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A NEW INTERNAL FRICTION PEAK ASSOCIATED
WITH TRACE HYDROGEN IN Ti-6Al-4V ALLOY
Du Ju
To cite this version:
Du Ju.
A NEW INTERNAL FRICTION PEAK ASSOCIATED WITH TRACE
CoZZoque C5, supplBcent au lzO1O, Tome 42, octobre 1981
A NEW INTERNAL F R I C T I O N PEAK ASSOCIATED WITH TRACE HYDROGEN I N T i - 6 A 1 - 4 V ALLOY
Du J i a J u
I n s t i t u t e o f Metal Hesearch, Academia o f Science, Shengang, China
i i b s t r a c t
.-
I n t e r n a l f r i c t i o n a e a s u r e m e n t s or1 comrnerical Ti-GN-4V a l l o y i n t h e r a n g e 100K t o 350X a t about 2 HIz f r e q u e n c i e s reve- ,ded t h a t t h e r e w a s n o t o n l y a Snoek r e l a x a t i o n peak of kydrogen a t o r i s i n t h e p - p h a s e a t 116K, b u t a l s o a new s m a l l r e l a x a t i o n peak a t 289E; caused by t h e s m d l amount of hydrogen atoms i n a- phase. The mechanism by which t h i s new peak i s produced i s sug- g e s t e d . The a c t i v a t i o n e n e r g i e s f o r d i f f u s i o n o f hydrogen atoms i n B -phase and a -phase riere found t o b e 5.6 i;cdl/inole and 1 1.1 Kcal/mole res e c t i v e l y . The f r e q u e n c y f a c t o r s were 4.0 x 1014s-'
and 2.1 r 101q s-I r e s p e c t i v e l y . A c c o r d i ~ g t o t h e h e i g h t o f t h e two pe,-s i t i s p o s s i b l e t o e v a l u a t e t h e d i s t r c b i t i o n o f hydrogen i n trio p h a s e s of Ti-GN-4V a l l o y .
1 . 1 P t r o d u c t i o n . - The h a r m f u l e f f e c t s of hydrogen on t i t n n i u m and i t s a l l o y s are w e l l known(' ). However t h e mschanisn o f hydrogen e m b r i t t l e - ment caused by small amount o f hydrogen i n Ti-6,21-4V a l l o y i s n o t c l e a r . I n t e r n a l f r i c t i o n measurement i s an u s e f u l t o o l f o r s t u d y i n g t h e beha- v i o r o f hydrogen i n t i t a n i u m and i t s a l l o y s . Some s t u d i e s on t h i s theme
have been Pour k i n d s of p e a k s have been o b s e r v e d . The cau-
s e s f o r t h e s e i n t e r n a l f r i c t i o n p e a k s a r e hydrogen Snoek r e l a x a t i o n i n p - p h a s e ( 3 ) ( 6 ) , p h a s e t r a n s f o r m a t i o n between h y d r i d e and d i s s o l v e d hy- d r o g e n i n a - p h a s e ( 2 ) , t h e Snoek r e l a x a t i o n of hydrogen atoms i n t i t a - nium h y d r i d e s ( 3 ) and t h e i n t e r a c t i o n between hydrogen an8 d i s l o c a t i o n ( 4 )
( 5 ) r e s p e c t i v e l y . R e c e n t l y Norman e t al. ( 6 ) measure& i n t e r n a l f r i c t i o n of h y d r o g e n a t e d Ti-6N-4V two p h a s e (a+@) a l l o y and o b s e r v e d a peC& caused by hydrogen atoms i n 0-phase. However, t h e b e h a v i o r o f hydrogen d i s s o l - ved i n t h e U-phase i s o b s c u r e t o d a t e , a s t h e s o l u b i l i t y limit o f hy- d r o g e n i n a - p h a s e i s v e r y s m a l l , b e i n g o f t h e o r d e r of 20 ppm a t room t e m p e r a t ~ r e ( ~ ) . I n t h e p r e s e n t i n v e s t i g a t i o n an a t t e m p t was maLe t o s t u d y t h i s problem.
