**4. Titanium alloys defect structure modification by hydrogen saturation method**

In ideal defect-free single crystals hydrogen dissolves in the metal, occupying the lattice interstitial positions and causing displacement of the metal atoms from their equilibrium positions.Inthe real crystals,thoughhydrogensegregates invarious latticedefects,whichleads toreductionofprobabilityofpositronscapture.Buthydrogensaturationofmaterialsinannealed state at *Т* = 200ºС does not practically affect annihilation parameters. If we increase the temperature of the hydrogen saturation process to up to Т=500ºС, then hydrogen absorption accelerates, which consequently causes more active hydrogenation of that material. This is effectively reflected in the respective increase of *F* probability, but angle of Fermi momentum θF remains constant in the range of calculation error. This means that the hydrogen saturation process is not accompanied by new defects formation in the metal's structure and electron

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143

subsystem in positrons locating places does not experience significant reconstruction.

bigger by volume and eventually cause sample's destruction.

is reflected in the annihilation parameter changes.

and radiative character.

eV, than simple vacancy defects.

(b) and defects annealing kinetics in titanium (с)

Plastically deformed metals facilitate accumulation of a considerable amount of hydrogen. The hydrogen saturation at comparatively low temperature (200ºС) is obviously accompanied by atomic hydrogen capture by structural damages. The new complexes appear in crystalline lattice which decrease the capture efficiency of positrons localization centers, previously introduced by the plastic deformation. The hydrogen saturation temperature increase up to 500ºС converts materials into a hydride state, which caused the cast, compact metals to crumble into powder. The reason for destruction of the compact metal after hydrogen saturation under 500ºС can be formation of cracks of deformative nature related to the hydrides formation. The penetrated hydrogen is dissociated in the internal surface of these defects but with formation of less mobile molecules which with more intensive arrival from outside gradually become

In order to establish the nature of the observed phenomena, the hydrogen accumulation nature in Ti and its alloys with Al in annealed state was investigated. In clean Ti, there are practically no reasons that could prevent hydrogen from accumulation to significant concentrations (Fig. 19a). At the same time, intensity of hydrogen absorption by annealed alloys of Ti-Al system sharply drops with an increase of Al concentration in the alloys (Fig.19b). Therefore, the capabilities of Al, as an absorber of hydrogen, are rather limited comparing to those of Ti. This

Thus, the observed changes in the electron structure of the defect material indicate, on the one hand, on hydrogen's significant role in its formation and, on the other hand, on enhancement of the interaction of hydrogen with the material due to the presence of damages of deformative

Isochronal annealing behavior of these materials is presented in Fig.19. For irradiated by electrons and not saturated by hydrogen Ti one stage of restoration is allocated under annealing in the temperature range 170-240ºС with *Е*а= 1.22 eV. As a result of irradiation of the hydrogen saturated metal, the displacement of the starting point of the first stage recovery up to 225- 230ºС is observed, which finishes near 330ºС. Therefore, the bound state vacancyhydrogen in Ti has a higher temperature range of dissociation and annealing with *Е*а = 1.38

Fig. 19 Hydrogen accumulation kinetics (a), Al influence on hydrogen accumulation rate in Ti

It is generally acknowledged that alterations in the metal electron structure caused by hydrogen should be taken into account when interpreting physical properties of the metalhydrogen system. This is especially important for the Ti–H system, because of the high absorption capacity of titanium with respect to hydrogen, which to a significant degree have an influence on its technological properties. According to the well-known proton model, the proton gas penetrates into the electron shells and changes their energy state. At the same time the intensity of the force fields grows with an increase of the temperature of the system, which is accompanied by intensification of interaction between proton gas and electron shells.

In order to tackle this task, as an objects of the experimental study iodide titanium and a system of Ti–Al alloys (up to 50 at.% Al) were taken [13,17]. For hydrogenation, the original materials were annealed at 9000 C, deformed by rolling by *ε* =50%, and irradiated by 50MeV *α*-particles up to a fluence of 5 1015 cm−2. Hydrogenation was implemented by Siverts saturation method at the temperature of 2000 C during 3 hours and under 5000 C during 1 hour. The hydrogen pressure was (4.9–5.9) 105 Pa. Hydrogen was produced by desorption of the hydrides LaNi5H*X* and TiH*X*. Before hydrogenation, the samples were kept under the room temperature in vacuum of 0.13–1.33 Pa for 10 hours directly in the reactor, when hydrogen was admitted after the previous processing. The pressure was measured by a standard manometer with accuracy of 300 Pa with the volume of the reactor system being equal to 4 × 10−4 m3 . After samples hydrogen saturation at Т=200ºС in any different initial state the change of their weight could not be locked. At Т=500ºС the hydrogen saturation flows more intensively due to hydrogen diffusion acceleration, and samples' weight substantially increases. For interpretation of the investigation results the annihilation parameters shown in Table 5 were used.


