High critical current densities in industrial scale composites made from high homogeneity Nb 46.5 Ti

269

IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-21, NO. 2, MARCH 1985

HIGH CRITICAL CURRENT DENSITIES I N INDUSTRIAL SCALE COMPOSITES

MADE FROM HIGH HOMOGENEITY NB 46.5

TI

D. C. L a r b a l e s t i e r , A. W. West, W. S t a r c h , W. Warnes, P. Lee A p p l i e dS u p e r c o n d u c t i v i t yC e n t e r U n i v e r s i t yo fW i s c o n s i n - M a d i s o n Madison, W I 53706 W. K. McDonaldand P. O'Larey Teledyne Wah Chang A1 bany, OR 97321

K. Hemachalamand B. Z e i t l i n IntermagneticGeneralCorporation Waterbury, CT 06704 R. Scanlanand C. T a y l o r LawrenceBerkeleyLaboratory 94720 Berkeley, CA Introduction Recentwork i no u rg r o u p on t h e f a b r i c a t i o n m i c r o s t r u c t u r e - s u p e r c o n d u c t i n gp r o p e r t i e so f composi t e s ofNb-Tihasproduced much new i n f o r m a t i o na b o u t t h ep r e c i p i t a t em o r p h o l o g y and o r i g i n s o f h i h critic udrceraenlns ti t y (J,)tPhreesi-ne cipitationofTi-rich phase i s seen t o commence as a f l i 2 4 nm t h i c k , t h e f m l i thendegrainboundary m v e l o p i n gi n t oa p p r o x i m a t e l ye q u i a x e dp a r t i c l e so fC t T i a tt h eb o u n d a r yt r i p l ep o i n t s . The t y p i c a ls i z e o f s u c hp r e c i p i t a t e si s 50 100 nm. C o n t r o l l e dd r a w i n g o f such a s t r u c t u r e p r o d u c e s a n a r r a y o f l o c a l l y o r d e r e dr i b b o np r e c i p i t a t e s These p r e c i p i t a t e sa r e typically 3 5 nm t h i c k b y 100 300 nm l o n g (when observed i nt r a n s v e r s es e c t i o n ) .T h e i rl e n g t hi nl o n g i t u d i n a ls e c t i o na p p e a r st o beseveralhundred nm, i n d i c a t i n gg r e a td u c t i l i t yi nt h e s es m a l lC t T ip r e c i p i t a t e s . The t y p i c a ls e p a r a t i o no ft h ep r e c i p i t a t e si s 20 30 nm. Thus t h ed i m e n s i o n so ft h ep r e c i p i t a t e arrayarequitecomparabletothatofthefluxlattice s i n c et h ef l u x o i ds e p a r a t i o ni s 22 nm a t 5 T and t h e f l u x o i d d i a m e t e r o f Nb 46.5 w t % T i i s a p p r o x i m a t e l y 10 nm. The f l u xp i n n i n gb e h a v i o ro ft h e e precipitate s t r u c t u r e si se x p e c t e dt ob ec o m p l e x : ? 94 t h ed e f e c t d e n s i t yi sv e r yh i g h ,t h ep r e c i p i t a t em o r p h o l o g y has a v e r yh i g ha s p e c tr a t i o and t h e e x t r e m e t h i n n e s s o f t h e p r e c i p i t a t e s mustpermit some supercondu t i v i t y t o be induced i n themby t h e p r o x i m i t y e f f e c t .

-

-

.

-

-

-

5

The d e t a i l s o f t h e abovestudiesl-'lhave l e d US t o p r o p o s ec o n s i d e r a b l er e v i s i o ni n a numbe f earlier i d e a sa b o u tf l u xp i n n i n gi nt h i s system.b-g The studieshavealsogivenus a model f o rt h ed e v e l o p m e n t o fm i c r o s t r u c t u r ew h i c ha p p e a r st ob ev a l i df o r a cons i d e r a b l er a n g eo fa l l o yc o m p o s i t i o n s( v i z . Nb 42 Nb 53 w t % T i , t o g e t h e r w i t h a l l o y s c o n t a i n i n g Ta and Zr a d d i t i o n s ) . A n a t u r a le v o l u t i o no ft h e s es t u d i e s was t h ed e v e l o p m e n to f a plantoattainhigh Jc on a reproducible basis

-

-

.

