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18КОНТРОЛЬ И МОНИТОРИНГ ОПАСНОСТЕЙ HARARD MANAGEMENT AND MONITORING
Оригинальная статья / Original article УДК 574.631
HEAT TREATMENT EFFECT ON THE MICROSTRUCTURE OF Lai.yFen.e Sii.4 ALLOY © Sun Kai1, Zhu Jia-Ying2
Innovation Practice College, Liaoning University of Engineering and Technology, Liaoning, 123000, China
ABSTRACT. PURPOSE. The non-stoichiometric ratio of La17Fe116 Si14 was prepared by adding La. The microstructure, phase formation and magnetocaloric property of La1.7Fe11.6Si1.4 were studied under different heat treatment conditions. METHODS. The experiments were carried out by vacuum levitation melting and quick quenching methods with pulverized quick-setting methods to obtain the quick-acting sheet of La17Fe116Si14 and the mother alloys were annealed at 850, 950, 1000, 1050 and 11000 respectively sample. The mother alloys and samples were examined using scanning electron microscopy and X-ray diffraction. RESULTS. The experimental results show that there are many similar a-Fe dendrites in the as-cast state at 9500 and agglomerate into the granular a-Fe at the proper temperature. There are many La (Fe, Si)13 phases at 1050°, a-Fe phase and LaFeSi phase decrease. It is verified that the La-Fe-Si based La-rich alloy can be annealed at a relatively low temperature for a short time and the La (Fe, Si)13 phase is transformed from the a-Fe phase and the LaFeSi phase. At 1100 there will be more a-Fe agglomeration into large particles, while the 1:13 phase tends to be stable. CONCLUSION. Finally, the magnetic properties of the better samples were tested to determine the best annealing time and annealing temperature.
Keywords: magnetic refrigeration material, non-stoichiometric ratio La1 jFe116Si1A, microstructure, magnetic property, annealing
Article info: received November 12, 2017; accepted November 22, 2018; available online March 21, 2018.
For citation: Sun Kai, Zhu Jia-Ying. Heat treatment effect on the microstructure of La17Fe11.6Si14 alloy. XXI century. Techosphere Safety. 2018, vol. 3, no. 1 (9), pp. 32-42.
ВЛИЯНИЕ ТЕРМООБРАБОТКИ НА МИКРОСТРУКТУРУ СПЛАВА La1.7Fe11.6Si1.4 Сун Кай, Чжу Цзя Ин
Инженерный Технологический Университет Ляонина, Колледж инновационной деятельности, Ляонин, 123000, Китай.
РЕЗЮМЕ. ЦЕЛЬ. Нестехиометрическое отношение La17Fe11.6Si14 было получено путем добавления La. Микроструктура, формирование фазы и магнитотепловые свойства La17Fe11.6Si14 изучались в различных условиях термообработки. МЕТОДЫ. Эксперименты выполнены вакуумным таянием поднятия и быстрым методом подавления с распылением для получения La17Fe11.6Si14. Базовые сплавы производились при температуре 850, 950, 1000, 1050 и 1100 градусов С, а затем изучались с помощью электронной микроскопии и дифракции рентгена. РЕЗУЛЬТАТЫ. Эксперимент показал, что возникает много подобных a-Fe дендритов в литом виде при 95000 и происходит скопление гранулированных a-Fe при соответствующей температуре. Доказано, что La-Fe- - основной сплав, а сплав La-rich может быть получен при относительно низкой температуре в течение короткого времени и La (Fe, СИ), 13 фаз, преобразованы от a-Fe-фазы в фазы LaFeSi. При температуре 11000 a-Fe концентрируется в большие скопления, в то время как фаза 1:13 имеет тенденцию к стабильности. ЗАКЛЮЧЕНИЕ. Исследование магнитных свойств полученных образцов помогло определить оптимальное и температуру отжига сплавов. Ключевые слова: магнитное охлаждение, нестехиометрическое отношение La 1.7Fe11,6Si1,4, микроструктура, магнитное свойство, отжиг.
Информация о статье: дата поступления 12.11.2017 г.; дата принятия к печати 22.11.2017 г; дата онлайн-размещения 21.03.2018 г.
