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1350 Materials Science a nd Engineering, A 134 ( 1991 ) 1350 -1353

U n i v e r s a l h i g h p e r f o r m a n c e b a l l -m i ll in g d e v i c e a n d i ts a p p l ic a t i o n fo rm e c h a n i c a l a l l o y i n gA. Calka and A. P . Radl inskiDep artm ent of Electronic Materials Engineering, The Austr al ian N ationa l University , GP O Bo x 4, Canberra, A CT 2601 (Australia)

AbstractW e d e s c r i b e t h e d e s i g n a n d m o d e s o f o p e r a t i o n o f a n o v e l b a l l m i ll d e v i c e in w h i c h t h e b a l l m o v e m e n tp a t te r n i s co n t r o l led b y an ex te r n a l mag n e t ic f ie ld . Ex am p les o f ap p l ica t io n s o f th i s b a l l mi l l to th e sy n -th es i s o f N i - Zr a l lo y s , h ig h mel t in g p o in t in te r meta l l i c s , Mg - Zn a l lo y s an d a lu min iu m- b ased a l lo y s a r eg iv en. I n p a r t i cu la r , v a r io u s mo d es o f o p er a t io n ma y r esu l t in a d i f f e ren t p a th f o r th e so l id s ta te r eac t io noccurr ing dur ing mil l ing .

1. I n t ro duct i o nT h e m e c h a n i c a l a l l o y i n g ( M A ) p r o c e s s w a s

f i r s t d e v e l o p e d o v e r 2 0 y e a r s a g o f o r p r o d u c t i o no f c o m p o s i t e m e t a l li c p o w d e r s [ 1] . O v e r t h e y e a r si t h a s b ee n s u cces s fu l ly u s ed t o s y n t h es i ze an u m b e r o f c o m m e r c i a l ly i m p o r t a n t a l lo y s a n dc o m p o s i t e s . R e n e w e d i n t e r e s t i n m e c h a n i c a la l l o y in g w as s p a rk ed i n t h e m i d -1 9 8 0 s b y th e d i s -c o v e r y t h at M A m a y b e u s e d f o r th e f o r m a t io n o ft h e a m o r p h o u s p h a s e [ 2]. A s a r e s ul t o f re c e n tv i g o r o u s r e s e a r c h , i t h a s b e e n d e m o n s t r a t e d t h a tM A m a y b e u s e d f o r t h e p r e p a ra t i o n o f n u m e r o u seq u i l i b r i u m an d n o n -eq u i l i b r i u m c ry s t a l l i n e ,q u as i c ry s t a l l i n e , n an o c ry s t a l l i n e an d amo rp h o u sma t e r i a l s . A t t h i s s t ag e , h o w ev e r , t h e fu n d a -men t a l s o f mech an i ca l a l l o y i n g r ema i n l a rg e l yu n e x p l o r e d .T h ree t y p es o f mi l l i n g d ev i ce s a r e g en e ra l l yused fo r mechan ica l a l loy ing : a t t r i to rs , v ib ra t ingmi ll s an d ro t a t i n g mi l ls . H o w e v e r , n o n e o f th eco mmerc i a l l y av a i l ab l e d ev i ce s w as d e s i g n ed w i t ht h e s p e c if i c n e e d s o f th e M A p r o c e s s i n m i n d .T h i s f a c t o r b e c a m e p a r t ic u l a rl y o b v i o u s i n r e c e n ty e a r s, w h e n t h e d e p e n d e n c e o f f in a l p r o d u c t o nt h e t y p e o f mi ll in g d ev i ce an d en e rg y r eg i m e u s edh a v e b e e n r e p e a t e d l y r e p o r t e d . N i - Z r a l lo y m a yb e c o n s i d e r e d a b e n c h m a r k s y s t e m i n t h i sr e s p e c t ; t h e k i n e t i c s o f a m o r p h o u s p h a s e f o r m a -t i o n a s w e l l a s t h e ex t en t o f t h e g l a s s - fo rmi n gr e g i o n w e r e s h o w n t o b e c r u c i a l l y d e p e n d e n t o nt h e t y p e o f mi l l i n g d ev i ce , b a l l mo v emen t p a t t e rnan d t h e mi l li n g en e rg y [3 -7 ] .