Priortotacklingthis problem, i t was foundnecess a r yt oc o n s i d e ra n o t h e ra s p e c to ft h em i c r o s t r u c t u r e . The c r i t i c a lc u r r e n td e n s i t yi ss e n s i t i v et o t h em i c r o s t r u c t u r ea tt h el e v e lo ft h ei n d i v i d u a l f l u x o i d - d e f e c ti n t e r a c t i o n (we c a l l t h i s a m i c r o s c o p i c i n t e r a c t i o n ) and a l s o on a moremacroscopicscale. T h i ss c a l ei st h a to ft h ef i l a m e n t . I f t h ef i l a m e n t i s non-uniform i n s t r u c t u r e because i t i s sausaged o r has a s i g n i f i c a n t c r o s s - s e c t i o n o f T i Cu p a r t i c l e s embedded i n i t o r because i t i s markegly c h e m i c a l l y wil h e t e r o g e n e o u s ,t h e nt h eo v e r a l lt r a n s p o r tc u r r e n t be s i g n i f i c a n t l y l i m i t e d b y s u c h m a c r o s c o p i c nonu n i f o r m i t i e s . We have p r e v i o u s l y shown t h a tt h e s e ManuscriptreceivedSeptember10,

1984

effectscan be v e r ys e r i o u si n Nb3Sn.l0The evidence i sl e s sc o n c l u s i v ei nN b - T i 2b u t we b e l i e v es u c h e f f e c t s t o be v e r yi m p o r t a n ti nt h i sc a s et o o . HighHomogeneityAlloy Previousworkhas

shown t h ee x i s t e n c eo fl a r g e

- 1 m) a - T ip r e c i p i t a t e si nc o n d u c t o r sg i v e ne x t e n d e d

(0.5

h e a t r e a t m e n t s( s e eF i g . 9 o f r e f . 11). P a r a l l e l i n v e s t i g a t i o n o f t h ed e v e l o p m e n to fs u b - s t r u c t u r ei n r o d so f Nb-TiandNb-Ti-Ta a l l o y s showed t h a t l o c a l d i f f e r e n c e so f f 5 w t % T i c o u l de x i 2 j ji nr o ds t o c k d e s t i n efdocro m p o s i tm e anufacture. These l o c a l d i f f e r e n c e si nc o m p o s i t i o np r o d u c e ds i g n i f i c a n tl o c a l s u b - s t r u c t u r eh e t e r o g e n e i t i e s , as w e l l as non-uniform p r e c i p i t a t i o n when heattreatmentsweregiven. An example o f t h e l i m i t a t i o n i n J, imposedbysuch diff e r e n c e s has been g i v e ni n a recentstudy.2Such resultsledtothedesiretoproduce a morechemically u n i f o r mr o ds t o c k ,i no r d e rt h a tt h ed e s i r e df i n a l m i c r o s t r u c t u r em i g h tb et h a to f a r e g u l a ra r r a yo f a-Tiribbons 20 -30 nm a p a r t . E v a l u a t i o no ft h ec h e m i c a lu n i f o r m i t yo f Nb-Ti i n g o t s canbeperformedatvariousstages and t h e s c a l e o f t h eo b s e r v e dh e t e r o g e n e i t yc l e a r l y dependson i n g o tm e l t i n g and f a b r i c a t i o np r a c t i c e .I n g o t chemic a lh e t e r o g e n e i t i e sc a nb er o u g h l yd i v i d e di n t ot w o types,thosewhicharecomparable tothescaleofthe i n g o t ( i .e. t o p t o b o t t o m and r a d i a li n h o m o g e n e i t i e s ) and t h o s e due t oc o r i n go ft h ei n g o t . The l a t t e r t e n d t o beon a s c a l eo f 50 250 am t e l t i n g t, h ef o r m e r b e i n ga t a s c a l e 10 - 20 t i m e sl a r g e r . The l a r g e r s c a l eh e t e r o g e n e i t i e sc a n be r e v e a l e di nv a r i o u s ways ( e . ? .b ym a c r o - e t c h i n go rf l a s hr a d i o g r a p h y ) ,w h i l e c o r i n gc a nb er e v e a l e db yl i g h tm i c r o s c o p yo re l e c t r o n b a c ks c a t t e ri m a g i n gi nt h e SEM. The i n g o t sf a b r i c a t e df o rt h i sc o m p o s i t ed e v e l o p m e n tp r o g r a mw e r e designatedhighhomogeneity (HH). T h i sd e s i g n a t i o n means t h a tl a r g es c a l eh e t e r o g e n e i t i e s werecharact e r i z e d as b e i n gu n d e t e c t a b l eb yf l a s hr a d i o g r a p h y . M i c r o s t r u c t u r a lh e t e r o g e n e i t i e s doremain,however.

