Influence of structural instability at the creep characteristics of constructing materials
The structural instability, which observed during the creep of constructing materials in different structural states, is the result from changes in the geometry of the applied stresses and strain rate and significantly influences on the creep characteristics. It is shown that the result of appearanc...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| Cite this: | Influence of structural instability at the creep characteristics of constructing materials / E.V. Karaseva // Вопросы атомной науки и техники. — 2015. — № 5. — С. 130-133. — Бібліогр.: 15 назв. — англ. |
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| citation_txt | Influence of structural instability at the creep characteristics of constructing materials / E.V. Karaseva // Вопросы атомной науки и техники. — 2015. — № 5. — С. 130-133. — Бібліогр.: 15 назв. — англ. |
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| description | The structural instability, which observed during the creep of constructing materials in different structural states, is the result from changes in the geometry of the applied stresses and strain rate and significantly influences on the creep characteristics. It is shown that the result of appearance of structural instability and the subsequent restructuring of Zr, ZrlNb, and Nb, subjected to severe plastic deformation, was the change in the law creep. Transformation of the structure of the steel 15Cr2NMFA during creep leads to changes in the character of plastic flow, the appearance of jumplike creep deformation especially at stresses close to the ultimate strength.
Нестабільність структурного стану, що спостерігається в умовах повзучості конструкційних матеріалів у різних структурних станах, є наслідком зміни геометрії прикладених напруг і швидкості деформування та істотно впливає на характеристики повзучості. Показано, що наслідком виникнення структурної нестабільності і подальшої перебудови структури для Zr, ZrlNb і Nb, що піддавалися інтенсивним пластичним деформаціям, є зміна закону повзучості. Перебудова структури в процесі повзучості сталі 15Х2НМФА призводить до зміни характеру пластичної течії і появі стрибкоподібної деформації повзучості.
Неустойчивость структурного состояния, наблюдаемая в условиях ползучести конструкционных материалов в различных структурных состояниях, является следствием изменения геометрии приложенных напряжений и скорости деформирования и существенно влияет на характеристики ползучести. Показано, что следствием возникновения структурной неустойчивости и последующей перестройки структуры для Zr, ZrlNb и Nb, подвергнутых большим пластическим деформациям, является изменение закона ползучести. Перестройка структуры в процессе ползучести стали 15Х2НМФА приводит к изменению характера пластического течения и появлению скачкообразной деформации ползучести.
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ISSN 1562-6016. PASТ. 2015. №5(99), p. 130
INFLUENCE OF STRUCTURAL INSTABILITY AT THE CREEP
CHARACTERISTICS OF CONSTRUCTING MATERIALS
E.V. Karaseva
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
Е-mail: vsokol@kipt.kharkov.ua
The structural instability, which observed during the creep of constructing materials in different structural states,
is the result from changes in the geometry of the applied stresses and strain rate and significantly influences on the
creep characteristics. It is shown that the result of appearance of structural instability and the subsequent
restructuring of Zr, ZrlNb, and Nb, subjected to severe plastic deformation, was the change in the law creep.
Transformation of the structure of the steel 15Cr2NMFA during creep leads to changes in the character of plastic
flow, the appearance of jumplike creep deformation especially at stresses close to the ultimate strength.
PACS: 62.20.HG, 61.72.FF, 61.10.-I
INTRODUCTION
It is known that non-equilibrium physical processes
and systems characterized by internal instability because
they contain elements of both the ordering and
imbalance (ie, order and chaos). However, according to
Prigogine, chaos is not only destructive force, but also
the source of a new order. It contains a certain positive
potential, and controlling it, can achieve improve the
whole system [13].
However, in order to control, it is necessary
understanding of causality, ie. which of actions will lead
to any result. Active plastic deformation is a non-
equilibrium and irreversible process. The condition of
the material continuity is reduced to the need to
maintain the rate of dissipation of energy, which
delivered to the sample, on the certain level, predefined
by external devices. In the course if this rate is less than
the rate of increase of energy, the critical structural state
appearing and cracks is forming. This or that structure
can be maintained during plastic deformation, and can
be completely destroyed.