2. E x p e r i m e n t a l procedure.- The m a t e r i a l u s e d i n t h i s s t u d y i s a commer- c i a l Ti-6A1-4V a l l o y . I t s c h e m i c a l c o m p o s i t i o n i s g i v e n i n T a b l e 1 . F o r Comparison t h e i n t e r n a l f r i c t i o n s o f commercial T i , Ti-51U-2.5Sn <and
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Ti-50Nb were a l s o measured.
A l l s p e c i m e n s r e c e i v e d an a n n e a l i n g h e a t t r e a t m e n t f o r 1 h r a t 8 0 0 ~ ~ . TWO s p e c i m e n s o f Ti-6Al-4V were c o l d worked(about 1 % and 10% area r d u c t i o n ) and machined, t h e r e s t were machined w i t h o u t c o l d work. F i n a l specimen s i z e is 5m i n d i a m e t e r and 100mm i n l e q g t h . The m i c r o s t r u c t u r e of Ti-6A1-4V c o n s i s t e d o f Q! and B p h a s e , whereas T i and Ti-5A1-2.5Sn were all a - p h a s e . Ti-50Nb was c o m p l e t e l y 8 .
The hydrogen l e v e l i n t h e commercial Ti-6A1-4V and Ti-5Al-2.5Sn s p e c i m e n s w a s f i r s t r e d u c e d t o below 1Oppm by dynamic vacuum a n n e a l i n g f o r 4 h r . at 4 x 1
o - ~
t o r r a t 800°C. T h e s e s p e c i m e n s were t h e n e l e c t r o - l y t i c a l l y charged w i t h hydrogen i n a IN s u l p h u r i c a c i d . The c u r r e n t den- s i t y was 1 0mA/cm2.I n t e r n a 3 f r i c t i o n was measured by t h e method of t r a n s v e r s e v i b r a - t i o n a t a b o u t 1800 Hz from lOOK t o 350X at a r i s i n g r a t e of a b o u t 0.6 ~ / m i n i n a vacuum a c o u s t i c f r e q u e n c y a p p a r a t u s f o r i n t e r n a l f r i c t i o n measurement, t h e background i n t e r n a l f r i c t i o n o f which i s l e s s t h a n 7 x 10-6.
3. E x ~ e r i m e n t a l r e s u l t s and d i s c u s s i o n . - Two i n t e r n a l f r i c t i o n p e a k s were o b s e r v e d i n Ti-6111-4V specimens c o n t a i n n i n g a b o u t 50ppm hydrogen w i t h and w i t h o u t b e i n g c o l d w o r k e d ( s e e F i g . 1 ) . One peak(P6) w a s l o c a t e d a t 1 1 6 K a t 1799 Hz. Another b r o a d e r p e a k ( P a ) was l o c a t e d a t 289K at 1744 H z . The h e i g h t s of t h e two peaks were r e d u c e d a f t e r vacuum degas- s i n g and i n c r e a s e d by c a t h o d i c c h a r g i n g w i t h h y d r o g e n ( s e e P i g . 2 ) . P o r commercial Ti-5Al-2.5SnP o n e peak l o c a t e d a t a b o u t 289K was o b s e r v e d . I t s peak h e i g h t w a s a l s o reduced a f t e r vacuum d e g a s s i n g and i n c r e a s e d by c a t h - o d i c c h a r g i n g w i t h hydrogen(Pig.3).110wever, f o r commercial Ti-50Nb t h e r e was o n l y a
Pe
peak and f o r commercial. T i no peak was o b s e r v e d f r o m 100K t o 350K(see F i g . 4 ) . A l l t h e s e o b s e m r a t i o n s s u g g e s t e d t h a t t h e two p e a k s were c o n c e r n e d w i t h hydrogen r a t h e r t h a n d i s l o c a t i o n and t h a t t h e peak PB a p p e a r e d o n l y w i t h t h e p r e s e n c e o f t h e B - p h a s e ( e . g . Ti-GW-4V, Ti- 50Nb) w h i l e peak Pa w a s o b s e r v e d o n l y i n a l l o y s c o n t a i n n i n g a - p h a s e ( e .g. Ti-6Al-4V, Ti-5A.1-2.5Sn).
