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A discussion on the mechanism of high permeability of 12% Al-Fe alloy
217
Journal of Magnetism and Magnetic Materials 26 (1982) 217-219 North-Holland Publishing Company
A DISCUSSION ON THE MECHANISM OF HIGH PEBMEABILITY OF 12% Al-Fe ALLOY LIU Da .Jun Precision Alloy Department,
Shanghai Iron & Steel Research Institute, Shanghai, People’s Republic of China
On the basis of the results such as thermal expansion coefficient under various temperatures, MSssbauer spectra and magnetic properties after different heat treatments and the investive results obtained by Kazuo and Hiromitsu, the mechanism of high permeability as well as the rule of the soft magnetic properties affected by the order-disorder transformation are discussed.
1. Introduction Some desirable soft magnetic properties of 12 wt% A-Fe alloy were obtained, i.e. ~o.oos = 12750 G/O,, clo.ol = 26600 G/O,, pm = 126000 G/O,, H, = 0.037 O,, B, = 14500 G, by using 0.3 mm thick samples. The soft magnetic properties of 12 wt% Al-Fe alloy are significantly affected by the order-disorder transformation as shown in fig. 1. We consider as follows: When the ordered and disordered phase regions coexist in this alloy, the following cases would happen: (1) The stress energy in the magnetic domains will greatly increase, because the specific volume of the ordered phase is different from that of the disordered one. Moreover, the values of & of the ordered and dis-
k .6
:k. I’/.)
- 30
.
-25
-20
-15
.2
When an ordered single phase DOa type has formed, we should further consider the following: The values of Ki will be varied by the change of the relative quantity of the atom configuration Fe&la and 4 Fe3Al, and hence an optimum Al content in this alloy then can be calculated. The value p will be controlled by the magnetoelastic energy when K, # 0, because the values of K1 vary significantly with any variation of Al content, and Aloo and Xr11 are always large in this alloy.
.2. Experimental procedure
%,
.
4
ordered phases are very large, thus resulting in an increase of an internal stress. (2) An internal magnetic spread field will appear in this specimen, because the value MS of the ordered phase is different from that of the disordered one.
- 10 5
Fig. 1. Curves of quenching temperature and BJB,.
as a function of If,
0304.8853/82/0000-0000/$02.75
0 1982 North-Holland
The Fe-Al alloys used in this study were prepared from 99.9% electrolytic iron remelted under the vacuum condition and 99.99% aluminum which were melted in a vacuum induction furnace and cast under the vacuum condition. Ingots of the alloy were forged and hot-rolled at 1000°C into plates of about 22 mm thickness, which were rolled again at about 500°C to 0.3 mm thick sheets, and only small part of these sheets were rolled at room temperature to 0.1 mm thickness. In a hydrogen furnace, the 0.1 mm thick specimens were annealed to remove stress and become disordered
218
Liu Da Jun / High permeability of 12% Al- Fe alloys
at 1000°C for 0.5 h, subsequently, cooled at the rate of 1.S’C!/min to 450,350 and 25O”C, and then quenched in the air from these temperatures, respectively. The soft magnetic properties were measured by using the specimens heat-treated in this way, and then these specimens were electrochemically thinned to about 0.03 mm thickness. Mijssbauer spectra were measured by using these 0.03 mm thick specimens. The Q3.5 X 50 mm2 specimens for expansion measurement and 0.3 mm thick specimens for measuring saturation magnetization MS were annealed in a hydrogen furnace to remove stress and get disordered at 1000°C for 0.5 h, and then cooled at the rate of l.S”C/m.in to 850°C. And then the expansionmeasuring specimens and part of the MS-measuring specimens were quenched into oil to obtain a fully disordered structure. The rest MS specimens were continuously cooled at the same rate to 5OO”C,subsequently cooled at the rate of 30°C/h to room temperature to obtain full order structure. A mass of the 0.3 mm thick ring-type specimens from the same heat were heated at 950°C in the air furnace for 0.5 h, and then cooled at the rate of 2.5”C/min to different temperatures, subsequently fast quenched into the air. H, and B,/B, of these ring specimens were measured by the “ballistic method”.
