Texture development of 50% NiFe strip by powder rolling

Journal of

ELSEVIER

J. Mater. Process. Technol. 45 (1994) 4 6 5 4 7 0

Materials Processing Technology

Texture Development of 5096 Ni-Fe Strip by Powder Rolling T. H. Yim a and Y. B. Park b aproduction T e c h n o l o g y Center, Korea A c a d e m y of Industrial Technology, Inchon 404-254, K o r e a bDept, of Materials Science and Metallurgical Engineering, Sunchon National University, Sunchon 540-742, Korea

T h e development of deformation and recrystallization textures has been i n v e s t i g a t e d with the help of orientation distribution function (ODF) a n a l y s i s in 50% N i - F e strip manufactured b y p o w d e r rolling. T h e deformation texture is the c o p p e r - t y p e containing {112}<111>, {011}<211> and {123}<634> as main texture components. On the other hand, the recrystallization texture after final annealing consists of only one p r e d o m i n a n t cube component, {100}<001>, which is referred to as the a l u m i n i u m - t y p e . T h e recrystallization t e x t u r e s depend directly upon the second cold rolling textures. It has been quantitatively discussed that the stronger the cube component in final product, the better the magnetic properties.

1. I N T R O D U C T I O N Powder rolling refers to continuous compacting of metal p o w d e r s by a rolling mill. T h e continuously compacted green strips or sheets undergo further p r o c e s s i n g by sintering and r e - r o l l i n g to produce an final product with desired material properties [1]. 50% N i - F e strip, used for the present work, has been made of pure iron and nickel powders by the p o w d e r rolling process. T h e N i - F e alloys are very important industrially since they are used as soft magnetical materials. In 50% N i - F e alloy, crystal anisotropy constant, kl is about 33,000 e r g / c m 3, that is positive [2] and thus <100> is the preferred direction for magnetization. T h i s means that the cube texture component {100}<001> is one of the most favorable to obtain good magnetic properties. In fact it has long been recognized that the s t r o n g e r the development of the cube texture, the more the improvement of coercive force

and rectangularity of h y s t e r e s i s loop [3]. Many studies [4-5] have commonly s u g g e s t e d the importance of annealing process, which defines the development of recrystallization textures. However, s y s t e m a t i c investigation into the t e x t u r e evolution of N i - F e alloys is n e c e s s a r y to control the development of the favorable textures for the magnetic property and thus find the optimum processing condition. With respect to N i - F e alloys by powder rolling, there have been a little reports [6-7] only on the magnetic characteristics in relation to the processing parameters. In the p r e s e n t work, therefore, the development of cold and recrystallization textures with p a r i n g some important processing parameters has been investigated with the help of O D F analysis in 50% N i - F e strip b y powder rolling. T h e aim is to clarify not only the evolution of recrystallization t e x t u r e s but also their relationship with the magnetic property.

0924-0136/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0924-0136(94)00225-8

466

2.

EXPERIlV[ENTAL

Some important properties of the powders used for the present work are given in T a b l e 1. T h e pure iron powders screened to 150 mesh and carbonyl nickel powders were mixed and then blended for 20 minutes in a laboratory V-blender. T h e blended powders were continuously compacted by a horizontal positioning mill, of which roll gap and speed were 0.8 mm and 2 rpm, respectively. The thickness of green strip with density of 6.66 g / c m a was 1.48 mm. After p r e - s i n t e r i n g in endo gas at 1000 °C for 30 minutes, homogenization of the p r e - s i n t e r e d strip was performed in mixed gas (H2 : N2 = 1 : 3) at 1000 °C for 48 hours. T h e thickness of the homogenized strip with density of 7.91 g/cma was 1.41 mm. T h e first and second cold rolling of the strip with different reduction ratios were carried out, between which intermediate a n n e a l i n g was performed in H2 gas at 700 °C for 30 minutes. The cold rolled sheets were finally annealed in H2 gas at 1100 °C for different heating times. T h e finally annealed sheets were cut off to make a core of stacked lamination or t a p e - w o u n d type for the measurement of the magnetic properties such as initial permeability (t0, m a x i m u m permeability (/2~), coercive force (Hc), saturation flux density at a magnetic field intensity of 10 Oe (Bin), etc.

