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THE INTERACTION BETWEEN 119Sn AND SOLUTE ATOMS IN DILUTE IRON ALLOYS
T. Cranshaw
To cite this version:
T. Cranshaw. THE INTERACTION BETWEEN 119Sn AND SOLUTE ATOMS IN DI- LUTE IRON ALLOYS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-167-C2-168.
�10.1051/jphyscol:1979259�. �jpa-00218657�
THE INTERACTION BETWEEN
1 1 9S n AND SOLUTE ATOMS IN DILUTE IRON ALLOYS
T.E. Cranshaw
Nuclear Physios Division, A.E.R.E., Harwell, Oxfordshire, 0X11 ORA
Abstract.-Mossbauer spectra have been taken of 1 1 9Sn (.2%) in Fe alloys, where X = Al, Si, V, Cr, Mn Ni, Cu, Ga, Ge, Mo, Ru, Rh, Pd, W, Os, Ir, Pt. In general, components are observed in the spectrawith fields greater and less than 82 kOe, the 1 1 9Sn field in pure iron. These components are attributed to X atoms in the second and first neighbour shell of the Sn atom. The intensities of the components do not correspond to the expectation on a random distribution, showing that attractive and repulsive potentials exist at the neighbour sites.
Introduction.- As part of an investigation of tem- per embrittlement, Mossbauer spectra were taken of iron-nickel alloys containing about 4 % Ni, and
.2 % 1 1 9Sn /l/. It was found that an attractive po-
tential exists between nickel and tin atoms, and that precipitates of a nickel tin intermetallic com- pound could be formed in regions of mutual solubili- ty of the binary alloys. In the present paper we discuss the results of investigation of FeXSn alloys where X is Al, Si, V, Cr, Mn, Ni, Cu, Ga, Ge, Mo,
Ru, Rh, Pd, W, Os, Ir, Pt. The investigation falls into two parts, first the measurement of hyperfine fields for different X configurations of the 1 1 9Sn atoms, and second, the determination of the proba- bilities of these configurations from the intensi- ties of the components in the Mossbauer spectra.
Unfortunately in practice the separation is by no means perfect, and we have to discuss the results together. The hyperfine field at 1 1 9Sn in iron at 77 K is - 82 kOe. In the spectra we find in general components with fields greater and less than - 82kOe.
Based on the work on Ni, we assume that the compo- nents with |H| > 82 kOe are due to Sn atoms with X atoms in the second neighbour shell, and compo- nents with |H| < 82 kOe are due to Sn atoms with X atoms in the first neighbour shell. It is difficult to find evidence to make a rigorous test of assign- ment. The line width of I 1 9Sn resonance corresponds
to a field of about 10 kOe, and therefore, bearing in mind that each component produces 6 lines, the resolution of the observed spectra into components is often hazardous. In most cases, spectra have been
taken of the samples with a) a small applied field (~ 1.5 kOe) to saturate the magnetization, and so define the intensities of the second and fifth lines and b) a field of 25 kOe along the direction of the y-ray, to reduce the intensity of the second and fifth lines to zero. In some cases, we have also applied c) a field of 60 kOe to determine the sign of component fields. Computer programs have been used to make simultaneous fits to the spectra.
Results.- In the following we describe the behaviour of several typical X atoms.
1.- Nickel alloys. Specimens containing 2, 4, 6, 8%
Ni have been examined, and components found with fields ~ - 105 kOe, and - 60, - 39 and - 14 kOe, as well as at - 82 kOe. The intensity of the high field component agrees well with the number expected for the number of Sn atoms with a Ni atom in the second neighbour shell on a random distribution of Ni atoms;
the other components are much stronger, indicating an attractive potential between Ni and Sn atoms in the first neighbour shell. To estimate the strength of the potential, we use a simple thermodynamic ex- pression for the probability P(i) that a tin atom has i Ni neighbours,
P(i) = Ci B(i) exp (- $£/T)
where C is the concentration, B is a geometrical term depending on the number of ways of forming the configuration with i neighbours, and (J), is the ener- gy associated with the configuration. We find that each nickel atom is bound with an energy .09 eV.
