FORMATION OF MAGNETIC ANISOTROPY AND STRUCTURAL CHANGES IN AN Fe-Ni BASE ALLOY BY ANNEALING

(1)

HAL Id: jpa-00219621

https://hal.archives-ouvertes.fr/jpa-00219621

Submitted on 1 Jan 1980

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

FORMATION OF MAGNETIC ANISOTROPY AND STRUCTURAL CHANGES IN AN Fe-Ni BASE

ALLOY BY ANNEALING

E. Wieser, C. Cruz, M. Müller, J. Henke

To cite this version:

E. Wieser, C. Cruz, M. Müller, J. Henke. FORMATION OF MAGNETIC ANISOTROPY AND

STRUCTURAL CHANGES IN AN Fe-Ni BASE ALLOY BY ANNEALING. Journal de Physique

Colloques, 1980, 41 (C1), pp.C1-365-C1-366. �10.1051/jphyscol:19801137�. �jpa-00219621�

(2)

JOURNAL DE PHYSIQUE CoIIoque C l , suppl&ment au n O 1, Tome41, janvier 1980, page C1-365

FORFnATION OF WGNETIC ANISOTROPY AND STRUCTURAL CHANGES I N AN Fe-Ni BASE ALLOY BY ANNEALING

X X

E. Wieser, C. Cruz, M. Miiller and J. Henke

ZentraZinstitut ftir Kemforschung, Rossendorf.

+ ZentraZinstitut far Festk8perphysik und Werkstofforschung, Dresden, der Akademie der wissenschaften der DDR.

Magnetic semi-hard a l l o y s a r e o f t e c h n i - t o a magnetic s o f t d i r e c t i o n .

c a l i n t e r e s t owing t o t h e i r s p e c i a l mag- The i n v e s t i g a t e d samples were o f t h e com- n e t i c p r o p e r t i e s

-

h i g h c o e r c i v e f o r c e p o s i t i o n 77.2 Fe, 18 N i , 3.8 A l , 1 T i and square h y s t e r e s i s loop. These d e s i r e d ( w t .%)

.

magnetic p r o p e r t i e s a r e caused b y a com- The f o r m a t i o n o f a magnetic t e x t u r e b y b i n e d t hermo-mechanical t r e a t m e n t

.

^{H i g h} ^{t h e}^thermo-mechanical t r e a t ment has been c o l d d e f o r m a t i o n i s f o l l o w e d b y annealing. s t u d i e d a s d i s c u s s e d above. One sample The a n n e a l i n g t r e a t m e n t l e a d s t o t h e was measured i n t h e c o l d r o l l e d s t a t e and o c c u r r e n c e o f a magnetic p r e f e r r e d d i r e c - a f t e r a n n e a l i n g a t 450 and 525 ^OC. F o r a t i o n and a l s o t o s t r u c t u r a l changes second sample t h e c o l d r o l l i n g was c a r r i e d

( o r d e r i n g e f f e c t s , p r e c i p i t a t i o n s , phase o u t i n two s t e p s w i t h an i n t e r m e d i a t e an- t r a n s f o r m a t i o n ) . F o r i r o n based a l l o y s n e a l i n g a t 700 0 C. T h i s sample was a l s o

5 7 ~ e Miissbauer s p e c t r o s c o p y i s w e l l s u i t e d measured a f t e r an a n n e a l i n g a t 450 ^OC.

t o p r o v i d e i n f o r m a t i o n s about b o t h e f f e c t s T a b l e 1 p r e s e n t s t h e c o r r e s p o n d i n g R-val- on a m i c r o s c o p i c s c a l e . ues f o r t h e t h r e e measuring g e o m e t r i e s The f o r m a t i o n o f a magnetic t e x t u r e can ( n

-

^beam

¹¹

normal. RD

-

beam// r o l l i n g

d i r e c t i o n , T.0

-

beam// t r a n s v e r s e d i r e c - be s t u d i e d b v t h e e v a l u a t i o n o f r e l a t i v e

t i o n ) . l i n e i n t e n s i t i e s o f Mossbauer s p e c t r a .

