THE DISLOCATION-ENHANCED SNOEK EFFECT - DESE IN IRON

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THE DISLOCATION-ENHANCED SNOEK EFFECT - DESE IN IRON

L. Magalas, S. Gorczyca

To cite this version:

L. Magalas, S. Gorczyca. THE DISLOCATION-ENHANCED SNOEK EFFECT - DESE IN IRON.

Journal de Physique Colloques, 1985, 46 (C10), pp.C10-253-C10-256. �10.1051/jphyscol:19851057�.

�jpa-00225441�

THE DISLOCATION-ENHANCED SNOEK EFFECT

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Academy of Mining and Metallurgy, Institut of Metallurgy, 30 Mickiewicza Av., 30-059 Cracow, Poland

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~ ' i n s t a b i l i t i thermique de l ' e f f e t DESE dans l e f e r e s t dimon- t r g e . Une d i s c u s s i o n de l ' e f f e t DESE dans l e s metaux bcc e s t donnie.

A b s t r a c t

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n i t r o g e n doped i r o n i s r e p o r t e d . The n i t r o g e n DESE shows s i m i l a r p r o p e r t i e s as a l r e a d y r e p o r t e d c a r b o n DESE i n i r o n . Thermal i n s t a b i l i t y o f t h e DESE i n i r o n i s c l e a r l y shown. A g e n e r a l d i s c u s s i o n on t h e DESE i n bcc m e t a l s i s g i v e n .

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The d i s l o c a t i o n - e n h a n c e d Snoek e f f e c t

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T h i s e f f e c t o c c u r s a t n e a r l y t h e same t e m p e r a t u r e as t h e n o r m a l Snoek e f f e c t and has v e r y c l o s e v a l u e s o f a c t i v a t i o n energy and r e l a x a t i o n t i m e t o t h e v a l u e s o f t h e n o r m a l Snoek e f f e c t . T h i s f e a t u r e i s r e g a r - ded as t h e main p r o p e r t y o f t h e DESE i n m e t a l s /7/. The DESE i n bcc and f c c m e r a l s has been r e c e n t l y reviewed by Magalas /7/. The o r i g i n o f t h e DESE l i e s i n t h e e l a s t i c i n t e r a c t i o n between moving d i s l o c a - t i o n s and p o i n t d e f e c t s which possess l o w e r symmetry than t h e lattice and have some m o b i l i t y i n t h e l a t t i c e a t t h e t e m p e r a t u r e o f t h e DESE.

S i n c e t h e DESE has been d i f f e r e n t l y named b y many a u t h o r s ( l i k e t h e f2 peak i n Ta-0 /Q,lo/,thef peak i n Fe /8,11/ a s w e l l a s i n d u c e d Snoek peak, enhanced Snoek p&k e f f e c t , t h e i n f l u e n c e o f d i s l o c a t i o n s on t h e Snoek peak, d i s l o c a t i o n enhanced i n d u c e d Snoek peak etc). i t i s suggested t o e l i m i n a t e t h i s gamut o f names b y u s i n g t h e f o l l o w i n g name " t h e d i s l o c a t i o n - e n h a n c e d Snoek effect-DESE " a s i n t r o d u c e d i n / 7 / ; o r when d e s c r i b i n g an i n t e r n a l f r i c t i o n peak t o use t h e name

" t h e d i s l o c a t i o n - e n h a n c e d Snoek peak-DESP "/5/.