-

The improvementsobtainedwith HH m a t e r i a l may be observed i n F i g . 1. Fig. l a i s anexample o f Nb 46.5 w t % T if a b r i c a t e d some y e a r s ago when c o m p o s i t i o n c o n t r o l was o fm i n o ri m p o r t a n c e ;F i g .l b shows r e c e n t l ym e l t e dn o r m a lq u a l i t ya l l o y ,w h i l eF i g . IC shows r e c e n t l ym e l t e d HH a l l o y . The SEM images a r e p r o d u c e db ye l e c t r o nb a c ks c a t t e ri ne a c hc a s e . The d a r kr e g i o n sa r eT ri i c h . A clearimprovement i n a1 l o y q u a l i t y i s seen as one progressesfromFig. la t o F i g . IC. However, t h e r ea r es t i l ll o c a lc o r i n gi n homogeneitiespresent i n t h e m a t e r i a l o f F i g . l b and IC. When measured a tl a r g e rs i z e s , HH m a t e r i a l was found t o have l o c a l v a r i a t i o n s o f ? 1.5 w t % T i( F i g . inthe 2) ascompared t o t h e +, 5 wt% Tifound

0018-9464/85/0300-0269$01.00@1985IEEE

F i g u r e 1. SEM e l e c t r o n back scattermicrographsofa)inhomogeneous,b)recentlymeltednormalmaterial c)highhomogeneity Nb 46.5 T i . inhomogeneous m a t e r i a l shown i nF i g .l a . These r e s u l t s do n o t y e t p e r m i t anunambiguousdetermination o f what c o n s t i t u t e s HH a l l o y , n o r do t h e ya d d r e s st h e q u e s t i o n o f w h a tv a r i o u sl e v e l so fi n h o m o g e n e i t yd o f o rt h e Jc. Suchwork i s i n progress now. The r e s u l t sp r e s e n t e di nF i g s . 1 and 2 do,however, demons t r a t e t h a t markedimprovements i n a l l o y q u a l i t y can be made. Such improvementshavebeen made i n q u a n t i t y p r o d u c t i o na n da l l o yo fh i g hh o m o g e n e i t ys p e c i f i c a t i o n i s now a v a i l a b l e on a l a r g es c a l e .

and

CompositeFabricationProgram f a b r i c a t e di no u r About 10 compositeshavebeen l a b o r a t o r i e su s i n g HH a l l o ym a t e r i a l . The m a j o r i t y o f t h e s ew e r ef a b r i c a t e du n d e rc o n t r o l l e dc o n d i t i o n sa t t h eU n i v e r s i t y o f Wisconsin-Madison. A v a r i e t y o f f a b r i c a t i o n and h e a tt r e a t m e n tc o n d i t i o n sh a v e been employed.Thisexperimentalprogram i st o oe x t e n s i v e t o r e p o r t here;what w i 11 be r e p o r t e d i s a s e r i e s o f experimentsconducted on p o r t i o n s o f a f u l l s i z e i n d u s t r i a le x t r u s i o n . CompositeFabrication

j/

t

X

0

--

A c r o s s - s e c t i o no ft h ec o m p o s i t e i s shown i n F i g . 3. The compositecontains 535 f i l a m e n t s andhas a nominal Cu:Nb-Ti r a t i o o f 1.3:l. A c t u a l measurements showed i t t o b e 1.35 - 1.37:l. The composite was d e s i g n e da t LBL f o r 23 and 30 s t r a n dc a b l e s ,t h e

RUN 1 RUN 2



X

J

F i g u r e 2. E l e c t r o np r o b et r a v e r s ea c r o s s HH r o da ta b o u te i g h tt i m e sl a r g e rs i z et h a nF i g .

F i g u r e 3. diameter.

C r o s s - s e c t i o no fc o m p o s i t e

d e s i g ns t r a n ds i z e sb e i n g 0.805 a p o r t i o no f mentdiameters a tt h e s es i z e sa r e IC.r e s p e c t i v e l y .

5183 a t 0.81 mm

and 0.645 mm. F i l a 23 and 1 8 pm,

.