Here t h e v a l u e R has been used which i s d e f i n e d i n t h e f o l l o w i n g way [I] :

R = 4 z n 2 0 / ( l c

G~G)

⁼^3(12/11)

o r 4(12/13)/(1 + 11/13)

(Ii

-

l i n e i n t e n s i t i e s s c a l e d from nega- t i v e t o p o s i t i v e v e l o c i t i e s , d

-

a n g l e between t h e a t o m i c magnetic moments and beam d i r e c t i o n ).

To d e t e c t a magnetic p r e f e r r e d d i r e c t i o n t h e samples ( s h e e t s o f w 30 um t h i c k n e s s )

/

were measured i n t h r e e d i f f e r e n t geome- t r i e s :

i) beam n o r m a l t o t h e r o l l i n g p l a n e i i ) s t r i k i n g i n c i d e n c e w i t h an a n g l e o f

20' t o t h e r o l l i n g d i r e c t i o n

i i i ) s t r i k i n g i n c i d e n c e w i t h an a n g l e o f 20' t o t h e t r a n s v e r s e d i r e c t i o n .

T a b l e 1: R-values

temp. t r e a t m e n t n RD TD

*/ 1.6 2.1 2.0

450 ^{O C / ~}h 3.1 1.3 1.8

525 ^{O C / ~}h 2.8 1.7 2.2

i n t ermed. anneal.

(700 OC) 2.8 1.6 2.5

c450 O C / ~ h 3.3 1.0 2.3

1000 'C/O - 5 h 2.0 1.9 2.0

The l a s t l i n e o f T a b l e 1 shows r e s u l t s f o r a sample tempered a t 1000 OC i n o r d e r t o a v o i d t h e i n f l u e n c e o f d e f o r m a t i o n . AS expected a l l t h r e e R-values a r e v e r y c l o s e t o 2. The c o l d d e f o r m a t i o n causes a weak p r e f e r e n c e o f t h e sheet n o r m a l by t h e magnetic moments. T h i s can be under- F o r random o r i e n t a t i o n o f t h e magnetic s t o o d b y t h e c r y s t a l l o g r a f i c t e x t u r e i n moments R x 2 s h o u l d be v a l i d f o r a l l three c o n j u n c t i o n w i t h t h e c r y s t a l a n i s o t ropy.

measurements. R < 2 h o l d s i f t h e d i r e c t i o n a t 450 OC the r o l l i n g dire=- marked b y t h e beam i s a magnetic p r e f e r - _ti o n becomes t h e magnetic p r e f e r r e d &rec-

r e d ( h a r d ) d i r e c t i o n . R > 2 corresponds

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801137

(3)

C1-366 JOURNAL DE PHYSIQUE

t i o n . I n t e r m e d i a t e a n n e a l i n g combined w i t h a 450 OC t e m p e r a t u r e t r e a t m e n t g i v e s t h e h i g h e s t magnetic a n i s o t ropy. The p r e f e r - ence o f t h e r o l l i n g d i r e c t i o n i s v e r y sharp. The t r a n s v e r s e d i r e c t i o n becomes a s o f t d i r e c t i o n . T h i s i s i n agreement w i t h c o e r c i v e f o r c e measurements i n [ 2 ]

.

I n c o n n e c t i o n ' w i t h t h e ol-

8

^phase^tr a n s f o r - mat i o n t h e magnetic t e x t u r e decreases a t a n n e a l i n g above 500 0 C. The s m a l l c e n t r a l l i n e o c c u r i n g a f t e r 525 OC a n n e a l i n g i n t h e Mossbauer s p e c t r a (see F i g . 1 b and c ) i n d i c a t e s t h e f o r m a t i o n o f t h e -phase.

