**1. Introduction**

Structural and phase transformations in metal alloys at deformation in the conditions of plasticity and superplasticity are a subject of long-term and systematic researches.

In scientific literature there are physical and mathematical models of deformation describing structural transformations in process as plastic and superplastic deformation of structural materials [1, 2].

However we have very few materials of publications in which results of the thermodynamic analysis directly correspond to researches of structural transformations. Authors of works [3–5] showed that one of the effective methods of studying of mechanisms of hot plastic deformation is the thermodynamic approach based on use of dynamic model of deformation of material.

According to the model of the elasto-visco-plastic environment, for any timepoint the power of the mechanical energy P coming to a deformable body is defined by the sum composed by G and J. Both are connected with production of entropy. However first (G) considers dissipation of energy through forming and hardening. Second (J) is connected with the adapting reorganizations in structure of grains of

a polycrystal directly in the course of action of the deforming tension. Hence it is connected with production of entropy in material:

$$\mathbf{P} = \mathbf{G} + \mathbf{J} = \sigma \mathbf{e}; = \mathbf{T} \text{(ds/dt)} \succcurlyeq \mathbf{0},\tag{1}$$

where σ is tension, ε; is strain rate, T is temperature, and dS/dt is the speed of production of entropy.

Division of power of dissipation between G and J is defined by strain rate sensitivity m:

$$\text{dJ/dG} = \Delta \text{log } (\sigma) / \Delta \text{log} \text{(e;)} = \text{m.} \tag{2}$$

It is shown that for quantitative assessment of nature of dissipative processes and practical application, it is convenient to use effectiveness ratio of dissipation of energy (η):

$$
\eta = 2\mathbf{m}/(\mathbf{m}+\mathbf{1}).\tag{3}
$$

The coefficient η characterizes ability of structure of material to dissipate the brought mechanical energy in the course of hot deformation.

Size η changes in the range from zero to unit and is interpreted as the relative speed of production of entropy.

In the present article, results of the research characteristics of dissipation of energy in industrial alloys in the course of uniaxial stretching and compression on the example of near-alpha titanium alloy are stated.

During the planning and implementation, the present article used system approach which included the detailed analysis of structure of alloy before deformation and comparison of results of structural researches to results of mechanical tests and calculation of coefficient of dissipation of energy.

### **2. Materials and experimental methods**

Mechanical tests of samples of titanium alloy cut from hot-rolled sheet products with thickness of 40 mm, the chemical composition of which is given in the **Table 1**, were made at different temperatures and speed parameters.

The initial microstructure of titanium alloy corresponded to a two-phase state which was created in the course of hot rolling.

The received structure is characterized by the large initial size of grains of a β-phase (~300 μm) and represents mix of the α-plates divided by β-phase layers (**Figure 1**).

Mechanical tests on stretching at room temperature were carried out on the tensile testing machine UEN30 "Shimadzu." At increased temperatures, the modernized universal testing machine UM5 was used.


**69**

logarithms.

**Figure 1.**

*Initial microstructure of alloy.*

interpolation.

style.

program.

*Characteristics of the Dissipation of Energy at Hot Plastic Deformation of Near-Alpha Titanium…*

In an experiment, standard explosive samples with a diameter of 6 mm were used. For tests for compression cylindrical samples with a diameter of 5 and 10 mm

At the same time deformation equaled ε = 0.3, and temperature of heating cor-

Calculation of effectiveness ratio of dissipation of energy at deformation of samples under various temperature and high-speed conditions consisted in formation of a matrix of values of true tension at the set extent of deformation and their

Calculation of coefficients of m and η and calculation of intermediate values of effectiveness ratio of dissipation of energy were made by a method of spline

Results of calculation can be presented in the tabular, analytical, or graphic

The most evident is representation of results of calculation η in the form of 3D plot and cards of constant levels of effectiveness ratio of dissipation of energy. Calculation and creation of cards were carried out with the use of the Mathcad 15

Microstructural researches were carried out on the polished samples of the deformed samples, which are cut out in the cross-sectional and longitudinal direc-

To get images, information technologies and specialized programs have been

According to results of mechanical tests, dependences are constructed *σ* = *f*(*ε*). The received dependences and their look do not contradict the settled ideas of behavior of metal polycrystals in the conditions of hot plastic deformation. So, in the

–10 s<sup>−</sup><sup>1</sup> .

on the high-temperature dilatometer DIL 805 were used.

responded 800–1040°С. Average strain rate ε; was 10<sup>−</sup><sup>3</sup>

tion with application of modern methods [5, 6].