T e x t u r e s of the specimens were measured with the help of X-ray diffraction. ODFs were determined by series expansion method (imax=22) [8] from the four pole figures of {111}, {200}, {220} and {113}. T h e orientation densities were displayed either in an orientation space formed b y the three Euler angles, ~01, $, $2 or along the orientation tubes such as a-fibre, [}-fibre and so on. Figure 1 shows some important orientations at $2 = 45 ° section of reduced Euler space for fcc materials.

!

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• {1Z3}<634> • {001}<100> • {258}<121> {111}<112>

1

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or . v ~

i

--

{124}<211> {236}<385> {554}<225> {111}<110>

Figure 1. Some important orientations at ~02 = 45 ° section of reduced E u l e r space for fcc materials.

Table 1 T h e properties of Fe and Ni powders Powder

Brand

Fe

KOBE 300M

Ni

Carbonyl Nickel

Powder making process

Apparent density(g/cm'~)

Fluidity (sec/50g)

Water atomization

2.85 - 3.10

30max

-150 mesh

6.95 g/cc at 5tonf/cm2

Carbonyl process

1.8 - 2.7

unmeasurable

3-7 llm

6.70 g/cc at 5tonUcm~

Size Compressibility

467

3. R E S U L T S

AND DISCUSSION

The pre-sintered strip reveals completely diffused t e x t u r e s as expected. On cold rolling with 30% reduction, however, the development of deformation t e x t u r e s begins with the appearance of the a - f i b r e which stretches from G o s s component {011}<100> to the b r a s s component {011}<211>. T h e orientation densities of the copper component {112} <111> and S {123}<634> become higher

with increasing reduction ratio and thus cold rolling textures after 9 0 % reduction shows a typical c o p p e r - t y p e [9] as shown in F i g u r e 2 and 3. T h e typical [o111

[Oil} {011] <211> < I I I >



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F i g u r e 2. {111} pole figure and ODFs of 90% cold rolled sheet.

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600

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60 °

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F i g u r e 3. ODFS of along the a - f i b r e and z - f i b r e in cold rolled sheet with 30%(0), 60% (o) and 90% (~) reductions.

468

c o p p e r - t y p e t e x t u r e is characterized by nearly equally s t r o n g Cu {112}<111>, S {123}<634> and b r a s s components. On intermediate annealing after the first cold rolling, the cold rolling t e x t u r e s are randomized e x c e p t for 90% reduction, with which w e a k cube t e x t u r e component appears. T h i s m e a n s that the distinctive d e v e l o p m e n t of the c o p p e r - t y p e texture can be t r a n s f o r m e d to the cube texture during the annealing. By the second cold rolling, the evolution of deformation t e x t u r e s t a r t s {1~1)

RD

LEVELS:

again after 60% reduction. F i g u r e 4 shows the c o p p e r - t y p e t e x t u r e developed after 83% second cold rolling. A s s h o w n in F i g u r e 5, the development of second "tl~21

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F i g u r e 4. {111} pole figure and O D F s a f t e r 83% second cold rolling ( l s t 60%).

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Figure 5. O D F s along the (~-fibre with combination of the first and second cold rolling reductions.

