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Order in commercial grain-oriented iron-silicon sheets
Physica B 180 & 181 (1992) North-Holland
PHYSICA 1
49-50
Order in commercial
grain-oriented
E. Nembach”,
Th.
K. Hilfrich”3b,
Ebelb
and
0.
iron-silicon
sheets
Scharpf’
“lnstitut fiir Metullforschung, Universitiit Miinster, W-4400 Miinster. Germany hWerkstofforschung, GKSS-Forschungszentrum, W-20-54 Geesthacht, Germany ‘Institut Laue-Langevin,
F-38042 Grenoble,
France
The state of order of commercial high permeability iron-silicon transformer sheets has been investigated by diffuse elastic neutron scattering. The silicon content was 6.1 at%. The sheets show a high degree of short range order.
1. Introduction Iron-rich iron-silicon sheets are used as transformer cores. Si has two favourable effects on the magnetic properties of Fe: (i) Si lowers the crystal anisotropy of Fe and thus the hysteresis losses and (ii) Si raises the electrical resistance of Fe and thus reduces eddy current losses. Recent neutron scattering experiments [l, 21 revealed that &Si alloys with 0.076 s cs, SO.102 (c,, = atomic fraction of Si) are DO, long range ordered. The diameter W of the antiphase domains is rather small. These findings were in contrast to the established phase diagram [3] and suggested the investigation of the structure of commercial high permeability grain-oriented &Si transformer sheets. Their Si content is normally below 0.08. The DO, structure is basically BCC. Its superlattice can be described best by the introduction of a new larger cubic elementary cell which consists of four interpenetrating FCC cells. Only sites in one of these four sublattices are correct for Si. The long range order parameter S of the DO, structure can be derived from the differential neutron scattering cross-section aa’id0 of superlattice reflections. aa’/dfi is governed by the structure factor which in turn depends on S. The relevant equations are given in refs. 1 and 2. au’ldn comprises nuclear and magnetic contributions. W is obtained from the widths of superlattice reflections [l, 2, 41. 2. Experiments
and results
The specimen was a stack of 20 strips of commercial high permeability grain oriented &Si sheets. cs, was 0.0612. The material was provided by Thyssen Stahl, Duisburg, Germany. Due to the sharp Goss texture of the sheets, the stack is nearly equivalent to a single crystal. The dimensions and orientations of the 20 strips were: 60mm [l i 01, 5.8mm [00 11, 0.3 mm [l lo]. They had been given the standard heat treatments; the final processing step was a slow cool from 1500K to 300K at the approximate rate of 20K/h. 0921-4526/92/$05.00
For comparison, a cylindrical single crystal of the same alloy was also studied. Its orientation was [lo 01, its length 60mm and its diameter 4mm. The experiments were performed on the diffuse elastic neutron scattering instrument D7 of the Institut Laue-Langevin, Grenoble, France. It was operated in its non-polarized mode, wavelength A = 0.31 nm. A time of flight analysis eliminated inelastically scattered neutrons and the h/2 contamination. The sheets were studied at 300 K and the single crystal at temperatures T up to 1073 K. In fig. 1, acT’/dR is plotted versus 28 for the (002)
0
1992 - Elsevier
Science
Publishers
0
20
40
60
60
‘00
2 e
Fig. 1. aa’l~?R in (mbarnisterad atom) of the &-Si versus 28 (“) for the (002) and (1 1 1) reflections.
B.V. All rights
reserved
sheets
50
E. Nembach
et al.