,.

,

27 1

The composite was stackedfrom 7.1 mm d i aa n n e a l e d HH rodssuppliedbyTeledyne Wah Chang and e x t r u d e d f r o m a n o m i n a l1 0 "s i z et or o ds t o c k .P r o c e s s i n gt o c o i ls i z e s was p e r f o r m e da t IGC, s h o r tl e n g t h so f m a t e r i a lb e i n gs u p p l i e dt ot h eU n i v e r s i t yo f Wisconsin-Madison f o rd r a w i n g and h e a tt r e a t m e n t i n t h e i rf a c i l i t i e s . A b o u th a l fo ft h ee x t r u s i o nb i l l e t was thenprocessed t ow i r eu s i n gs t a n d a r ds c h e d u l e s ; theotherhalf was processedaccording t o s p e c i a l schedulesdeveloped i n t h e c o u r s e o f t h i s p r o g r a m . HeatTreatmentSchedule The g e n e r a la i mo fo u rf a b r i c a t i o np r o c e d u r e was t o p r o d u c es p e c i f i cm i c r o s t r u c t u r a lf e a t u r e si nt h e comp o s i t e .I nt h ee x p e r i m e n t sd e s c r i b e dh e r e ,t w o s p e c i f i cm o r p h o l o g i e sw e r ed e s i r e d . The f i r s t was t h a to fg r a i n boundary f m l i p r e c i p i t a t eo n l y .P r e v i ous experimentshavesugg s ed t h a t 10 h r s a t 375 C produces t h i s morphology The second was t h aotf e q u i a x e d ,g r a i nb o u n d a r yt r i p l ep o i n tp r e c i p i t a t i o n . Two s u c ht r e a t m e n t sw e r ea p p l i e d :8 0h r sa t 375 C has been e s t a b l i s h e d t o p r o d u c e W T i p r e c i p i t a t e s o f o r d e r 50 nm w h i l e 4 r s a t 375 C produces somewhat s m a l l e r precipitates

.7 ,k

The e f f e c t s o f t h e above t r e a t m e n t sh a v en o ty e t been v e r i f i e d f o r t h i s p a r t i c u l a r c o m p o s i t e , suchwork b e i n g o i np r o g r e s s . As has p r e v i o u s l y been t h e r e i s a s t r o n gc o u p l i n gb e t w e e nt h e p r e c i p i t a t e m i c r o s t r u c t u r e and t h e d e g r e e o f c o l d work n o ty e tc o n o ft h em i c r o s t r u c t u r e . As a general c l u s i v e l py r o v e nr)u l e i t may be s a i dt h atth e s u b - s t r u c t u r ei sw e l l - d e v e l o p e da f t e r a coldstrainof about 5 - 6. The s t r a i n i n q u e s t i o n i s t h e t r u e s t r a i n , E ( = I n Ao/A, where A, i s t h e o r i g i n a l and A t h ep r e s e n tc r o s s - s e c t i o n a la r e a ) . By we1 1-developed s u b - s t r u c t u r e , we mean t h a t t h e c h a r a c t e r i s t i c e l o n g a t e ds u b - b a n do rg r a i ns t r u c t u r ei sd e v e l o p e d . Such a s t r u c t u r e a p p e a r s t o be r e q u i r e d f o r t h e g r a i n boundary film p r e c i p i t a t e t o a p p e a r .

work was performed on samplesgiven a f o u r t hh e a t t r e a t m e n t( 5 1 8 3 - 1 ,2o r 3-XXX). The d e s i g n a t i o ng i v e n t h eh e a t r e a t m e n t sc o n s i s t so ft h r e ep a r t s : 5183 i s t h e b i l l e t number, t h e secondnumber d e f i n e st h e presenceorabsenceof a h e a tt r e a t m e n ta t a strainof 4.6, w h i l e t h e l a s t g r o u p d e f i n e s t h e f i n a l sequence o f h e a tt r e a t m e n t sa p p l i e da f t e r a s t r a i no fa b o u t 6. CompositeTesting C r i t i c a lc u r r e n td e n s i t yr e s u l t sr e p o r t e dh e r e were p e r f o r m e da tt h eU n i v e r s i t yo fW i s c o n s i n - M a d i s o n , using 0.7 m o f w i r e mounted on a r r e l s .R e s u l t sa r e r e p o r t e d a t a s e n s i t i v i t y o f lo-''an (- 2-5 uV/m), e x c e p t where s t a t e d . The Cu:NbTi r a t i o s weredeterminedbyetching and weighing.