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The samples o f 1 mm d i a m e t e r and 100 mm i n l e n g t h were p r e p a r e d f r o m h i g h p u r i t y CEN.G i r o n /8,11/ doped w i t h 40 ppm o f n i t r o g e n /6,7/

and a r e r e f e r r e d t o as Fe-N/OO/. The c a r b o n c o n c e n t r a t i o n i n Fe-N/40/

i r o n a f t e r s a t u r a t i o n from 823 K was l o w e r t h a n 5 ppn /6/. The samples o f t e c h n i c a l p u r i t y Armco i r o n were annealed i n hydrogen atmosphere a t 823 K f o r 2,3,4, and 5 h r s and c o o l e d down w i t h t h e furnace. The i n t e r n a l f r i c t i o n / I F / was measured i n i n v e r t e d t ~ r s i o n ~ p e n d u l u m ope- r a t i n g w i t h a maximum shear s t r a i n a m p l i t u d e o f 1 . 9 ~ 1 0 ' and w i t h c o n t r o l e d h e a t i n g o r c o o l i n g r a t e o f 200 ~ h - ' . A f t e r t o r s i o n a l c o l d work /CW/ i n s i d e t h e pendulum t h e samples were i m m e d i a t e l y c o o l e d down t o 7 7 K w i t h i n 15 sec.

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The t r a n s f o r m a t i o n o f n i t r o g e n Snoek e f f e c t / c u r v e O/ i n t o t h e

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851057

C10-254 JOURNAL DE PHYSIQUE

n i t r o g e n DESE/N/ i n Fe-N/40/ i s shown i n Fig.1 a f t e r 6% CW a t room temperature /RT/ /curve 1/ and 13% CW a t R T /curve 2/. The h e i g h t o f t h e DESE/N/ i s p r o p o r t i o n a l t o t h e amount o f CW a t RT. The same r e l a - t i o n s h i p had a l r e a d y been found f o r carbon DESE/C/ i n i r o n / 5 / . Fig.2 i l l u s t r a t e s thermal i n s t a b i l i t y o f t h e DESE/N/ generated by 12% CW a t RT. I F and modulus " l o o p s " a r e c r e a t e d i n subsequent runs on warm-up from 100 K t o 280 K and cool-down f o l l o w e d by new r u n s up t o h i g h e r temperatures. Simultaneously t h e shear modulus measured a t 100 K was i n c r e a s e d i n each new run. T h i s e f f e c t can be accounted f o r i n terms o f successive d i s l o c a t i o n p i n n i n g by n i t r o g e n atoms which was r e c e n t l y discussed i n /7/.

The DESE/C/ i n i r o n doped w i t h 25 ppm of carbon i s 30% h i g h e r than i n i r o n doped w i t h 1000 ppm o f C a f t e r t h e same CW /7/. Sugeno /13/

observed a s i m i l a r e f f e c t i n n i t r o g e n doped i r o n which was reviewed i n / 7 / . As shown i n Fig.3 t h e DESE i n Armco i r o n a f t e r 10% CW B t RT i s h i g h e r f o r l o n g e r annealing time i n hydrogen atmosphere. T h i s expe riment was repeated a few times and each t i m e f o r l o w e r FIAs concent- r a t i o n a h i g h e r DESE was detected. I t can be concluded, t h e r e f o r e , t h a t t h e DESE i s s t r o n g e r f o r l o w e r c o n c e n t r a t i o n o f FIAs i n i r o n . The n i t r o g e n DESE/N/ can a l s o be observed i n Fe-N a l l o y s a f t e r a r e d e f o r m a t i o n a t RT o f en a l r e a d y deformed and aged sample / f o r d e t a i l s see / 7 / / m r e f e r s b o t h t o Fe-C and Fe-N a l l o y s and c o n f i r m s t h e s u g g e s t i o n t h a t f r e s h d i s l o c a t i o n s a r e i n v o l v e d i n t h e .DESE / 5 / .

I t should be mentioned t h a t t h e

P

/c< 5 ppm/ which occurs around 338 K /8.11/ i s . i n f a c t . t h e DESE/C/

/7/

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The a c t i v a t i o n parameters o f t h e DESE i n bcc metals a r e c o l l e c t e d i n Table I which i n d i c a t e s t h a t t h e a c t i v a t i o n parameters o f t h e DESE and t h e normal Snoek e f f e c t a r e n e a r l y t h e same. The g e n e r a l proper-

t i e s o f t h e DESE i n bcc m e t a l s can be e x p l a i n e d b y t h e f o l l o w i n g models.

1. The f i r s t model i s v e r y c l o s e t o t h e o r i g i n a l hdea o f Schoeck /14/.

The DESE i s caused by a movement o f non-screw / 7 1 / d i s l o c a t i o n s /which possess s m a l l P e i e r l s b a r r i e r / i n a c l o u d o f FIAs. For an a p p r o p r i a t e frequency o f d i s l o c a t i o n v i b r a t i o n a drag f o r c e occurs.

The drag f o r c e r e s u l t s from t h e f a c t t h a t an area i n which a r e d i s t r i - b u t i o n o f e l a s t i c d i p o l e s took p l a c e l a g s behind moving dislocations.

Since t h e drag f o r c e i s p r o p o r t i o n a l t o t h e r e l a x a t i o n t i m e o f Snoek e f f e c t t h e DESE should have s i m i l a r a c t i v a t i o n parameters t o t h e Snoek e f f e c t /see Table I/.

2. I n t h e second model t h e mode o f d i s l o c a t i o n movement i s d e s c r i b e d i n terms o f k i n k p a i r f o r m a t i o n on non-screw d i s l o c a t i o n s /16/. T h i s mo i s o n l y v a l ' d i f l o n g range m i g r a t i o n o f FIAs i s n e g l e c t e d and

'q:L>) 1 /

9e4-'

tbg

which i s i n e x c e l l e n t agreement w i t h t h e experiment on t h e carbon DESE i n i r o n / 5 / , see Table I.A s i m i l a r agreement can be e a s i l y

found f o r Ta-0.

3. The t h i r d model was proposed by O g u r t a n i and Seeger /3,4/. They c a l c u l a t e d t h e I F e f f e c t due t o t h e motion o f FIAs i n t h e presence of a h a r m o n i c a l l y o s c i l l a t i n g / w i t h s m a l l amplitude/ elementary r i g i d k i n k a l o n g t h e d i s l o c a t i o n l i n e o f screw and non-screw o r i e n t a t i o n on

1110) plane. According t o O g u r t a n i /4/ t h e r e l a x a t i o n s t r e n g t h o f t h e

where C i s t h e mean c o n c e n t r a t i o n o f FIAs i n t h e sample b e f o r e a rearr8ngement o f FIAs i n t h e s t r e s s f i e l d took place, N i s t h e d e n s i t y o f k i n k s , h i s t h e p r i n c i p a l v a l u e o f t h e e l a s t i k d i p o l e tensor, a n d a i s a cgnstant. The r e l a x a t i o n s t r e n g t h f o r screw and non-screw d i s l o c a t i o n s i s r o u g h l y t h e same /4/. According t o t h i s model t h e DESE should resemble an i d e a l Debye peak w i t h o n l y p o s s i b l e s m a l l broadening a t t h e h i g h temperature side.

Although a d i r e c t e x p e r i m e n t a l v e r i f i c a t i o n o f t h e O g u r t a n i model /4/

i s n o t p o s s i b l e , t h i s model can be a t l e a s t p a r t i a l l y v e r i f i e d i n tungstem which i s considered as an i s o t r o p i c bcc metal.

The model o f O g u r t a n i and Seeger does n o t agree w i t h t h e experimen- t a l r e s u l t s o f h i g h e r DESE f o r l o w e r FIAs c o n c e n t r a t i o n /Fig.3/ and can not e x p l a i n t h e broadening o f t h e DESP i n doped i r o n / t h e broade- n i n g parameter

p

As mentioned above t h e DESE i s a metastable e f f e c t i n i r o n w h i l e i n Ta and Nb i t i s f a i r l y s t a b l e a g a i n s t a n n e a l i n g treatment. D i f f e - r e n t annealing behaviour can be, however, e x p l a i n e d i n terms o f d i f f e r e n t b i n d i n g energies o f p o i n t d e f e c t s and d i s l o c a t i o n s /7,16/, which r e s u l t s i n d i f f e r e n t s t a b i l i t y o f t h e corresponding Snoek atmospheres i n Fe-C,Fe-N and Ta-0,Nb-0 a l l o y s .