**Table 5.** Annihilation parameters of hydrogenated titanium alloys

In ideal defect-free single crystals hydrogen dissolves in the metal, occupying the lattice interstitial positions and causing displacement of the metal atoms from their equilibrium positions.Inthe real crystals,thoughhydrogensegregates invarious latticedefects,whichleads toreductionofprobabilityofpositronscapture.Buthydrogensaturationofmaterialsinannealed state at *Т* = 200ºС does not practically affect annihilation parameters. If we increase the temperature of the hydrogen saturation process to up to Т=500ºС, then hydrogen absorption accelerates, which consequently causes more active hydrogenation of that material. This is effectively reflected in the respective increase of *F* probability, but angle of Fermi momentum θF remains constant in the range of calculation error. This means that the hydrogen saturation process is not accompanied by new defects formation in the metal's structure and electron subsystem in positrons locating places does not experience significant reconstruction.

**4. Titanium alloys defect structure modification by hydrogen saturation**

It is generally acknowledged that alterations in the metal electron structure caused by hydrogen should be taken into account when interpreting physical properties of the metalhydrogen system. This is especially important for the Ti–H system, because of the high absorption capacity of titanium with respect to hydrogen, which to a significant degree have an influence on its technological properties. According to the well-known proton model, the proton gas penetrates into the electron shells and changes their energy state. At the same time the intensity of the force fields grows with an increase of the temperature of the system, which is accompanied by intensification of interaction between proton gas and electron shells.

In order to tackle this task, as an objects of the experimental study iodide titanium and a system of Ti–Al alloys (up to 50 at.% Al) were taken [13,17]. For hydrogenation, the original

*α*-particles up to a fluence of 5 1015 cm−2. Hydrogenation was implemented by Siverts saturation method at the temperature of 2000 C during 3 hours and under 5000 C during 1 hour. The hydrogen pressure was (4.9–5.9) 105 Pa. Hydrogen was produced by desorption of the hydrides LaNi5H*X* and TiH*X*. Before hydrogenation, the samples were kept under the room temperature in vacuum of 0.13–1.33 Pa for 10 hours directly in the reactor, when hydrogen was admitted after the previous processing. The pressure was measured by a standard manometer with accuracy of 300 Pa with the volume of the reactor system being

state the change of their weight could not be locked. At Т=500ºС the hydrogen saturation flows more intensively due to hydrogen diffusion acceleration, and samples' weight substantially increases. For interpretation of the investigation results the annihilation

**F**

0.34 0.33 0.46 0.46 0.48 0.45

C, deformed by rolling by *ε* =50%, and irradiated by 50MeV

. After samples hydrogen saturation at Т=200ºС in any different initial

**Titanium Ti-5.2 at. % Al Ti-1.4 at. % V**

**ΔF %**

**F**

0.27 0.29 0.33 0.38 0.46 0.39

Error ± 0.01 0.05 1.0

**θ***F* **mrad**

> 6.12 5.92 5.91 6.22 5.03 5.63

**ΔF %**

**θ***F* **mrad**

> 5.61 5.83 5.92 5.82 5.33 5.61

**method**

materials were annealed at 9000

142 Titanium Alloys - Advances in Properties Control

parameters shown in Table 5 were used.

**F**

0.26 0.29 0.37 0.32 0.47 0.34

Ti pressed powder 0.40 5.25 54

TiH*x* Pressed powder 0.50 5.00 90

**Table 5.** Annihilation parameters of hydrogenated titanium alloys

**θ***F* **mrad**

> 5.82 5.85 5.92 6.05 5.18 6.03

**ΔF %**

equal to 4 × 10−4 m3

**Material state**

Annealed (before hydrogenation) Annealed+Н (200ºС) Annealed+Н (500ºС) ε **50%**+Н (200ºС) α+Н (200ºС) α+Н (500ºС)

Plastically deformed metals facilitate accumulation of a considerable amount of hydrogen. The hydrogen saturation at comparatively low temperature (200ºС) is obviously accompanied by atomic hydrogen capture by structural damages. The new complexes appear in crystalline lattice which decrease the capture efficiency of positrons localization centers, previously introduced by the plastic deformation. The hydrogen saturation temperature increase up to 500ºС converts materials into a hydride state, which caused the cast, compact metals to crumble into powder. The reason for destruction of the compact metal after hydrogen saturation under 500ºС can be formation of cracks of deformative nature related to the hydrides formation. The penetrated hydrogen is dissociated in the internal surface of these defects but with formation of less mobile molecules which with more intensive arrival from outside gradually become bigger by volume and eventually cause sample's destruction.

