PLASTIC DEFORMATION IN BONDING ZONE UNDER EXPLOSIVE WELDING AND ITS ROLE IN BONDING FORMATION

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PLASTIC DEFORMATION IN BONDING ZONE UNDER EXPLOSIVE WELDING AND ITS ROLE IN

BONDING FORMATION

M. Bondar, V. Ogolikhin

To cite this version:

M. Bondar, V. Ogolikhin. PLASTIC DEFORMATION IN BONDING ZONE UNDER EXPLOSIVE WELDING AND ITS ROLE IN BONDING FORMATION. Journal de Physique Colloques, 1985, 46 (C5), pp.C5-379-C5-384. �10.1051/jphyscol:1985548�. �jpa-00224779�

JOURNAL DE PHYSIQUE

Colloque C5, suppl6rnent au n08, Tome 46, aoOt 1985 page C5-379

PLASTIC DEFORMATION IN BONDING ZONE UNDER EXPLOSIVE WELDING AND ITS ROLE IN BONDING FORMATION

M.P. Bondar and V.M. Ogolikhin*

k v r e n t y e v I n s t i t u t e o f Hydrodynamics, S i b e r i a n D i v i s i o n o f t h e USSR Academy o f S c i e n c e s , N o v o s i b i r s k 630090, U.S.S.R.

* ~ y d r o p u Z s e TechnoZogy Bureau, S i b e r i a n D i v i s i o n o f t h e USSR Academy o f S c i e n c e s , Novosibirsk 630090, U. S.S. R.

Resume - Par 1 , B t u d e d e s macles nous avons pu d e t e r m i n e r 1 ' B t a t de d e f o r m a t i o n e t mesurer l a v a l e u r d e l a d e f o r m a t i o n d a n s l a zone p r o c h e d e l a soudure dans du c u i v r e soud6 p a r e x p l o s i f . Ce t r a v a i l nous a p e r m i s ' d e comprendre l e s mdcanismes r e s p o n s a b l e s du p r o c e s s u s d e l i a i s o n l o r s du soudage p a r e x p l o s i f .

A b s t r a c t - I n t h e p r e s e n t p a p e r t h e d e f o r m a t i o n s t a t e h a s been de- termined and t h e v a l u e o f d e f o r m a t i o n h a s been measured i n t h e near-weld zone w i t h t h e u s e of a n n e a l i n g t w i n s i n c o p p e r . T h i s h a s e n a b l e d u n d e r s t a n d i n g o f t h e mechanisms o f t h e p r o c e s s e s r e s - ponsible f o r bonding under e x p l o s i v e welding.

I N T R O D U C T I O N

I n e x p l o s i v e welding t h e j o i n t p l a s t i c d e f o r m a t i o n o f c o l l i d i n g s u r f a c e s i s one o f t h e major f a c t o r s r e s p o n s i b l e f o r r e l i a b l e bond f o r m a t i o n . The r o l e o f p l a s t i c d e f o r m a t i o n i n bond f o r m a t i o n under e x p l o s i v e weld- i n g was a n a l y z e d i n /1-5/. On t h e b a s i s o f e x p e r i m e n t a l d a t a t h e a u t h o r s 'of /1, 2 , 3/ have Found t h e f o l l o w i n g r e l a t i o n s h i p between t h e mate-

r i a l s h e a r x i n t h e near-weld zone and t h e d i s t a n c e t o t h e weld y:

( I ) x = x o e x p ( - B Q ) / l / a n d / 2 / x = x o e x p ( - B y ) /2,3/.

A common d i s a d v a n t a g e o f t h e s e methods i s t h a t t h e m a t e r i a l c o n t i n u i t y i s broken b e f o r e c o l l i s i o n which r e s u l t s i n t h e flow i r r e g u l a r i t i e s i n t h e v i c i n i t y of t h e t a p s . I t i s t h u s d i f f i c u l t t o d e t e r m i n e t h a t t h e near-weld s h e a r s i s o f major s i g n i f i c a n c e f o r t h e j o i n i n g f o r m a t i o n between t h e c o l l i d e d p l a t e s .