A p l a t o f t h e h e i g h t o f t h e peak PLY VS c a t h o d i c c h a r g i n g t i m e is g i v e n i n Fig.5. The s l o p e o f t h e s t r a i g h t l i n e drawn t h r o u g h p o i n t s w i t h l o w hydrogen c o n c e n t r a t i o n s is found equal. t o one. Assuming t h a t hydrogen c o n c e n t r a t i o n i s p r o p o r t i o n a l t o t h e c h a r g i n g t i m e i n t h e e a r l y s t a g e o f c a t h o d i c c h a r g i n g , t h e peak h e i g h t i s p r o p o r t i o n a l t o t h e hy- d r o g e n c o n c e n t r a t i o n a t low hydrogen c o n c e n t r a t i o n s . A f t e r r e a c h i n g t h e maxirmzm ' t h e ljeak h e i g h t . i s i n d e p e n d e n t o f hydrogen c o n c e n t r a t i o n s . A l l t h e s e o b s e r v a t i o n s s u g g e s t t h a t p e a k Por i s caused b y hydrogen atoms i n
f o r s o l u b i l i t y l i m i t o f hydrogen ins-phase is much s m a l l e r t h a n t h a t o f t h e Snoek peak o f hydrogen i n B -phase o r i n h y d r i d e s .
The c h a r g e o f i n t e r n a l f r i c t i o n w i t h measurement r u n s o n specimen c h a r g e d w i t h hydrogen a t room t e m p e r a t u r e f o r 1 0 min i s shown i n Pig.6. After measurement at t e m p e r a t u r e s h i g h e r t h a n room t e m p e r a t u r e , peak Pa( w a s r e d u c e d w i t h accompanying r i s e o f peak Pg. T h i s i s b e l i e v e d t o b e a s s o c i a t e d w i t h t h e d i s t r i b u t i o n o f hydrogen i n t h e s e two p h a s e s . As
t h e m i c r o s t r u c t u r e s o f Ti-6Al-4V c o n s i s t o f a b o u t 80% c o n t i n u o u s
a-
p h a s e and 20% i n t e r g r a n u l a r 6-phase, a l s o t h e d i f f u s i - o n o f hydrogen i n a - p h a s e i s v e r y s l o w , d u r i n g c a t h o d i c c h a r g i n g t h e d i s t r i b u t i o n o f hy- d r o g e n i s i n a n o n - e q u i l i b r i u m s t a t e and t h e r e l a t i v e amount o f hydro- g e n d i s s o l v e d i n &-phase is more t h a n t h a t i n 19-phase, c o n s e q u e n t l y p e a k Pa r i s e d markedly. However when m e a s u r i n g a t t e m p e r a t u r e s h i g h e r
t h a n room t e m p e r a t u r e , an a n n e a l i n g e f f e c t t a k e s p l a c e . ks t h e s o l u b i - l i t y o f hydrogen i n &phase i s much l a r g e r t h a n t h a t i n a - p h a s e , t h e hydrogen atoms d i f f u s e f r o m a - p h a s e i n t o 6 -phase. Thus peak Pa i s r e - duced w h i l e peak P s is i n c r e a s e d .
When m e a s u r i n g a t a b o u t 5 KHz, t h e peaks Pg and P a were l o c a t e d a t 121K and 305K r e s p e c t i v e l y . The s h i f t s of t h e p e a k s t e m p e r a t u r e s w i t h f r e q u e n c y i n d i c a t e d t h a t t h e two p e a k s were of r e l a x a t i o n t y p e . The a c t i v a t i o n e n e r g i e s a s s o c i a t e d w i t h t h e s e p e a k s were found t o b e 5 . 6 k 0.5 ~ c a . l / m o l e and 1 1 .I 0.6 ~ c a l / m o l e r e s p e c t i v e l y which a r e i n agree- ment w i t h t h e a c t i v a t i o n e n e r g i e s f o r d i f f u s i o n o f hydrogen i n & - p h a s e and i n a - p h a s e r e p o r t e d i n t h e l i t e r a t u r e s ( 8 ) ( 9 ) . The f r e q u e n c y f a c t o r of 4.0 x 1014 S" f o r peak Pg a l s o a g r e e d w i t h t h e v a l u e s o b t a i n e d f o r Snoek r e l a x a t i o n ( l O ) , w h i l e t h e f r e q u e n c y f a c t o r Of 2.3 x 1012 S" f o r peak Pbc w a s smaller t h a n t h a t f o r Snoek r e l a x a t i o n .
