CC BY
6Scientific Notes of Taurida National V. I. Vernadsky University
Series : Physics and Mathematics Sciences. Volume 26 (65). 2013. No. 2. P. 143-150
UDK 539.213
THE RESEARCH OF NANOSTRUCTURAL MATERIALS' PROPERTIES OBTAINED THROUGH PARTIAL CRYSTALLIZATION OF AMORPHOUS
ALLOYS
Lysov V. I., Tsaregradskaya T. L., Turkov O. V., Saenko G. V., Teselko P. O.
Taras Shevchenko National University of Kyiv, 64/13 Volodymyrska Street, Kyiv 01601, Ukraine
E-mail: tsar srdCaukr.net
The research of heat treatment influence and thermomechanical processing concerning amorphous alloys stability has been conducted. It has been shown that these effects significantly enhance the thermal stability of amorphous alloys based on iron. The increase of thermal stability and diminishing of microhardness of amorphous alloys is explained by the fact that the conducted treatment results in substantial displacement of phase equilibrium in the heterogeneous system, amorphous matrix-frozen crystallization centers which is accompanied by diminishing of frozen crystallization centers sizes and amorphous-nanocrystalline state forming.
Keywords: amorphous alloys, crystallization, thermal stability. PACS: 81.40. ± z
INTRODUCTION
The topical matter of metallic glasses research is the development of nanostructure receipt methods through partial crystallization of amorphous alloys due to external influences. These influences are as following - heat treatment (isothermal and unisothermal annealing at temperatures below than temperature of crystallization, thermocycling, cryotreatment); intensive plastic deformation; irradiation of different nature particles. The great attention to heat treatment of alloys with the amorphous structure can be explained by acquisition of the special properties option in the nanorystalline state. In this regard, the study of the amorphous alloys properties under external influences is of keen interest. Moreover the issues of the external factors influence mechanisms on the materials properties are still underestimated [1-2].
For a number of amorphous alloys the certain experiments have been carried out on heat treatment and thermomechanical processing for the purpose of enhancing the alloys thermal stability and the developing of the ways to obtain the nanostructured alloys. The mechanical properties of the nanostructured materials obtained have been also researched.
1. METHOD OF EXPERIMENT
The parameter that determines thermal stability of amorphous alloys is the temperature of intensive crystallization beginning Tk which has been determined by
means of highly sensitive dilatometer method. The method of the conducted dilatometric researches is as follows [3]. While amorphous alloy heating its volume grows droningly (density goes down correspondingly), at certain temperature (the temperatures of
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beginning of intensive crystallization) the volume sharp diminishing and alloy density increasing can be observed that proves the beginning of crystallization. Consequently, it is possible to probe the process of crystallization of amorphous alloy, fixing the change of length of standard and transferring it in volume changes or changes of density. The temperatures of beginning of intensive crystallization for the initial amorphous alloys and after the executed thermal or termomechanical treatment have been determined by dilatometer.
For a number of amorphous alloys in the initial amorphous state and after the processing conducted microhardness by Vikkers on the device PMT-3 has been measured. The method of microhardness measuring is based on of the measuring of imprint diagonal linear size that appears while pressing of a diamond pyramid in the probed material under the certain loading. The device allows to measure microhardness at pressing of the diamond pyramid with the square basis and the top corner of 1360 between the opposite verges with the appendix of loadings (2-200) gramme. As a result of measurings the length of diagonal of imprint obtained by an eyepiece-micrometer has been determined. While measuring microhardness volume deformed by pressure must be less than the amount of a grain being measured. The sample has being pressed 10 seconds.
The number of hardness (for Vikkers) is accounted by the formula:
At the microhardness measuring it has been taken into account the possibility to spread the values of microhardness due to the influence of neighboring structural components with different microhardness. The measurings have been carried out 10 times in the same conditions, the load equals 200 g, and the repeated measuring has been carried out in a new place of structural constituent.