The p r e s e n t work d e a l s w i t h t h e methods o f measuring d e f o r m a t i o n i n t h e bonding zone by a n a l y z i n g d i r e c t i o n s and c r o s s - s e c t i o n s o f t w i n s which v a r y a s t h e p l a t e s c o l l i d e . T h i s method e n a b l e s b o t h t h e d e t e r m i n a t i o n o f a g e n e r a l d e f o r m a t i o n s t a t e o f t h e m a t e r i a l s i n t h e c l o s e v i c i n i t y t o t h e i n t e r f a c e , w i t h o u t t a k i n g i n t o a c c o u n t t h e m a t e r i a l c o n t i n u i t y fai- l u r e , and t h e measurement of d e f o r m a t i o n a t a d i s t a n c e t o t h i s i n t e r - - f a c e where t h e i n i t i a l s t r u c t u r a l b o u n d a r i e s a r e p r e s e r v e d . Exact mea- s u r e m e n t s o f d e f o r m a t i o n and s t r u c t u r a l i n v e s t i g a t i o n s i n t h e bonding zone c o n t r i b u t e t o u n d e r s t a n d i n g t h e bonding f o r m a t i o n p r o c e s s under e x p l o s i v e welding.

I1 - EXPERIMENTAL METHODS

Commercial$y pure copper p l a t e s w i t h t h i c k n e s s e s of 5 and 1 0 mm and a 190x190 nun welding a r e a were used i n t h e e x p e r i m e n t s . A £ t e r b e i n g pre-anneal-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985548

C5-380 JOURNAL DE PHYSIQUE

ed in avaccuml .v 10 -4 Hg mm) at 1000°C for three hours, the grain size in the plates was 'several millimeters, and the grains contained a lot of twins. A nonsymmetrical collision scheme was used, with parent plates 10 mm thick. The collision parameters listed in the Table ( v is the ve- locity of the flyer plate, vkis the collision point velocity?are such that they keep within the,explosive welding for copper.

The twp 4011-long microsections_ were cut from a central section of each welded specimen-whose surfaces were parallel to the welding direction.

There were several grains in the microstructure of the specimens, where an initial twin direction was 60°to 90°to the interface. The type and value of deformation in the vicinity of.the weld was determined by the character of their form variation. The shear deformation was determined by the twin boundary deviation from the tangential to its initial direc- tion. Fig.la,b displays the twins in the bottoms and crests of the wavy interface. The twins,parallel to th? collision surface in an initial state and entering the grains of such size which can comprise more than one wave after welding (Fig.1~) give ajgenbml picture of mater4al shear after explosive welding. Using explosive welded specimens, w e suc-

ceeded in determining the length/C and amplitdde a of the wave, as well as measuring microhardness H under a loadicg of 50 g and rupture strength 6 8 (see Table). With xhe use of a tfansmissional electronic mi- croscope, structural measurements were made.

Fig. 1

-

(b) the twin enters the crest,

(c) the twins are parallel to an initial collision surface.

I11

-

The thickness of the flyer plate (5mm) was,chosen experimentally from thicknesses'of .2 to 5 nun. Deformation of the flyer and parent plates after explosive welding did not differ when the flyer plate thickness was 5 mrn.

VO VK 2 (%)ifoo h ^(@)K{oo A- a sg Hv

m / s m / s mm % mm % mm mn MPa MPa

T a b l e .

A g e n e r a l p i c t u r e o f e x p l o s i v e l y welded m a t e r i a l d e f o r m a t i o n i s shown i n F i g . 1 . I n n e r l a y e r s o f t h e c o l l i d e d p l a t e s undergo a complex ununi- form d e f o r m a t i o n , e s p e c i a l l y i n t h e c a s e o f a wavy i n t e r f a c e . The de- f o r m a t i o n l i n e d r r e c t i o n i s c o n n e c t e d w i t h t h e s h e a r d i r e c t i o n . A t t h e p o i n t s o f h i g h c o m p r e s s i b l e s t r e s s e s , t h e s h e a r d i r e c t i o n i s a l w a y s c l o - s e t o 4 5 O w i t h r e s p e c t t o t h e s t r e s s d i r e c t i o n . I n p r o x i m i t y t o t h e f r e e s u r f a c e t h e m a t e r i a l s h e a r , direc1,ion i s a i n ~ o s t normal t o t h i s s u r f a c e .

