Observation of internal hydrogen-induced cracks in iron
- PDF / 1,161,220 Bytes
- 2 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 176 Views
Fig. 1--X-ray projection radiography and Kossel geometry
Fig. 2---Several hydrogen induced cracks. l a t i n g the s p e c i m e n with r e s p e c t to the X - r a y s o u r c e and taking a s e c o n d e x p o s u r e . The a n g u l a r c a l i b r a t i o n of the K o s s e l p a t t e r n a s shown in F i g . 3, i s d e t e r m i n e d by m e a s u r i n g the s e p a r a t i o n b e t w e e n c o r r e s p o n d i n g K ~ and K~ c o n i c s : C(degrees/mm)
= (Oce~- O~)/Lc~:-6
w h e r e the Os a r e the B r a g g a n g l e s for the two c o n i c s and La~__6 is the d i s t a n c e in m m b e t w e e n t h e m , F i g . 3(b). F i g . 2 i s an i l l u s t r a t i v e m i c r o r a d i o g r a p h of a 150 p m t h i c k , p u r i f i e d i r o n s i n g l e c r y s t a l , o b t a i n e d with an i r o n foil X - r a y t a r g e t . The c r y s t a l had p r e v i o u s l y been c a t h o d i c a l l y c h a r g e d at r o o m t e m p e r a t u r e for 1 h r at a c u r r e n t d e n s i t y of 30 m A / c m 2 and in the a b s e n c e of any e x t e r n a l s t r e s s . l I n t e r n a l c r a c k i n g a s w e l l a s s e v e r a l K o s s e l a b s o r p t i o n and d i f f r a c t i o n c o n i c s a r e v i s i b l e . T h e c r a c k s a r e 50 to 75 ~ m in s i z e and have a f l u t e d , f e a t h e r y a p p e a r a n c e which i s much m o r e a p p a r e n t when they a r e v i e w e d s t e r e o s c o p i c a l l y . Such d i s t o r t i o n s a r e p r o b a b l y a r e s u l t of the VOLUME 3, SEPTEMBER 1972-2533
Fig. 4--Region of high plastic deformation accompanying several closely spaced cracks. significant plastic deformation accompanying crack f o r m a t i o n in this p u r e m a t e r i a l . The effects of such p l a s t i c d e f o r m a t i o n a r e m o r e e a s i l y s e e n in F i g . 3(a) which is an e n l a r g e d view of the r e g i o n around c r a c k A; F i g . 3(b) shows, for c o m p a r i s o n , the K o s s e l p a t t e r n obtained f r o m a much more perfect crystal.
2534-VOLUME 3, SEPTEMBER 1972
The c r y s t a l o r i e n t a t i o n was such that the c r a c k r e g i o n coincided with the i n t e r s e c t i o n of 3{110} type c o n i c s . The s e v e r e d e f o r m a t i o n n e a r the c r a c k m a n i f e s t s itself as a s m e a r i n g of the (110)~ conic. T h i s can be v i s u a l i z e d as r e g i o n s with l a t t i c e m i s o r i e n t a t i o n s of • deg 20 p m f r o m the c r a c k edge, and d e c r e a s i n g to 9 0.1 deg at 50 ~tm. U s u a l l y the d i s t o r t i o n is l o c a l i z e d to within 100 ~tm of the defect and does not appear g e n e r a l l y throughout the c r y s t a l . As m o r e c r a c k s n u c l e a t e and grow, the r e g i o n s of high p l a s t i c d e f o r m a t i o n s u r r o u n d i n g the c r a c k begin to o v e r l a p and the lattice d i s t o r t i o n is m o r e p r o n o u n c e d , F i g . 4. R e g i o n s a r e o b s e r v e d w h e r e the a b s o r p t i o n c o n i c s a r e d i s t o r t e d
Data Loading...