Internal stresses field is very heterogeneous and in
the local places near the top of dislocation clusters it
may be sufficient for the nucleation of microcracks on
the relatively early stages of deformation. To avoid such
a turn of events the crystal changes the response to an
external load, acting in accordance with the principle of
self-preservation. of plastic deformation. According to
it, such changes of the geometry or the mechanism of
plastic deformation should occur, which will reduce the
work hardening coefficient, i.e. should occur significant
structural transformation, the essence of which
accommodative adaptation. Accommodative processes
there are under the influence of the field of internal
stress and executes it plastic relaxation. The nature of
the external action uniquely determines the type of the
stable structural state with respect to it. With respect to
active plastic deformation at moderate temperatures, i.e.
if to the crystal is constantly introduced dislocation the
motion of which is given by the stress field, the
fragmented structure will be kinetically stable The
reason of stability is that the fragmented structure is not
the simply barriers to strain, it takes in a plastic
deformation of the sample directly involved.
Fragmentation is the dominant mode of evolution of the
defect structure at the stage of plastic deformation.
Another cause of kinetic instability may be the
change in geometry of plastic deformation and
deformation speed mode that will be accompanied by
structural adjustment so as to cause the maximum
intensity of the relaxation of internal stresses in
accordance with the desire of the crystal to maintain its
continuity. The newly formed structure as a result of the
restructuring can also be fragmented but stable with
respect to the new scheme of the elastic-stress state and
temperature-speed mode of deformation [17].
Restructuring processes lead to changes in macro
characteristics of the crystal.
In purpose of study the effects of structural
instability on the creep characteristics of various
fragmented structures carried out a number of studies in
which investigated the creep of different materials and
alloys with a structure formed by severe plastic
deformation.
MATERIAL AND EXPERIMENTAL
PROCEDURE
The material investigated was polycrystalline Zr,
and ZrlNb, deformed by rolling at 300 K on different
degrees of deformation. The object of investigation was
also the 99.9% niobium, deformed by drawing 80% at
77 K and the ferrite pearlitic steel 15Cr2NMFA after
standard processing factory.
Creep tests were carried out in the step loading
regime at 300, 600, and 700 K, the measurement
accuracy was 5·10
-5
сm. The activation parameters and
level of internal stresses were determined using the
differential methods described in [8]. Tempering was
carried out using a cylindrical heater, inside of which is
located the sample. Limiting heat increase achieved by
using special screens and isolations. The sample
temperature to within 10
-2
was measured by differential
thermocouple chromel-alumel, EMF is measured with a
digital voltmeter.
Measurements of the electrical resistance were made
by the compensation scheme. The error of resistivity
determination was 3 %. Investigations of the electron-
microscopic structure were made on the microscope
EMV-100BR.
mailto:vsokol@kipt.kharkov.ua
RESULTS AND DISCUSSION
Studies Zr, Zr1Nb, and Nb, which were subjected to
severe plastic deformation, have shown [913], that
under conditions of constant rise of energy (rolling,
drawing) is formed the fine fragmented structure with a
high level of internal stresses.
If the elastic-stress state and the mode of speed
deformation to change, i.e., under creep conditions, such
structures becomes kinetically unstable and rearranges
even at stresses below the yield strength, what is
accompanied by a decrease in the level of internal
stresses [913].
Fig. 1 show the structure which formed after creep
Zr, strained by rolling at 300 K. As can be seen, as a
result of the return process, a less strenuous structure is
formed. For example in samples deformed by rolling on
0.35 cellular structure between powerful high-angular
boundaries is formed (see Fig.1,a) and as a result of the
restructuring of the samples, deformed by rolling on 2.5,
fragmented structure is formed, but less intense and
more resistant to subsequent deformation under creep
conditions.
a b
Fig. 1. TEM images of zirconium after rolling at 300 K
and subsequent creep at 300 K
and σ 0,9σВ, 0,35 (а), 2.5 (b)
It seems that the plastic flow during creep first
carried out by sliding the free intra-bloc dislocations and
output them to the boundaries.
Next, with the strain raise, the contribution of the
relaxation mechanisms (dislocation creep at grain
boundaries, annihilation of opposite dislocations and
absorption the dislocation of boundaries) increases.
Thus in boundaries also there can be a redistribution of
dislocations, accompanied by some ordering. All these
processes lead to micro localization of deformation and
stress relaxation [913].
Structural investigation of specimens of niobium
after creep deformation to ~ 1% (Fig. 2) has shown that
the defect structure of niobium predeformed by drawing
becomes instable, when the deformation conditions are
changing. Thus, the density of randomly distributed
dislocations sharply decreases, the dense elongated like-
sign dislocation formations are nucleated, creating a
rather large gradient of local internal stresses. The old
boundaries are broken and new boundaries with smaller
disorientation angles are formed. In the remained
boundaries the processes of dislocation redistribution
occur, being accompanied by some ordering, i.e. the
effects of deformation microlocalization are observed.
a b
Fig. 2. TEM images of niobium after drawing to 80%
at 77 K (a); after creep deformation at 77 К (b)
It is necessary to note that the development of creep
processes in the highly distorted fragmented structures
(Zr, Zr1Nb, Nb) cannot be described by the classical
representations. The transition from the logarithmic
creep to the power law creep, characteristic for much
higher temperatures is observed, at same time the total
level of internal stresses being decreased [913].
During the creep of steel samples at T = 600 K and
strain slightly higher than the yield stress observed local
area of inhomogeneous plastic flow. This is expressed
in a sharp increase the magnitude instantaneous
deformation. The average value of the creep rate does
not change.
As a result of the processes that led to a jump in
instantaneous deformation, the further character of
plastic flow of the material ceases to be monotonic. The
jumplike creep is observed, especially at stresses close
to the ultimate strength [14].
The observed effect is the result of the kinetic
instability of the structure that has arisen as a result of
changes in the conditions of deformation. The structure
of steel after processing factory – is a structure that was
formed during hot forging of the material and
subsequent annealing. In creep process, i.e during
deformation under the action of the slowly increasing
stresses, the elements of the recovery structure can be
formed (Fig. 3). Their stability will determine the
further evolution of the structure of the material and its
creep resistance [15].
At stresses above the yield point, this structure is
destroyed, which results in a sharp splash the value of
the instantaneous deformation. This means that the
energy imparted to the metal was more of binding
energy between dislocations and point defects, which
have ceased to be effective brakes.
a b
Fig. 3. TEM images of steel 15Cr2NMFA:
a after creep at Т=600 К и 0.2;
b after creep at Т=600 К и В
However, the processes of the slip do not obtained
development because of the high density of defects and
boundaries. With further increase of stress the new
dislocations boundaries are generated. They are more
resistant to new conditions of deformation, however, the
process creep achieves the jumplike character, and
instability of plastic flow is enhanced at stresses close to
the ultimate strength.
CONCLUSIONS
It is shown, that the observed during creep
conditions instability of the structural state of the
investigated materials is a result of the change in the
geometry of the applied stress and low strain rate and
significantly influences on the creep characteristics.
Consequence of the formation of structural
instability and the subsequent restructuring of Zr,
ZrlNb, and Nb, subjected to severe plastic deformation,
transition from the logarithmic creep to the power law
creep is observed, at same time the total level of internal
stresses being decreased, which is the result of
simultaneous work the processes of hardening and
return.
Restructuring of the steel 15Kh2NMFA during creep
leads to appearance a local region of inhomogeneous
plastic flow at stresses slightly above the yield stress
and, as a consequence, to change in the characters of
further plastic flow, namely the emergence of jumplike
creep.
REFERENCES
1. V.V. Ribin. Large plastic deformation and
fracture of metals. M.: “Metallurgy Publ.”, 1986, 224
p.
2. P. Glensdorf, I. Pregogin. Thermodynamics
theory of structures of stability and fluctuations. M.:
“Mir Publ.”, 1973, 280 p.
3. H. Haken. Synergetics M.: “Mir”, 1980, 404 p.
4. V. Ebeling. Formation of Structures at the
Irreversible Processes. M.: “Mir Publ.”, 1979, 325 p.
5. N.Yu. Zolotarevsky, V.V. Ribin. Deformation of
fragmented polycrystalline and texture // Physics of
Metals and Materials Science. 1985, v. 50, N 3, p. 440-
449.
6. V.V. Ribin, A.A. Zisman. Structural micro-
mechanics of plastic deformation and fracture of the
fragmented crystals // Problemy Prochnosti. 1985, N 3,
p. 70-77 (in Russian).
7. A.N. Vergazov, V.I. Lihachov, V.V. Ribin.
Research of the fragmented structure, appearing in a
molybdenum during the active flowage // Physics of
Metals and Materials Science. 1976, v. 42, N 6,
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8. V.K. Aksenov, I.A. Gindin, V.P. Lebedev,
Ya.D. Starodubov. Structural and activating descriptions
of creep of nickel in the interval of temperatures 4,2-
140 K // Low Temp. Phys. 1980, v. 6, N 1, p.118-129.
9. E.V. Karaseva, A.V. Matz, V.I. Sokolenko,
V.A. Frolov. Effect of structural instability on creep of
zirconium subjected to severe plastic deformation /
// Problems of Atomic Science and Technology. Series
“Vacuum, Pure materials, Supreconductors”. 2014,
N 1, p. 106-109.
10. E.V. Karaseva, D.G. Malykhin, A.V. Matz,
V.I. Sokolenko. Creep of Zr1Nb alloy in different
structural state in temperature range 300…700 K //
Problems of Atomic Science and Technology. Series
“Physics of Radiation Effect and Radiation Materials
Science”. 2011, N 4, p. 45-48.
11. І.F. Borisova, I.N. Butenko, E.V. Karaseva,
D.G. Malyhin, A.V. Mats, V.I. Sokolenko, V.A. Frolov,
I.F. Borisova. Texture formation peculiarities of
zirconium in condition of large plastic deformation and
its influence on characteristics of creep in the
temperatures range 300…700 K // Problems of Atomic
Science and Technology. Series “Physics of Radiation
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12. E.V. Karaseva, V.I. Sokolenko. Influence of
different thermomechanical treatments on mechanical
properties and creep of ZR1NB alloy in the
temperatures range 300…700 K // Problems of Atomic
Science and Technology. Series “Physics of Radiation
Effect and Radiation Materials Science”. 2014, N 1,
p. 70-73.
13. Е.V. Karaseva, А.V. Mats, V.I. Sokolenko.
Structural and activation characteristics of the creep in
niobium in the temperature range 77…300 К //
Problems of Atomic Science and Technology. Series
“Vacuum, Pure materials, Supreconductors”. 2007,
N 4, p. 34-37.
14. E.V. Karaseva, A.V. Mats, E.S. Savchuk,
V.I. Sokolenko. Structural instability 15Cr2NMFA steel
under creep at 600 K // Vestnik of Kharkov Univ.
№1075, serіya “Fizyka”. 2013, v.18, p.83-86 (in
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Article received 18.02.2015
ВЛИЯНИЕ СТРУКТУРНОЙ НЕУСТОЙЧИВОСТИ НА ХАРАКТЕРИСТИКИ
ПОЛЗУЧЕСТИ КОНСТРУКЦИОННЫХ МАТЕРИАЛОВ
Е.В. Карасева
Неустойчивость структурного состояния, наблюдаемая в условиях ползучести конструкционных
материалов в различных структурных состояниях, является следствием изменения геометрии приложенных
напряжений и скорости деформирования и существенно влияет на характеристики ползучести. Показано,
что следствием возникновения структурной неустойчивости и последующей перестройки структуры для Zr,
ZrlNb и Nb, подвергнутых большим пластическим деформациям, является изменение закона ползучести.
Перестройка структуры в процессе ползучести стали 15Х2НМФА приводит к изменению характера
пластического течения и появлению скачкообразной деформации ползучести.
ВПЛИВ СТРУКТУРНОЇ НЕСТАБІЛЬНОСТІ НА ХАРАКТЕРИСТИКИ ПОВЗУЧОСТІ
КОНСТРУКЦІЙНИХ МАТЕРІАЛІВ
Є.В. Карасьова
Нестабільність структурного стану, що спостерігається в умовах повзучості конструкційних матеріалів у
різних структурних станах, є наслідком зміни геометрії прикладених напруг і швидкості деформування та
істотно впливає на характеристики повзучості. Показано, що наслідком виникнення структурної
нестабільності і подальшої перебудови структури для Zr, ZrlNb і Nb, що піддавалися інтенсивним
пластичним деформаціям, є зміна закону повзучості. Перебудова структури в процесі повзучості сталі
15Х2НМФА призводить до зміни характеру пластичної течії і появі стрибкоподібної деформації повзучості.
|
| id | nasplib_isofts_kiev_ua-123456789-112307 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T17:31:13Z |
| publishDate | 2015 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Karaseva, E.V. 2017-01-19T20:32:07Z 2017-01-19T20:32:07Z 2015 Influence of structural instability at the creep characteristics of constructing materials / E.V. Karaseva // Вопросы атомной науки и техники. — 2015. — № 5. — С. 130-133. — Бібліогр.: 15 назв. — англ. 1562-6016 PACS: 62.20.HG, 61.72.FF, 61.10.-I https://nasplib.isofts.kiev.ua/handle/123456789/112307 The structural instability, which observed during the creep of constructing materials in different structural states, is the result from changes in the geometry of the applied stresses and strain rate and significantly influences on the creep characteristics. It is shown that the result of appearance of structural instability and the subsequent restructuring of Zr, ZrlNb, and Nb, subjected to severe plastic deformation, was the change in the law creep. Transformation of the structure of the steel 15Cr2NMFA during creep leads to changes in the character of plastic flow, the appearance of jumplike creep deformation especially at stresses close to the ultimate strength. Нестабільність структурного стану, що спостерігається в умовах повзучості конструкційних матеріалів у різних структурних станах, є наслідком зміни геометрії прикладених напруг і швидкості деформування та істотно впливає на характеристики повзучості. Показано, що наслідком виникнення структурної нестабільності і подальшої перебудови структури для Zr, ZrlNb і Nb, що піддавалися інтенсивним пластичним деформаціям, є зміна закону повзучості. Перебудова структури в процесі повзучості сталі 15Х2НМФА призводить до зміни характеру пластичної течії і появі стрибкоподібної деформації повзучості. Неустойчивость структурного состояния, наблюдаемая в условиях ползучести конструкционных материалов в различных структурных состояниях, является следствием изменения геометрии приложенных напряжений и скорости деформирования и существенно влияет на характеристики ползучести. Показано, что следствием возникновения структурной неустойчивости и последующей перестройки структуры для Zr, ZrlNb и Nb, подвергнутых большим пластическим деформациям, является изменение закона ползучести. Перестройка структуры в процессе ползучести стали 15Х2НМФА приводит к изменению характера пластического течения и появлению скачкообразной деформации ползучести. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Процессы пластической деформации Influence of structural instability at the creep characteristics of constructing materials Вплив структурної нестабільності на характеристики повзучості конструкційних матеріалів Влияние структурной неустойчивости на характеристики ползучести конструкционных материалов Article published earlier |
| spellingShingle | Influence of structural instability at the creep characteristics of constructing materials Karaseva, E.V. Процессы пластической деформации |
| title | Influence of structural instability at the creep characteristics of constructing materials |
| title_alt | Вплив структурної нестабільності на характеристики повзучості конструкційних матеріалів Влияние структурной неустойчивости на характеристики ползучести конструкционных материалов |
| title_full | Influence of structural instability at the creep characteristics of constructing materials |
| title_fullStr | Influence of structural instability at the creep characteristics of constructing materials |
| title_full_unstemmed | Influence of structural instability at the creep characteristics of constructing materials |
| title_short | Influence of structural instability at the creep characteristics of constructing materials |
| title_sort | influence of structural instability at the creep characteristics of constructing materials |
| topic | Процессы пластической деформации |
| topic_facet | Процессы пластической деформации |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/112307 |
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