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Residual microstructures in explosively formed tantalum penetrators
Scripta Metallurgica et Materialia, Vol. 31, No. 3, pp. 297-302, 1994 Copyright @1994 Elsevier Science Ltd Printed in the USA. All rights reserved 0956-716X/94 $6.00 + 00
Pergamon
RESIDUAL
MICROSTRUCTURES L.
E.
IN
Murr,
EXPLOSIVELY C-S.
NiOu
FORMED a n d C.
TANTALUM
PENETRATORS
Feng*
Department of M e t a l l u r g i c a l and M a t e r i a l s E n g i n e e r i n g The University of Texas at E1 Paso, E1 Paso, TX 79968 and *U.S. A r m y A r m a m e n t Research, Development, and E n g i n e e r i n g Center, P i c a t i n n y Arsenal, NJ 07806
(Received November 5, 1993) (Revised April 7, 1994) T a n t a l u m has found e x t e n s i v e use in recent p e n e t r a t i n g w e a p o n s / w a r h e a d applications, e s p e c i a l l y e x p l o s i v e l y f o r m e d p e n e t r a t o r s (EFP's), p r i m a r i l y b e c a u s e of its ductility, formability, and high density (16.7 g/cm3) . While c o n s i d e r a b l e effort has been e x p e n d e d in the forging and d e v e l o p m e n t of starting w a r h e a d liners to p r o d u c e e q u i a x e d grain s t r u c t u r e s (varying from 50-150 ~m (1,2)), there are no systematic records of the m i c r o s t r u c t u r e s in recovered EFP's from d e t o n a t e d t a n t a l u m liners. However, Shih, et al (3) have very recently p e r f o r m e d a d e t a i l e d m i c r o s t r u c t u r a l a n a l y s i s on the t a n t a l u m shaped charge regime where significant r e d u c t i o n s (by a factor of nearly 102 ) of the s t a r t i n g e q u i a x e d liner grain structure were o b s e r v e d in a r e c o v e r e d slug and jet fragments by t r a n s m i s s i o n electron microscopy. A l t h o u g h EFP formation and the d e v e l o p m e n t of a conical shaped charge jet are c o n s i d e r a b l y different, each r e p r e s e n t s a unique example of extreme, dynamic, p l a s t i c flow in which an e x p l o s i v e l y g e n e r a t e d shock wave initiates a highrate forming process. In this study we have e x a m i n e d the m i c r o s t r u c t u r e s in a recovered, t a n t a l u m (99.95% Ta with n o m i n a l l y 50 ppm O and 80 p p m W) EFP by r e p r e s e n t a t i v e light and t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y (TEM) of a half section. The e s s e n t i a l features of EFP formation are i l l u s t r a t e d s c h e m a t i c a l l y in,Fig. 1 which shows a b a c k w a r d - f o l d i n g , s e l f - f o r m i n g fragment (SFF) d e v e l o p e d from a detonated, u n i f o r m thickness, convex liner (4). Figure 2 shows a s o f t - r e c o v e r e d t a n t a l u m EFP which has been sliced in half axially to reveal a surface (plane) section view c h a r a c t e r i s t i c of the s c h e m a t i c a l l y formed EFP in Fig. i, and p o l i s h e d to reveal the c o r r e s p o n d i n g
FIG. i: S c h e m a t i c view of EFP development during high e x p l o s i v e (H.E.) detonation, liner d e f o r m a t i o n and free flight, and self formation.