I n t h i s p ap e r w e d e s c r i b e a b a l l m i l l i n w h i cht h e p a t t e r n o f b a l l m o v e m e n t c a n b e e x t e r n a l l yco n t ro l l ed . W e h av e p r ev i o u s l y u s ed t h i s d ev i ce t op ro d u ce A 1 -Pd a l l o y s [8 ] , h i g h me l t i n g p o i n tT i - B a l l o y s [ 9 ] a n d t o a m o r p h i z e M g - Z n [ 1 0 ]an d Fe -B a l l o y s [1 1 ] . I n a l l t h e s e ca s e s w ee m p l o y e d t h e b a ll m o v e m e n t c o n t r o l t o i n d u c e o ren h an ce t h e s o l i d s t a t e r eac t i o n l e ad i n g t o ad es i r ed p ro d u c t . S i n ce a t t h e p r e s en t s t ag e o fr e s ea r ch v e ry l i t t l e i s k n o w n ab o u t w h a t mi l l i n gc o n d i t io n s a r e t o b e s e l e c t e d t o p r o d u c e a n a l l oyw i t h an a p r i o r i ch o s en s t r u c t u r e , t h e r e i s a n eedt o d ev e l o p a s i mp l e an d v e r s a t i l e d ev i ce w h i chco u l d b e u s ed fo r s t u d i e s o n mech an i ca l a l l o y i n g .Id ea l l y , s u ch a mi l l s h o u l d o f f e r ( 1 ) a w i d e r an g eo f mi l l i n g co n d i t i o n s ( i n c l u d i n g t h o s e en co u n -t e r ed i n co mmerc i a l d ev i ce s ) an d (2 ) co n t ro l o fmi l li n g p a r ame t e r s . T h e b a l l m il l d e s c r i b ed i n th i sp a p e r c o m e s c l o s e t o t h o s e r e q u i re m e n t s .

2 . D es cr i p t i o n o f t he ba ll mi l lFi g u re 1 i l lu s t ra t e s t h e co n cep t o f o u r mi l l in gdev ice . Th i s i s a p lanar - type ba l l mi l l t ha t cons i s t so f a f ew h a rd en e d s t ee l b a l ls co n f i n ed t o a s ta i n -l e s s - s t ee l , h o r i zo n t a l t y p e ce l l . T h e b a l l mo v e -m en t d u r i n g t h e mi l li n g p ro c es s i s co n f i n ed t o t h ever t i ca l p lane by the ce l l wal l s and i t i s con t ro l l edb y an ex t e rn a l mag n e t i c f i e l d . T h e i n t en s i t y an dd i r ec t i o n o f t h e f i e ld can b e ex t e rn a l l y ad j u s t ed .In a s i mp l e v e r s i o n o f th e mi l l p e rm an en t mag n e t s

a r e u s e d . H o w e v e r , t o a c h i e v e b e t t e r c o n t r o l o f0921-5093/91/$3.50 Elsevier Sequoia/Printed in Th e Netherlands

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Fig . 1 . Schem at ic d iagram of the ba l l -mi l l ing dev ice wi thcon t ro l led ba l l movement . I : ro ta t ing ce l l ; 2 : ba l l s ; 3 : mag-ne t s .

(a) (b) (c) x~

i ~ e)Fig . 2 . Mod es o f opera t io n o f the ba l l mi l l. ( a ) High energymod e , h igh ro ta t ion f reque ncy ; (b ) low energy mod e , lowro ta t ion f req uency ; (c ) h igh energy mod e , two po in t s o f equ i -l ib r ium ; (d , e) h igh energy m ode , in te rm edia te ro ta t ionf requenc y ; th is i s a va r ia t ion o f mode (a ).

t h e b a l l m o v e m e n t e l e c t r o m a g n e t s s h o u l d b eem p lo y ed . By ad ju s t i n g th e sp a t i a l an d /o r t em -p o r a l p r o f i le s o f t h e m ag n e t i c f i eld , t h e b a l l t r a j ec -to r i e s , im p ac t en e r g y an d th e sh ea r in g en e r g y canb e v a r i ed .I n F ig . 2 t h e t h r ee g en e r a l p a t t e r n s o f b a l lm o v e m e n t t h a t c a n b e a c h i e v e d u s in g t hi s d e v i c eare shown. In the case i l lus t ra ted in Fig . 2 (a) , them ag n e t i c f i e ld h o ld s t h e b a l l s i n t h e b o t to m p a r to f t h e ce l l r o t a t i n g w i th t h e f r eq u en cy ~ c . F r i c -t i o n cau se s t h e b a l l s t o r o t a t e i n t h e sam e d i r ec -t i o n w i th t h e f r eq u en cy ~ O b = O g c R / r w h e r eR is the rad ius o f the ce l l and r i s the rad iuso f t h e b a l l . Pe r io d i ca l ly , t h e o u t e r b a l l o n th er ig h t - h an d s id e g e t s r e l ea sed , co m p le t e s m o s t o fth e c i r c l e b e in g p u sh ed ag a in s t t h e ce l l wa l l b y th ecen t r i f u g a l f o r ce , an d h i ts t h e l e f t - m o s t b a l l a t t h eb o t t o m . I n t hi s m o d e o f o p e r a t i o n t h e p o w d e r i sw o r k e d b o t h b y i m p a c t a n d b y s h e ar i ng . T h e b a ll sm a y b e c o n f i n e d t o t h e b o t t o m p a r t o f t h e c e ll f o ra l l t im e e i t h e r b y in c r ea s in g th e i n t en s i ty o f t h em a g n e t i c fi e ld o r b y d e c r e a s i n g t h e f r e q u e n c y W oThis i s i l lus t ra ted in Fig . 2 (b) . In th is mode, the

