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INTERACTION BETWEEN SUBSTITUTIONAL AND
INTERSTITIAL SOLUTES IN DILUTE Fe-V-N
ALLOYS
Tingguo Chen, Chao Jiang, Ziliang Wu
To cite this version:
INTERACTION BETWEEN SUBSTITUTIONAL AND INTERSTITIAL SOLUTES IN
DILUTE Fe-V-N ALLOYS
TINGGUO CHEN, CHAO JZANG AND ZILIANG WU
Shanghai Institute of Metallurgy, Academia Sinica,
Shanghai
200050,
China
A b s t r a c t
- A s e r i e s of i n t e r n a l f r i c t i o n peaks were measured from Fe-1.1 a t %
V w i r e specimens n i t r o g e n a t e d a t 5 0 0 ' ~ t o d i f f e r e n t n i t r o g e n c o n c e n t r a t i o n s . Each of t h e s e c u r v e s was decomposed i n t o t h r e e subpeaks by c u r v e f i t t i n g through a computer program. R e s u l t s were e x p l a i n e d i n t e r m s of n i t r o g e n d i f f u s i o n i n t h r e e t y p e s of d e f e c t s .I n 1953 F a s t / l / f i r s t r e p o r t e d a n 8 7 ' ~ i n t e r n a l f r i c t i o n peak i n quenched Fe-9.5 a t % V specimens a f t e r b e i n g n i t r o g e n a t e d above 9 0 0 ~ ~ . T h i s peak h a s s i n c e been a c c e p t e d / 2 , 3 / a s a S-i peak caused by i n t e r a c t i o n between s u b s t i t u t i o n a l vanadium and i n t e r s t i t i a l n i t r o g e n atoms. However, t h i s r a t h e r broadened peak was knovm t o be v e r y u n s t a b l e and d e c l i n e d remarkably even a t peak t e m p e r a t u r e . I t was p o i n t e d o u t e l s e w h e r e t h a t F a s t ' s 8 7 ' ~ peak i s , i n f a c t , n o t a S-i peak b e c a u s e t h e i r specimens were p r e p a r e d a t such h i g h t e m p e r a t u r e s t h a t d i f f u s i o n r a t e o f b o t h vanadium and n i t r o g e n atoms were h i g h enough t o enhance voluminous p r e c i p i t a t i o n of vanadium n i t r i d e phase. The l a t t e r i s b e l i e v e d t o be c l o s e l y r e l a t e d t o t h e emergence of t h e 8 7 ' ~ peak.
I1 - EXPERIPIENTAL DATA
Fe-1.1 a t % V w i r e specimens o f 0.71 mm I$ were loaded w i t h d i f f e r e n t amounts of
n i t r o g e n a t 5 0 0 ~ ~ under hydrogen p l u s amnonia atmosphere f o l l o w e d by 40 h r s horno-. g e n i z a t i o n a t 350'~. A t s u c h low t e m p e r a t u r e s , d i f f u s i o n of vanadium atoms was p r a c t i c a l l y s u p p r e s s e d . Both vanadium and n i t r o g e n s h o u l d remain i n s o l i d s o l u t i o n , t h e r e f o r e d i s p l a y of S-i peaks becomes a c c e s s i a b l e t o t h e s e specimens. I n t e r n a l f r i c t i o n c u r v e s of s e v e n specimens l o a d e d t o d i f f e r e n t n i t r o g e n c o n c e n t r a t i o n s a r e shown i n F i g . l . A s m a l l b u t r e c o g n i z a b l e 8 7 ' ~ peak c h a r a c t e r i s t i c t o t h e p r e s e n c e of vanadium n i t r i d e was always found on t h e i n t e r n a l f r i c t i o n c u r v e s of t h i s s o r t of specimens. These vanadium n i t r i d e i n c l u s i o n s l a r g e l y came from m a s t e r a l l o y and were unavoidably e n t r a p p e d i n t h e a l l o y i n g o t . Curves shosm i n F i g . 1 have t h e 8 7 O ~ peak and t h e background i n t e r n a l f r i c t i o n s a l r e a d y been deducted from t h e e x p e r i - mental c u r v e s . ' N i t r o g e n c o n c e n t r a t i o n s and peak t e m p e r a t u r e s a r e a l l l i s t e d i n Fig.1. I t i s noteworthy t o p o i n t o u t t h a t t h e s e a r e broadened peaks w i t h peak tem- p e r a t u r e s g r a d u a l l y s h i f t i n g toward low t e m p e r a t u r e s i d e a s n i t r o g e n c o n c e n t r a t i o n
i s i n c r e a s e d .
C10-40
JOURNAL
DE
PHYSIQUE
Each of t h e c u r v e s Q-l's shown i n F i g . 1 o7as decomposed i n t o t h r e e subpeaks
0-lI,
q-lIX,
Q ' - ' ~ ~ ~ . A c u r v e f i t t i n g computer program h a s b e e n worked o u t i n which s i x a d j u s t a b l e p a r a m e t e r s - t h r e e subpeak t e m p e r a t u r e s ( T p ' s ) and t h r e e h a l f w i d t h s ( y l , y2,y3) of box d i s t r i b u t i o n p e r t i n e n t t o e a c h subpeak were u s e d f o r m a n i p u l a t i o n . For e a s e o f computation, a box d i s t r i b u t i o n of r e l a x a t i o n t i m e s was a d o p t e d / 4 / . It was assumed b e f o r e hand t h a t t h e s i m p l e Yert-Marx / 5 / r e l a t i o n s h i p between peak tem- p e r a t u r e and a c t i v a t i o n e n e r g y f o r n i t r o g e n d i f f u s i o n h o l d s t r u e t o t h e s e subpeaks. V a l u e s o f t h e s e s i x p a r a m e t e r s were d e t e r m i n e d i n s u c h a way t h a t a l e a s t s q u a r e f i t t i n g of each e x p e r i m e n t a l c u r v e was o p t i m i z e d , k e e p i n g h e i g h t s o f t h e t h r e e sub- p e a k s t o b e t h e o n l y v a r i a b l e s . An example f o r t h i s i s i l l u s t r a t e d i n F i g . 2 where a n e x p e r i m e n t a l c u r v e D i n F i g . 1 i s decomposed i n t o t h r e e subpeaks. T h e i r subpeak t e m p e r a t u r e s a r e r e s p e c t i v e l y ~ ~ ~ = 2 0 3 ~ ~ , T 11=1790~, ~ ~ ~ ~ ~ A c t i v a t i o n = 1 4 9 ~ ~ . e n e r g i e s were d e t e r m i n e d t o b e : EI=1.37 e t , EII=l .30 eV, EIII=l. 21 eV.F i g . 1
-
I n t e r n a l f r i c t i o n c u r v e s f o r F i g . 2-
Decomposition o f e x p e r i - Fe-l. l a t % V-
N system. m e n t a l c u r v e D i n F i g . 1 .A t low n i t r o g e n c o n c e n t r a t i o n o n l y t h e h i g h t e m p e r a t u r e subpeak ( i . e . , 0-11) c o u l d b e o b s e r v e d . Then i t became p o s s i b l e t o measure d i r e c t l y t h e a c t i v a t i o n e n e r g y of t h i s peak by changing e x p e r i m e n t a l f r e q u e n c y w i t h o u t r e s o r t i n g t o t h e p a i n s t a k i n g
t e c h n i q u e of c u r v e f i t t i n g . A specimen of Fe-0.76 a t % V a l l o y n i t r o g e n a t e d a t 4 5 0 ~ ~ t o a c o n c e n t r a t i o n of 0 . 1 a t %
N
s e r v e d f o r t h i s p u r p o s e and a n a c t i v a t i o n e n e r g y of 1.35 eV was o b t a i n e d . T h i s i s i n agreement w i t h t h e v a l u e EI=1.37 eV f o r Q-lI g i v e n above.
111
-
DEFECT MODELS@ V
atom
@
Fe
at?
o
moctoh.interstices
nm.octah.interst ices
F i g . 3
.-
Three t y p e s of d e f e c t s c a p a b l e of producing t h r e e S-i i n t e r a c t i o n peaks. (b) T r i o d e f e c t N-V-N: The most s t a b l e s i t e f o r t h e second incoming n i t r o g e n atom i s t h e 0 ' 1 3 i n t e r s t i c e . T h e r e f o r e a t r i o d e f e c t i s a N-V-N m o l e c u l a r c h a i n w i t h t h e d e f e c t t e t r a g o n a l a x i s p a r a l l e l t o < l o o > . I n r e s p o n s e t o a n a l t e r n a t e l o a d t h e c h a i n a x i s w i l l r o t a t e by s y n c h r o n i z e d jumping of t h e two t e r m i n a l n i t r o g e n atoms through s u b s t e p s 01-011-01.( c ) Quadruple d e f e c t
N-l-N
: Occupancy of 0113 i n t e r s t i c e by t h e t h i r d incoming n i t r o g e n atom i s f a v o r e d because i n s o doing t h e t e t r a g o n a l a x i s of t h e 0113 n i t r o - gen i s a l s o i n t h e X3 d i r e c t i o n . T h i s i s i n p a r a l l e l w i t h t h e c h a i n a x i s o f t h e o r i g i n a l t r i o d e f e c t . Such a c o n f i g u r a t i o n ought t o b e s t a b l e under t e n s i l e s t r e s s . I n t h e n e x t compression h a l f c y c l e , t h r e e n i t r o g e n atoms i n t h e q u a d r u p l e d e f e c t w i l l jump s y n c h r o n i c a l l y a l o n g t h e p a t h s 01-011-OI ( f o r 013 and Qf3 n i t r o g e n ) and 011-01-011 ( f o r t h e 0113 n i t r o g e n ) r e s p e c t i v e l y t o a l t e r n a t e o r i e n t a t i o n of t h e t e t r a g o n a l a x e s w i t h o u t changing c o n f i g u r a t i o n of d e f e c t i t s e l f .I V - ACTIVATION ENERGY AND PZLAXATION STRENGTII
Chemical bonds a r e known t o b e of s h o r t range i n n a t u r e w i t h s t r o n g d i r e c t i o n a l i t y . These c h e m i c a l bonds a r e formed by o v e r l a p p i n g of t h e p - e l e c t r o n s of n i t r o g e n and t h e d - e l e c t r o n s of vanadium atom 161. These h y b r i d p-d bonds w i l l assume two t y p e s of d i r e c t i o n s ,
<loo> and <110>
171. For a vanadium c e n t e r e d u n i t c e l l , t h e 01 t y p e i n t e r s t i c e s l i e a l o n g < l o o > , w h i l e t h e 011 t y p e i n t e r s t i c e s b e i n g i n t h e d i r e c t i o n <110>. T h e r e f o r e t h e d i f f u s i o n p a t h s 01-011-01 and 011-0 11 we assumed seems r e a s o n a b l e t o f i t t h e d i r e c t i o n a l p r o p e r t y of t h echemicaf-:and
model.C10-42 JOURNAL
DE
PHYSIQUER e l a x a t i o n s t r e n g t h s of t h e t h r e e subpeaks a r e d i f f e r e n t , a s shown i n Fig.4.