Fig. 2. The differential-temperature curves for the disordered specimen during heating and cooling at a rate of 2..5”C/min.
is shown in Fig. 3. In the Massbauer spectra for the specimen slowly cooled to 450°C, the absorbing peaks shown by 7 Fe-l Al, 6 Fe-2 Al and 8 Fe-O Al, 5 Fe-3 Al and 4 Fe-4 Al in the nearest atom round Fe atom are obvious, and 8 Fe-O Al and 5 Fe-3 Al represent Fe &l3 atom configuration, while 8 Fe0 Al and 4 Fe-4 Al mean Fe&l atom configuration, 7 Fe-l Al and 6 Fe-2 Al mean disorder phase. For those spectra cooled to 350 and 25O”C, the absorbing peaks shown by 7 Fe-Al and 6 Fe-2 Al indicating disorder phase are not obvious. 40
3. Results and discussion In the sixties, Lawley and Cahn [ 11, Liitjering and Warlimont [2] and others had drawn, on the basis of the results obtained by X-ray diffractions, thermal expansion variations and the electron microscopic observations. The same conclusion that the order and disorder phase regions coexisted in 12 wt% Al-Fe alloy at about 450°C. In the early seventies, Kazuo and Hiromitsu [3] investigated 21.9-24.1 at% Al-Fe alloys with the electron microscope and Miissbauer effect. They indicated that those alloys containing 21.9-24.1 at% Al ordered sufficiently by slowcooling consist of a DO, type order phase only, and there is no FelsAls order phase region in them. A discussion was once carried out between J.W. Cahn and the author and Prof. Cahn considered that a DOB type order single phase might be formed from the theoretical viewpoint. The Miissbauer spectra measured by us
80
120
160
240 236 i 2321
260
298 294
t
Fig. 3. Mijssbauer spectra for 12 wt% AI-Fe alloy slowly cooled to 450,350 and 250°C, and initially quenched from these temperatures.
Liu Da Jun /High permeability of 12% Al-Fe alloys
In order to seek for the cause of the rapid increase of H, and the drastic reduction of B, at about 450°C, as shown in fig. 1, the differential-temperature curves were obtained by using a DP type photographic dilatometer under the condition that the specimen was heated and cooled at a rate of 2S°C/min as shown in fig. 2. The curves having remarkable turns indicate a difference of the specific volume between order and disorder phases, thus resulting in an increase of internal stress, and moreover, the value of X, of the order and disorder phases are larger than 30 X 10s6 [4], therefore the stress energy in the domains will greatly increase. The saturation magnetization M, of the two phases was determined by a method based on approaching saturation law, i.e. for order Msao= 1330 G, for disorder Msa = 1433 G, and hence, an internal magnetic spread field wiIl appear in this specimen because the value of MS of the order phase is different from that of the disorder one. According to the results gained by Kazuo and Hiromitsu [3] in their investigations, 21.9-24.1 at% Al-Fe alloys ordered sufficiently by slow-cooling consist of a DO3 type order single phase only, and there is no Fe1 sA1s order phase region in them. In MGssbauer spectra, it is remarkable that the subspectra of the atom configurations Fe 1s Als and 4 Fe,Al are shown by the atoms in the nearest neighbors round the Fe atom. These nearest neighbor atoms are 8 Fe-O Al and 5 Fe-3 Al as well as 8 Fe0 Al and 4 Fe-4 Al, respectively. In the DO3 type order single phase containing 21.9-24.1 at% Al, when Al content increases (or decreases), 4 Fe-4 Al composition will increase and 5 Fe-3 Al will decrease (or 5 Fe-3 Al will increase and 4 Fe-4 Al will decrease) 131. Hence, within the foregoing Al content, the curve Kr-Al % [4] determined by Hail may be considered as the relationship curve between K1 and the interchangeable fraction of the atom configurations FersAls and 4 Fe&l. Near the composition of 12 wt% Al, K1 approaches zero and there exists almost a linear region in the curve of K 1 - Al %. Therefore, we may empirically suppose that the quantity of positive value K1 increased (or decreased) by a mole increase (or decrease) of an atom configuration Fe 1&lJ equals the quantity of negative value K 1 increased (or decreased) by a mole increase of 4 Fe& The Al content corresponding to Kl = 0 in the curve determined by Hall approximates to 11.9 wt% [4]. The optimum statistical Al content from