Формат цитирования: Сун Кай, Чжу Цзя Ин. Влияние термообработки на микроструктуру сплава La17Fe116Si14 // XXI век. Техносферная безопасность. 2018. Т. 3. № 1 (9). С. 32-42.
1
Sun Kai, Research Associate, e-mail: [email protected] Сун Кай, научный сотрудник, e-mail: [email protected]
2Zhu Jia-Ying, Research Associate, e-mail: [email protected] Чжу Цзя Ин, научный сотрудник, e-mail: [email protected]
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Introduction
Magnetic refrigeration technology has a long history of research. As early as 1881, Warburg [1] first observed the thermal effect of metallic iron in the applied magnetic field, and then opened the door to magnetic refrigeration materials, people continue to explore the field of magnetic refrigeration. The NaZn13-type cubic La-Fe-Si alloy [2-5] is a magnetocaloric material with a giant magneto-calorific effect. The major constituent element of the alloy is Fe, and Fe is abundant in nature. Moreover, the preparation of La(Fe, Si)13 compounds requires very low purity of Fe, 99.9%, so the cost is low. And the material is non-toxic and pollution-free, Curie temperature easy to adjust, Magneto-thermal properties such as the advantages of widespread attention, has also become one of the most promising magnetic refrigeration materials [6-7]. However, there are still a series of problems to be solved in the current stage of LaFe13-ySiy magnetic refrigeration materials: The LaFe13-xSix compound does not appear in the alloy ingot obtained by conventional ingot casting or smelting process in the 1:13 phase [8], except that a large amount of dendritic a-(Fe, Si) phase is present, and under the as-cast condition 1:13 difficult to form; La(Fe, Si)i3 is more difficult and requires 7 days or longer annealing at high temperature to obtain a single NaZn13
type LaFe13-ySiy compound, which not only has a long preparation period but also consumes a large amount of energy [8]; NaZn13 type structure LaFe13-ySiy compound formation mechanism of less research needs to be explored. The decrease of Fe content will weaken the magnetic transition behavior of parade electrons and thus reduce the magnetocaloric effect of the compounds, on the other hand, the iron content needs to be reduced to generate a 1:13 phase [9, 10].
This article is mainly the use of a more comprehensive vacuum suspension melting, rapid quenching strip method to obtain the mother alloy, different temperatures, short annealing time. Then the sample was examined by scanning electron microscopy and X-ray diffraction, the microstructure and phase analysis were carried out to obtain the best annealing temperature and annealing time, and then select the best sample for magnetic properties testing. The following content verification and research: the feasibility of the La-Fe-Si based La-Fe-Si-based alloys prepared by the melt-fusing method at low temperature and short-time annealing; To determine the best annealing time and annealing temperature of La17Fe116Si1.4 rapid coagulation chip; Observe the mechanism of 1:13 phase formation and the a-Fe diffusion mode.
Experimental
In this experiment, the lanthanum block with the purity of 99.5%, the iron with the purity of 99.9% and the silicon with the purity of 99.99% (all the mass fractions) were used. The master alloy was prepared by vacuum suspension melting and rapid solidification. The samples were respectively heated at a temperature of 850, 950, 1000, 1050 and 11000 for 0h (reaching the holding temperature) 1h, 5h, 12h annealing at high temperature. The field emission electron microscope
(EDS) was used to analyze the microstructure of the samples by backscattered electron bombardment of the sample surface by high energy incident electron and the secondary electron observation. The XRD test uses Ka radiation from a Cu target (measuring the abraded X-ray diffraction pattern of the block using a structural analysis of the experimental results to determine the phase composition of the sample.
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Results and discussions Master alloy structure analysis (fig. 1).
□
-unanneale d
LaFeSi LaFeSi
1 La5Si3 1 a-Fe
VihhJ
20 30 40 50 60 70 SO
2 theta (deg.)