1351b a ll s b o th r o t a t e an d o sc i l la t e a r o u n d th e eq u i l ib -r i u m p o s i t i o n a t t h e b o t t o m a n d t h e p o w d e r i sw o r k e d m o s t l y b y s h e a ri n g .In the th i rd case , i l lus t ra ted in Fig . 2 (e), the ba llm o v e m e n t c a u s e d b y t h e c e n t ri f u ga l f o r c e c a n b eh a l t ed i n two o p p o s i t e p o s i t i o n s ; a t t h e l o wes t an dh ig h es t p o in t i n s id e t h e cel l. T h e b a ll t r ap p e d b yth e m ag n e t i c a t t r a c t i o n in t h e u p p e r p o s i t i o nr o t a t e s w i th t h e f r eq u e n cy ~ob a n d c a n b e r e l e a s e dto f a l l v e r t i c a ll y o n to p o f o n e o f t h e b o t to m b al ls .T h e two co l l i d in g b a l l s r o t a t e i n t h e o p p o s i t ed i r ec t io n s , wh ich r e su l t s i n a co m b in a t io n o fsh ea r in g an d u n iax i a l p r e ssu r e a t t h e su r f ace o fco n tac t .T wo u se f u l v a ri a t i o n s o f m o d e ( a) a r e sh o w n inFigs . 2 (c) and 2(d). By s lowing dow n the ce l l ro ta -t i o n f r eq u en cy ~Oc, a s i t u a tio n m ay b e ach iev edw h e n t h e b a l l r e l e a s e d f r o m t h e b o t t o m i s n o tf u l ly p in n ed to t h e wa l l b y th e cen t r i f u g a l f o r cean d can e i t h e r h i t o n e o f t h e b o t to m b a l l s ( F ig .2(c)) or the opposite cell wall (Fig. 2(d)) . Mill ingconditions in si tuations (a) , (d) and (c) , (e) ares imi lar, respe c t ive ly .3 . C om p ar i s on w i t h o t h e r m i l l in g d e v i c e s

Mech an ica l a l l o y in g i s a co m p lex p r o cess o fd e f o r m a t io n , f r ag m en ta t io n , co ld we ld in g an dm ic r o - d i f f u s io n , o ccu r r in g wi th in a t h in l ay e r o fp o w d e r t r a p p e d b e t w e e n t h e t w o c o l l i d i n g s u r -f ace s d u r in g im p ac t . I n co m m e r c i a l b a ll m i ll s ty p i -ca l im p ac t t im es a r e o f t h e o r d e r o f 1 0 - 5 s an dt h e p e a k s t r es s c a n r e a c h 5 0 k b a r. D e p e n d i n g o nth e co l l i s i o n p a r am e te r s , t h e o r i en t a t i o n o f t h ei m p a c t s tr a in m a y b e q u i t e c o m p l e x a n d t h e t e m -p e r a tu r e r i se i n t h e co l l i s i o n r eg io n m ay v a r yf r o m a f ew d eg r ee s t o a f ew h u n d r ed d eg r ee s [ 1 2,1 3] . T h e m ec h an ica l en e r g y is u t i li z ed m o s t e f fi -c i en t ly if t h e b a l ls co l l i d e h ea d - o n wi th m ax im u mpossib le ve loc i t ies . Davice e t a l . [13] repor tede ig h t h ead - o n co l l i s i o n s o u t o f t h e t o t a l o f 2 1 3 2col l i s ions per sec ond in a v ib ra t ing mi l l ag i ta ted a t1 2 0 0 r ev . m in - ~. T h e r e a r e o n ly o n e to tw o co l l i-s io n s p e r seco n d in o u r d ev ice , b u t t h ey a r es t ri c t ly h ead - o n b ecau s e o f t h e g u id in g o f t h e b a l lm o v e m e n t b y th e m ag n e t i c f ie ld . T h e f r ee - f a l l b a llve loc i ty dur in g impac t is 1 .5 m s I ( it i s incre ase din t h e p r e sen ce o f t h e m ag n e t i c f i e ld ) . Fo r co m -par ison , the average re la t ive ba l l ve loc i ty in av ibra t ing mi l l var ies f rom 3 .9 m s-1 [12] to 6 ms- ~ [ 1 3 ] ; i n t h e p l an e t a r y b a ll m i l l u sed b y E ck e r te t a l . i t r em ains in the rang e 2 .5 -4 .7 m s J [6] ,an d i t is abo ut 0.5 m s 1 in attr i tor s ! i12]. Us ing