469

cold rolling textures does not depend on the first cold rolling reduction. For example, even though total deformation a m o u n t is the same as 90%, in case of 30% second rolling the intensities of the [3-fibre, which composes of orientation density maxima, are lower than that of 30% first cold rolling as well as the main texture components deviate from the exact positions of the copper-type texture. T h e reason is attributed to the randomization of the first cold rolling textures during intermediate annealing. Since the second cold rolling textures are developed from completely random texture, they follow the same way that the first cold rolling textures evolve with reduction ratio. Therefore, the typical copper-type texture is developed in case of high rolling reduction. When the second cold rolled sheets are finally annealed above 1100 °C, recrystallization textures reveal the cube component {100}<001> as a main texture component. T h e orientation density of the cube component is rarely affected by heating time, with which increases slightly, but sensitive to the second cold rolling reduction ratio. Besides, texture inhomogeneity through the sheet thickness is found in case of low reduction ratio. T h e texture of the surface layer is more or less diffused with weak cube component. The orientation density of cube component increases with the second rolling reduction and thus it dominates the recrystallization textures as shown in Figure 6. It is known that the recrystallization texture of pure aluminium consists of only one very sharp component, that is the cube while in recrystallized pure copper, the main texture component is the cube with a volume fraction of about 55%, the rest being made up by recrystallization twins [9]. In fact the deformation textures of 50% N i - F e alloy are more like those of pure copper than aluminium. However, It

is noticeable that the recrystallization textures of the material is rather closer to those of pure aluminium. T h e stacking fault energies of nickel and iron are so high [10] that recrystallization behavior of 50% N i - F e alloy may be similar to that of pure aluminium, the stacking fault energy of which is also very high. Table 2 shows various magnetic properties of the final products with different processing parameters. As described above, the recrystallization ltli}

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LEVELS:

0.5

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MAX- l i . O

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~2=cons t

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LEVELS: 24712 20 30 40

Figure 6. {111} pole figure and ODFs after 8396 second cold rolling and then final annealing at 1100 °C for 1 hour.

470

Table 2 Magnetic properties of annealed 50% Ni-Fe alloy

Type of core

1st cold rolling reduction ratio (%)

Stacked laminations

60

2nd cold rolling Heating reduction ratio time (hr) (%) at 1100Z;

60

D.C. magnetic properties //i

/~x

Hc(Oe) Blo(G)

0.5

2727

3 0 5 8 8 0 : 1 1 2 13425

1

3333

2 9 2 3 0 0 . 1 1 2 i3200

5

4285

4 5 3 3 3 0 . 0 9 8 13400

Tape -

60

60

1

2608

17000

0.13

13400

wound core

60

83

1

4615

28000

0.14

16000

textures are not sensitive to annealing time and so do the magnetic properties. In the material annealed for 5 hours, however, the texture inhomogeneity through the sheet thickness disappears contrary to others annealed for relatively short time although all of them reveal the similar orientation density of cube texture component. Thus the longer the annealing time, the higher the initial and maximum permeabilities. On the other hand, the annealing texture of the material depends directly upon the second cold rolling reduction. That is, the orientation density of the cube texture component in the finally annealed sheet increases with rolling reduction ratio. As a result, all magnetic properties are much better in case that the second rolling is performed with great deformation amount. 4. C O N C L U S I O N

The deformation texture of 50% Ni-Fe alloy manufactured by powder rolling is the copper-type containing {112}<111>, {011}<211> and {123}<634> as main texture components. On the other hand, the recrystallization texture of the material consists of only one predominant cube component, {100}<001>, which is

referred to as the aluminium-type. It has been clarified that the recrystallization textures depend directly upon the second cold rolling textures. REFERENCES

1. E. Klar, Metals Handbook 9th ed., Am. Soc. Met., 7 (t984) 401. 2. R. M. Bozorth, Ferromagnetism, D. Van Nostrand Comp. Inc., New York (1951) 570. 3. M. F. Littmann, J. Met., May (1956) 593. 4. F. Pfeifer and C. Radeloff, J.Magn. Magn. Mat., t9 (1980) 190. 5. I. K. Kang, H. H. Scholefield and A. P. Martin, J. Appl. Phys. 38 (1967) 1178. 6. E. M. Minaev. Poroshkovaya Metallugiya, 279 (1986) 24. 7. E. V. Walker and R. E. S. Waiters, Powder Metali., No. 4 (1959) 23. 8. H. J. Bunge, Mathematische Methoden der Texturanalyse, Akademie-Verlag, Berlin (1969)31. 9. R. K. Ray and K. LOcke, Proc. 7th ICOTOM, Holland, Noordwijkerhout, September (1984) 287. 10. P. C. J. Gallagher, Met. Trans., 1 (1970) 2429.