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m e t a l l o g r a p h i c structures shown r e p r o d u c e d as a n u m b e r e d sequence (I to 3) from t h e EFP head [i] to the tail section [3]. The m i c r o g r a p h s shown in sequence in Fig. 2 (marked 1 to 3 c o r r e s p o n d i n g to regions 1 to 3 in the EFP cross-section) correspond to v a r i a t i o n s in strains from a few tens of percent to a p p r o x i m a t e l y 300 p e r c e n t (5). The tail section shows ([3] in Fig. 2) remnants of the original g r a i n s t r u c t u r e (and grain size) in the starting liner but there is e v i d e n c e for d e f o r m a t i o n w i t h i n these grains r e v e a l e d in the metallographic etch (3). Heavy d e f o r m a t i o n which occurs near the inner region, [2], of the c o l l a p s e d liner in the r e c o v e r e d EFP in Fig. 2 is in sharp contrast to the l i g h t l y d e f o r m e d EFP tail section, while the light microscope view of a region near the head of the EFP ([i] in Fig. 2) illustrates a range of h e a v y d e f o r m a t i o n m i c r o s t r u c t u r e s including significant grain distortion, refinement, and r e c o v e r y / r e c r y s t a l l i z a t i o n . Figure 3 shows a series of TEM o b s e r v a t i o n s which c o r r e s p o n d roughly to the EFP regions i l l u s t r a t e d in Fig. 2. Figure 3(a), typical of the deformation in the EFP tail ([3] in Fig. 2), shows p o l y g o n i z e d d i s l o c a t i o n walls and a c o n s i d e r a b l e n u m b e r of d i s l o c a t i o n loops. Figure 3(b), c o r r e s p o n d i n g to the h e a v i l y d e f o r m e d region i l l u s t r a t e d in [2] of Fig. 2 shows e l o n g a t e d d i s l o c a t i o n cells and r e c o v e r e d or p o l y g o n i z e d d i s l o c a t i o n walls with spacings as small as 0.2 ~/n, and m i s o r i e n t a t i o n s of 1 to 2 ° . Figure 3(c) shows d i s l o c a t i o n cells and r e c o v e r e d or r e c r y s t a l l i z e d grains having b o u n d a r y m i s o r i e n t a t i o n s r a n g i n g from a p p r o x i m a t e l y 1° to greater than 6° typical of the h e a v i l y d e f o r m e d and g r a i n - r e f i n e d regions in both regions [2] and [I] in Fig. 2. These features are shown in more detail in the bright-field, d a r k - f i e l d TEM s e q u e n c e in Fig. 4 which also shows the range of m i s o r i e n t a t i o n s indicated, and c h a r a c t e r i s t i c of d i s l o c a t i o n walls and h i g h e r - a n g l e (>5 °) grain b o u n d a r i e s . A c o m p a r i s o n of the original grain size of roughly 75 ~m in the light m i c r o s c o p e view of the EFP tail section ([3]) in Fig. 2, with an a v e r a g e "grain" size of a p p r o x i m a t e l y 0.8 ~Lm in the r e c o v e r e d or g r a i n - r e f i n e d r e g i o n s c h a r a c t e r i s t i c of heavy d e f o r m a t i o n shown in the TEM views of Fig. 3(c) and Fig. 4, provides evidence for dynamic recovery in the t a n t a l u m EFP. This reduction in grain size from 75 ~m in the initial liner to cell b l o c k s t r u c t u r e s of ~ 0.8 ~m in the heavily d e f o r m e d regions of the EFP is similar to the roughly 102 r e d u c t i o n in s t a r t i n g cone grain size in a d e t o n a t e d t a n t a l u m shaped charge a t t r i b u t e d to continuous (or discontinuous) d y n a m i c r e c r y s t a l l i z a t i o n (3). W o r s w i c k et al. (5) r e c e n t l y d e s c r i b e d t a n t a l u m impacting cylinders to exhibit r e m a r k a b l e ductility, very low h a r d e n i n g rates, and d e f o r m a t i o n m i c r o s t r u c t u r e s c h a r a c t e r i z e d by d i s l o c a t i o n cells. EFP simulations by Worswick, et al. (5) p r e d i c t e d strains to 300%, an a s s o c i a t e d t e m p e r a t u r e rise of 600°C, and "initial strain rates > 105 s -I. w i t t m a n et al. (6) also recently e x a m i n e d defect s t r u c t u r e s in shocked t a n t a l u m and o b s e r v e d s c a t t e r e d twins which were not s u p p o r t e d by s e l e c t e d - a r e a e l e c t r o n d i f f r a c t i o n or m i c r o d i f f r a c t i o n evidence. We did not observe any evidence for d e f o r m a t i o n - i n d u c e d t w i n n i n g (Figs. 3 and 4) and W o r s w i c k et al. (5) also noted the absence of twins in their t a n t a l u m impactors. In the p r e s e n t work (Figs. 3 and 4) as well as other o b s e r v a t i o n s of heavily worked or deformed tantalum, d i s l o c a t i o n loops were a prominent feature of