In order to establish the nature of the observed phenomena, the hydrogen accumulation nature in Ti and its alloys with Al in annealed state was investigated. In clean Ti, there are practically no reasons that could prevent hydrogen from accumulation to significant concentrations (Fig. 19a). At the same time, intensity of hydrogen absorption by annealed alloys of Ti-Al system sharply drops with an increase of Al concentration in the alloys (Fig.19b). Therefore, the capabilities of Al, as an absorber of hydrogen, are rather limited comparing to those of Ti. This is reflected in the annihilation parameter changes.

Thus, the observed changes in the electron structure of the defect material indicate, on the one hand, on hydrogen's significant role in its formation and, on the other hand, on enhancement of the interaction of hydrogen with the material due to the presence of damages of deformative and radiative character.

Isochronal annealing behavior of these materials is presented in Fig.19. For irradiated by electrons and not saturated by hydrogen Ti one stage of restoration is allocated under annealing in the temperature range 170-240ºС with *Е*а= 1.22 eV. As a result of irradiation of the hydrogen saturated metal, the displacement of the starting point of the first stage recovery up to 225- 230ºС is observed, which finishes near 330ºС. Therefore, the bound state vacancyhydrogen in Ti has a higher temperature range of dissociation and annealing with *Е*а = 1.38 eV, than simple vacancy defects.

Fig. 19 Hydrogen accumulation kinetics (a), Al influence on hydrogen accumulation rate in Ti (b) and defects annealing kinetics in titanium (с)

**•** for the initial state the alloys electron structure reveals a weak dependence on type and concentration of an alloying element, whereas the structure modification by plastic defor‐ mation causes nonmonotonic changes to the annihilation parameters. At the same time, the main changes in the character of the annihilation parameters are observed at deformations

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**•** it was shown by X-ray investigations that in the metals modified by deformation one can find a certain amount of new phase precipitates which are interpreted as the β - phase of base metal in the matrix of α-phase, with vacancy-dislocation structure and electron density

**•** it was shown that after electron irradiations, mono vacancies emerge in the titanium crystalline lattice and they remain at the room temperature; these mono vacancies ensure capture of positrons, electron structure and configuration of which do not depend on electrons fluence and significantly differ from the corresponding characteristics of vacancy

**•** it was established that the electron structure and stability of each alloys system to the influence of high energy α-particles are the function of alloying elements nature and their

**•** the possibility of the irradiation-induced swelling suppression in the titanium alloys by selective alloying and preliminary structure defects introduction was experimentally

**•** the role of the initial structure defects in titanium alloys under the high energy proton irradiation is manifested in their transformation, evolution and redistribution with sharply

**•** it was shown that in the deformed state hydrogen accumulation in titanium occurs in the defect regions with hydride formation which afterwards leads to sample destruction; **•** for hydrogen corrosion reduction it is necessary to use titanium alloyed by Al (over 5.2 at.

**•** the radiation effects in preliminary hydrogen saturated titanium manifested themselves in

1 Department of the Theoretical and Experimental Physics of the National Pedagogical Un‐

2 Department of Geology and Earth Physics of the Kazakh-British Technical University, Al‐

of up to ε≤30 %, above which saturation is observed;

substantially smaller than in the initial phase;

formations generated by plastic deformation;

emergence of hydrogen atom-vacancy coupled state.

and Farid F. Umarov2

concentration;

demonstrated;

%);

**Author details**

maty, Kazakhstan

Kanat M. Mukashev1

versity after Abai, Almaty, Kazakhstan

distinct electron structure;

**Figure 19.** a. Kinetics of hydrogen accumulation ΔF in titanium. b. Effect of aluminum addition on hydrogen accumu‐ lation ΔF in titanium.c. Annealing kinetics of radiation defects in titanium

#### **5. Conclusion**

Complex and systematic investigations of the electron structure of the titanium binary alloys depending on the type and concentration of the alloying elements and the modification degree by plastic deformation method enabled formulation of the following conclusions:

