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мають бiльшi значення в порiвняннi з плiвкою № 2, що може бути пов'язано з наявшстю в першш групi поль мерiв б^ьшо'! кiлькостi гiдрофiльних функцiональних груп. Але даш плiвки не розчиняються в мильно-содо-вому розчинi при невисоких теплових обробках (400С), порiвняннi з плiвкою з ПВА, розчиннiсть яко! в серед-ньому в 2 рази бшьша при 1000С в порiвняннi з плiв-ками iз акрилових сополiмерiв. Пiдвищити стiйкiсть дослщуваних плiвок iз акрилових дисперсiй можливо шляхом введення в склади додаткових компонентпв, наприклад предконденсати термореактивних смол, яю утворять мщш ковалентнi зв'язки з гiдрофiльними функцiональними групами акрилових сополiмерiв.
Таким чином, отриманi результати та 1х аналiз вия-вили перевагу вггчизняних полiмерних дисперсiй № 1, № 5 (Лакриекс 272, Лакриекс 273), плiвки з яких е про-зорими, гiгроскопiчними, мають високу еластичшсть та незначну розчиншсть при мильно-содових обробках над полiвiнiлацетатною дисперсiею, яка на даний час використовуетья текстильними тдприемствами для апретування тканин. Тому даш термореакцшноздатш акриловi полiмери можуть бути використаннi в опе-рацiях апретування тканин i тим самим розширити обсяг текстильно-допомiжних речовин в процесах за-вершально! обробки текстильних матерiалiв.
Лiтература
1. Глубш П.А. Х1м1чна технолопя текстильних матер1ашв (Завершальне оброблення): Навчальний поабник. - К.: Арютей, 2006. - 304 с.
2. Кричевский Г.Е. Химическая технология текстильных материалов: Учеб. для вузов. - М.: РЗИТЛ, 2000. - Т.3. - 436 с.
3. Петерс Р.Х. Текстильная химия. (Физическая химия крашения). Ч.2., - М.: Легпромбытиздат, 1989. - 382 с.
4. Ребиндер П.А. Поверхностные явления в дисперсных системах. - М.: Наука, 1978. - 308 с.
5. Фролов Ю.Г. Курс коллоидной химии. Поверхностные явления и дисперсные системы: Учеб. Для вузов - М.: Химия, 1988. - 464 с.
6. Липатов Ю.С. Физико-химические основы наполнения полимеров: Монография. - М.: Химия, 1991. - 260 с.
7. Липатов Ю.С. Коллоидная химия полимеров: Монография. - К.: Наукова думка, 1984. - 344 с.
8. Охрименко И.С., Верхоланцев В.В. Химия и технология пленкообразующих веществ.- Л.: Химия- 1975.-392с
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The distribution of hydrogen between the different states was estimated from hydrogen permeation and hydrogen extraction measurements and was correlated with the microstructure features of Al-Mg-Mn, Al-Mg-Mn-Fe and Al-Zn-Mg-Mn-Fe alloys. Hydrogen lattice diffusivity was found to depend on the mean free paths between the main phase precipitate complexes. The content of reversibly trapped hydrogen correlated with the volume fraction of precipitates
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удк
RELATIONSHIPS BETWEEN HYDROGEN AND MICROSTRUCTURAL FEATURES OF AL ALLOYS
O. Chernyayeva and D. Lisovytskiy
Institute of Physical Chemistry of the Polish Academy of Sciences ul.Kasprzaka 44/52, 01-224 Warsaw, Poland, olgacher@ichf.edu.pl
INTRODUCTION
Active dissolution and hydrogen embrittlement have been considered to cause the stress corrosion cracking of Al and its alloys [1, 2]. The data on hydrogen diffusivity in Al alloys, being the key factor in hydrogen embrittlement, are rather scarce. For pure Al, the hydrogen diffusivity at room temperature ranged from 10-2 to 10-10 cm2/s-1[3].
The reason might be the presence of the oxide film on the surface or the hydrogen interaction with traps in the metal. In commercial Al alloys, precipitates of various phases as well as un-homogeneity of solid solution (presence of the Guinier-Preston zones) formed depending on their chemical composition and heat treatment [4], should highly affect the hydrogen transport. Hydrogen present in the solid solution or segregated in precipitates of aluminum alloys also affects
the processes of metal deformation and cracking. The hydrogen-induced cracking, hydrogen-induced modification of deformation processes, and hydrogen-enhanced plasticity of metals can be expected to operate during stress corrosion cracking of aluminum alloys depending on the morphology and chemistry of precipitates.
In present work, the effect of the morphology of precipitates on hydrogen diffusivity and trapping was studied for several commercial Al alloys of different chemical and phase composition, by means of electrochemical measurements of hydrogen permeation.
MATERIALS AND EXPERIMENTAL METHODS
The code, chemical composition, standard heat treatment and possible phase composition of precipitates of the alloys are shown in Table 1. Membranes (1x15x15mm) were machined from the middle part of alloy slabs in the direction of rolling.
The X-ray diffraction spectra were recorded on Siemens D5000 at Cu radiation. The phase composition was evaluated from the obtained spectra using the JCPDS PDF-2/2001 database [5].
Microstructure of studied alloys was observed by optical microscope "NEOPHOT-2" at magnification up to 1000X and by scanning electron microscope (SEM) "Hitachi S4-200" at magnification pu to 10,000X. Characteristic structural features of studied materials were determined by the standard quantitative metallography methods [6].
Hydrogen permeation was measured by electrochemical method using the double cell divided by studied membrane [7]. The special attention was paid to select and check the proper experimental conditions providing the hydrogen permeation not affected by the surface processes. To keep the egress hydrogen content C=0 and to allow the free hydrogen egress from the membrane, the egress side of membrane was galvanostatically coated with Pd and at immersion in electrolyte was polarized with constant potential within the passive region (+150 mV (Hg/HgO).
Table 1
Code, chemical composition and heat treatment of studied materials
Material code Material Heat treatment Composition Possible precipitates [4]
Alustar AA5059 - Dutch (Hoogovens) alloy H321 Al-4.45%Mg-0.8%Mn-0.1%Fe Mg2Al3, MnAl6
PA13 AA 5083 - Dutch (Hoogovens) alloy (AlMg4.5Mn0.7) H321 Al-4.6%Mg-0.69%Mn-0.18%Fe-0.14%Si-0.12%Cr Mg2Al3, (Mn,Fe)Al6
PA47 AA7010 - Polish alloy (AlZn5Mg1) T6 Al-4.7%Zn-1.3%Mg-0.24%Mn-0.35%Fe-0.3%Si MgZn2, Mg3Zn3Al2, the Guinier-Preston zones
The test solution was 0.01M NaOH. After pouring test electrolyte into the ingress cell and applying cathodic polarization current (iC) to the ingress side of a membrane, the anodic current (J) being the measure of hydrogen permeation rate, was recorded in the egress cell. The build-up hydrogen permeation transient was recorded up to the steady state value of hydrogen permeation current (J~). After that, the cathodic polarization of the ingress side was switched off, and decay permeation transient was recorded in the egress cell.
For these transients, the following hydrogen parameters were calculated [8]:
D*o.63 = 12/6to.63 (1)
Dtb = 0,051L2/Ttb (3)
where: D*063 - the apparent diffusivity of hydrogen estimated for build-up transients, Dtb - the apparent diffusivity of hydrogen estimated for decay transients, L - membrane thickness; T0.g3- time to rich the permeation current of 0.63*J~ in the build-up transient, Tb - the breakthrough time of the decay transient (Figure 1).
Figure 1. The scheme of the run of test at the electrochemical
measurements of hydrogen permeation through studied membrane at application (on) and cessation (off) of cathodic polarization, ic.
The mean value of residual content of hydrogen left in the studied membranes after the competing the hydrogen permeation test was measured by vacuum extraction at 2600C and 2 hours.
_RESULTS AND DISCUSSION_
X-ray diffraction patterns of the studied alloys are shown in Figure 2. It can be seen from the patterns that fcc-Al (JCPDF card Nr 851327) is a dominant phase for all materials. On the x-ray patterns there are small peaks at positions close to MnAlg phase described by JCPDF card Nr 39-0950 (for Alustar and PA13 alloys) and at positions close to MgZn2 phase (for PA47 alloy) described by JCPDF card Nr 77-1177.
An exact phase analysis is difficult because of a very low intensity and overlapping of diffraction peaks attributed to the above phases.
In the studied alloys, the matrix contained the main alloying precipitates, which are agglomerated in the bands situated along the rolling direction, as schematically shown in Figure 3.
Precipitates in alloys were arranged into the chains along the rolling direction. For this reason, the estimated parameters of microstructure features, shown in Table 2 for alloys corresponded to the precipitates bands (agglomerates): X - mean free distance between precipitate bands; Vv - precipitate volume fraction.
The parameters of hydrogen permeation and hydrogen extraction are presented in Table 2.
Hydrogen, absorbed by metals exists in the solid solution and as bound with reversible and irreversible traps.
PA13 PA47 Alustar
30 35 40 45 50 55
20, deg. CuK
Figure 2. XRD spectra of studied alloys
Figure 3. Schematic sketch of morphology and distribution of precipitates of studied alloys.
Table 2
The structure features and the hydrogen parameters of studied alloys
Material X, ^m Vv, % Dtb, cm2/s D0.63, cm2/s Content of extracted hydrogen, PPm
Alustar 300 8 10.2 3.62 7.47
PA13 198 12 10.2 1.14 3.6
PA47 54 7 5.1 4.9 4.93
C - J"L D
Cdif_ g Dtb
were S - working area of the membrane.
Reversible hydrogen trapping. If hydrogen transport through the membrane is governed by the diffusion processes, the values of Do.63 and Dtb should be similar [8]. However, quite substantial differences between the values of above coefficients were observed for studied materials (Table 2), suggesting the effect of reversible hydrogen trapping on hydrogen permeation [9]. The build-up hydrogen permeation transient is affected by the hydrogen interaction with the reversible traps [9]. Without this interaction, the transient would be described by the lattice diffusivity (Dtb). The difference between the area below the experimental transient and below the transient corresponding to diffusion process is accounted for the amount of hydrogen interacting with the reversible traps (CR), cf. Figure 4.
40
35
30
< 25
A
20
< 15
10
5
0
transient
- ✓calculated for D
-~acr
- \ y \
- / experimental
'Ltx transient
gfi X i\ x iy 1 xi Al|
Diffusible hydrogen. According to [9], the value of hydrogen diffusivity, established from the decay permeation transient (Dtb), is the most close to the value of the lattice diffusivity. As the intrinsic property of the solid solution, the hydrogen lattice diffusivity should depend on the chemistry of the solid solution and its possible un-homogeneity.
Taking into account the Dtb value, the concentration of the diffusible hydrogen (Cdif) on the ingress side of a membrane may be calculated from according to equation [8]:
(4)
60 . 120 180 time, s
Figure 4. Scheme for calculation of hydrogen content, bound with reversible traps (CR) from the comparison of experimental build-up permeation transient with that calculated for Dtb value.
Irreversible hydrogen trapping. Since the vacuum extraction has been done after completing the hydrogen permeation test and thus after leaning all the movable hydrogen, the residual hydrogen left in membrane has been measured. This amount of hydrogen may be adopted as the hydrogen irreversibly bound with traps (ViR). The contents of irreversible trapped hydrogen for studied alloys are presented in Table 2.
The hydrogen distribution between the different states depends on chemical and phase composition of material [9, 10]. Despite the differences in chemical and phase composition of studied alloys, the attempt has been made to found some apparent relationships between microstructural features and hydrogen parameters.
Figure 5 presents the relationship between the amount of diffusible hydrogen and mean free path between precipitates in studied alloys. The content of diffusible hydrogen should depend on chemistry of the solid solution lattice. However, it is also seen that in the case of the similar matrix chemistry (Table 1) in ALUSTAR and PA13 alloys the lower amount of diffusible hydrogen has been obtained for material with higher free path (Figure 5). This may be explained by higher unhomogeneity of the matrix chemistry in the case of more dense precipitates. As has been detected (Figure 5), the chemical composition of matrix changes in the vicinity of precipitate. Therefore, the unhomogeneity of solid solution chemistry may be associated with morphology of precipitates.