To d e s c r i b e deformation o f c o l l i d i n g p l a t e s more p r e c i s e l y , l e t u s c o n s i d e r F i g . 1 w i t h r e s p e c t t o t h e p a r e n t p l a t e . I n s o d o i n g t h e r e - g i o n A i s assumed t o be t h e bo;:c)n~ and t h e l'egion P - i h e c r e s t . I t i s s e e n t h a t t h e m a t e r i a l . i n t,he bot;iom suffer,^ s h e a r deJ"r)r.n,ation w i t h c o m p r e s s i o n . T h i s i s c o n f i r m e d by t h e form v a r i a t i o n o f t h e t w i n 1 ( F i g . l a ) ( t h e w e l d i n g d i r e c t i o n i s shown by an a r r a y ) and t h e s h e a r l i n e d i r e c t i o n i n t h e r e g i o n A. I n t h e c r e s t t h e . m a t e r i a l s u f f e r s a more complex d e f o r m a t i o n . The d e f o r m a t i o n l i n e d i r e c t i o n i n t h e r e g i o n B and t h e d e f o r m a t i o n c h a r a c t e r o f t h e t w i n 2, whose c r o s s - s e c t i o n de- c r e a s e s a t t h e e n t r a n c e t o t h e c r e s t , t e s t i f y t h a t t h e m a t e r i a l s u f f e r s a t e n s i l e d e f o r m a t i o n . I n t h e r e g i o n B, t h e c l o s e r t o t h e i n t e r f a c e , t h e g r e a t e r t h e s h e a r d e f o r m a t i o n , a s i s s e e n f r o m t h e d i r e c t i o n and f r e - quency o f t h e d e f o r m a t i o n l i n e s . The s h e a r d e f o r m a t i o n v a l u e i s maxi- mum ( 3 100%) a l o n g t h e bonding l i n e . A s i s shown i n F i g . 1 , t h e s t r u c - t u r a l b o u n d a r i e s 02 n e a r - i n t e r f a c e l a y e r s a r e o b l i t e r a t e d due t o l a r g e s h e a r s , and l a y e r s w i t h a q u a l i t a t i v e l y new s t r u c t u r e a r e formed.

T h e i r t h i c k n e s s e s , h , were measured and l i s t e d i n t h e l a b l e . T h e m i c r o - s t r u c t u r e s i n F i g . 1 s h o w t h a t , i n t h e c a s e of t h e wavy i n t e r f a c e , t h e de- f o r m a t i o n s t a t e i n t h e v i c i n i t y of t h e w e l d i s c o n d i t i o n e d b y t h e i n t e r - a c t i o n between t h e d e f o r m a t i o n hump b e f o r e t h e c o 1 , l i s i o n p o i n t and t h e f l y e r p l a t e . A t r e l a t i v e l y low c o l l i s i o n p o i n t v e l o c i t i e s , t h e symmetric- a l c r e s t d e v e l o p s . I t i s t y p i c a l f o r c o p p e r , s i n c e i n a n a n n e a l e d s t a t e i t h a s no e x a c t y i e l d l i m i t / 7 / , i t s v a l u e d o e s n o t exceed 20 MPa and t h u s t h e m a t e r i a l s u f f e r s d e f o r m a t i o n a t low s t r e s s e s . The c r e s t form development i s d e t e r m i n e d by t h e c o l l i s j o n p a r a m e t e r s a n d i s t i m e depen- d e n t on t h e r e l a t i o n between v and c r ( c c i s t h e t r a n s v e r s e wave v e l o c i t y ) . A . t h i g h vk t h e c r e s t s a r e nonsymmetric, k i . e . t h e y a r e s t e e p - e r i n t h e w e l d i n g direction u n d e r c o l l i s i o n w i t h t h e f l y e r p l a t e s u r - f a c e . T h i s i s c o n f i r m e d by t h e form v a r i a t i o n of t h e t w i n 2 and i n t e r - t w i n l a y e r i n t h e s e c o n d c r e s t , a s w e l l a s by t h e t w i n b e n d i n g i n F i g . l b .