-

Results An i n i t i a l benchmark o f t h e b e h a v i o r o f t h e HH m a t e r i a l was p r o v i d e d b y t h e p r o c e s s i n g o f t h e f i r s t h a l f b i l l e t by a c o n v e n t i o n a pl r o c e s s i n g sc d u l e . F a b r i c a t i n wentwelland J v l u e s( a t lo-" an) o f 2365 A/mm ( 5 T) and1015 ASmm? ( 8 T)were obtained. The r e s i s t i v e t r a n s i t i o n s wereverysharpand n values r a n g i n gf r o m 25 a t 8 T t o 70 a t 5 T wereobtained. By

8

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500C

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I

I

I

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4 - 4 0 3 FINAL HT - 4 0 3 NO FINAL HT

ING

+ 4 -403

INDUSTRIAL FABRICATION

E

C 0

The r e s u l t i n gf a b r i c a t i o ns c h e d u l ei s shown i n F i g . 4. P r i n c i p a el m p h a s i s was p l a c e d on samplesgiven2 o r 3heattreatments(5183-4-XXX); some a d d i t i o n a l

PROCESSINGSEQUENCE FOR BILLET 5183

T

o_

3000

t

W

a a

3

"

1000

a VARIABLE HT

C --- 23I 51425 51400 C 5/375 c -4 -

0

!= a 0

0

3 . 4

5

6

7

8

9

IO

FIELD (TI F i g u r e 5.

Jc

J r e s u l t so b t a i n e di s shown i n An o v e r v i e wo ft h e F i g .5w h i l em o r ed e t a i t e dr e s u l t sa r eg i v e ni nT a b l e 1. The f i r s ts e r i e so fe x p e r i m e n t a lh e a tt r e a t m e n t s w e r et h o s ei n v o l v i n gt w oo rt h r e ei n t e r m e d i a t es i z e h e a tt r e a t m e n t s ,t o g e t h e rw i t ha no p t i o n a lf i n a ls i z e heattreatment.Thissequence i sn o t a b l ef o rs h o w i n g t h a tt h r e eh e a tt r e a t m e n t so f 40 o r 80hoursare s i g n i f i c a t l y more e f f e c t i v et h a nt w o . Jc v a l u e so f 2740 A/mm (5 T) w e r e o b t a i n e d w i t h t h r e e 40 hr/375 C t r e a t m e n t s , 2560 A/mm2 o b t a i n e dw i t ht h r e e8 0h r t r e a t m e n t sb u to n l y 2295and 2225 w i t ht w o 40 h r and 80 h rt r e a t m e n t sr e s p e c t i v e l y . The dataappears to

!

F i g u r e4 .P r o c e s s i n gs e q u e n c ef o rb i l l e t

5183.

an) v e rfsi eu lsd .

1020

1220

1070

212

show some o v e r a g i n gf o rt h e8 0h rt r e a t m e n t s .S i m i l a r improvementsareseen i n t h e 8 T v a l u e s( T a b l e1 ) . T h r e e1 0h o u rh e a tt r e a t m e n t sw e r es i g n i f i c a n t l yl e s s e f f e c t i v et h a nt h el o n g e r ones. The omission o f a f i n a ls i z eh e a tt r e a t m e n t (3hrsy300 C) had l i t t l e 5 f f e c t on t h e 5 T Jc v a l u e (2725 A/mm2 vs.2740 A/mm f o r t h e 3 x 40 h r sequence but it didmarkedlyimprovethe 8 T values (1140 A/mm vs.1020 A/mm2). The e f f e c t o f t h e f i n a l HT was t o p i v o t t h e Jc/H c u r v e a t a b o u t t h e 5 T p o i n t ;h e a t t r e a t m e n td e c r e a s e dt h eh i g h e rf i e l dv a l u e sw h i l e i n c r e a s i n gt h el o w e rf i e l dv a l u e s .