Fig. 1. Unannealed parent alloy XRD spectrum Рис. 1. Рентгеновская дифракция неотожжённого исходного сплава
The mother alloy with an agate grinding setting master alloy has a very high a-Fe
bowl ground to a smaller particle size powder, peak, and a small amount of LasSi3 and
measured XRD patterns, given by Figure 1. LaFeSi peak, no La(Fe,Si)i3 features. Comparison of the card shows that quick-
Fig. 2. The restricted area, back-roll area, cross-section organization of unannealed parent alloy: (a) stick roller surface; (b) back roller surface; (c) cross section; (d) stick roller surface (30ym) Рис. 2. Ограниченная зона, опорная зона, поперечная организация неотожженного исходного сплава: (a) поверхность манипулятора; (b) поверхность заднего цилиндра; (c) crosssection; (d) поверхность манипулятора (30мм)
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Fig. 2 shows the secondary backscattered electron image of the unannealed mother alloy under the field emission scanning electron microscopy, which is respectively the roll surface, back roll surface and cross section. Through the comparison found that the mother alloy paste roller surface and back roller surface of the same organization, but also did not find the cross-section of the organizational differences on both sides, are extremely small dendrite, fully proved that the process reached a refinement of the organization Effect. By EDS EDS analysis of the white, gray and
black regions of the alloy, it can be seen that the black region is a-Fe with a dendritic structure and a relatively fine structure, which makes it possible to increase the diffusion rate between atoms, In order to achieve the rapid formation of 1:13 phase in La-rich alloys, the contrast ratio of image contrasting with matlab was 72.31%. The white area is La5Si3 phase (5:3 phase), accounting for 10.73%. The gray area LaFeSi phase (1:1:1 phase) about 16.96%, the phase is a metastable phase, indicating that the alloy is in an unstable state.
Different temperature annealing 5h XRD pattern comparison (fig. 3).
Fig. 3. 5h heat preservation in different temperature XRD spectrum Рис. 3. Пятичасовое сохранение тепла при различных XRD спектрах температур
Short-term treatment temperature has a good representation of the heat treatment process, the energy is also more economical to determine 5h is more appropriate, you can effectively get the best annealing temperature. Respectively, were 850, 950, 1000, 1050, 11000 temperatures 5h annealing treatment, compared with the unannealed XRD, as shown in fig. 3. It can be very intuitive to find that the XRD patterns at 850, 950 and 1000° are almost the same as the unannealed XRD he samples are mainly composed
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of a-Fe phase with a certain amount of La5Si3 phase (5: 3) and LaFeSi phase 1:1:1 phase). However, many La (Fe, Si)i3 phases were formed at 10500 with a higher peak and the a-Fe peak decreased accordingly. Thus, the La-rich alloy can be largely eliminated by conventional short-Fe phase, generate more 1:13 useful phase. At the same time, it was found that the LaFeSi phase decreased gradually, while the La5Si3 phase increased. The 1100°C spectrum was very similar to the 1050°C spectrum. Fig. 3 Determines that a
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suitable temperature of 1:13 should be between 1000°C and 1100°C, and again verifies the feasibility of the melt-flotation process.
10000 sample analysis. According to the XRD patterns of the samples annealed at different temperatures for 5h, three reference experiments were conducted at 10000. The ice-water quenching (ice 0h) was carried out at 10000 with the temperature rising to 10000 for 5h and then for 12h, Samples were subjected to XRD analysis and SEM observation.
Fig. 4 respectively, 0h, 5h, 12h XRD pattern comparison of heat-treated samples and found that the 0h and annealed at the same pattern, once again fully proved that no 10000 below 1:13 phase formation. However, in the analysis of 12h, it is found that there is a clear 1:13 phase peak generation, so the next 10500 experiment can be carried out. At the same time, it is found that the characteristic peak of LaFeSi decreases and the characteristic peak of La5Si3 obviously increases. It is preliminarily presumed that the composition of the alloy gradually evolves from a-Fe phase, LaFeSi phase and a small amount of La5Si3 phase to 1:13 phase, a-Fe phase, La5Si3 phase and a small amount of LaFeSi Phase, the process is the formation of a-Fe and LaFeSi phase reduction.
