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Electromechanics and Mechanical Engineering
UDC 539.3
THE STUDY OF THE EFFECT OF TEMPERATURE ON THE ABILITY OF METALS TO ACCUMULATE ENERGY DURING THEIR PLASTIC DEFORMATION
Vyacheslav F. BEZYAZYCHNYI1, Marian SZCEREK2, Mikhail L. PERVOV1, Mikhail V. TIMOFEEV1, MAKSIM A PROKOFIEV1
1 Rybinsk State Aviation Technical University named afterP.A.Solovyov, Rybinsk, Russia
2 Institute for Sustainable Technologies - National Research Institute, Radom, Poland
The subject of research is the surface layer of highly loaded parts, friction units of mining machines and equipment. The article presents a theoretical analysis of the factors that determine the ability of the material of the surface layer of parts to accumulate energy in the process of plastic deformation. It is suggested that the activation character of the accumulation of energy by metals.
Based on the theory of diffusion, it was shown that the mobility of atoms, as well as the accumulated energy, are determined by the ratio of the test temperature to the melting temperature.
Key words: machine parts; surface layer; accumulated energy; temperature; degree of deformation; tensile strength
How to cite this article: Bezyazychnyi V.F., Szcerek M., Pervov M.T., Timofeev M. V., Prokofiev M.A. The Study of the Effect of Temperature on the Ability of Metals to Accumulate Energy During Their Plastic Deformation. Journal of Mining Institute. 2019. Vol. 235,'p. 55-59. DOI: 10.31897/PMI.2019.1.55
Introduction. It is known that the surface layer of highly loaded parts, friction units of mining machines and equipment is a key element in ensuring the required operational properties. As a rule, it is the surface material volumes that perceive the greatest external influences during the machine operation and are the main object of technological operations of mechanical, electrophysical and a whole range of other processing methods that affect the structure, chemical composition, material properties [3, 5-8].
When solving problems of describing, evaluating and predicting the state of the surface layer after technological or operational impacts, many researchers determine a set of individual and complex indicators that directly or indirectly reflect the physical processes occurring in the material. These indicators include the microhardness, depth, degree and hardening gradient, the magnitude and sign of residual stresses of the first kind, the specific accumulated deformation energy. The specific accumulated deformation energy is of particular interest for studying in view of the close relationship of the accumulated deformation energy with the regime parameters of technological effects [9].
Formulation of the problem. The theory of dislocations allows us to determine the magnitude of the specific energy of defects (dislocations) formed during plastic deformation using the formula [4]
W = OGb2 A, (1)
where W - specific energy stored, J/m3; O - proportionality coefficient depending on the ratio of dislocation types, O = 0.5-1; G - shift modulus, Pa; b - Burgers vector, m; A - dislocation density, m2.
The change in the density of dislocations in metals during their strain hardening is due to the physical and mechanical property - the increment of the conditional yield strength by the quadratic dependence
a = ct(1 3 + aGb Va , (2)
where a - stress required to effect plastic deformation; G0.2 - stress meaningful material yield strength; a - coefficient (inter-dislocation interaction parameter).
Then, taking into account (1) and (2), we obtain the expression [4]
W = -^-(a-a02)2- (3)
a/G
Formula (3) indicates the effect on the stored energy of the deformation mechanism of strain hardening. Taking into account the thermally activated nature of the processes in the zone of plastic deformation, other significant factors include the temperature of deformation, as well as the struc-tural-sensitive properties of metals, including the physical and mechanical ones. Thus, first of all, a theoretical analysis of the influence of temperature conditions on the ability of metals and alloys to absorb energy during their plastic deformation is of interest.
Methodology. It is known that the temperature affects the mobility of the atoms of the crystal lattice, the closer the current temperature to the melting point, the greater the mobility of the atoms. The temperature dependence of the diffusion coefficient is described by the Arrhenius equation:
H
D = D0e«*, (4)
where D0 - preexponential factor; H - activation energy; R - absolute gas constant; T - absolute temperature.
Taking into account the known correlation between the activation energy of self-diffusion H and the melting point of metals Tme\ [2], expression (4) can be represented as follows:
D = D0e , (5)
where KN- almost constant value.
Figure 1 shows the dependence of the accumulated strain energy (at T= 293 K and the degree of deformation e = 20 %) on the homological temperature. With an increase in the homologous temperature, the accumulated strain energy during the transition from a more refractory metal to a less refractory metal decreases at the same accumulated strain and temperature (in Fig.l, they correspond to 20 % and 293 K) [4].
Discussion. As a result of statistical processing of the accumulated strain energy data for various degrees of plastic deformation, its dependence on the homological temperature and degree of plastic deformation was established:
(6)
where W - accumulated deformation energy, MJ/m3; s - degree of deformation; rmei - melting temperature, K; R -absolute gas constant, J/(K-mol); T - absolute temperature, K.
The obtained dependence, which is valid for the second stage of deformation hardening of materials, reveals a linear relationship between the accumulated energy, the degree of deformation, and the density of dislocations. Thus, in the first approximation for the studied metals it is possible to assume the linear nature of the change in the accumulated energy with increasing degree of deformation.
W = 5.7se RT ,
W,
Fig. 1. Change in stored deformation energy from homological temperature at s = 20 % 1 - calculated values of W} 2 - experimental values of IF; 3 — regression line, R2 = 0.84
Of particular interest is the analysis of the effect of ultimate strength on the accumulated strain energy at the same homologous temperature. The correlation dependence shown in Fig.2 with the degree of deformation 8=10 %, indicates that the stronger the material, the more it accumulates energy, all other things being equal.
