Papers by Author: V. Rumyantsev

Abstract: The paper demonstrates the possibility to control the degree of tetragonal zirconia stabilization, microstructure and physical and mechanical behavior of Al2O3 -ZrO2(Y2O3) ceramic composite. Control is exerted via the process variables during deposition synthesis of nanosized composite powders from hydroxide salts, and their subsequent heat treatment and consolidation. Morphology features of nanosized powder systems and microstructures of the consolidated nanostructured materials were characterized by BET surface are measurements, scanning electron microscopy (both standard and HR), and large-angle X-ray diffraction. Correlations are established between microstructure parameters, physical and mechanical behavior of composite ceramics and a degree of stabilization of tetragonal ZrO2.

Abstract: Within unified stereological approach the silicon carbide-based ceramics SiSiC , SSiC, and LPSiC are treated as binary compositions, that despite certain structure ordering differences might be similarly described as comprising topologically continuous component (that provides the high level of physical and mechanical properties), and a discrete component. The paper demonstrates the necessity of using dimensionless criterial parameters for adequate description of the integral microstructure ordering level; said parameters including the characteristics of both continuous and discrete components of the composite ceramic material. Generalized equations are derived for compound stereological parameters of the discussed materials, along with statistically reliable approximations of the strength characteristics as functions of these parameters.

Abstract: Ceramics based on nanosized plasma chemistry Si3N4 powder compositions s (30-100 nm) is processed by activated pressureless sintering, hot pressing and hot isostatic pressing. Microstructure characterization of the obtained materials by means o light and scanning microscopy revealed no correlation between microstructure and the bulk consolidation method . Average grain size in all cases was 200-500 nm. Comparative characterization of the physical and mechanical behavior of the analyzed samples showed the following results: relative density - over 99 %, flexural strength – over 700 MPa, Vickers hardness - 16-17GPa, fracture toughness – 6.5-7.4 MPa·m1/2. The activated pressureless sintered samples demonstrated physical and mechanical behavior comparable to the samples consolidated by other methods. Activated pressureless sintering of nanosized plasma chemistry Si3N4 powders led to considerable economic advantages in processing Si3N4 spherical rotation bodies for hybrid roller bearings and cutting tools. Silicon nitride (Si3N4)-based structural ceramics is widely studied and used for over half a century due to its unique properties: low density, combined with high strength and wear-resistance, high decomposition temperature, high oxidation resistance, low friction coefficient and high resistance to chemical corrosion[1].

Abstract: The paper is dedicated to the study of the interdependence of structure and properties of sintered heterophase ceramic composition based on ultra-fine (nanosized) powders. The compositions based on brittle oxygen-free high-strength compounds under certain conditions are able to demonstrate micro-plasticity. Microstructure of such materials typically features homogeneous fine grains with certain critical maximum grain size. The substantial contribution of interphase boundaries and their dislocation structure to the non-trivial mechanical properties is discussed. Special features of interphase boundaries are demonstrated to contribute to the change in rupture resistance of the heterophase ceramics. Correlations between strength and elastic properties and results of tribological tests using «pin and disk» arrangement were studied. Increased fracture resistance, wear resistance, and micro-plasticity of heterophase ceramics is found to be due to the modification microstructure size parameters and distinctive features of interphase boundaries. The generally formulated purpose of the present study is a search for the solution to the problem of production of the advanced structural ceramic materials based upon oxygen-free refractory compounds with improved physical and mechanical properties.