9 2

;

v [mmh]

F i g u r e 1 : Mossbauer s p e c t r a

a ) c o l d deformed sample, beam p e r p e n d i c - u l a r t o t h e r o l l i n g p l a n e

b ) sample annealed a t 525 OC, beam perpen- d i c u l a r t o t h e r o l l i n g p l a n e

c ) sample annealed a t 525 OC, beam under 200 t o t h e r o l l i n g d i r e c t i o n

I t has been p r o v e d t h a t t h e t e m p e r a t u r e t r e a t m e n t r e s p o n s i b l e f o r t h e format i o n o f t h e magnetic t e x t u r e does not change t h e c r y s t a l l o g r a f i c t e x t u r e . T h e r e f o r e i t i s o f i n t e r e s t t o l o o k f o r o t h e r s t r u c - t u r a l changes caused b y t h e - a n n e a l i n g .

t e n s i t i e s connected w i t h t h e magnetic t e x - t u r e a l s o s t r u c t u r a l changes can be observ-

ed. The a n n e a l i n g t r e a t m e n t o b v i o u s l y l e a d s t o d e c r e a s i n g l i n e w i d t h and t o an i n c r e a s e o f t h e average magnetic hyperfine f i e l d ( f r o m 317 t o 331 kG). A1 as a near- e s t n e i g h b o u r o f an i r o n atom decreases i t s e f f e c t i v e magnetic h y p e r f i n e f i e l d ( AH1 = -23 kG) 1 3 3 , and a n e a r e s t N i n e i g h b o u r i n c r e a s e s t h e f i e l d

AH^

⁼9.4 kG) [ 4 ] . T h e r e f o r e t h e d i s - t r i b u t i o n o f A1 .and N i i n t h e i r o n m a t r i x causes t h e l a r g e l i n e w i d t h and t h e l a r g e r i n f l u e n c e o f A1 l e a d s t o t h e decrease o f t h e average magnetic f i e l d compared w i t h p u r e i r o n . The decrease o f l i n e w i d t h and t h e i n c r e a s e o f t h e e f f e c t i v e magnetic

f i e l d b y t h e t e m p e r a t u r e t r e a t m e n t i n d i - c a t e an a t o m i c o r d e r i n g process. T h i s p r o c e s s s h o u l d decrease t h e p r o b a b i l i t y t o f i n d a N i o r A1 atom, r e s p e c t i v e l y , i n t h e f i r s t n e i g h b o u r s h e l l around an i r o n atom. T h e r e f o r e t h e f o r m a t i o n o f an o r d e r e d Ni-A1 phase b y a n n e a l i n g can e x p l a i n t h e observed changes o f t h e Moss- bauer s p e c t r a . T h i s has been c o n f i r m e d by X-ray d i f f r a c t i o n measurements on o u r samples. Weak (100) and (111) s u p e r s t r u c - t u r e r e f l e x i o n s have been found. The Moss- bauer s p e c t r a i n d i c a t e t h e Ni-A1 forma- t i o n a t l o w e r a n n e a l i n g t emperat u r e s t h a n t h e X-ray experiments. T h e r e f o r e we con- c l u d e t h a t t h e f i r s t coherent s t a g e o f t h e Ni-A1 p r e c i p i t a t i o n i s i m p o r t a n t f o r t h e Tormation o f magnetic t e x t u r e i n t h i s a l l o y .

References :

[I] Barton,J. ,Wieser,E, ,Muller,M., phys.stat .sol.(a)

39

(1977) 259 [ 2 ] Tokuyoshi,M.,Hirabayashi,F., Review

o f t h e E l e c t r . Commun. Lab.

19

(1971) 58 5

[ 4 ] Vincze, I. ,Campbell, I .A., 3. Phys. F, M e t a l Phys.

3

(1973) 647

F i g u r e 1 shows Mossbauer s p e c t r a o f t h e c o l d deformed sample and o f t h e sample an- n e a l e d a t 525 OC f o r two measuring geome- t r i e s . Besides t h e changes o f r e l a t i v e in-