Many researchers in the study of the accumulation of energy by metals during plastic deformation were limited to considering only pure metals, which are characterized by a uniform crystal structure. It should be noted that Steel and iron-based alloys differ from pure from the strength limit of the metals under study ¡; = 10 % (accuracy iron by the structure characteristics (amount ofapproximationR~ = 0,75)
of carbon, alloying elements, impurities, etc.).
Consequently, in the transition from pure iron to steel, we should expect changes in the structural-sensitive properties, the most important of which are mechanical properties. In this connection, it is important, in addition to considering the influence of homologous temperature, to study the influence of the structure of the material on the accumulated deformation energy.
Influence of material structure. Three groups of materials related to carbon, alloyed steels and nickel-based superalloys were selected as the object of research. Baseline data for the calculation are presented in the table. The value of the coefficient Ha was calculated on the basis of a hypothesis based on the regularities of the accumulated deformation energy revealed by V.M.Gresh-nov [1]
100
a = 0,159e^, (7)
where T- temperature, K.
w,
MJ/rn3 10
Ta
Mo'
0 100 200 300 400 a«, MPa
Fig.2. The amount of stored energy depending
Physical and mechanical properties of materials and coefficient calculated for them a
Material
Strength limit, as, MPa
Yield limit. Or, MPa
Shift modulus, G.GPa
Burgers vector, b • 1(T10, m
Coefficient a
08
10, IOkii 15
20, 20KH
25
30
35
40
45
50
55
30r 5 Or
60r
35r2 30X 5 OX 20Xr 15X
330 340 380 410 530 540 520 570 600 630 640
550 650 700 630 900 1100 800 750
Carbon steel
200 210 225 250 275
320 80
310 320 340 350 360
Alloy steels and alloys
290 370 380 370 700 900 600 560
2,87
80
2,87
0.20 0.20 0.22 0.22 0.26 0.26 0.26 0.26 0.28 0.28 0.28
0.28 0.28 0.30 0.28 0.21 0.20 0.23 0.23
End of a table
Material Strength limit, as, MPa Yield limit, CTj-, MPa Shift modulus. G, GPa Burgers vector, b- l(T10,m Coefficient a
40X 1000 800 0.22
50ХФА 1250 1080 0.20
X18H9T 600 280 0.30
H23H18 920 630 0.28
12X18H9T 620 320 0.30
Heat resistant nickel base alloys
ХН77ТЮР 1020 660 0.34
ХН70ВМТЮ 1140 750 0.34
ХН73МБТЮ 1200 800 80 3,5 0.34
ХН50ВМКТЮР 1220 785 0.35
ХН70МВФ 800 370 0.39
ХН62ВМКЮ 950 500 0.39
Let us consider the effect of strength limit on the ability of the studied steels and alloys to absorb deformation energy during plastic deformation. Fig.3 shows the dependence of the accumulated energy on the tensile strength at the degree of deformation s = 20 % for carbon steels (Fig.3, a), alloyed steels (Fig.3, b), heat-resistant alloys (Fig.3, c).
A combination of the graphs under consideration (Fig.3), as well as dependencies for pure metals (see Fig.2), is presented in Fig.4 [4]. There is a close correlation between the values under consideration, which is valid for all groups of metals under consideration.
The authors obtained a linear regression equation of the following form
W = 0,12sc5 , (8)
W, M.T/1113 20
где as - material strength limit, MPa.
Equation (8) clearly demonstrates the linear dependence of the accumulated energy on the degree of plastic deformation of the material and its tensile strength.
Conclusion
1. The dependence of the accumulated energy on the degree of metal deformation and dislocation density is established. At the second stage of strain hardening, the dependence becomes linear.
w,
M.T/m3 35 30 25 20 15
500 600 700 800 900 1000 1100 1200 as,MPa
3 -,
W, MJ/rn 35 30 25 20
1150 us, MPa
Fig.3. Dependence of the accumulated energy on the limit of strength of carbon steel (a) alloyed steels (b) and superalloys (c) at s = 20 %
W, MJ/m3 35 30 25 20 15 10 5
0 200 400 600 800 1000 1200 <js, MPa
Fig.4. Dependence of the accumulated energy on the strength of pure metals, carbon, alloyed steels and high-temperature alloys at e = 20 % 1 - pure metals; 2 - carbon steel; 3 - alloyed steels; 4 - heat resistant alloys
2. The influence of the material structure as a factor determining the ability of materials to accumulate energy during plastic deformation is shown.
3. A linear relationship has been established between the accumulated energy of the deformation of metals and the ultimate strength of the material.
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Authors: Vyacheslav F. Bezyazychnyi, Doctor of Engineering Sciences, Professor, Head of the Department, tehnology&j-satu.ni (Rybinsk State Aviation Technical University named after P. A. Solovyov, Rybinsk, Russia), Marian Szcerek, Doctor of Engineering Sciences, Deputy Director for Science and Research, marian.szcerek(a).gniail.com (Institute for Sustainable Technologies — National Research Institute, Radom, Poland), Mikhail L. Pervov, Doctor of Engineering Sciences, Professor, omd&rsatu.ru (Rybinsk State Aviation Technical University named after P.A.Solovyov, Rybinsk, Russia), Mikhail V. Timoveev, Candidate of Engineering Sciences, Associate Professor, mv-timofeev(q)yandex.ru (Rybinsk State Aviation Technical University named after P.A.Solovyov, Rybinsk, Russia), Maksim A. Prokofiev, Candidate of Engineering Sciences, Associate Professor, rgata2004(a)mail.ra (Rybinsk State Aviation Technical University named after P.A.Solovyov, Rybinsk, Russia).
The paper was received on 2 April, 2018.
The paper was accepted for publication on 21 June, 2018.