I Order
and the (1 1 1) super-lattice reflections of the strips. 20 is the angle between the incoming and the scattered neutrons. au’la.0 comprises ag’ia.0 mentioned in section 1 and the contribution of Laue monotonic scattering. arr’/aa of the single crystal showed a weak (0 0 2) reflection for T s 873 K. So far the [l 0 0] orientation of the crystal precluded the observation of its (1 1 1) reflection. 3. Discussion The two peaks shown in fig. 1 are so broad that the diameter of DO, antiphase domains would hardly exceed the lattice constant of the DO, structure. Since c,, is 0.0612, such an antiphase domain would contain just about one Si atom. Therefore the state of order of the &Si sheets cannot be described as DO, long range ordered. One has to try a description based on the Warren-Cowley short range order parameters cr, instead. Fitting the equations given in ref. [4] to the data presented in fig. 1, yields (Y(,, (Y, and cy,. The results are compiled in table 1. The fact that cy,,, which is supposed to equal unity, exceeds this value is no serious deficiency of this model. It mainly reflects shortcomings of the background subtraction and of the estimate of the magnetic scattering length of Fe. B2 long range order leads to Table 1 Warren-Cowley
ff,, ai n,
in grain-oriented
Fe-S
(Y, < 0 and LY?> 0, whereas DO, requires (Y, < 0 and (Y, < 0. Thus the experimental results hint at a DO,like order. Though ]cy,l is rather small, (Y, indicates a high degree of short range order. Since the (00 2) reflection is narrower than the (1 1 1) reflection, I~y~(O02)1 exceeds lu,(l 1 l)i, The (002) reflections of &Si alloys with higher Si contents were also less wide than the respective (1 1 1) reflections [l, 21. The reason for this difference is that the two displacement vectors which lead to antiphase domains in the DO, structure, affect these two reflections differently. 4. Conclusions Commercial high permeability grain oriented &0.061-Si sheets are rather strongly short range ordered. Acknowledgements Discussions with Dr. W. Kolker, Schwarzenbek, Germany, are gratefully acknowledged. Drs. F. Bolling and H. Hastenrath of Thyssen Stahl, Duisburg, Germany, are thanked for providing the transformer sheets and for discussions. References
III W. Kdlker. short
range
order
parameters
(Y,.
1 I) reflection
(0 0 2) reflection
(1
1.61 -0.0’) -0.40
1.22 -0.02 -0.20
sheets
R. Wagner and E. Nemhach. J. Phys. F 18 (1988) 2513. I21 K. Hilfrich, W. Kiilker, W. Petry, 0. Scharpf and E. Nemhach, Scripta Metall. Mater. 24 (1990) 39. Iron-Binary Phase Diagrams (SpringPI 0. Kuhaschewski, cr. Berlin, 1982) p. 136. X-Ray Diffraction (Addison-Wesley. New 141 B.E. Warren. York, 196’)) p. 227.
PHYSICA 1
49-50
Order in commercial
grain-oriented
E. Nembach”,
Th.
K. Hilfrich”3b,
Ebelb
and
0.
iron-silicon
sheets
Scharpf’
“lnstitut fiir Metullforschung, Universitiit Miinster, W-4400 Miinster. Germany hWerkstofforschung, GKSS-Forschungszentrum, W-20-54 Geesthacht, Germany ‘Institut Laue-Langevin,
F-38042 Grenoble,
France
The state of order of commercial high permeability iron-silicon transformer sheets has been investigated by diffuse elastic neutron scattering. The silicon content was 6.1 at%. The sheets show a high degree of short range order.
1. Introduction Iron-rich iron-silicon sheets are used as transformer cores. Si has two favourable effects on the magnetic properties of Fe: (i) Si lowers the crystal anisotropy of Fe and thus the hysteresis losses and (ii) Si raises the electrical resistance of Fe and thus reduces eddy current losses. Recent neutron scattering experiments [l, 21 revealed that &Si alloys with 0.076 s cs, SO.102 (c,, = atomic fraction of Si) are DO, long range ordered. The diameter W of the antiphase domains is rather small. These findings were in contrast to the established phase diagram [3] and suggested the investigation of the structure of commercial high permeability grain-oriented &Si transformer sheets. Their Si content is normally below 0.08. The DO, structure is basically BCC. Its superlattice can be described best by the introduction of a new larger cubic elementary cell which consists of four interpenetrating FCC cells. Only sites in one of these four sublattices are correct for Si. The long range order parameter S of the DO, structure can be derived from the differential neutron scattering cross-section aa’id0 of superlattice reflections. aa’/dfi is governed by the structure factor which in turn depends on S. The relevant equations are given in refs. 1 and 2. au’ldn comprises nuclear and magnetic contributions. W is obtained from the widths of superlattice reflections [l, 2, 41. 2. Experiments
and results
The specimen was a stack of 20 strips of commercial high permeability grain oriented &Si sheets. cs, was 0.0612. The material was provided by Thyssen Stahl, Duisburg, Germany. Due to the sharp Goss texture of the sheets, the stack is nearly equivalent to a single crystal. The dimensions and orientations of the 20 strips were: 60mm [l i 01, 5.8mm [00 11, 0.3 mm [l lo]. They had been given the standard heat treatments; the final processing step was a slow cool from 1500K to 300K at the approximate rate of 20K/h. 0921-4526/92/$05.00
For comparison, a cylindrical single crystal of the same alloy was also studied. Its orientation was [lo 01, its length 60mm and its diameter 4mm. The experiments were performed on the diffuse elastic neutron scattering instrument D7 of the Institut Laue-Langevin, Grenoble, France. It was operated in its non-polarized mode, wavelength A = 0.31 nm. A time of flight analysis eliminated inelastically scattered neutrons and the h/2 contamination. The sheets were studied at 300 K and the single crystal at temperatures T up to 1073 K. In fig. 1, acT’/dR is plotted versus 28 for the (002)
0
1992 - Elsevier
Science
Publishers
0
20
40
60
60
‘00
2 e
Fig. 1. aa’l~?R in (mbarnisterad atom) of the &-Si versus 28 (“) for the (002) and (1 1 1) reflections.