219
experimental data is 11.8-l 1.9%. When the mole is used as a measure unit and if the absolute value of K1 of pure FersAls is equal to the absolute value of pure 4 Fe& and hence when the quantity of the atom configuration Fe, sAls is equal to the quantity of 4 FesAl, then K1 = 0. However, when the two configurations are equal, the Al content is just 11.9 wt% (K1 = 0). The above is merely the author’s assumption, since the determination of K1 of pure FersAls is difficult without an order phase region of Fe,&+ Between two cells of 4 FesAl and FersAls, 4 FesAl results from substitution by substituting an Al atom for an Fe atom in FersAls. The relative quantity of the atom configurations Fe,& and 4 Fe&l are remarkably varied with a variation of Al content, and hence, the value of K, will greatly be affected by Al content and, moreover, X111 and hloo are rather large, consequently the value p will be controlled by the energy when K1 # 0 in this alloy. 4. Conclusions 1. Rith a view to ensuring K, value approaching to zero, the aluminium content in 12% Al-Fe alloys has to be approximate to 11.9 wt%. Because of the pronounced effect of the variation of aluminium content on K1 value as well as both hloo and hrr 1 being very large, the magnetoelastic energy plays an important role in controlling the /.Lvalue when K1 # 0. 2. Slow cooling should be adopted below 500°C so as to develop a single order phase, otherwise rapid cooling would lead to the coexistence of order and disorder phases. Due to the strong influence of stress energy and internal spread magnetic field, the I-(value would be greatly reduced. Acknowledgements The author wishes to thank Mr. Li Ming-fang and Mr. Jiang Chen-ying for their checking and approving this manuscript. References [l] A. Lawleyand J.W.Cahn, J. Phys. Chem. Solids 20 (1961) 204. [2] G. Liitjering and H. Warlimont, 2. Metallk. 56 (1965) 1. 131 Y. Kazuo and I. Hiromitsu, J. Japan Inst. Metals 35 (1971) 566. [4] KC. Hall, J. Appl. Phys. 30 (1959) 816.
Journal of Magnetism and Magnetic Materials 26 (1982) 217-219 North-Holland Publishing Company
A DISCUSSION ON THE MECHANISM OF HIGH PEBMEABILITY OF 12% Al-Fe ALLOY LIU Da .Jun Precision Alloy Department,
Shanghai Iron & Steel Research Institute, Shanghai, People’s Republic of China
On the basis of the results such as thermal expansion coefficient under various temperatures, MSssbauer spectra and magnetic properties after different heat treatments and the investive results obtained by Kazuo and Hiromitsu, the mechanism of high permeability as well as the rule of the soft magnetic properties affected by the order-disorder transformation are discussed.
1. Introduction Some desirable soft magnetic properties of 12 wt% A-Fe alloy were obtained, i.e. ~o.oos = 12750 G/O,, clo.ol = 26600 G/O,, pm = 126000 G/O,, H, = 0.037 O,, B, = 14500 G, by using 0.3 mm thick samples. The soft magnetic properties of 12 wt% Al-Fe alloy are significantly affected by the order-disorder transformation as shown in fig. 1. We consider as follows: When the ordered and disordered phase regions coexist in this alloy, the following cases would happen: (1) The stress energy in the magnetic domains will greatly increase, because the specific volume of the ordered phase is different from that of the disordered one. Moreover, the values of & of the ordered and dis-
k .6
:k. I’/.)
- 30
.
-25
-20
-15
.2
When an ordered single phase DOa type has formed, we should further consider the following: The values of Ki will be varied by the change of the relative quantity of the atom configuration Fe&la and 4 Fe3Al, and hence an optimum Al content in this alloy then can be calculated. The value p will be controlled by the magnetoelastic energy when K, # 0, because the values of K1 vary significantly with any variation of Al content, and Aloo and Xr11 are always large in this alloy.
.2. Experimental procedure
%,
.
4
ordered phases are very large, thus resulting in an increase of an internal stress. (2) An internal magnetic spread field will appear in this specimen, because the value MS of the ordered phase is different from that of the disordered one.