Fig. 5 is a backscatter electron image of a sample at 1000°C for different holding times. Figure (a) is obviously as-cast microstructure. The XRD pattern analysis is completely consistent with the mother alloy. The main phase is a-Fe, LaFeSi phase and a small amount of La5Si3 phase, indicating that no new phase is formed at 10000. It is clear that the dendritic a-Fe "melts" and begins to agglomerate in figure (b). Further from figure (c) can be observed at 1000 °C for 12h heat treatment at the same time the existence of large particles agglomeration a-Fe, is agglomeration a-Fe and dendritic a-Fe. The high proportion of La alloy has a lower melting point than the low proportion of La alloy, which is more conducive to the atomic diffusion at higher temperature and promotes the a-Fe agglomeration caused by inappropriate temperature. Observation of its tissue enlargement found that dendritic a-Fe aggregates and diffuses into granular a-Fe. A small amount of La (Fe,Si)i3 phase was found during the 12-hour heat preservation process. The boundary was a standard square structure with a size of about 50^m. It was very similar to the LaFe13 hypothetical diagram. At the same time, Brittle, broken in the mosaic when the boundary, indicating its poor mechanical properties.
1:13 113 о ? j 1:13 □ 12h
LapeSi LaSi LaFeSi Í ' ít J I „, л 5h
a- • -A-nwinrj, Oil
unannealed
20 30 40 50 60 70 SO
2 theta (deg.)
Fig. 4. Different heat preservation period in 10000 temperature XRD spectrum Рис. 4. Различные периоды сохранения тепла в XRD спектре 1000°
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Fig. 5. Organization of 1000° annealing sample Рис. 5. Отжиг при температуре 1000
1050° sample analysis. For XRD at
1050° for 5h, it is found that a large amount of 1:13 phase is formed in the phase at 1050°, and only 1:12 at 10000 for 12h. It can be roughly determined that the optimal treatment temperature should be at 10500, so 10500 were done with the furnace temperature 0 min, 10 min, 30 min, 1h, 3h, 5h, 12h multiple experiments.
The XRD patterns of 0 min, 10 min, 30 min, 1h, 3h, 5h and 12h after heat preserva-
tion are shown in fig. 6, respectively. From this comparison, it can be concluded that the a-Fe peak gradually decreases with increasing holding time, 13-phase peak increased, more 1:13 phase peak appeared, and stabilized in the 5h. On the other hand, the characteristic peaks of LaFeSi phase decrease (some overlap with the 1:13 phase peak), and the characteristic peak of La5Si3 phase is obviously increased. After annealing, a-Fe and LaFeSi are transformed into La(Fe, Si)13 and La5Si3.
Fig. 6. Different heat preservation period in 10500 temperature XRD spectrum Рис. 6. Различные периоды сохранения тепла в XRD спектре 10500
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Fig. 7.1050 annealing organization Рис. 7. Организация отжига при температуре 10500
Fig. 7 is a backscattered electron image taken at different holding times of 1050°C. In Fig. 7, there are dendritic a-Fe phase, agglomerated a-Fe phase, LaFeSi phase, La5Si3 phase and La(Fe,Si)13 co-exist, indicating that the state of the sample is not stable, belonging to the 1:13 phase of nascent stage, the growth from the outside of the first generation to reach the temperature range of the region did not reach the temperature range. The grain boundaries with a 1:13 phase are observed, which are roughly regular hexagons. The energy spectrum of the black lines at the grain boundaries is a-Fe. Then the white area dis-
tributed in 1:13 phase is analyzed as 5:3, and the black grain boundary and the white area of other samples with the same holding time are also the same. Figure, (b), (c), (d), is a 1:13 phase growth phase, the size has not yet fully grown, a-Fe is the relatively small particles, did not reunite into 5h, 12h the existence of large particles in the figure, and It was found at 10 min and 30 min that the extremely small a-Fe in the 1:13 phase boundary was "dissolving" in the 1:13 phase, indicating that a-Fe was required for the matrix to form a 1:13 phase. At the time of compositional analysis LaFeSi phase was found. Once again proved
H
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the phase mechanism of the 1:13 phase is: a-Fe and LaFeSi into La(Fe, Si)13 and La5Si3. However, there is a large amount of 1:13 phase formation from figures (a) to (b) only for 10 min, which shows the feasibility of short-time annealing of La-rich La-Fe-Si alloy. In the 1:13 phase EDS line scan of the image, it was found that the components of 5h and 12h were basically stable and the microstructure was
maximized to about 300^m. At this time, no 1:1:1 phase was found in the matrix, and the optimal sample analysis.