C5-382 JOURNAL DE PHYSIQUE

I n b o t h p l a t e s t h e measurements o f d e f o r m a t i o n were made a t t h e p o i n t s where defor'mation had a s i m p l e s t form, i . e . s h e a r w i t h conlpression. I n t h e d e f i n i t i o n s assumed t h e s e p l a c e s a r e under t h e bottom and above t h e c r e s t . The p l o t o f t h e s h e a r v a l u e , x , v e r s u s t h e d i s t a n c e t o t h e w e l d , y , c o i n c i d e s w i t h t h e c v r v e for. boundary v a r i a t i o n s o f t h e t w i n s e n t e r - i n g t h e weld. The s i t u a t i o n i s c h a r a c t e r i z e d by a s i g n i f i c a n t i n c r e a s e i n s h e a r a t some d i s t a n c e from t h e i n t e r f a c e , r ( s e e T a b l e ) . To compare t h e r e s u l t s on x v s y , t h e p l o t method o f r e p r e s e n t i n g t h e r e s u l t s i n a h e m i l o g a r i t h m i c c o o r d i n a t e system I n x-y i s s u g g e s t e d . I n a c c o r d a n c e w i t h ( I ) , t h i s dependence h a s a p a r a b o l i c form ( F i g . 2 a ) w i t h ( 2 ) i t i s a s t r a i g h t l i n e ( F i g . 2 b ) . The r e s u l t s o b t a i n e d a r e d e s c r i b e d , as a r u l e , by a broken l i n e ( F i g . 2 b ) , w i t h t h e b r e a k p o i n t c o r r e s p o n d i n g t o r.

F i g . 2 - - T h e p l o t o f t h e m a t e r i a l s h e a r x

.)

a>

The c h a r a c t e r of t h i s c u r v e i l l u s t r a t e s t h e above-mentioned p e c u l i a r i t i e s i n t h e d e f o r m a t i o n mechanism by a p p r o a c h i n g t h e bonding zone.

The d i s t a n c e r ( s e e T a b l e ) , which c o r r e p o n d s t o t h e b r e a k p o i n t c o o r d i n a t e when t h e d e f o r m a t i o n c h a r a c t e r c h a n g e s , depends a n c o l l i s i o n p a r a m e t e r s . A t t h e same v a l u e s of vo t h e s m a l l e r vk, t h e g r e a t e r b; f o r c l o s e v a l s e s o f vk t h e d i s t a n c e r i n c r e a s e s w i t h v o . The same dependence on t h e c o l l i s i o n p a r a m e t e r s i s c h a r a c t e r i s t i c f o r /1 , a and h. The above-mentioned c h a r a c t e r o f t h e e f f e c t o f t h e c o l l i s i o n B p a r a m e t e r s on r,h ^{, a} and h s t a t e s t o

The o b t a i n e d r e s u l t s a r e a l s o c h a r a c t e r i z e d by t h e f a c t t h a t when r and h depend on v and v k , t h e s h e a r d e f o r m a t i o n a t a d i s t a n c e o f r from t h e bonding z8ne i s always 3 1 0 0 % a t any c o l l i s i o n p a r a m e t e r s . T h i s i n d i c a t e s t h a t a d o m i n a t i n g c r i t e r i a o f e x p l o s i v e w e l d i n g i s t h e i n t e n - s i v e p l a s t i c f l o w development a t t h e i n t e r f a c e between m e t a l s . The va- l u e of r d e t e r m i n e s t h e i n t e n s i v e p l a s t i c d e f o r m a t i o n a r e a ; t h e v a l u e of h d e t e r m i n e s t h e r e g i o n where t h e m a t e r i a l i s i n a s t a t e c a p a b l e o f p r o v i d i n g t h e m e t a l bonding.

t h e i r dependence on b o t h t h e c o l l i s i o n

L x A

\ ,

L i s t e d i n t h e T a b l e a r e t h e v a l u e s o f r u p t u r e s t r e n g t h a n d d e f o r m a t i o n a t t h e c o n t a c t p o i n t u n d e r c o l l i s i o n ; t h e r e l a t i o n s h i p between them h a s n o t been r e v e a l e d . A minimum v a l u e o f 244 MPa h a s been o b t a i n e d f o r t h e specimens, where t h e r u p t u r e o c c u r s a l o n g t h e weld. T h i s i s c o n n e c t - e d , as a r u l e , w i t h h i g h v a l u e s o f v k ( 1 ~ 0 . 1 m m ) . The v a l u e s o f S8 do n o t c h a r a c t e r i z e t h e m a t e r i a l s t r e n g t h a t t h e bonding zone. I t i s

0.

s t r e s s d e t e r m i n e d by vo a t t h e same t h i c k - n e s s e s o f t h e p l a t e s c o l l i d e d i n a l l t h e e x p e r i m e n t s and t h e d e f o r m a t i o n develop- ment t i m e . The s m a l l e r v k , t h e g r e a t e r t h e ,

d e f o r m a t i o n development t i m e ; t h e d e f o r - mation,developrnent i s c o n d i t i o n e d by t h e p r e s e n c e o f a f r e e s u r f a c e b e f o r e t h e c o l - l i s i o n p o i n t . A s i s known, i n t h e c a s e o f t m !+ a p l a n e l o a d i n g o f t h e specimens by h i g h -

a m p l i t u d e shock waves ( 7 n x 10GPa) ac- c o r d i n g t o a c l o s e d scheme l i m i t i n g d e f o r - m a t i o n , t h e r e a r e no r i g o r o u s l y d i r e c t e d s h e a r s i n t h e s t r u c t u r e / 8 / .