**3. Results of researches and discussion**

used ("Expert Pro", "Fractal") [7, 8].

*DOI: http://dx.doi.org/10.5772/intechopen.88845*

#### **Table 1.**

*Chemical composition of the studied alloy.*

*Characteristics of the Dissipation of Energy at Hot Plastic Deformation of Near-Alpha Titanium… DOI: http://dx.doi.org/10.5772/intechopen.88845*

**Figure 1.** *Initial microstructure of alloy.*

*Titanium Alloys - Novel Aspects of Their Manufacturing and Processing*

connected with production of entropy in material:

η = 2m/

the example of near-alpha titanium alloy are stated.

and calculation of coefficient of dissipation of energy.

**2. Materials and experimental methods**

which was created in the course of hot rolling.

ernized universal testing machine UM5 was used.

speed of production of entropy.

brought mechanical energy in the course of hot deformation.

production of entropy.

sensitivity m:

energy (η):

a polycrystal directly in the course of action of the deforming tension. Hence it is

where σ is tension, ε; is strain rate, T is temperature, and dS/dt is the speed of

It is shown that for quantitative assessment of nature of dissipative processes and practical application, it is convenient to use effectiveness ratio of dissipation of

The coefficient η characterizes ability of structure of material to dissipate the

Size η changes in the range from zero to unit and is interpreted as the relative

In the present article, results of the research characteristics of dissipation of energy in industrial alloys in the course of uniaxial stretching and compression on

During the planning and implementation, the present article used system approach which included the detailed analysis of structure of alloy before deformation and comparison of results of structural researches to results of mechanical tests

Mechanical tests of samples of titanium alloy cut from hot-rolled sheet products with thickness of 40 mm, the chemical composition of which is given in the

The initial microstructure of titanium alloy corresponded to a two-phase state

The received structure is characterized by the large initial size of grains of a β-phase (~300 μm) and represents mix of the α-plates divided by β-phase layers

Mechanical tests on stretching at room temperature were carried out on the tensile testing machine UEN30 "Shimadzu." At increased temperatures, the mod-

**Al V Mo Fe Si C O H N Ti** 5.4 2.0 1.2 0.25 0.3 0.1 0.15 0.08 0.04 The rest

**Table 1**, were made at different temperatures and speed parameters.

Division of power of dissipation between G and J is defined by strain rate

P = G + J = σε;= T(ds/dt) ≥ 0, (1)

dJ/dG = ∆log (σ)/∆log(ε; ) = m. (2)

(m + 1). (3)

**68**

**Table 1.**

(**Figure 1**).

**Element content, % wt.**

*Chemical composition of the studied alloy.*

In an experiment, standard explosive samples with a diameter of 6 mm were used. For tests for compression cylindrical samples with a diameter of 5 and 10 mm on the high-temperature dilatometer DIL 805 were used.

At the same time deformation equaled ε = 0.3, and temperature of heating corresponded 800–1040°С. Average strain rate ε; was 10<sup>−</sup><sup>3</sup> –10 s<sup>−</sup><sup>1</sup> .

Calculation of effectiveness ratio of dissipation of energy at deformation of samples under various temperature and high-speed conditions consisted in formation of a matrix of values of true tension at the set extent of deformation and their logarithms.

Calculation of coefficients of m and η and calculation of intermediate values of effectiveness ratio of dissipation of energy were made by a method of spline interpolation.

Results of calculation can be presented in the tabular, analytical, or graphic style.

The most evident is representation of results of calculation η in the form of 3D plot and cards of constant levels of effectiveness ratio of dissipation of energy. Calculation and creation of cards were carried out with the use of the Mathcad 15 program.

Microstructural researches were carried out on the polished samples of the deformed samples, which are cut out in the cross-sectional and longitudinal direction with application of modern methods [5, 6].

To get images, information technologies and specialized programs have been used ("Expert Pro", "Fractal") [7, 8].