1

The a d d i t i o n o f a f o u r t h i n t e r m e d i a t e h e a t t r e a t ment ( E = 4.57) was s t u d i e d f o r t h e 5183-X-403 sequence o fh e a tt r e a t m e n t s .I nt h i sc a s e ,t h et i m e was h e l dc o n s t a n ta t 5 h r s ,t h et e m p e r a t u r eb e i n g v a r i e df r o m 375 C t o 425 C. B e s tr e s u l t s were o b t a i n e d w i t h 5183-3-403 ( f i r s t HT o f 5/375 C), Jc v a l u e so f 2350 A/mm ( 5 T) and 1220 A/mm ( 8 T) b e i n g o b t a i n e d .T h i s 8 T v a l u ei se x t r a o r d i n a r i l y good. Subsequent i n d u s t r i a lp r o c e s s i n go ft h e second h a l f o f t h e b i l l e t t o 0.645 mm d i a w i r e used t h e 5183-4-403 heattreatmentsequence(3 x 40/375 C), t o g e t h e r w i t h a s h o r tf i n a ls i z eh e a tt r e a t m e n t . The b i l l e t f a b r i c a t e dv e r yw e l l and Jc v a l u e s a l m o s t i d e n t i c a l t o t h e laboratoryprocessedsampleswereobtained(2 45 A/mm2 v s 2740 A/mm2 a t 5T; 1070 A/mm2 vs.1020 A/mm a t 8 T ) .

?

Table 1.

Jc Values o fV a r i o u s l yT r e a t e dC o m p o s i t e s J,

Designation

Size mm

Value(10-14 5 T A/mm2

m)

8 T2 A/mm

f o l l o w i n gt h el a s ti n t e r m e d i a t es i z eh e a tt r e a t ment.' The i n c r e a s ei sr a t h e r marked;whereasinhomogeneous m a t e r i a l has a Jc t h a tp e a k sa t a strainof about 2.5, t h eh i g hh o m o g e n e i t ym a t e r i a lc o n t i n u e st o i n c r e a s et o a s t r a i n o f 3.5 - 4. Thus a p a r t i c u l a r l y s i m p l e way t o r a i s e J c i s t o move t h e h e a t t r e a t m e n t s t ol a r g e rs i z e . The q u e s t i o no f what c o n s t i t u t e s a h i g hh o m o g e n e i t ys p e c i f i c a t i o ni ss t i l ln o tc l e a ry e t , however. The m a t e r i a li sc l e a r l yi m p r o v e dw i t h r e s p e c tt ot h a tw h i c h was normalseveralyears ago. Normalgrades o fm a t e r i a l have a l s oc o n t i n u e dt o improve,however,and t h es i g n i f i c a n td i f f e r e n c e a s s o c i a t e d with highhomogeneitymaterialremainsto be d e f i n e d

.

A second p o i n t c o n c e r n s t h e q u e s t i o n o f a1 l o y composition. I t haslong beendebatedwhether Nb 50 w t % T i was i n t r i n s i c a l l y c a p a b l e o f h i g h e r Jc t h a n Nb 46.5 w t % T i . The p r e s e n tr e s u l t si n c l i n eu st ot h e v i e w t h a t Nb 46.5 w t % T i i s j u s t as c a p a b l eo fh i g h J, as Nb 50 wt% T i . A markedadvantage o f Nb 46.5 w t % TI i s i t s h i g h e r Hc2: t h i s i s about 10.7 - 10.9 T, as compared t o 9.5 9.9 T. Thishas a s t r o n ge f f e c to n t h e Jc above 5 - 6 T. The v a l u s o f Jc a t 8 T obtained here (1000 1220 A/mm ) a r e s u p e r i o r t o a n y Jc v a l u e so b t a i n e d w i t h Nb 50 w t % T i

-

-

5

.

The e f f e c t o f t h e f i n a l s i z e HT on t h e h i g h f i e l d J ci si n t e r e s t i n g .F i n a ls i z e HT o fo r d e r 3 hrs/300 C have h i s t o r i c a l l y been g i v e nt oa n n e a lt h ec o p p e r m a t r i x ; however,theycanproducefurtherprecipitat i o n and t h i s may b ec h a n g i n gt h em a t r i x HC2. F u r t h e r smallchanges ( - 1 - 2%) i n a l l o y c o m p o s i t i o n may be helpfulinraisingstillfurtherthe 7 8 T Jc v a l u e s i n Nb-Ti a l l o y s .

-

SFi iznea l H.T.