b e l i e v e d t h a t they show s t r e n g t h e n i n g o f t h e m a t e r i a l as a whole a f t e r c o l l i s i o n a t h i g h - q u a l i t y welding.Throughout t h e welding s e c t i o n t h e s t r e n g t l i e n i n g v a l u e accounted f o r 80 t o 90%. We c a n judge a b o u t s t r e n g - t h e n i n g by microhardness H measured a l o n g t h e i n t e r f a c e from t h e s i d e of each c o l l i d e d @ a t e \ ( A s i s s e e n from t h e T a b l e , Hv f o r t h e s p e c i - mens w i t h r 0 . 1 mm l i e i n t h e same s p r e a d r a n g e ; r 4 0 . 1 mm c o r r e s - ponds t o t h e specimens f o r which t h e m e l t i n g i s observed i n t h e bond- i n g zone, and Hv a l o n g t h e weld c a n n o t be measured.In t h e p e r i p h e r y o f t h e welded speclrnens H i s ranged o v e r 850 t o 950 Mpa. I n an i n i t i a l s t a t e t h e p l a t e s have Ev ^{= 480 MPa.}

I n t h e s t u d y o f t h e bonding zone by t h e e l e c t r o n i c microscope i t was r e v e a l e d t h a t i n l a y e r h t h e s t r u c t u r e i s inhomogeneous. Near t h e edg 10- -10-5 2 s o f them t h e s t r u c t u r e r e p r e s e n t s e x t e n d e d c e l l s which a r e bands mm wide ( F i g . 3 a ) c o n t a i n i n g i n p e r f e c t i o n s i n t h e i r volumes.

While approaching t h e c e n t e r o f t h i s l a y e r , t h e c e l l w i d t h i n c r e a s e s a s t h e i m p e r f e c t n e s s d e g r e e d e c r e a s e s ( F i g . 3 b ) ; and t h e p o l y g o n i z a t i o n s t r u c t u r e i s o b s e r v e d a t t h e c e n t r e of t h e l a y e r ( F i g . 3 b ) . The c a s t s t r u c t u r e f e a t u r e s were n o t r e v e a l e d i n t h e bottoms and c r e s t s of t h e welded specimens w i t h r > 0 . 1 mm. The p o i n t e l e c t r o n g r a m s w i t h r e f l e x d i s t o r t i o n s t y p i c a l f o r t e x t u r e were observed i n t h e s t r u c t u r e of a l l t y p e s ( F i g . 3d.)

.

F i g . 3 - Transmission e l e c t r o n micrographs o f t h e as-bonded i n t e r f a c e zone - h : a ) boundary of zone h , x 22500

b ) a r r i v a l from t h e boundary t o t h e ~ e n t r e , ~ 22500 c ) t h e c e n t r e o f t h e zone h , x 22500

d ) d i f f r a c t i o n .

Taking i n t o account t h a t on t h e boundary o f t h e r e g i o n h deformat;ion r e a c h e s 400 t o 1000 % depending on t h e c o l l i s i o n p a r a m e t e r s and t h e de-.

f o r m a t i o n grows from t h e boundary t o t h e c e n t r e o f h , t h e observed va- r i a t i o n s i n t h e zone s t r u c t u r e can b e e x p l a i n e d by a t h e r m a l e f f e c t which i n c r e a s e s w i t h d e f o r m a t i o n .

The measured v a l u e s o f d e f o r m a t i o n r e a l i z e d i n . t h e zone h d u r i n g ex-

C5-384 J O U R N A L DE PHYSIQUE

plosive welding can not be achieved by a pure dislocation mecha ism,sin- 2

ce in this case,the dislocation velocity would have to be

-

CONCLUSION

1. The use of twins as taps enables us to establish a general picture of deformation state in the near-boundary layers of the plates to be weld- ed and to measure its value in the vicinity to the bonding zone.

2. It has been found that the shear deformation sharply increases at a distance r to the bonding surface.

3. The region has been revealed with a qualitatively new structure con- taining the bonding surface, its thickness h being correlated with r.

4. The presence of the region h

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REFERENCES

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