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1 3 5 2t h e H e r t z t h e o r y o f c o l l i s i o n s a s f o r m u l a t e d b yM a u r i c e a n d C o u r t n e y [ 1 2 ] o n e c a n c a l c u l a t eo th e r ch a r ac t e r i s t i c s o f t h e b a l l - o n - b a l l co l l i si o n sin o u r d ev ice : co l l i s i o n t im e 6.5 10 -5 s , He r tzr ad iu s 4 .6 1 0 4 m , an d m ax im u m im p ac t s t r e s s3 7 k b a r . A l l t h e se v a lu e s a r e c lo se t o t h e co r r e -s p o n d i n g v a l u es q u o t e d f o r c o m m e r c i a l v i b ra t in gm i ll s. T h u s , t h e en e r g y r e l ea sed p e r im p ac t i n o u rm i l l i s n o t m u ch d i f f e r en t f r o m th a t ch a r ac t e r i s t i co f o th e r d ev ice s . A f ea tu r e t h a t i s u n iq u e to o u rd es ig n , h o wev e r , i s t h e sp ec i f i c b a l l m o v em en tp a t t e rn . I n e v e r y m o d e o f o p e r a t i o n t h is p a t t e r n iswe l l d e f in ed an d h ig h ly r ep r o d u c ib l e . T h i sc o n t r a s t s w i t h t h e c h a o t i c a n d u n p r e d i c t e d b a l lm o v em en t ch a r ac t e r i s t i c o f t h e o th e r b a l l - m i l l i n gd ev ice s .

4 . A p p l i c a t i o n s4.1. Res ults o f ball mil l ing o f the Ni62Zr38 test alloyT h e a m o r p h o u s p h a s e f o r m a t i o n i n N i - Z rm ix tu r e s b y b a l l m i l l i n g was s tu d i ed in d e t a i l b yo t h e r w o r k e r s [ 3 -7 ] . I t w a s f o u n d t h a t a m o r p h i z a -t i o n o f t h e se m ix tu r e s u s in g v a r io u s m i l l in g eq u ip -m e n t o c c u r s v i a t w o d i f f e r e n t p a t h s . T h ea m o r p h o u s p h a s e i s f o r m e d d i r e c t ly w h e n e i t h e rth e v ib r a t i n g f r am e [ 5 ] o r a F r i t sch " Pu lv e r i se t t e5 " p l an e t a r y m i l l [ 6 ] a r e u sed , b u t a c r y s t a l l i n ein t e r m e ta l l i c p h ase f o r m s in i t i a l l y wh en a d i f f e r -en t t y p e o f p l an e t a r y m i l l i s em p lo y ed [ 5 ] . Fu r -t h e r m o r e , i t h a s b e e n d e m o n s t r a t e d t h a t v a r i o u sm i l l in g in t en s it i e s [ 6] an d d i f f e r en t co m b in a t io n so f t h e p l an e t a r y m i l l r o t a t i o n p a t t e r n s [ 7 ] m ayi n f l u en c e t h e o u t c o m e o f t h e r e a c t i o n.W e h a v e r e p r o d u c e d b o t h o f t h e a m o r p h i z a -t i o n p a th s f o r 6 2 a t .% Ni an d 3 8 a t .% Z r m ix tu r eu s i n g t w o d i f f e r e n t m o d e s o f o p e r a t i o n o f o u rd e v ic e . W h e n t h e h i g h - e n e r g y m o d e o f F ig . 2 ( c) isu s e d , t h e a m o r p h o u s p h a s e i s f o r m e d d i r e c t l yf r o m t h e m i x tu r e . X - r a y d i f f r a c t o m e t r y r e ve a l sth a t u p o n m i l l in g th e i n t en s i ty o f d i f f r ac t io n p eak sd u e t o e l e m e n t a l z i rc o n i u m a n d n i c k e l d e c r e a s e sa n d s i m u l t a n e o u s ly a w a s h e d - o u t a m o r p h o u sp e a k e m e r g e s . T h e d i f fr a c t io n p a t t e rn t a k e n a f t e r60 h o f mi l l ing i s sho wn in Fig . 3 (a). In con t r as t toth is , wh en th e l o w - en e r g y m i ll i n g m o d e ( b ) i su sed , t h e i n t e r m e ta l l i c p h ase s f o r m f i r s t an d th ens lo wly t r an s f o r m in to t h e am o r p h o u s p h ase . A d i f-f r ac t io n p a t t e r n t ak en o v e r 1 8 0 h o f m i l li n g i ssh o wn in F ig . 3 ( b ) . E v en a f t e r v e r y l o n g m i l l i n g( 2 4 0 h ) so m e t r ace s o f t h e c r y s t a l li n e p h ase r em a inv i si b le o n t o p o f t h e a m o r p h o u s p e a k .

