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coefficient of nitrogen or oxygen in titanium Panasyuk, Metin, Kofstad, . This is why investigations experimental and theoretical aimed at elucidating the kinetic regularities and peculiarities of the distribution of interstitial elements in a surface layer, which determines the changes of its physicomechanical characteristics, are urgent.Diffusive processes determine changes of properties of surface layers of the structural materials in many cases, for example, in the process of their thermochemical treatment or in the conditions of operation at high temperature. However, the diffusion in solids is often accompanied by the structural phase transformations. These processes are interconnected and interdependent diffusion of the elements can stimulate structural phase transformations, and the latter change the conditions of diffusion. It is difficult to describe these processes analytically. Titanium, which undergoes the polymorphic transformation at, is interesting for such theoretical and experimental investigations, in particular its high-temperature interaction with nitrogen or oxygen. Due to high affinity of these elements with titanium nitride or oxide layer forms and grows on the surface. Unlike many alloying elements, in particular vanadium, molybdenum, which are -stabilizers, above mentioned interstitial elements are -stabilizers, which can stimulate structural phase transformations in titanium. The microstructural evolution during ↔ phase transformation as a result of migration of -stabilizers is presented in Malinov et al.,. However, the authors did not take into consideration the role of nitrogen as -stabilizer in the structural transformations. It was demonstrated Matychak, in the studies of interconnection of nitrogen diffusion and structural phase transformations during high-temperature nitriding that, in particular, under the rarefied atmosphere, the continuous nitride layer on the surface was absent for a long time. The aim of work is• to establish the kinetic peculiarities of interaction of titanium with the interstitial element " nitrogen or oxygen at the temperature lower and higher than temperature of allotropic transformation T ↔• to investigate experimentally and model analytically the process of diffusive saturation of -titanium with the interstitial element from a rarefied atmosphere taking into account the surface phenomena• to model the interdependence of the processes of external supply of the interstitial element to the surface and its chemosorption with diffusive dissolution and segregation on defects, caused by the chemical interaction with the titanium atoms• to estimate the influence of temperature-time parameters of treatment on the depth of diffusion zone and change of its microhardness• to establish the kinetic peculiarities of diffusive saturation of titanium with the interstitial element caused by the structural phase transformations.Titanium Alloys -Advances in Properties Control 46

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