- 10 5
Fig. 1. Curves of quenching temperature and BJB,.
as a function of If,
0304.8853/82/0000-0000/$02.75
0 1982 North-Holland
The Fe-Al alloys used in this study were prepared from 99.9% electrolytic iron remelted under the vacuum condition and 99.99% aluminum which were melted in a vacuum induction furnace and cast under the vacuum condition. Ingots of the alloy were forged and hot-rolled at 1000°C into plates of about 22 mm thickness, which were rolled again at about 500°C to 0.3 mm thick sheets, and only small part of these sheets were rolled at room temperature to 0.1 mm thickness. In a hydrogen furnace, the 0.1 mm thick specimens were annealed to remove stress and become disordered
218
Liu Da Jun / High permeability of 12% Al- Fe alloys
at 1000°C for 0.5 h, subsequently, cooled at the rate of 1.S’C!/min to 450,350 and 25O”C, and then quenched in the air from these temperatures, respectively. The soft magnetic properties were measured by using the specimens heat-treated in this way, and then these specimens were electrochemically thinned to about 0.03 mm thickness. Mijssbauer spectra were measured by using these 0.03 mm thick specimens. The Q3.5 X 50 mm2 specimens for expansion measurement and 0.3 mm thick specimens for measuring saturation magnetization MS were annealed in a hydrogen furnace to remove stress and get disordered at 1000°C for 0.5 h, and then cooled at the rate of l.S”C/m.in to 850°C. And then the expansionmeasuring specimens and part of the MS-measuring specimens were quenched into oil to obtain a fully disordered structure. The rest MS specimens were continuously cooled at the same rate to 5OO”C,subsequently cooled at the rate of 30°C/h to room temperature to obtain full order structure. A mass of the 0.3 mm thick ring-type specimens from the same heat were heated at 950°C in the air furnace for 0.5 h, and then cooled at the rate of 2.5”C/min to different temperatures, subsequently fast quenched into the air. H, and B,/B, of these ring specimens were measured by the “ballistic method”.
Fig. 2. The differential-temperature curves for the disordered specimen during heating and cooling at a rate of 2..5”C/min.
is shown in Fig. 3. In the Massbauer spectra for the specimen slowly cooled to 450°C, the absorbing peaks shown by 7 Fe-l Al, 6 Fe-2 Al and 8 Fe-O Al, 5 Fe-3 Al and 4 Fe-4 Al in the nearest atom round Fe atom are obvious, and 8 Fe-O Al and 5 Fe-3 Al represent Fe &l3 atom configuration, while 8 Fe0 Al and 4 Fe-4 Al mean Fe&l atom configuration, 7 Fe-l Al and 6 Fe-2 Al mean disorder phase. For those spectra cooled to 350 and 25O”C, the absorbing peaks shown by 7 Fe-Al and 6 Fe-2 Al indicating disorder phase are not obvious. 40
3. Results and discussion In the sixties, Lawley and Cahn [ 11, Liitjering and Warlimont [2] and others had drawn, on the basis of the results obtained by X-ray diffractions, thermal expansion variations and the electron microscopic observations. The same conclusion that the order and disorder phase regions coexisted in 12 wt% Al-Fe alloy at about 450°C. In the early seventies, Kazuo and Hiromitsu [3] investigated 21.9-24.1 at% Al-Fe alloys with the electron microscope and Miissbauer effect. They indicated that those alloys containing 21.9-24.1 at% Al ordered sufficiently by slowcooling consist of a DO, type order phase only, and there is no FelsAls order phase region in them. A discussion was once carried out between J.W. Cahn and the author and Prof. Cahn considered that a DOB type order single phase might be formed from the theoretical viewpoint. The Miissbauer spectra measured by us
80
120
160
240 236 i 2321
260
298 294
t
Fig. 3. Mijssbauer spectra for 12 wt% AI-Fe alloy slowly cooled to 450,350 and 250°C, and initially quenched from these temperatures.