2. THE EXPERIMENT'S RESULTS AND THEIR DISCUSSION
By means of high-sensitivity dilatometry there have been obtained the dependences on the relative change of density for initial alloys and alloys underwent thermal or termomechanical processing. From the dependencies received there have been identified certain temperatures of intensive crystallization beginning for initial samples and those which have been earlier treated. Three types of thermal treatment have been conducted,
namely: thermocycling (3 cycle of heating to T = Tk — 50°C); isothermal annealing
during 1 hour at T = Tk — 500C; heating to T = Tk — 500C (time under this temperature
is 1 minute) and sharp cooling to the temperature of liquid nitrogen 77 K with the purpose of stabilizing of the nanostructural state obtained.
H
where P is the pressure , d is the length of diagonal of imprint in microns.
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On Fig. 1 the temperature dependence of relative change of density-(T) is
P
resulted for amorphous alloy Fe80Bi4Si6 in initial state (Curve 1) and after thermal treatment: thermocycling (3 cycle of heating to T = Tk — 500 C) (Curve 2); isothermal
annealing during 1 hour at T = Tk — 500 C (Curve 3) and heating to T = Tk — 500 C (time
under this temperature is 1 minute) with following cryotreatment (Curve 4).
The tempererure of intensive crystallization beginning for Fe80BMSi6 makes 5000C, consequently the previous thermal treatment has been conducted under T=4500C. From Fig.1 it is evidently that the temperature of intensive crystallization beginning after thermocycling has been increased to 150C, after the isothermal annealing - to 300C, and after cryotreatment - up to 400C.
FcsoBuSib
5 4
3
I2 1
0
-1 :
T, °c
Fig. 1. Relations between relative changes in density and temperature for amorphous alloys Fe80B14Si6 obtained with continuous heating and cooling: (1) initial sample; (2) after thermocycling; (3) after isotermal annearling; (4) after cryotreatment.
On Fig. 2 temperature dependence of relative change of density —P(T) is resulted
P
for amorphous alloy Fe70Cri5Bi5 in initial state (Curve 1) and after thermal treatment: thermocycling (3 cycle of heating to T = Tk — 500C ) (Curve 2); isothermal annealing
during 1 hour at T = Tk — 50°C (Curve 3) and heating to T = Tk — 50°C (time under this
temperature is 1 minute) with following cryotreatment (Curve 4). The temperature of intensive crystallization beginning for Fe70Cri5Bi5 makes 4800C. Consequently, the
FesoB ijSib
T, °c
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previous thermal treatment has been conducted at T=4300C. From Fig.2 it is evident that the temperature of intensive crystallization beginning after thermocycling has not changed, after the isothermal annealing it has increased to 600C, and after cryotreatment -to 200C.
Fig. 2. Relations between relative changes in density and temperature for amorphous alloys Fe70Cr15B15 obtained with continuous heating and cooling: (1) initial sample; (2) after thermocycling; (3) after isotermal annearling; (4) after cryotreatment.
For amorphous alloys Fe80B14Si6 and Fe76Ni4Si6B14 the influence of the combined thermomechanical treatment on thermal stability has been researched.
The thermomechanical processing of amorphous alloy samples has been performed in two steps. Thermal treatment has meant isothermal annealing at temperature
T = Tk — 500C for 10 min, while mechanical treatment has been performed on a
hydraulic press with a quintuple cyclic loading of 225 MPa. Fig. 3 and Fig. 4 show the temperature dependence
P \
P
after thermomechanical treatment (Curve 2). The temperature of intensive crystallization beginning for amorphous alloy Fe80B14Si6 makes 5000C, so the previous thermal treatment has been conducted under T=4500C. The temperature of intensive crystallization beginning for amorphous alloy Fe76Ni4Si6B14 makes 4500C, thus the previous thermal treatment has been conducted under T=4000C. It becomes clear from Fig.3 and Fig.4 that the temperature of intensive crystallization beginning for amorphous alloy Fe80B14Si6 after combined thermomechanical treatment has increased to 400C and for amorphous alloy Fe76Ni4Si6B,4 - to 500C.