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10 30 5 0 70 90 110D e g r e e s 2 0

F i g . 3 . X - r a y p a t t e r n s t a k e n f r o m m i x t u r e s o f 6 2 a t .% N i a n d38 a t .% Z r a f te r (a ) 60 h o f mi l l ing us ing mo de (c ) and (b )180 h o f mi l l ing us ing mode (b ) o f F ig . 2 .

4 .2 . High m el t ing po i n t mater ia lsI t is w e ll d o c u m e n t e d t h a t m e t a l - m e t a l t y p ei n t e r m e t a l l i c s c a n b e p r o d u c e d b y M A u s i n gco m m er c i a l b a l l m i l l s . Ho wev e r , v e r y l i t t l e wo r kh a s b e e n r e p o r t e d o n t h e s y n t h e s i s o fm e ta l - m e ta l lo id sy s t em s . I t i s b e l i ev ed th a t v e r yh ig h m i l l i n g en e r g i e s a r e n ecessa r y t o p r o d u ceth e se i n t e r m e ta l l i c s . Us in g o u r b a l l m i l l we h av es y n t h e s i z e d a l a r g e n u m b e r ( m o r e t h a n 5 0 ) o fm e ta l - m e ta l lo id h ig h m e l t i n g p o in t i n t e r m e ta l l i c sb y m ech an ica l a ll o y in g . T h i s wo r k i s d e sc r ib ed indeta i l e l se wh ere [14].I t i s im p o r t an t t o n o t e t h a t t h e h ig h m e l t i n gp o i n t m a t e r ia l s p r o d u c e d w i t h o u r e q u i p m e n t a r ec o n t a m i n a t e d w i t h i r o n ( c o m i n g f r o m t h e b a l l san d ce l l m a te r i a l ) a t a l ev e l g en e r a l ly b e lo w 1a t.%. T h e d i f f r ac t io n p eak s d u e to i r o n we r en e v e r i d e n t if i e d o n t h e X - r a y p a t t e r n s a n d o t h e rm e t h o d s ( e l e c t r o n m i c r o p r o b e a n d R u t h e r f o r db a c k s c a t t e r i n g ) w e r e u s e d t o d e t e c t t h e i r o nimpur i t ies .S im i l a r to t h e ca se o f N i - Z r a l lo y s , t h e so l ids t a t e r eac t io n p a th f o r t h e h ig h m e l t i n g p o in tm a te r i a l s c an b e d r am a t i ca l ly a f f ec t ed b y th e m i l l-i n g co n d i t i o n s . As an i l l u s t r a t i o n we p r e sen t i nF ig . 4 two X- r ay d i f f r ac to g r am s o b ta in ed f r o mtwo b a l l - m i l l ed m ix tu r e s o f th e n o m in a l co m p o s i -t i o n 3 3 a t .% T i an d 6 7 a t .% B [ 9 ] . T h e u p p e rt r ace , o b t a in ed f r o m a sam p le m i l l ed f o r 8 0 hu s in g th e m o d e ( c ) o f F ig . 2 , co r r e sp o n d s t o t h ep u r e T i B 2 p h a s e. T h e l o w e r t r a c e w a s o b t a i n e df r o m a s a m p l e m i l l e d u s i n g t h e s a m e t i m e a n dr o t a t i n g sp eed b u t w i th o u t t h e m ag n e t i c f i eld . T h e

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(b) ' "i T i B 2. . T i

: il B ( a m o r p h o u s )i" Ii ~ ~ i I !

