The department was founded in 1991. The researchers of the department have proposed and developed the idea about the heat strengthening process, based on the usage of the incomplete homogenization effect, the key point of which is obtaining in the high temperature solid solution of controlled in magnitude chemical inhomogeneity, rendering further decisive impact on the microstructure and properties of heat-strengthened metallic materials. It was found that the creation of controlled concentration gradients in non-equilibrium conditions on rapid heating is only possible due to the development of phase transformations through the diffusion mechanism, a characteristic feature of which is the achievement of local equilibrium at the α/β interface (O.M. Ivasishin, P.E. Markovsky).
The mechanism of dispersion of rapidly heat-strengthened microstructure with the usage of the incomplete homogenization effect of alloys was determined. This mechanism consists in delayed-action on moving of the high angle grains boundaries and growing of martensite crystals` in concentration-non-equilibrium solid solution and division of grains into micro-volumes, in which depending on concentration state the different metastable phases are formed on quenching.
A new approach to the problem of properties stability of heat-strengthened alloys was proposed. It consists in choosing of thermo-kinetic parameters, which provide the uniqueness of decomposition mechanisms of the metastable phases irrespective of oscillations of their concentration and defect states.
The results of the fundamental research of phase and structural transformations in the titanium alloys and proposed methods for creation of the controlled inhomogeneous structural states were taken as a base for the development of new technological processes of their heat-strengthening.
On the basis of the fulfilled research of plastic deformation impact on evolution of microstructure, phase composition, crystallographic texture and a set of the mechanical properties of a wide range of titanium alloys the new methods of their thermo-mechanical treatment, providing the creation of the unique, including those of submicron structural states, were proposed. On the basis of the obtained results a new complex approach, joining the deformation factor (usage of crystal structure defects introduced by plastic deformation) and thermo-kinetic factor of rapid heat treatment was developed.
A considerable success was achieved in the theoretical and experimental research of martensite transformations in titanium alloys developing by imposition of spinodal martensite decomposition. The mechanism of α"-martensite formation in the titanium alloys containing isomorphic β- stabilizers was proposed and nature of appeared crystal structure was explained (O.M. Ivasishin, N.S. Kosenko).
The approaches obtained in the researching of phase and structural transformations in titanium alloys have been successfully applied to zirconium based alloys, which are used in nuclear power engineering and medicine. The technological approaches providing the obtaining of the optimized microstructure, crystallographic texture and mechanical characteristics in the alloy Zr–1%Nb, made of domestic raw materials were proposed. The alloys of the Zr–Ti–Nb system having low values of elastic modulus and high value of reversible deformation for the medical implants were developed.
A perspective direction is the development of the physical bases of solid-phase synthesis of titanium alloys with high set of physical-and-mechanical characteristics from heterogeneous powder systems, which consist of particles of titanium base and particles of alloying elements. (O.M. Ivasishin, D.G. Savvakin). The department has developed the physical principles of hydrogen usage as a temporal alloying element to titanium for positive impact on processes of consolidation and chemical homogenization of heterogeneous systems on the basis of the particles of hydrogenated titanium (titanium hydride) by their transformation into the titanium alloys of different chemical composition. The activation of solid-phase diffusion and titanium purification from the impurities (oxygen, chlorine, carbon) occurs under the hydrogen extraction during synthesis. As a result the specific structural states of the titanium alloys are formed with homogeneous phase composition and microstructure having high relative density (up to 99% from theoretical), low content of admixtures and high mechanical properties, that is inaccessible without usage of hydrogen. The basic principles of hydrogen application as a temporal alloying element were also employed by synthesis of zirconium alloys of the heterogeneous systems on the base of particles of zirconium hydride.
A group of researchers that deals with study of the physical processes occurring on high- temperature creep of the metals and alloys works in the department. The studies in this field started in the 50th by G.Ya. Kosyrskii, and in the 70th-80th were developed by research team led by Dr. Kononenko V.A. The following main results have been obtained:
1) The dislocation mechanisms controlling the creep velocity by different temperature-applied stress conditions have been determined as well as their relation to the development of the dislocation structure (P.N. Okrainets, V.K. Pishchak);
2) The physical bases of substructure strengthening under the conditions of high-temperature creep have been developed (V.A. Kononenko, V.K. Pishchak);
3) The modern X-ray diffraction methods for study of the substructure parameters and their evolution during plastic deformation, in particular on high-temperature creep, have been developed.
At the present time the emphasis in the research of high-temperature creep is focused on commercial titanium alloys and alloys on the intermetallic basis.
A special attention is paid to the development of modeling of the formation processes by deformation and further evolution on heating of structure, crystallographic texture, phase composition and concentration states of metals. The 2D- and 3D- models describing the behavior of recrystallization and further grain`s growth taking into consideration the energy dependencies of grains` boundaries on their misorientation have been created using the Monte-Carlo method (O.M. Ivasishin, S.V. Shevchenko).
A new research direction of the department is a computer modeling of an atomic structure and properties of the alloys alloyed by interstitial and substitutional atoms aiming on creation of the physical bases for search of new materials and prediction of their physical properties (O.M. Ivasishin, A.N. Timoshevskii, B.Z. Yanchitskii).| © G.V. Kurdyumov Institute for Metal Physics, N.A.S.U., 2024 |