of density relative change
v^ ) for amorphous alloys Fe80B14Si6 and Fe76Ni4Si6B14 in initial state (Curve 1) and
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FcsoBuSift
3 —
2 —
îi ~
-1
400
T, "C
Fig. 3. Relations between relative changes in density and temperature for amorphous alloys Fe80B14Si6 obtained with continuous heating and cooling: (7) initial sample; (2) thermomechanically processed sample.
* 2 I,
■1
400
T, °c
Fig. 4. Relations between relative changes in density and temperature for amorphous alloys Fe76Ni4Si6B14 obtained with continuous heating and cooling: (7) initial sample; (2) thermomechanically processed sample.
Table 1 shows the beginning of intensive crystallization temperature for a number of initial amorphous alloys and after the thermal or thermomechanical processing.
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Table 1
The onset intense crystallization temperatures for initial amorphous alloys and the alloys after heat treatment or thermomechanical processing
Composition of amorphous alloy The beginning of intensive crystallization temperature Tk , °C
initial alloys after thermo- cycling after isotermal annearling after cryotreat-ment thermomecha-nically processed alloys
Fe8oB2o 380 440 420 440 460
Fe83Bi7 400 460 440 480 480
Fe7oCri5Bi5 480 480 540 500 500
Fe8oBi4Si6 500 515 530 540 540
Fe76Ni4Si6Bi4 500 520 520 540 550
Fe77.5Bi6Si2Ni3.5Mo1 480 500 520 500 520
As a comparison parameter elastic properties of metallic glasses in the initial state and after a processing used the microhardness Table 2 shows the results of microhardness measurements.
Table 2
Microhardness for initial amorphous alloys and after a processing
Composition of amorphous alloy h , f g ] ^ mm )
initial alloys alloys after isotermal annearling
Fe83Bi7 758±38 658±330
Fe70Cri5 B15 526±21 416±26
initial alloys thermomechanically processed alloys
Fe80BMSi6 747±37 648±32
Fe76Ni4Si6Bi4 605±30 512±25
It has been experienced thermal stability increasing, as it is evidenced by increasing of temperature of intensive crystallization beginning and microhardness diminishing, for all investigational amorphous alloys after thermal conducted or termomechanical
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treatment. This fact can be explained by dissolution of existing in the amorphous phase some frozen crystallization centers and the amorphous-nanocrystalline state forming [4-5]. The amorphous alloys are the heterogeneous systems: amorphous matrix is frozen crystallization centers existed in the metastable state, therefore their properties depend on external terms influence substantially (temperature, pressure, time, etc), especially in the area of phase transitions. There are always some frozen crystallization centers in the amorphous samples newly obtained, while the volume fraction of crystalline phase in the sample don't not exceed X =10-6 (condition amorphous material). Over time and under the influence of external influences the size of frozen crystallization centers can vary. They can grow, and then temperature and time stability of amorphous alloys become decreasing. It is observed while aging of amorphous binary alloys. The size of frozen crystallization centers can also decrease and dissolve which result in increased thermal stability of amorphous alloys. The condition of the thermodynamic equilibrium of a system with an amorphous matrix and frozen crystallization centers for component i is described by the equality = 0 [1]. Nucleation is therefore influenced considerably by
the difference A^i between the chemical potentials of the amorphous and crystal phases,
with a drop in A^i raising the alloy's thermal stability.
The conducted treatment of amorphous alloys has resulted in substantial displacement of phase equilibrium in the heterogeneous system: amorphous matrix as frozen centers of crystallization which leads to an increase in thermal stability interval. More considerable increase of temperature of intensive crystallization beginning for binary alloys can be explain by the fact that multicomponent amorphous alloys are more stable in comparing to binary ones, since the addition of silicon and high temperature alloying admixtures such as molybdenum and niobium, the basic binary alloys of the system Fe-B, inhibit the diffusion of boron in alloys, thus the crystallization process.