Confirmation of the assignment above of field to neighbour configuration can be found in the observa-
JOURNAL DE PHYSIQUE
Colloque C2, supplément au n° 3, Tome 40, mars 1979, page C2-167
Résumé.- Nous décrivons les spectres Mossbauer de 1 1 9Sn (0,2 X) dans des alliages Fe-X
(X = Al, Si, V, Cr, Mn, Ni, Cu, Ga, Ge, Mo, Ru, Rh, Pd, W, Ps, Ir, Pt). En général les composantes des spectres ont des champs supérieurs ou inférieurs à 82 kOe (valeur du champ relatif à 1 1 9Sn dans le fer pur). Ces composantes peuvent être attribués aux atomes X premiers et deuxièmes plus proches voisins de l'étain. Les intensités ne sont pas en accord avec ce que l'on attendrait d'une distri- bution régulière, montrant que des potentiels attractifs ou répulsifs existent entre les sites voisins.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979259
C2- 168 JOURNAL DE PHYSIQUE
t i o n of t h e e f f e c t of p a s s i n g through t h e m a r t e n s i - t i c t r a n s f o r m a t i o n . I n t h e t r a n s f o r m a t i o n from FCC t o BCC, t h e 12 atoms which were f i r s t n e i g h b o u r s i n t h e FCC phase p r o v i d e t h e 8 f i r s t neighbours of t h e BCC phase; t h e remaining 4 atoms go i n t o t h e second neighbour s h e l l . By making u s e of t h e h y s t e r e s i s , we can quench specimens from t h e same t e m p e r a t u r e , b u t i n t h e FCC o r BCC phase. We always f i n d t h a t
I
s p e c t r a of specimens quenched from t h e FCC p h a s e c o n t a i n an enchanced h i g h f i e l d c o n t r i b u t i o n , presu- mably due t o t h e i n c r e a s e d number of second-neigh- bours. Below c e r t a i n t e m p e r a t u r e s , t h e specimens c o n t a i n i n g 4,6 and 8 % N i show p r e c i p i t a t i o n of an i n t e r m e t a l l i c compound, whose spectrum i s i d e n t i c a l w i t h t h a t of Ni,Sn2. A p l o t of t h e l o g of t h e per-
centage of Sn i n s o l u t i o n a g a i n s t 1/T y i e l d s a s t r a i g h t l i n e .
2.- Pd a l l o y s . Specimens c o n t a i n i n g 1 , 2 , 3 % Pd have been examined. The b e h a v i o u r i s s i m i l a r t o N i , b u t t h e a t t r a c t i v e p o t e n t i a l i s about . I 1 eV. Below t h e m a r t e n s i t i c t e m p e r a t u r e , n e a r l y a l l t h e Sn i s p r e c i p i t a t e d a s an i n t e r m e t a l l i c compound, s o f a r u n i d e n t i f i e d . No h i g h f i e l d component i s observed;
e i t h e r t h e change i n f i e l d produced by a second / 1 / Edwards, B.
neighbour Pd atom i s n e g l i g i b l e , o r a s t r o n g r e p u l - N a t u r e
47
s i v e p o t e n t i a l e x i s t s a t second n e i g h b o u r s . 3 . - C o a l l o y s . Specimens c o n t a i n i n g 3 and 6 % Co have been examined. A weak a t t r a c t i v e p o t e n t i a l
(- .05 eV) e x i s t s i n t h e f i r s t neighbour s h e l l , and no Co second neighbour components a r e observed. The f i e l d a t Sn atoms w i t h no Co atom neighbour i s ob- s e r v e d t o i n c r e a s e w i t h Co c o n c e n t r a t i o n , a t about .6 kOe/%Co. T h i s i s a l i t t l e f a s t e r t h a n t h e change i n m a g n e t i z a t i o n .
4.- V and C r a l l o y s . Specimens c o n t a i n i n g 3 % have been examined. A weak r e p u l s i v e p o t e n t i a l may e x i s t . No second neighbour components a r e seen.
5.- Al, S i , Ga, G e , a l l o y s . Specimens c o n t a i n i n g about 3 % have been examined. S t r o n g r e p u l s i v e po- t e n t i a l s e x i s t i n b o t h t h e f i r s t and second neigh- bour s h e l l s . Components produced b y t h e s e atoms can o n l y b e e a s i l y s e e n i n r o l l e d specimens; a f t e r hea- t i n g a t 250°c, t h e neighbour atoms d i f f u s e away.
I n t a b l e I we p r e s e n t t h e r e s u l t s on h y p e r f i n e fields f o r t h e a l l o y s s o f a r s t u d i e d . The numbers g i v e n a r e AH1 and AH2, t h e change i n f i e l d produced by 1 X atom i n t h e f i r s t and second neighbour s h e l l respec- t i v e l y . Where AH2 i s n o t g i v e n , no component g r e a t e r t h a n 82 kOe was observed. T h i s may mean t h a t AH2 i s s m a l l , o r t h a t a r e p u l s i v e p o t e n t i a l e x i s t s a t t h e second neighbour s h e l l .
Table I
References
C . , Eyre, B.L.
(1977) 269.
and Cranshaw, T . E . ,
