**Author details**

The large gradient of microhardness is characteristic for zone A. It is caused by β→ α trans‐ formation as a result of saturation by nitrogen as α-stabilizer and comparatively its high solubility in α-phase. With increasing distance from surface the microhardness is decreased sharply (Fig. 16 a) that is explained by decrease of nitrogen concentration (Fig. 16 b). The hardness of zone B is considerably less than zone A because of large difference of nitrogen solubility in α- and β-phases. The thickness of these zones is increased with the increase of duration of nitriding (Fig. 16 a). In particular, the thickness of zone A is 34 µm for τ= 1 h and 69 µm for τ=5 h. It can be noticed that this thickness is larger than corresponding thickness, determined by the data of metallographic analysis. The total depth of diffusion zone (zone A

The received analytical distribution of nitrogen (Fig. 16 b) and results of microhardness measurements (Fig. 16 a) confirm the correlation between model calculations and experimental

The process of high-temperature interaction of titanium with gaseous medium (nitrogen or oxygen) was modelled at temperatures T<Tα↔β and T>Tα↔β considering the surface processes

The kinetics of surface processes is reflected by the mass balance equation, which takes into account the interaction of an external flux of impurities to the surface and its chemisorption with diffusion dissolution and segregation on defects as a result of a chemical interaction with

The kinetics of diffusion saturation of α-titanium by nitrogen under rarefied atmosphere (1

The influence of time and temperature parameters on the depth of the nitrided layer and a

It was shown the role of these interstitial elements as α-stabilizers in forming the diffusion

It was received the solution of the formulated task as for diffusion of nitrogen or oxygen in

The constants of parabolic growth of layers were calculated. It allowed to foresee the kinetics of their growth and distribution of interstitial elements (nitrogen or oxygen) in diffusion zone.

The adequacy of the proposed model representations was confirmed by the results of experi‐

processing times of 1 and 5 h) of the diffusion zone which is caused by the structural phase

zone which contains three layers based on α-phase, α+β-phases and β-phase.

such a heterogeneous medium taking into account the motion of interfaces.

transformations during diffusion of nitrogen was examined experimentally.

C was investigated experimentally and analytically.

C. The microstructural evolution (after

+ zone В) is 185 µm for τ= 1 h and 425 µm for τ=5 h (Fig. 16 a).

data.

**4. Conclusions**

titanium atoms.

and structural phase transformations.

66 Titanium Alloys - Advances in Properties Control

Pa) in the temperature range of 750-850 0

change of its microhardness was estimated.

mental investigations on nitriding of titanium at Т=950 0

Yaroslav Matychak\* , Iryna Pohrelyuk, Viktor Fedirko and Oleh Tkachuk

Karpenko Physico-Mechanical Institute of National Academy of Sciences of Ukraine, Lviv, Ukraine