F u r t h e r i n v e s t i g a t i o n on t h e temperature dependence o f t h e r e l a x a t i o n s t r e n g t h a n d p parameter should p r o v i d e an argument i n favour o f t h e 1 s t and 3 r d o r t h e 2nd model. Nevertheless. i t can be p o i n t e d o u t t h a t non-screw f r e s h d i s l o c a t i o n segments a r e m a i n l y r e s p o n s i b l e f o r t h e DESE. Although no e x p e r i m e n t a l r e s u l t s a r e a v a i l a b l e so f a r t o r e v e a l one o f t h e above mentioned modes o f d i s l o c a t i o n movement ham- pered by p o i n t d e f e c t s and t o d e f i n e t h e r e l a x a t i o n mechanism o f t h e DESE i t seems t h a t t h e 1 s t model o f f e r s a reasonable e x p l a n a t i o n o f t h e DESE.

ACKNOWLEDGEMENT

The a u t h o r s wish t o thank Dr.P.Moser f o r h i s i n t e r e s t and h e l p i n t h i s work. Thanks a r e extended t o P r o f . T.6.Ogurtani who k i n d l y made h i s papers a v a i l a b l e p r i o r t o p u b l i c a t i o n .

REFERENCES

/1/ Nowick,A.S.,Berry,B.S.,Anelastic R e l a x a t i o n i n C r y s t a l l i n e S o l i d s , Academic Press, New York and London, 1972.

/2/ Magalas,L.B.,Proc. Conf. I n t e r n a l F r i c t i o n and Magnetic A f t e r E f f e c t , RENIOM-1984 K a t o w i c 8 , S i l e s i a n U n i v e r s i t y Press,in press.

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/ 8 / Moser,P.,Magalas,L.B.,Proc. Conf. I n t e r n a l F r i c t i o n and Magnetic

A f t e r E f f e c t , RENXOM-1982 Katowice,Silesian U n i v e r s i t y Press No 615 /1984/ p.25.

/9/ Rodrian,U.,Schultz,n.,J.de Phys.C5,42 /1981/79.

/lo/ Rodrian,U.,Schultz,H.,Z.Metallkde.

3

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617.

/12/ D i e h l 3. w e l l e r M. Mensch W.,V Conf. P o i n t D e f e c t s and Defect

~ n t e r & c t i o n s i n ' ~ e t a 1 s , u n i v e r s i t y o f Tokyo Press /1982/ p.413.

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/13/ Sugeno,T.,Sakamoto,K.,Ino,H.J.,Phys.Soc,apan

28

/14/ Schoeck,G.,Phys.Rev. 102 /1956/ 1458.

/15/ Weller ,M. ,Diehl,J. ,Proc .ECIFUAS-3 /1980/ p.223.

/16/ Seeger ,A. ,Weller ,M. ,Diehl ,J. ,Pan ,Z.I. ,Zhang ,J .X. ,K& ,T.s., Z. Metallkde. 73 /1982/ 1.

/17/ WeAler,M. , L ~ , G T . ,Zhang.J.X.

,KG

1047. ^,

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C '" 10. .

8.

1.

O . , . . . .

loo

Fig.3

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200 400 deformed 10% at RT, curves 0,2,

300 T ~ K I 3,4,5, respectively.

the DESE and the Snoek effect in bcc

alloys. - - a^.h. - U)O ' TPI

Fig.2

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DESE/N/

CW at RT shown in successfve IF runs from 100 K to the follo- wing temperatures: 280 K,300 K,310 K,320 K,330 K,340 K,360 K, 380 K, curves 1,2,3,4,5,6,7,8, respectively.The changes of the shear modulus are shown in the upper part o f the figure.