3 0 5 0 7 0 g 0 1 1 0D e g r e e s 2 0

Fig. 4 . X-ray pat te rns taken f rom m ix tures o f 33 a t .% T i and6 7 a t .% B a f te r ( a ) 8 0 h o f mi l l in g u s in g mo d e (c ) an d (b ) 8 0 ho f m i l l i n g u s i n g c o n d i t i o n s a s i n ( a ) , b u t w i t h o u t t h e m a g n e t i cf ie ld .

l a t te r d i f f r a c to g r a m c o r r e s p o n d s t o a m i x t u r e o fc r y s t a l l in e t i t an iu m an d a sm a l l am o u n t o f T iB 2.U s i n g t h e s e c o n d i t i o n s w e w e r e u n a b l e t o o b t a i np u r e Y i B 2 e v e n af te r 40 0 h o f mi ll ing .4 .3 . L o w c ry s ta l l iza t i o n t e m p e ra tu re : M g - Z na m o r p h o u s a l l o y sT o p r o d u c e f u l ly am o r p h o u s Mg v 0Z n 30 a l l oy sf r o m th e c r y s t a l l i n e m a s t e r a l l o y a two - s t ep b a l l -mi l l ing p rocedure has to be used [10] . In i t ia l ly ,t h e m i l l i n g i s p e r f o r m ed u s in g th e h ig h - en e r g ym o d e ( d ) ( F ig . 2 ) , wh ich r e su lt s i n a m ix tu r e o f t h ea m o r p h o u s p h a s e a n d t h e m e t a s t a b l e c r y s t a l l i n ep h ase Mg s~ Z n 2 0 . Un d e r t h e h ig h - en e r g y m i l l i n gco n d i t i o n s t h i s m ix tu r e co r r e sp o n d s t o a s t e ad y -s t at e d y n a m i c a l e q u il i b ri u m b e t w e e n a m o r p h i z a -t i o n an d c r y s t a l l i z a t i o n ( t h e c r y s t a l l i z a t i o nt em p e r a tu r e o f am o r p h o u s Mg v 0Z n 30 i s ab o u t9 5 C) . Fu l l am o r p h iza t io n can b e ach iev ed b yswi tch ing to the low energy mode (b ) (Fig . 2 ) .De ta i l s o f t h e ex p e r im en ta l r e su l t s a r e p r e sen tedin ref . 10.4 .4 . A h ~ m in iu m - b a s e d a l l o y sT h e h ig h en e r g y m i l l in g m o d e ( d ) (F ig . 2 ) i s n o ts u it a bl e f o r M A o f A I -V , A 1 - T i , a n d o t h e r a l u -m i n i u m - b a s e d a n d m a g n e s i u m - b a s e d a l lo y s. T h i s

1 3 5 3

m o d e f a v o u r s t h e c o l d w e l d i n g p r o c e s s a n d l e a d sto t h e f o r m a t io n o f l a r g e l u m p s o f t h e m i l l ed m ix -tu r e s . T h e a p p r o p r i a t e m i l li n g p r o ced u r e i s t o u seth e l o w en e r g y m o d e ( b) u n t il t h e m ean g r a in s i z ed ec r ea se s t o ab o u t 0 .1 /~ m an d th en to swi t ch tot h e i n t e r m e d i a t e e n e r g y m o d e (e ). S u c h a p r o c e -d u r e en ab le s o n e to su ccess f u l ly b a l l- m i l l t h e a lu -m in iu m - b ased a l l o y s w i th o u t u s in g su r f ac t an t s t oc o n t r o l t h e b a l a n c e b e t w e e n f r a c t u r in g a n d c o l dweld ing [15].5. Summary

W e h a v e d e s c r i b e d t h e d e s i g n a n d m o d e s o fo p e r a t io n o f a b a l l m i l l w i th a co n t r o l l ed b a l lm o v e m e n t p a t t e r n . T h e p e r f o r m a n c e o f t h i sd ev ice i s co m p ar ed wi th t h a t o f o th e r b a l l m i l l sa n d e x a m p l e s o f a p p l i c a t i o n s t o M A o f v a r i o u sa l loys a re d iscusse d .R e fe r e n c e s

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