing the laws of pressureless sintering, reactive sintering under pressure, the features of microstructure formation from submicron compounds with heterodesmic interatomic bonds and control of structure-sensitive properties. Scientific positions and research results of structural mechanisms of formation of nanopowders TiN, TiC by pressureless sintering, radical influence of oxygen on recrystallization processes are defended. pressureless sintered self-reinforced Si3N4-materials from nanodispersed powder compositions have been produced, which made it possible to produce the ceramics with submicron anisometric grains, simultaneous growth of strength to 1000 MPa and fracture toughness to (6.6-8.5) MPaхm1/2. For the first time was observed pop-in under nanoindentation of B4C, an experimental estimate of the theoretical shear strength has been defined as 23 GPa (G/9) and the ulimate (ideal) hardness has been found to be 50 GPa. For the first time a computer model was developed and a comparative analysis of the growth of cracks in brittle heteromodule B4C-MeB2 materials was carried out, which makes it possible to evaluate the fracture toughness of the material and optimize its structure. It has been established that during reaction sintering under pressure in the systems B4C-(VC-TiН2), B4C-(TiB2-TiН2) the formation and decomposition of solid solutions of Ti-(V)-B-С(-О) provide dispersion strengthening of composites due to in situ formation solid solution of diborides of TiВ2-TiB2-secondary and VB2-TiB2 and causes growth of fracture toughness to 60% and strength to 40%. The structure of the AlN-Mo material with a dielectric matrix and metallic inclusions has been optimized to achieve maximum dielectric permittivity. For a two-phase composite an estimation of the attenuation L has been proposed.