The growth of grain boundary cavities under applied stress and internal pressure
- PDF / 573,859 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 168 Views
C a v i t i e s w e r e p r o d u c e d by methane r e a c t i o n r e s u l t i n g f r o m e x p o s i n g the n i c k e l s p e c i m e n s containing d i s s o l v e d c a r b o n to high p r e s s u r e h y d r o g e n g a s at 500~ 1 Two t y p e s of e x p o s u r e c o n d i t i o n s w e r e u s e d . One p r o d u c e d g r a i n b o u n d a r y c a v i t i e s that contained e x c e s s g a s p r e s s u r e which p r o v i d e d a d r i v i n g f o r c e f o r c o n tinued c a v i t y g r o w t h upon s u b s e q u e n t annealing in the a b s e n c e of a h y d r o g e n e n v i r o n m e n t . The o t h e r s e t of e x p o s u r e conditions y i e l d e d c a v i t i e s with an e q u i l i b r i u m g a s p r e s s u r e . T h e s e c a v i t i e s g r e w only u n d e r an a p p l i e d s t r e s s in the a b s e n c e of a h y d r o g e n e n v i r o n ment. G r o w t h s t u d i e s without a p p l i e d s t r e s s w e r e p e r f o r m e d by v a c u u m a n n e a l s at 500, 550 and 600~ with the i n t e r n a l methane p r e s s u r e of the c a v i t y a s the d r i v i n g f o r c e for g r o w t h . F o r e a c h e x p e r i m e n t a l s e quence at a given t e m p e r a t u r e a s i n g l e 6 c m r o d was u s e d . A s e c t i o n of the r o d was r e m o v e d at d i f f e r e n t t i m e i n t e r v a l s to d e t e r m i n e c a v i t y s i z e s a s a function of. t i m e . T h e c a v i t y c r o s s - s e c t i o n a l a r e a s w e r e d e t e r mined f r o m i n t e r g r a n u l a r f r a c t u r e s u r f a c e s by s c a n ning e l e c t r o n m i c r o s c o p y (SEM). The d e t a i l e d method of p r e p a r i n g the f r a c t u r e s u r f a c e s is d e s c r i b e d in Ref. 7. A t y p i c a l SEM p h o t o m i c r o g r a p h of c a v i t i e s on a g r a i n b o u n d a r y is shown in F i g . 1. An e x a m p l e of the c a v i t y s i z e d i s t r i b u t i o n s obtained is shown in the h i s t o g r a m s in F i g . 2. M o r e than 100 c a v i t i e s w e r e counted for the d e t e r m i n a t i o n of an a v e r a g e c a v i t y s i z e . The s t u d y of c a v i t y g r o w t h u n d e r a p p l i e d t e n s i l e s t r e s s e m p l o y e d s p e c i m e n s that had a 3.1 c m g a g e length and contained c a v i t i e s with an e q u i l i b r i u m m e t h a n e g a s p r e s s u r e . The e x p e r i m e n t s w e r e p e r f o r m e d u n d e r c o n s t a n t load at 500 and 550~ S t r a i n of the s p e c i m e n w a s m o n i t o r e d d u r i n g the e x p e r i m e n t s .
EXPERIMENT The detailed description of the experimental procedure is given in Reference 7. Nickel 270 specimens were fabricated from 2.4 c m diem bar stock obtained from International Nickel Inc. The bar was swaged to a diameter of 0.36 a m and recrystallized to achieve the desired grain size. The final specimen length was a p p r o x i m a t e l y 6 c m f o r g r o w t h s t u d i e s without a p p l i e d s t r e s s and 3.1 c m f o r g r o w t h s t u d i e s u n d e r an a p
Data Loading...