Thus, the results of the experimental studies confirm the conclusions of the theory of amorphous alloys thermodynamic stability [1], which shows the possibility to shift the phase equilibrium in the system amorphous matrix-freezes centres of crystallization by directional external influences (temperature, pressure) and can be defined by modes of the temperature interval extension of amorphous state existence.
CONCLUSIONS
1. It is shown that for binary and multicomponent amorphous alloys based on iron the increase in thermal stability after thermal or termomechanical treatment conducted on (20-80)0C has been observed.
2. It is established that microhardness of materials received has been reduced compared to the initial amorphous state, which can be explained by the dissolution of freezes centers crystallization in the initial samples and the formation of nanostructural state.
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References
1. A. P. Shpak, V. I. Lysov, Yu. A. Kunits'kii, and T. L. Tsaregradskaya, Crystallization and Amorphysation of Metal Systems (Akademperiodika, Kiev, 2002) [in Ukrainian].
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4. M. E. Dokukin, N. S. Perov, Chong-Oh Kim, Cheol Gi Kim, Physica Status Solidi (a) 202, 1988 (2004).
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Лисов В. I. Дослвдження властивостей наноструктурних матер1ал1в, отриманих частковою кристал1защею аморфних сплав1в / В. I. Лисов, Т. Л. Цареградська, О. В. Турков, Г. В. Саенко, П. О. Теселько // Вчен записки Тавршського национального уншерситету iMeHi В. I. Вернадського. Серiя : Фiзико-математичнi науки. - 2013. - Т. 26 (65), № 2. - С. 143-150.
Проведено дослвдження впливу термiчноl i термомеханчио! обробки на стабшьшсть аморфних сплавш та показано, що цi впливи значно пiдвищують температуру початку штенсивно! криcталiзацu. Збiльшення термiчноl cтабiльноcтi та зменшення мiкротвердоcтi аморфних сплавш пояснюеться тим, що проведена обробка призводить до icтотного змщення фазово! ршноваги в гетерогеннш система аморфна матриця-вмороженi центри криcталiзацп, що супроводжуеться зменшенням розм1рш вморожених цен^в кристатзаци та формуванням аморфно-нанокриcталiчного стану. Krn4esi слова: аморфш сплави, крист^зацш, термпчна cтабiльнicть.
Лысов В. И. Исследование свойств наноструктурных материалов, полученных частичной кристаллизацией аморфных сплавов / В. И. Лысов, Т. Л. Цареградская, О. В. Турков, Г. В. Саенко, П. О. Теселько // Ученые записки Таврического национального университета имени В. И. Вернадского. Серия : Физико-математические науки. - 2013. - Т. 26 (65), № 2. - С. 143-150. Проведено исследование влияния термической и термомеханической обработки на стабильность аморфных сплавов и показано, что эти влияния значительно повышают температуру начала интенсивной кристаллизации. Увеличение термической стабильности и уменьшение микротвердости аморфных сплавов объясняется тем, что проведенная обработка приводит к существенному смещению фазового равновесия в гетерогенной системе: аморфная матриця-вмороженные центры кристаллизации, что сопровождается уменьшением размеров вморожених центров кристаллизации и формированием аморфно-нанокристаличного состояния.
Ключевые слова: аморфные сплавы, кристаллизация, термическая стабильность.
Список литературы
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4. The cryogenic treatment effect on the magneto-impedance properties of the Co- and Fe-based amorphous ribbons / M. E. Dokukin, N. S. Perov, Chong-Oh Kim, Cheol Gi Kim // Physica Status Solidi (a). - 2004. - Vol. 202. - P. 1988-1991.
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Received 3 September 2013.
