• PDF / 1,956,010 Bytes
• 5 Pages / 612 x 792 pts (letter) Page_size
• 78 Downloads / 200 Views

DOWNLOAD

REPORT

---

IT

is g e n e r a l l y a g r e e d that at low s t r e s s e s slip is i n i t i a t e d in the s u r f a c e l a y e r s of p o l y c r y s t a l l i n e m e t a l s . 1-5 H o w e v e r , c o n t r o v e r s y s t i l l e x i s t s in r e g a r d to the n at u r e of the s l i p s o u r c e s . F o r e x a m p l e , in niobium 1 and 3 pct s i l i c o n - i r o n 2'~ e v i d e n c e f a v o r s s l i p n u c l e a t i o n at g r a i n b o u n d a r i e s . Conflicting with t h e s e o b s e r v a t i o n s , e t c h - p i t s t u d i e s 4'5 indicate that the only r o l e of g r a i n b o u n d a r i e s in the p r e y i e l d d e f o r m a t i o n of l a r g e - g r a i n e d p o l y c r y s t a l l i n e c o p p e r is to act as b a r r i e r s to m o v i n g d i s l o c a t i o n s and not as s o u r c e s of d i s l o c a t i o n s . The p u r p o s e of this p a p e r is to r e p o r t the r e s u l t s of a s y s t e m a t i c e t c h - p i t study of the d i s t r i b u t i o n of slip s o u r c e s in s u c c e s s i v e l a y e r s of s i l i c o n - i r o n in its e a r l y s t a g e s of d e f o r m a t i o n . The r e s u l t s a r e a n a l y z e d to d e t e r m i n e w h e t h e r the s l i p s o u r c e s a r e a s s o c i a t e d with the f r e e s u r f a c e of the s p e c i m e n o r with the g r a i n b o u n d a r i e s . F u r t h e r m o r e , an a t t e m p t is made to e x plain the c o n f l i c t i n g r e s u l t s in s i l i c o n - i r o n and co p p er .

:i]

>>

,oo . ~ _

o._

80

~D Z

60

~.Omm

~r~

~.

D

~ E

o

I cO (D

40

"

-

-

I

l

I

9

8

I

0

0

f

Igrain

2.~0~ 2 grains

I

I

I

I

~ 500 ~ 3grains 4 groins

~

I

, 7 5 0 J.rn 5 grains

DEPTH FROM SURFACE, X

1. E X P E R I M E N T A L P R O C E D U R E F l a t t e n s i l e s a m p l e s of F e - 3 pct Si (C ~ 0.02 pct) w e r e p r e p a r e d by v a r i o u s r o l l i n g and a n n e a l in g t r e a t m e n t s with a final anneal at 1165~ f o r 45 m i n and a i r cooling. The r e s u l t i n g g r a i n d i a m was ~ 140 ~ m . F o u r such s a m p l e s w e r e pulled at r o o m t e m p e r a t u r e in an I ns t r o n t e s t i n g m a c h i n e to the s t r e s s e s (A to D) indic a ted on the i n s e r t in Fig. 1. S a m p l e s w e r e mounted in a j i g s p e c i a l l y d e s i g n e d to e n s u r e p r o p e r a l i g n m e n t and uniaxiality. T h e s e s a m p l e s w e r e then aged at 200~ f o r 1 h and then e l e c t r o p o l i s h e d and e l e c t r o e t c h e d in the M o r r i s c h r o m i c - a c e t i c acid solution 8 to r e v e a l slip by the a p p e a r a n c e of r o w s of e t c h - p i t s . Two kinds of s l i p i n v e s t i g a t i o n s w e r e p e r f o r m e d . In the f i r s t study, s u c c e s s i v e l a y e r s of ~ 75 ~ m t h i c k n e s s w e r e r e m o v e d f r o m the s u r f a c e of the d e f o r m e d and aged s p e c i m e n by a c o m b i n a t i o n of m e c h a n i c a l and e l e c t r o p o l i s h i n g ; at each depth the s p e c i m e n s u r f a c