C5-778 JOURNAL DE PHYSIQUE
s i t e s a r e p o s s i b l e . However t h e o c t a h e d r a l s i t e s a r e symmetric i n an un- s t r a i n e d l a t t i c e and h e n c e no r e l a x a t i o n i s p o s s i b l e . T h i s e x p l a i n s why i n commerical t i t a n i u m c o n t a i n n i n g hydrogen which i s o f a l l a - p h a s e t h e r e i s n e i t h e r Pa n o r P a ( F i g . 4 ) . While i n Ti-6A1-4V t h e r e a r e s u b s t i - t u t i o n s o l u t e atoms Al and V. The a t o m i c d i a m e t e r s of them a r e 2.8% and 75% Less t h a n t h a t o f T i r e s p e c t i v e l y . The s u b s t i t u t i o n a l atoms d i s t u r b t h e i s o t r o p i c n a t u r e o f t h e o c t a h e d r a l i n t e r s t i t i a l s i t e s i n t h e i r neigh- borhood and hence i n t e r s t i t i a l atoms w i l l jump from o n e p o s i t i o n t o ano- t h e r u n d e r t h e i n f l u e n c e o f an e x t e r n a l l y a p p l i e d stress. The a c t i v a t i o n e n e r g y of t h i s p r o c e s s i s c l o s e t o t h a t f o r d i f f u s i o n of hydrogen i n & - p h a s e , s i n c e t h e b i n d i n g e n e r g y between t h e s u b s t i t u t i o n a l atom and hy- d r o g e n atom is p r o b a b l y s m a l l i n comparison t o t h e e n e r g y f o r d i f f u s i o n o f hydrogen. However, f o r d i f f e r e n t s u b s t i t u t i o n a l atoms t h i s b i n d i n g e n e r g y i s d i f f e r e n t owing t o t h e d i f f e r e n c e of t h e i r a t o m i c s i z e and c h e m i c a l c h a r a c t e r i s t i c . So t h a t peak Pa i s a b r o a d o n e which i s asso- c i a t e d w i t h two o r more r e l a x a t i o n p r o c e s s e s w i t h similar a c t i v a t i o n e
nergy. The a c t i v a t i o n e n e r g y measured b a s e d on t h e s h i f t o f peak tempe- r a t u r e w i t h f r e q u e n c y i n t h i s s t u d y i s of s t a t i s t i c a l n a t u r e and a g r e e s w i t h t h a t f o r d i f f u s i o n of hydrogen i n R-phase r e p o r t e d i n t h e l i t e r a - ture.
4. C o n c l u s i o n s
( 1 ) B y means o f a vacuum a c o u s t i c f r e q u e n c y i n t e r n a l f r i c t i o n measu- r i n g a p p a r a t u s w i t h background l e v e l l e s s t h a n 7
x
two p e a k s were o b s e r v e d i n commercial Ti-6&-4V a l l o y c o n t a i n n i n g a b o u t 50ppm hydrogen.( 2 ) A t a b o u t 1800 Hz, one p e a k ( P 8 ) was l o c a t e d a t 116K. It appeared o n l y w i t h t h e p r e s e n c e o f hydrogen and t h e B-phase(e.g. Ti-6A1-4V, Ti- 50Nb). The a c t i v a t i o n e n e r g y a s s o c i a t e d w i t h i t was found t o b e 5.6 ~ c a l / m o l e which a g r e e d w i t h t h a t f o r d i f f u s i o n o f hydrogen i n 8 - p h a s e and t h e f r e q u e n c y f a c t o r of 4.0
x
1014 3-l f o r i t a l s o a g r e e d w i t h t h e v a l u e s o b t a i n e d f o r Snoek r e l a x a t i o n . Thus i t can b e concluded t h a t peak Pg i s a hydrogen Snoek peak i n &phase.( 3 ) A new b r o a d e r peak(Po() w a s l o c a t e d a t 289K.