Acknowledgments

2740

2850

2645

UW Processed no4-1031060 2275 0 -572 4-402 6.572 895 2295 0.511 4-403 0.5111140 2725 4-802 0.566850 2225 4-803 915 2560 0 -577 1-403 0.572 1150 2785 2-403 0572 1145 2810 0.511 3-403 I G C Processed normal1015 23650 -645 0.805 930 2280 0.648 4-403 0.808 1030 2545

Ye S Yes no yes Yes no no no Yes yes Yes Yes

S. K r e i l i c k & We w o u l d p a r t i c u l a r l y l i k e t o t h a n k R. Samuel f o r w i r e d r a w i n g & metallographic assistance.

Thework a t UW and LBLwas supportedby D i v i s i o no fH i g hE n e r g yP h y s i c su n d e rc o n t r a c t s AC02-82ER40077 and DE-AC03-76SF0098.

DOEDE-

References

A.W. West, D.C. L a r b a l e s t i e r .M e t a l . Trans.,15A, p.843,1984. 2. D.C. L a r b a l e s t i e r . A.W. West. t o a m, e* a r i n A c t a Metall 1984. 3. D.C. L a r b a l e s t i e r , A.W. West, t o appear i n Ann.de Chimie-SciencedesMateri aux,Dec.1984. 4. A.W. West, D.C. L a r b a l e s t i e r , "The I m p o r t a n c eo f P r e c i p i t a t e Morph:logy i n ProducingHigh Jc i n Nb-TiComposites, t o besubmitted t o Cryogenics , Oct 1984. 5. E .J Kramer, H .C. F r e y h a r d t , J Appl Phys 51 , p.4930,1980. 6. K. Osamura, H. Tsunekawa, Y . Monju, T. H o r i u c h i , P h i l . Mag., A49, p.205,1984. 7. H. Hillmann,SuperconductorMaterialsScience, ed. S. Foner, B.B. Schwartz, New York:PlenumPress, P981,p.275. 8. J. W i l l b r a n d , W. Schlump, Z. Meta11,66,p.714,1975. 9. O.F. Neal, A.C. Barber, A. Woolcock, J.F. G i d l e y , A c t aM e t a l l . , 19,p.143,1971. 10. D.B. Smathers, K.R. Marken, D.C. L a r b a l ' e s t i e r , R.M. Scanlan, IEEE Trans,Vol .MAG-19,p.1417,1983. 11. A.W. West, D.C. L a r b a l e s t i e r , I E E E Trans,Vol. MAG-19, p.548,1983. 12. A.W. West, W.H. Warnes, D.L. Moffat, D.C. L a r b a l e s t i e r , I E E E Trans,Vol .MAG 19, p.749, 1983. 1 3 .L i Chengren, Wu Xiao-zu, Zhou Nong, I E E E Trans, VOl MAG-19, p. 284, 1983. 1.

.,

2 Discussion The r e s u l t so ft h e s ei n i t i a le x p e r i m e n t sw i t hh i g h homogeneity b i l l e ts t o c ka r ee x t r e m e l ye n c o u r a g i n g . The compositeshaveprocessedverywell,theyhave respondedverywell t om u l t i p l eh e a tt r e a t m e n t s and v e r yc o n s i d e r a b l ei m p r o v e m e n t si n Jc valueshave been p o s s i b l e . The h e a tt r e a t m e n t st h a t we have a p p l i e d h e r ea r eo n l y one s u b s e to f a w i d er a n g eo fp o si b l e h e a tt r e a t m e n t s .H i g h e r Jc v a l u e s o f 3190 A/mm (5T) h a v eb e e no b t a i n e dw i t ha l t e r n a t i v ep r o c e s s i n g scheduleson a model c o m p o s i t eT h i sv a l u e i sc l o s e tothehighvalueof 3400 A/mmZ obtainedon Nb 50 w t % T im a t e r i a lf a b r i c a t e db yL i Cheng-ren e t a1 .13

2

A l t h o u g ho u ri n v e s t i g a t i o n sa r es t i l li np r o g r e s s , some g e n e r a lp o i n t sc a ns t i l l be made a tt h ep r e s e n t t i m e . Our b a s i ch y p o t h e s i s i s t h a t homogeneousNb-Ti a l l o w s a more u n i f o r mp r e c i p i t a t ea r r a y .T h i sr a i s e s Jc, r e d u c e sp r o d u c tv a r i a b i l i t y ,i n c r e a s e sd u c t i l i t y and tends t o i n c r e a s e t h e optimumdrawing s t r a i n

. .

.

.

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.,