the m i c r o s t r u c t u r e s (5-7). The o b s e r v a t i o n of what a p p e a r s to be "grain" refinement in the heavily d e f o r m e d regions of the EFP (Fig. 3(c)) is different from the e q u i a x e d grain structure with c h a r a c t e r i s t i c a l l y higher m i s o r i e n t a t i o n angles (>15 ° ) in t a n t a l u m s h a p e d charges e x a m i n e d p r e v i o u s l y (3), and a t t r i b u t e d to dynamic recrystallization. The m i c r o s t r u c t u r e s shown in Fig. 3(c) are more c h a r a c t e r i s t i c of c e l l b l o c k s t r u c t u r e s or cell b l o c k walls c o m p o s e d of g e o m e t r i c a l l y n e c e s s a r y b o u n d a r i e s whose m i s o r i e n t a t i o n s i n c r e a s e with strain (or w o r k - h a r d e n i n g (8,9)). Consequently, these r e f i n e d grains seem fully c h a r a c t e r i s t i c of d y n a m i c a l l y r e c o v e r e d s u b s t r u c t u r e s as o p p o s e d to dynamically recrystallized microstructures. Consequently, it is p o s s i b l e that strains of 300 p e r c e n t in the EFP are b e l o w the requisite strains to promote d y n a m i c r e c r y s t a l l i z a t i o n . In addition, the EFP t e m p e r a t u r e would be e x p e c t e d to vary widely but not to reach requisite r e c r y s t a l l i z a t i o n
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t e m p e r a t u r e s of >0.5T M. While we do not know the strains accurately, simple averages of (compressive) strains m e a s u r e d b e t w e e n the r e l a t i v e l y u n d e f o r m e d grain structures for Fig. 2[3] and the h e a v i l y d e f o r m e d grains in Fig. 2[2] yields a value ranging f r o m 80 to 95% (or true strains of about -1.5 to -3). It might be n o t e d in summary that the t a n t a l u m EFP is c o n s i d e r a b l y different, m i c r o s t r u c t u r a l l y , than the t a n t a l u m shaped charge (3) p r i m a r i l y because the shaped c h a r g e (especially the e l o n g a t i n g jet) e x h i b i t s extensive dynamic r e c r y s t a l l i z a t i o n while the EFP e x h i b i t s locallized, d y n a m i c recovery in regions of m a x i m u m strain. In addition, the EFP m i c r o s t r u c t u r e varies considerably within the EFP (Fig. 2), and this c o n s i d e r a b l e n o n - u n i f o r m i t y of strain and m i c r o s t r u c t u r e may be an important c o n s i d e r a t i o n in design strategies which c u r r e n t l y rely upon c o n s t i t u t i v e a p p r o a c h e s b a s e d upon rather conventional t r e a t m e n t s of s t r a i n - r a t e and t e m p e r a t u r e (10-13). This work was s u p p o r t e d in part by a M u r c h i s o n E n d o w e d Chair (L.E.M.), and GSA Grant PF90-018 for S t r a t e g i c M a t e r i a l s R e s e a r c h at The U n i v e r s i t y of Texas at E1 Paso. Refer@nces I. 2. 3. 4. 5. 6. 7.
8. 9. I0. II. 12. 13.
C. Feng and P. Kumar, JOM, 41(I0), 40(1989). C. A. Michaluk, "Methods for Producing W a r h e a d Liners from T a n t a l u m Powder", TMS Symposium on High Strain Rate Behavior of Refractory Metals and Alloys, Cincinnati, OH, Oct, 1991. H. K. Shih, C-S. Niou, L. E. Murr, and L. Zernow, Scripta Metall. et Material., 29, 1291 (1993). W. P. Walters and T. A. Zukas, Fundamentals of Shaped Charges, WileyInterscience, New York, 1989, p. 358. M. J. Worswick, N. Qiang, P. Niessen, and R. J. Pick, Chap. 6 in Shock Wave and High-Strain-Rate Phenomena in Materials, Ed. M. W. Meyers, L. E. Mutt, and K. P. Staudhammer, Marcel Dekker, Inc., New York, 1992, p. 87. C. L. Wittman, R. K. Garrett, J. B. Clark, and C. M. Lopatin, Chap. 86, ibid, p. 925 C. Feng, T. K. Chatterjee, and L. Ting, "Material C h a r a c t e r i z a t i o n of T a n t a l u m for D i f f e r e n t M a n u f a c t u r i n g P r o c e s s e s , " in High Strain Rate Behavior Refractory Metals and Alloys, R. Astahani, E. Chen, and A. Crowson, Eds., The Minerals, Metals and M a t e r i a l s Society, 1992, p. 45. D. K u h l m a n n - W i l s d o r f , Material. Sci. Engr., All3, 1 (1989). D. K u h l m a n n - W i l s d o r f and N. Hansen, Scripta Metall. et Material., 25, 1557 (1991). F. J. Zerilli and R. W. Armstrong, J. Appl. Phys., 61, 1816 (1987). R. W. A r m s t r o n g and F. J. Zerilli, J. Physique, 49, 105 (1988). G. R. Johnson, J. M. Hoegfeldt, U. S. Lindholm, and A. Nagy, ASME J. Engr. Materials and Tech., 105, 42 (1983). G. R. Johnson and W. H. Cook, in Proc. 7th Int. Symposium on Ballistics, The Hague, The N e t h e r l a n d s , 1983, p. 541.