B.V. All rights
reserved
sheets
50
E. Nembach
et al.
I Order
and the (1 1 1) super-lattice reflections of the strips. 20 is the angle between the incoming and the scattered neutrons. au’la.0 comprises ag’ia.0 mentioned in section 1 and the contribution of Laue monotonic scattering. arr’/aa of the single crystal showed a weak (0 0 2) reflection for T s 873 K. So far the [l 0 0] orientation of the crystal precluded the observation of its (1 1 1) reflection. 3. Discussion The two peaks shown in fig. 1 are so broad that the diameter of DO, antiphase domains would hardly exceed the lattice constant of the DO, structure. Since c,, is 0.0612, such an antiphase domain would contain just about one Si atom. Therefore the state of order of the &Si sheets cannot be described as DO, long range ordered. One has to try a description based on the Warren-Cowley short range order parameters cr, instead. Fitting the equations given in ref. [4] to the data presented in fig. 1, yields (Y(,, (Y, and cy,. The results are compiled in table 1. The fact that cy,,, which is supposed to equal unity, exceeds this value is no serious deficiency of this model. It mainly reflects shortcomings of the background subtraction and of the estimate of the magnetic scattering length of Fe. B2 long range order leads to Table 1 Warren-Cowley
ff,, ai n,
in grain-oriented
Fe-S
(Y, < 0 and LY?> 0, whereas DO, requires (Y, < 0 and (Y, < 0. Thus the experimental results hint at a DO,like order. Though ]cy,l is rather small, (Y, indicates a high degree of short range order. Since the (00 2) reflection is narrower than the (1 1 1) reflection, I~y~(O02)1 exceeds lu,(l 1 l)i, The (002) reflections of &Si alloys with higher Si contents were also less wide than the respective (1 1 1) reflections [l, 21. The reason for this difference is that the two displacement vectors which lead to antiphase domains in the DO, structure, affect these two reflections differently. 4. Conclusions Commercial high permeability grain oriented &0.061-Si sheets are rather strongly short range ordered. Acknowledgements Discussions with Dr. W. Kolker, Schwarzenbek, Germany, are gratefully acknowledged. Drs. F. Bolling and H. Hastenrath of Thyssen Stahl, Duisburg, Germany, are thanked for providing the transformer sheets and for discussions. References
III W. Kdlker. short
range
order
parameters
(Y,.
1 I) reflection
(0 0 2) reflection
(1
1.61 -0.0’) -0.40
1.22 -0.02 -0.20
sheets
R. Wagner and E. Nemhach. J. Phys. F 18 (1988) 2513. I21 K. Hilfrich, W. Kiilker, W. Petry, 0. Scharpf and E. Nemhach, Scripta Metall. Mater. 24 (1990) 39. Iron-Binary Phase Diagrams (SpringPI 0. Kuhaschewski, cr. Berlin, 1982) p. 136. X-Ray Diffraction (Addison-Wesley. New 141 B.E. Warren. York, 196’)) p. 227.