Optimal sample analysis and selection (fig. 8). Fig. 8 shows a comparatively good XRD pattern of the sample with more favorable pattern of the sample with more favorable 1:13 morphologies.
Fig. 8. Optimal sample analysis and Рис. 8. Анализ оптимального образца
In the fig. 8, a-Fe peak is low, there are a lot of La(Fe, Si)i3 peaks and a small amount of LasSi3 peak. It is impossible to analyze which of the several samples has the most ideal microstructure. Therefore. To visually analyze the sample content of various components.
From table we can very intuitively see 10500 12h after heat treatment of the sample, a-Fe content and the minimum content of 1:13 phase, the proportion is already high, and
The composition ratio Состав лучших
should be able to meet to some extent magnetic refrigeration material After all, the 5:3 phase cans not be completely eliminated due to the introduction of La-rich La. The addition of La promotes the formation of La5Si3 phase, thus taking away a large amount of Si, which leads to a large reduction of the Si content in the matrix. Less 1:13 more difficult to become phase.
of best sample образцов
Ingredients / Компоненты 1:13 (gray area / серая зона) La5Si3 (white area / белая зона) a-Fe (black area / черная зона)
105005h 71.32% 15.96% 12.72%
1050u12h 74.85% 15.49% 9.66%
1100u1h 73.23% 12.01% 14.76%
110005h 60.42% 15.70% 23.88%
Note: The composition of the table based on SEM calculated using matlab, as the approximate volume percentage. Примечание: SEM рассчитывается в программе Matlab как приблизительный процент объема.
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The first three annealed samples have a 1:13 phase volume fraction of about 70%, while the corresponding annealing temperature of 1100°C for 5h annealed sample volume fraction of 60.42% did not increase the content of 1:13 phase, Decrease; and further promote the a-Fe agglomeration, making the 5:3 phase content increased. This is most likely characterized by a high temperature anneal during the initial anneal, while increasing the high temperature anneal time caused the 1:13 phase to decompose. Therefore, the low content of 1:13 phase annealed at 1100 °C is not
due to the short annealing time, but the annealing temperature is not suitable.
For the traditional La-Fe-Si magnetic refrigeration materials, high-temperature longtime annealing preparation method is to make the system infinitely close to its thermodynam-ically stable state, and for the La-Fe-rich non-stoichiometric La-Fe-Si alloy, high temperature Long annealing should also play a role, but the energy spent and played a role in whether the match needs further study. So in this experiment the best sample is 1050012h.
The best sample magnetic properties test (fig. 9-11).