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0.5cm II
FIG. 2: Cross-section of recovered tantalum EFP (top) and optical metallographic views of corresponding areas showing characteristic microstructures (bottom).
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FIG. 3: B r i g h t - f i e l d TEM views of d i s l o c a t i o n cells, sub-boundarles, and r e c r y s t a l l i z e d grains in c o r r e s p o n d i n g regions of a r e c o v e r e d t a n t a l u m EFP. (a) D i s l o c a t i o n cells and loops in the EFP tail region ([3] in Fig. 2). (b) E l o n g a t e d d i s l o c a t i o n cell walls in h e a v i l y deformed region c o r r e s p o n d i n g to [2] in Fig. 2. (c) R e c o v e r e d or r e c r y s t a l l i z e d region typical of the heavily d e f o r m e d regions near the EFP head in [I], and [2], in Fig. 2.
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FIG. 4: Bright (top) and d a r k - f i e l d (bottom) image sequence along with a s e l e c t e d - a r e a e l e c t r o n d i f f r a c t i o n p a t t e r n i l l u s t r a t i n g a r a n g e of b o u n d a r y m i s o r i e n t a t i o n s (at 1 and 2 noted for example). The imaging reflection (dark-field) is d e n o t e d 3 and corresponds to a m i s o r i e n t a t i o n of 6° shown at 2 on the SAD p a t t e r n insert.
Pergamon
RESIDUAL
MICROSTRUCTURES L.
E.
IN
Murr,
EXPLOSIVELY C-S.
NiOu
FORMED a n d C.
TANTALUM
PENETRATORS
Feng*
Department of M e t a l l u r g i c a l and M a t e r i a l s E n g i n e e r i n g The University of Texas at E1 Paso, E1 Paso, TX 79968 and *U.S. A r m y A r m a m e n t Research, Development, and E n g i n e e r i n g Center, P i c a t i n n y Arsenal, NJ 07806
(Received November 5, 1993) (Revised April 7, 1994) T a n t a l u m has found e x t e n s i v e use in recent p e n e t r a t i n g w e a p o n s / w a r h e a d applications, e s p e c i a l l y e x p l o s i v e l y f o r m e d p e n e t r a t o r s (EFP's), p r i m a r i l y b e c a u s e of its ductility, formability, and high density (16.7 g/cm3) . While c o n s i d e r a b l e effort has been e x p e n d e d in the forging and d e v e l o p m e n t of starting w a r h e a d liners to p r o d u c e e q u i a x e d grain s t r u c t u r e s (varying from 50-150 ~m (1,2)), there are no systematic records of the m i c r o s t r u c t u r e s in recovered EFP's from d e t o n a t e d t a n t a l u m liners. However, Shih, et al (3) have very recently p e r f o r m e d a d e t a i l e d m i c r o s t r u c t u r a l a n a l y s i s on the t a n t a l u m shaped charge regime where significant r e d u c t i o n s (by a factor of nearly 102 ) of the s t a r t i n g e q u i a x e d liner grain structure were o b s e r v e d in a r e c o v e r e d slug and jet fragments by t r a n s m i s s i o n electron microscopy. A l t h o u g h EFP formation and the d e v e l o p m e n t of a conical shaped charge jet are c o n s i d e r a b l y different, each r e p r e s e n t s a unique example of extreme, dynamic, p l a s t i c flow in which an e x p l o s i v e l y g e n e r a t e d shock wave initiates a highrate forming process. In this study we have e x a m i n e d the m i c r o s t r u c t u r e s in a recovered, t a n t a l u m (99.95% Ta with n o m i n a l l y 50 ppm O and 80 p p m W) EFP by r e p r e s e n t a t i v e light and t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y (TEM) of a half section. The e s s e n t i a l features of EFP formation are i l l u s t r a t e d s c h e m a t i c a l l y in,Fig. 1 which shows a b a c k w a r d - f o l d i n g , s e l f - f o r m i n g fragment (SFF) d e v e l o p e d from a detonated, u n i f o r m thickness, convex liner (4). Figure 2 shows a s o f t - r e c o v e r e d t a n t a l u m EFP which has been sliced in half axially to reveal a surface (plane) section view c h a r a c t e r i s t i c of the s c h e m a t i c a l l y formed EFP in Fig. i, and p o l i s h e d to reveal the c o r r e s p o n d i n g
FIG. i: S c h e m a t i c view of EFP development during high e x p l o s i v e (H.E.) detonation, liner d e f o r m a t i o n and free flight, and self formation.