It
a p p e a r e d o n l y w i t h t h e p r e s e n c e o f hydrogen and i n T i a l l o y s c o n t a i n n i n g a - p h a s e ( e . g . Ti- 6A1-4V, Ti-5A1-2.5~n). Moreover, i t w a s r e l a t e d t o t h e hydrogen atoms i n a - s o l i d s o l u t i o n r a t h e r t h a n h y d r i d e . The a c t i v a t i o n e n e r g y a s s o c i - ated w i t h i t w a s found t o b e 1 1 .I ~ c a l / m o l e which a g r e e d w i t h t h a t f o r d i f f u s i o n o f hydrogen i n a - p h a s e . Thus t h i s new peak is b e l i v e d t o be a s s o c i a t e d w i t h t h e jump o f hydrogen atoms d i s s o l v e d i n t h e a - p h a s e . Ast h e s o l u b i l i t y l i m i t of hydrogen i n a - p h a s e w a s v e r y s m a l l , peak Pa was
( 4 ) According t o t h e h e i g h t o f t h e two p e a k s i t i s p o s s i b l e t o evalu- a t e t h e d i s t r u b i t i o n o f hydrogen i n two p h a s e s o f Ti-6A1-4V a l l o y . k e f e r e n c e s
( 1 ) N.X.Paton, J .C. W i l l i a m s , inVHydrogen i n I.letals" 1.M.Bernstein and A. W.Thompson, 1973, p. 409.
( 2 ) ~ . ~ 8 s t e r , L.Bangert and N.krers, 2. M e t a l l k d e , 4 7 , 564(1956). ( 3 ) M.Someno, H.Saito, i n "The S c i e n c e , Technology and A p p l i c a t i o n o f
T i t a n i u m " , J a f f e e and P r o m i s e l , 1 970, p .393.
( 4 ) P.P.Tung and A. W.Somrner, Acta Met., Vo1.22, 791 ( 1 974).
( 5 ) Besse,S., Owntard,M., Mazot,Ph.-Petit ,J., Second i n t e r n a t i o n a l con- g r e s s on hydrogen i n m e t a l s , 1976, P r a n c e , 2C17.
( 6 ) N.L.Guiles, K.One, i n " E f f e c t o f Hydrogen on B e h a v i o r o f M a t e r i d l s I f A. W.Thompson, I.M.Bernstem, 1976, p.666.
( 7 ) G.A.Lenning, C.M.Graighead, R . I . J a f f e e , J . M e t a l s , 6 , 367, 1954. ( 8 ) R.J.Wasilewski, G.L.Keh1, M e t a l l u r g i a , 50, 225, 1954,
( 9 ) W.A.Holrnan, R.W.Crawford, P a r e d e d , T r a n s . M e t a l l . Soc. A I M E , 233, 1836( 1965)
( 1 0 ) ii.S.iqowick, B.S.Berry, h n e l a s t i c H e l a x a t i o n i n C r y s t a l l i n e Y o l i d s , Academic p r e s s , 1 972.
( 1 1 ) T.S.Ke and C.T.Tsien, S c i . S i n . , 5 , 625(1956) ( 1 2 ) D . k p t a and S e i n i g , A c t a Met., 1 0 , 292(1962).
C5-780 JOURNAL DE PHYSIQUE
I NO COW WOW
2 I%COU)WORX
3 WI. COU) nORK
T Fig.1 I n t e r n a l f r i c t i o n o f Ti- F i g . 2 I n t e r n a l f r i c t i o n of 6 A1-4V Ti-6Al-4V I !NITlAL STATE 2 V WDtGAsSING 3 CATH001C ~ 1 ~ 1mi,,) 1 0 4 C A T ~ ~ I C MLRGIWSI min) T i n ) F i g . 3 I n t e r n a l f r i c t i o n of Ti-5111-2.5Sn Fig.4 I n t e r n a l f r i c t i o n o f Ti(Hydrogen c o n t e n t +3O ppm) and Ti-50Nb(hydro- g e n c o n t e n t +70 ppm)
P i g . 5 The r e l a t i o n s h i p between Fig.6 The change o f Q-I w i t h t h e h e i g h t o f t h e peak measurement nuls for Pa and c h a r g i n g t i m e specimen c h a r g e d w i t h