Through the above analysis, the mag- samples were tested and compared. neti properties of 10500 5h and 10500 12h
12h
80 100 120
140 160 180 200 Temperature(K)
220 240 260
90 80 70 60
'S
"Э 50
E ш
ii 40 £=
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S
20 10 0
60
50
с 40
30
0
_I_i_I_._I_._I_i_I_i_I_i_I_
120 140 160 180 200 220 240
Temperature(K)
Fig. 9. M-T curves Рис. 9. Кривые M-T
Magnetic Field (Oe) Magnetic Field (Oe)
Fig. 10. Isothermal magnetization curve Рис. 10. Изотермальная кривая намагниченности
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Fig. 11. Sample under different external magnetic field, the magnetic entropy changes with the temperature change curve Рис. 11. Образец в различных внешних магнитных полях, магнитная энтропия изменяется с изменением кривой температуры
For La-Fe-Si compounds with NaZn13 structure, the field-induced magnetic transition of the parasite occurs near its Curie temperature, and the paraelectric magnetic transition is related to the Fe-Fe bond in its unit cell [3]. The Fell-Fell bond plays a dominant role and the Fel-Fell bond relatively weak. Since Si replaces only Fell atoms, the more the Fe content is, the stronger the paraelectric magnetic transition is. The more obvious the first order phase transition is, the larger the magnetic entropy change is, but the greater the hysteresis is. ln this paper, the magnetic properties of La1.7Fe11.6Si14 were measured by MPMS. The MT curves (Fig. 9), isothermal magnetization curves (Fig. 10), and the magnetic entropy change curves (Fig. 11). The analysis of figure 9 shows that the Curie temperatures of samples annealed at 10500 for 12h and annealed at 10500 for 5h are 180.4K and 179.6K, respectively, and the Curie temperature is not very different. The phase of the sample at these two annealing temperatures is basically the same. The results showed that the performance of samples after 12h treatment was better than that of 5h, which was consistent with the observation of its microstructure. From the isothermal magnetization curve of figure 10, the La-rich alloy has a large hyste-
resis, indicating that the first-order phase-change cruise electron is more intense. The latter 10500 annealing 5h isothermal magnetization curve distortion (a clear line in the figure is not consistent with other lines), indicating that the sample magnetic instability, and from the curve lag point of view, compared to 10500 annealing 12h, its Magnetic performance is poor. Then calculate the magnetic entropy change of each compound according to Maxwell's equation. The results are shown in fig. 11, which shows that the maximum magnetic entropies of samples annealed at 10500 for 12 hours and annealed at 10500 for 5h are 17.9J/Kg*K and 16.8J/Kg*K, respectively. By isothermal magnetic entropy change chart we can see isothermal magnetic entropy change has a step, expanding its refrigeration temperature zone. And we know that the refrigeration capacity of magnetic refrigeration material is the integral of temperature isothermal magnetic entropy change, that is the area surrounded by the curve, the emergence of the step greatly increases the area enclosed by the curve, thus greatly increasing its magnetic cooling capacity. After analysis and calculation, it is found that the cooling ability of the sample annealed at 10500 for 12h is better than that of the sample annealed at 10500 for 5h.
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Conclusion
1. The La-rich La^Fe^Si^ alloy prepared by the melt-fusing method has a refined structure. After annealing at 1050°C for 12h, the structure with better magnetic properties can be obtained. La La-Fe-Si-based alloys at low temperature short-time annealing is entirely feasible, and can be applied to large-scale production.
2. By comparing the phase and microstructure of the samples before and after annealing, it was found that with the formation of La(Fe, Si)i3 phase, a-Fe and LaFeSi decrease successively, indicating that the formation mechanism of the La(Fe, Si)13 phase is that a-Fe and LaFeSi are transformed into La(Fe, Si)13 .
3. In the annealed microstructure at 1000°, different forms of a-Fe were observed in one and the same sample. It was found that in the non-positive ratio La1.7Fe11.6Si1.4 alloy, a-Fe is dispersed in the form of agglomeration.
4. By analyzing the microstructure of the samples with different annealing temperature
References
and annealing time and testing the magnetic properties, it is found that the samples annealed at 10500 for 12h have the best performance, which shows that annealing at 10500 for 12h is the best annealing temperature and annealing time.
5. The La1.7Fe116Si14 coupon itself is very brittle, whereas the La(Fe, Si)13 phase formed by heat treatment makes the matrix more brittle.
6. Compared with 1h and 5h incubation at 11000, it was found that prolonging the holding time did not increase the content of 1:13 phase, but decreased the proportion and further promoted the aggregation of a-Fe, making the content of 5:3 phase rise. The reason is that in the initial annealing showed the characteristics of high temperature annealing, and increasing the high temperature annealing time makes the 1:13 phase decomposition. Therefore, the low content of 1: 13 phase annealed at 1100° is not due to the short annealing time, but the annealing temperature is not suitable.
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Sun Kai, Zhu Jia-Ying have equal author's rights and bear the responsibility for plagiarism.
Conflict of interests
The authors declare no conflict of interests regarding the publication of this article.
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Сун Кай, Чжу Цзя Ин имеют равные авторские права и несут ответственность за плагиат.
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