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m e t a l l o g r a p h i c structures shown r e p r o d u c e d as a n u m b e r e d sequence (I to 3) from t h e EFP head [i] to the tail section [3]. The m i c r o g r a p h s shown in sequence in Fig. 2 (marked 1 to 3 c o r r e s p o n d i n g to regions 1 to 3 in the EFP cross-section) correspond to v a r i a t i o n s in strains from a few tens of percent to a p p r o x i m a t e l y 300 p e r c e n t (5). The tail section shows ([3] in Fig. 2) remnants of the original g r a i n s t r u c t u r e (and grain size) in the starting liner but there is e v i d e n c e for d e f o r m a t i o n w i t h i n these grains r e v e a l e d in the metallographic etch (3). Heavy d e f o r m a t i o n which occurs near the inner region, [2], of the c o l l a p s e d liner in the r e c o v e r e d EFP in Fig. 2 is in sharp contrast to the l i g h t l y d e f o r m e d EFP tail section, while the light microscope view of a region near the head of the EFP ([i] in Fig. 2) illustrates a range of h e a v y d e f o r m a t i o n m i c r o s t r u c t u r e s including significant grain distortion, refinement, and r e c o v e r y / r e c r y s t a l l i z a t i o n . Figure 3 shows a series of TEM o b s e r v a t i o n s which c o r r e s p o n d roughly to the EFP regions i l l u s t r a t e d in Fig. 2. Figure 3(a), typical of the deformation in the EFP tail ([3] in Fig. 2), shows p o l y g o n i z e d d i s l o c a t i o n walls and a c o n s i d e r a b l e n u m b e r of d i s l o c a t i o n loops. Figure 3(b), c o r r e s p o n d i n g to the h e a v i l y d e f o r m e d region i l l u s t r a t e d in [2] of Fig. 2 shows e l o n g a t e d d i s l o c a t i o n cells and r e c o v e r e d or p o l y g o n i z e d d i s l o c a t i o n walls with spacings as small as 0.2 ~/n, and m i s o r i e n t a t i o n s of 1 to 2 ° . Figure 3(c) shows d i s l o c a t i o n cells and r e c o v e r e d or r e c r y s t a l l i z e d grains having b o u n d a r y m i s o r i e n t a t i o n s r a n g i n g from a p p r o x i m a t e l y 1° to greater than 6° typical of the h e a v i l y d e f o r m e d and g r a i n - r e f i n e d regions in both regions [2] and [I] in Fig. 2. These features are shown in more detail in the bright-field, d a r k - f i e l d TEM s e q u e n c e in Fig. 4 which also shows the range of m i s o r i e n t a t i o n s indicated, and c h a r a c t e r i s t i c of d i s l o c a t i o n walls and h i g h e r - a n g l e (>5 °) grain b o u n d a r i e s . A c o m p a r i s o n of the original grain size of roughly 75 ~m in the light m i c r o s c o p e view of the EFP tail section ([3]) in Fig. 2, with an a v e r a g e "grain" size of a p p r o x i m a t e l y 0.8 ~Lm in the r e c o v e r e d or g r a i n - r e f i n e d r e g i o n s c h a r a c t e r i s t i c of heavy d e f o r m a t i o n shown in the TEM views of Fig. 3(c) and Fig. 4, provides evidence for dynamic recovery in the t a n t a l u m EFP. This reduction in grain size from 75 ~m in the initial liner to cell b l o c k s t r u c t u r e s of ~ 0.8 ~m in the heavily d e f o r m e d regions of the EFP is similar to the roughly 102 r e d u c t i o n in s t a r t i n g cone grain size in a d e t o n a t e d t a n t a l u m shaped charge a t t r i b u t e d to continuous (or discontinuous) d y n a m i c r e c r y s t a l l i z a t i o n (3). W o r s w i c k et al. (5) r e c e n t l y d e s c r i b e d t a n t a l u m impacting cylinders to exhibit r e m a r k a b l e ductility, very low h a r d e n i n g rates, and d e f o r m a t i o n m i c r o s t r u c t u r e s c h a r a c t e r i z e d by d i s l o c a t i o n cells. EFP simulations by