A ~ = Q ~ ixf ( y i ) , where f (Yi)=2Yi/ [ tan-leYi-tan-le-Yi], i = I , 11,111 s i g n i f y t h e t h r e e subpeaEs, s e e ~ e f . / 4 / . I t was found i n peak decomposition t h a t y1=1.6, yII=1.6, y111=2.4, s o t h a t f ( y I ) , f ( y I I ) , f ( y I I I ) a r e known. We d e f i n e :
where A l , 42, A3 a r e r e l a x a t i o n s t r e n g t h p e r jumping n i t r o g e n atom i n e a c h t y p e of d e f e c t s , C f i ( i = I , I I , I I I ) i s t h e n i t r o g e n c o n c e n t r a t i o n i n each t y p e of d e f e c t s , A i s
a p r o p o r t i o n a l c o n s t a n t , (XI-A3) i s t h e e l l i p t i c i t y of t h e p r i n c i p a l s t r a i n e l l i p - s o i d . I f we are i n t e r e s t e d i n s o l v i n g f o r t h e r a t i o s A2/A1, A3/A1, we h a v e o n l y f i v e unknowns i n t h e above t h r e e e q u a t i o n . By c u r v e f i t t i n g o f t h e s e v e n e x p e r i - m e n t a l curves shown i n F i g . 1 , t o g e t h e r w i t h t h e c o n s t r a i n t of C~=C&+C:*+C&~I
,
and mass a c t i o n law among t h e d e f e c t s , we found A2/A -1.07, A3/Alf1.20. T h i s means t h a t e l l i p t i c i t y o f t h e p r i n c i p a l s t r a i n e l l i p s o i a - i n c r e a s e s w l t h i n c r e a s i n g n i t r o - g e n atoms i n a d e f e c t . I t c a n b e v i s u a l i z e d t h a t s q u e e z e - i n of t h e second incoming n i t r o g e n atom i n t o Of3 i n t e r s t i c e produces a b o u t t h e same e l l i p t i c i t y a s does t h e f i r s t n i t r o g e n i n 013 s i t e . Bowever, occupancy of t h e t h i r d incoming n i t r o g e n i n 0113 s i t e g r e a t l y e x t e n d s t h e two a d j c e n t c o r n e r Fe atoms, making more room f o r t h e o t h e r s i x c o r n e r Fe atoms t o s h r i n k , t h i s , o r c o u r s e , enhances t h e e l l i p t i c i t y of t h e q u a d r u p l e d e f e c t . 12 - 10- F i g . 4 -- P , e l a t i o n s h i p between r e l a x a - 8- t i o n s t r e n g t h of subpeaks and n i t r o - gen c o n c e n t r a t i o n s ./ l / F a s t , J . D . and M e i j e r i n g , J.L., P h i l i p s Res. Rep. 8 (1953) 1.
/2/ Basson, D.F. and A r s e n a u l t , R. J.
,
i n T r e a t i s e on ~ g t e r i a l s S c i . and Tech., Ed. by Herman, E., Academic P r e s s , New York, Vol.1, 1972, p179.131
Z g a d z a j , J . , I l c z u k , J. and ~ c o r d n , J.W., ICIFUAS-7, J. d e P h y s i q u e (1981) 835. /4/ Nowick, A.S. and B e r r y , B.S., A n e l a s t i c P.elaxation i n C r y s t a l l i n e S o l i d s ,Academic P r e s s , New York, 1972.
/ 5 / l q e r t , C. and Karx, J., Acta Met.
1
(1953) 113.1 6 1 C.D. G e l a t t , Jr. A.R. Williams, and V.L. I l o r u z z i , Phys. P.ev. B27 (1983) 2005.