Liu Da Jun /High permeability of 12% Al-Fe alloys
In order to seek for the cause of the rapid increase of H, and the drastic reduction of B, at about 450°C, as shown in fig. 1, the differential-temperature curves were obtained by using a DP type photographic dilatometer under the condition that the specimen was heated and cooled at a rate of 2S°C/min as shown in fig. 2. The curves having remarkable turns indicate a difference of the specific volume between order and disorder phases, thus resulting in an increase of internal stress, and moreover, the value of X, of the order and disorder phases are larger than 30 X 10s6 [4], therefore the stress energy in the domains will greatly increase. The saturation magnetization M, of the two phases was determined by a method based on approaching saturation law, i.e. for order Msao= 1330 G, for disorder Msa = 1433 G, and hence, an internal magnetic spread field wiIl appear in this specimen because the value of MS of the order phase is different from that of the disorder one. According to the results gained by Kazuo and Hiromitsu [3] in their investigations, 21.9-24.1 at% Al-Fe alloys ordered sufficiently by slow-cooling consist of a DO3 type order single phase only, and there is no Fe1 sA1s order phase region in them. In MGssbauer spectra, it is remarkable that the subspectra of the atom configurations Fe 1s Als and 4 Fe,Al are shown by the atoms in the nearest neighbors round the Fe atom. These nearest neighbor atoms are 8 Fe-O Al and 5 Fe-3 Al as well as 8 Fe0 Al and 4 Fe-4 Al, respectively. In the DO3 type order single phase containing 21.9-24.1 at% Al, when Al content increases (or decreases), 4 Fe-4 Al composition will increase and 5 Fe-3 Al will decrease (or 5 Fe-3 Al will increase and 4 Fe-4 Al will decrease) 131. Hence, within the foregoing Al content, the curve Kr-Al % [4] determined by Hail may be considered as the relationship curve between K1 and the interchangeable fraction of the atom configurations FersAls and 4 Fe&l. Near the composition of 12 wt% Al, K1 approaches zero and there exists almost a linear region in the curve of K 1 - Al %. Therefore, we may empirically suppose that the quantity of positive value K1 increased (or decreased) by a mole increase (or decrease) of an atom configuration Fe 1&lJ equals the quantity of negative value K 1 increased (or decreased) by a mole increase of 4 Fe& The Al content corresponding to Kl = 0 in the curve determined by Hall approximates to 11.9 wt% [4]. The optimum statistical Al content from
219
experimental data is 11.8-l 1.9%. When the mole is used as a measure unit and if the absolute value of K1 of pure FersAls is equal to the absolute value of pure 4 Fe& and hence when the quantity of the atom configuration Fe, sAls is equal to the quantity of 4 FesAl, then K1 = 0. However, when the two configurations are equal, the Al content is just 11.9 wt% (K1 = 0). The above is merely the author’s assumption, since the determination of K1 of pure FersAls is difficult without an order phase region of Fe,&+ Between two cells of 4 FesAl and FersAls, 4 FesAl results from substitution by substituting an Al atom for an Fe atom in FersAls. The relative quantity of the atom configurations Fe,& and 4 Fe&l are remarkably varied with a variation of Al content, and hence, the value of K, will greatly be affected by Al content and, moreover, X111 and hloo are rather large, consequently the value p will be controlled by the energy when K1 # 0 in this alloy. 4. Conclusions 1. Rith a view to ensuring K, value approaching to zero, the aluminium content in 12% Al-Fe alloys has to be approximate to 11.9 wt%. Because of the pronounced effect of the variation of aluminium content on K1 value as well as both hloo and hrr 1 being very large, the magnetoelastic energy plays an important role in controlling the /.Lvalue when K1 # 0. 2. Slow cooling should be adopted below 500°C so as to develop a single order phase, otherwise rapid cooling would lead to the coexistence of order and disorder phases. Due to the strong influence of stress energy and internal spread magnetic field, the I-(value would be greatly reduced. Acknowledgements The author wishes to thank Mr. Li Ming-fang and Mr. Jiang Chen-ying for their checking and approving this manuscript. References [l] A. Lawleyand J.W.Cahn, J. Phys. Chem. Solids 20 (1961) 204. [2] G. Liitjering and H. Warlimont, 2. Metallk. 56 (1965) 1. 131 Y. Kazuo and I. Hiromitsu, J. Japan Inst. Metals 35 (1971) 566. [4] KC. Hall, J. Appl. Phys. 30 (1959) 816.