Worswick, et al. (5) p r e d i c t e d strains to 300%, an a s s o c i a t e d t e m p e r a t u r e rise of 600°C, and "initial strain rates > 105 s -I. w i t t m a n et al. (6) also recently e x a m i n e d defect s t r u c t u r e s in shocked t a n t a l u m and o b s e r v e d s c a t t e r e d twins which were not s u p p o r t e d by s e l e c t e d - a r e a e l e c t r o n d i f f r a c t i o n or m i c r o d i f f r a c t i o n evidence. We did not observe any evidence for d e f o r m a t i o n - i n d u c e d t w i n n i n g (Figs. 3 and 4) and W o r s w i c k et al. (5) also noted the absence of twins in their t a n t a l u m impactors. In the p r e s e n t work (Figs. 3 and 4) as well as other o b s e r v a t i o n s of heavily worked or deformed tantalum, d i s l o c a t i o n loops were a prominent feature of the m i c r o s t r u c t u r e s (5-7). The o b s e r v a t i o n of what a p p e a r s to be "grain" refinement in the heavily d e f o r m e d regions of the EFP (Fig. 3(c)) is different from the e q u i a x e d grain structure with c h a r a c t e r i s t i c a l l y higher m i s o r i e n t a t i o n angles (>15 ° ) in t a n t a l u m s h a p e d charges e x a m i n e d p r e v i o u s l y (3), and a t t r i b u t e d to dynamic recrystallization. The m i c r o s t r u c t u r e s shown in Fig. 3(c) are more c h a r a c t e r i s t i c of c e l l b l o c k s t r u c t u r e s or cell b l o c k walls c o m p o s e d of g e o m e t r i c a l l y n e c e s s a r y b o u n d a r i e s whose m i s o r i e n t a t i o n s i n c r e a s e with strain (or w o r k - h a r d e n i n g (8,9)). Consequently, these r e f i n e d grains seem fully c h a r a c t e r i s t i c of d y n a m i c a l l y r e c o v e r e d s u b s t r u c t u r e s as o p p o s e d to dynamically recrystallized microstructures. Consequently, it is p o s s i b l e that strains of 300 p e r c e n t in the EFP are b e l o w the requisite strains to promote d y n a m i c r e c r y s t a l l i z a t i o n . In addition, the EFP t e m p e r a t u r e would be e x p e c t e d to vary widely but not to reach requisite r e c r y s t a l l i z a t i o n
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t e m p e r a t u r e s of >0.5T M. While we do not know the strains accurately, simple averages of (compressive) strains m e a s u r e d b e t w e e n the r e l a t i v e l y u n d e f o r m e d grain structures for Fig. 2[3] and the h e a v i l y d e f o r m e d grains in Fig. 2[2] yields a value ranging f r o m 80 to 95% (or true strains of about -1.5 to -3). It might be n o t e d in summary that the t a n t a l u m EFP is c o n s i d e r a b l y different, m i c r o s t r u c t u r a l l y , than the t a n t a l u m shaped charge (3) p r i m a r i l y because the shaped c h a r g e (especially the e l o n g a t i n g jet) e x h i b i t s extensive dynamic r e c r y s t a l l i z a t i o n while the EFP e x h i b i t s locallized, d y n a m i c recovery in regions of m a x i m u m strain. In addition, the EFP m i c r o s t r u c t u r e varies considerably within the EFP (Fig. 2), and this c o n s i d e r a b l e n o n - u n i f o r m i t y of strain and m i c r o s t r u c t u r e may be an important c o n s i d e r a t i o n in design strategies which c u r r e n t l y rely upon c o n s t i t u t i v e a p p r o a c h e s b a s e d upon rather conventional t r e a t m e n t s of s t r a i n - r a t e and t e m p e r a t u r e (10-13). This work was s u p p o r t e d in part by a M u r c h i s o n E n d o w e d Chair (L.E.M.), and GSA Grant PF90-018 for S t r a t e g i c M a t e r i a l s R e s e a r c h at The U n i v e r s i t y of Texas at E1 Paso. Refer@nces I. 2. 3. 4. 5. 6. 7.