The larger distance between precipitates, the more uniform the chemical composition of the solid solution between them. Therefore, the precipitate morphology affecting unh-omogeneity of solid solution chemistry influences the hydrogen lattice solubility. Increase in unhomogeneity of solid solution promotes the hydrogen solubility.
ü'
■ | PA47 |
Al-Zn-Mg
| PA13 | ■ Al-Mg
| ALUSTAR |
■ Al-Mg '
50
100
150 200 X, ^m
250
300
Figure 5. Effect of the mean free distance between precipitate bands (\) of studied alloys on content of diffusible hydrogen (Cdif)
From Figure 6 it follows that content of reversibly trapped hydrogen (CR) increases with increase in precipitate volume fraction, despite the different chemical composition of the precipitates. The assumption can be made that the precipitates serve as the reversible traps of hydrogen.
1 :
lPA13l ■ Al-Mn-Fe-Cr-Si, Al-Mg
D
Al-Mn-Mg-Fe-Si
o
0,1
PA47
Al-Fe-Mn-Zn-Si-Mg, Al-Fe-Si
10
12
Vv %
Figure 6. Relation ship between the content of reversible trapped hydrogen (CR) and precipitate volume fraction (VV)
ALUSTAR
I Al-Mn-Mg-Fe-Si
Al-Fe-Mn-Zn-Si-Mg, Al-Fe-Si
Al-Mn-Fe-Cr-Si, Al-Mg
Figure 7 presents relationship between the content of irreversibly trapped hydrogen (VIR) and the volume fraction of precipitates. Increase in precipitate volume fraction gives decrease in the content of irreversibly trapped hydrogen. This rather unexpected result should be accounted for the difference in the chemistry of precipitates in studied alloys (Table 1) as well as by the morphology of precipitate particles forming the precipitates bands. Effect of chemical and phase composition of precipitates on the hydrogen behavior in Al alloys should be studied and discussed in more details in the future.
_SUMMARY_
1. The hydrogen diffusivity was calculated for studied (ALUSTAR, PA13 and PA47) alloys.
2. Certain correlation between the content of diffusible hydrogen and mean free distance between the precipitate bands has been observed suggesting that the unhomogeneity of solid solution promotes the hydrogen solubility.
3. Certain relationship between the amount of reversibly trapped hydrogen and the volume fraction of precipitates suggests that in studied alloys precipitates serve as reversible hydrogen traps.
4. The above suggestions need to be verified by the thorough studies of the effects of kind, chemistry and morphology of precipitates on hydrogen diffusivity and trapping.
5. Irreversible hydrogen trapping has been mostly affected by the precipitate chemical composition.
REFERENCES
1.
Holroyd N.J.H.: Environment-induced cracking of high-strength aluminum alloys. Proc. Conf. Environment-Induced Cracking, NACE, Kohler, USA, 1988, 311. Holroyd N.J.H., Vasudevan A.K., Christodolou L.: Stress corrosion of high-strength aluminum alloys. Treat. Mater. Sci. Technol. 31 (1989) 463.
Zielinski A.: Niszczenie wodorowe metali nezelaznych i ich stopow. GTN, Gdansk, 1999.
Arzamasov B.N.: Materialovedenie. Meszinostrojenie, Moskwa, 1986.
JCPDS PDF-2/2001 database.
DeHoff D.T., Rhines F.N.: Quantitative Microscopy. McGraw-Hill, New York:, 1973.
Devanathan M.A., Stachurski Z.: J.Electrochem. Soc. 111 (1964) 619.
Barrer R.M.: Diffusion Through and in Solids, Univ. Press, Cambridge, 1941.
Pressouyre G.M., Bernstein I.M.: Metall. Trans. 9a (1978) 1571.
10. Iino M., Acta metal. 30 (1982) 367.
Vv %
Figure 7. Relation ship between the content of reversible trapped hydrogen (VIR) and precipitate volume fraction (VV)
1
0,01
6
8
6
8