8. 9. I0. II. 12. 13.
C. Feng and P. Kumar, JOM, 41(I0), 40(1989). C. A. Michaluk, "Methods for Producing W a r h e a d Liners from T a n t a l u m Powder", TMS Symposium on High Strain Rate Behavior of Refractory Metals and Alloys, Cincinnati, OH, Oct, 1991. H. K. Shih, C-S. Niou, L. E. Murr, and L. Zernow, Scripta Metall. et Material., 29, 1291 (1993). W. P. Walters and T. A. Zukas, Fundamentals of Shaped Charges, WileyInterscience, New York, 1989, p. 358. M. J. Worswick, N. Qiang, P. Niessen, and R. J. Pick, Chap. 6 in Shock Wave and High-Strain-Rate Phenomena in Materials, Ed. M. W. Meyers, L. E. Mutt, and K. P. Staudhammer, Marcel Dekker, Inc., New York, 1992, p. 87. C. L. Wittman, R. K. Garrett, J. B. Clark, and C. M. Lopatin, Chap. 86, ibid, p. 925 C. Feng, T. K. Chatterjee, and L. Ting, "Material C h a r a c t e r i z a t i o n of T a n t a l u m for D i f f e r e n t M a n u f a c t u r i n g P r o c e s s e s , " in High Strain Rate Behavior Refractory Metals and Alloys, R. Astahani, E. Chen, and A. Crowson, Eds., The Minerals, Metals and M a t e r i a l s Society, 1992, p. 45. D. K u h l m a n n - W i l s d o r f , Material. Sci. Engr., All3, 1 (1989). D. K u h l m a n n - W i l s d o r f and N. Hansen, Scripta Metall. et Material., 25, 1557 (1991). F. J. Zerilli and R. W. Armstrong, J. Appl. Phys., 61, 1816 (1987). R. W. A r m s t r o n g and F. J. Zerilli, J. Physique, 49, 105 (1988). G. R. Johnson, J. M. Hoegfeldt, U. S. Lindholm, and A. Nagy, ASME J. Engr. Materials and Tech., 105, 42 (1983). G. R. Johnson and W. H. Cook, in Proc. 7th Int. Symposium on Ballistics, The Hague, The N e t h e r l a n d s , 1983, p. 541.
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FIG. 2: Cross-section of recovered tantalum EFP (top) and optical metallographic views of corresponding areas showing characteristic microstructures (bottom).
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FIG. 3: B r i g h t - f i e l d TEM views of d i s l o c a t i o n cells, sub-boundarles, and r e c r y s t a l l i z e d grains in c o r r e s p o n d i n g regions of a r e c o v e r e d t a n t a l u m EFP. (a) D i s l o c a t i o n cells and loops in the EFP tail region ([3] in Fig. 2). (b) E l o n g a t e d d i s l o c a t i o n cell walls in h e a v i l y deformed region c o r r e s p o n d i n g to [2] in Fig. 2. (c) R e c o v e r e d or r e c r y s t a l l i z e d region typical of the heavily d e f o r m e d regions near the EFP head in [I], and [2], in Fig. 2.
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FIG. 4: Bright (top) and d a r k - f i e l d (bottom) image sequence along with a s e l e c t e d - a r e a e l e c t r o n d i f f r a c t i o n p a t t e r n i l l u s t r a t i n g a r a n g e of b o u n d a r y m i s o r i e n t a t i o n s (at 1 and 2 noted for example). The imaging reflection (dark-field) is d e n o t e d 3 and corresponds to a m i s o r i e n t a t i o n of 6° shown at 2 on the SAD p a t t e r n insert.