An electron microscopy study of carbide precipitation in vanadium
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The precipitation of carbon from supersaturated solid solution in vanadium has been investigated using transmission electron microscopy techniques on thin foils. High purity vanadium strip was doped to a carbon content of about 0.2 at. pct and rapidly quenched in high vacuum, followed by aging treatments for various times in the temperature range f r o m 300 ~ to 600~ The s t r i p was then thinned for 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 . The c a r b o n is o b s e r v e d to p r e c i p i t a t e i n i t i a l l y as v e r y finely d i s p e r s e d c a r b i d e s v i s i b l e through s t r u c t u r e factor c o n t r a s t . With i n c r e a s i n g aging the p r e c i p i t a t e d i s t r i b u t i o n c o a r s e n s , and the c a r b i d e s appear as v e r y thin c o h e r e n t p l a t e l e t s on {310} p l a n e s , showing a p r o n o u n c e d d i s p l a c e m e n t f r i n g e c o n t r a s t . The c o h e r e n t p r e c i p i t a t e a p p e a r s to have a bcc s t r u c t u r e c l o s e l y r e l a t e d to that of the m a t r i x . With f u r t h e r aging these p l a t e l e t s a r e o b s e r v e d to thicken and p a r t i a l l y lose c o h e r e n c y , punching out p r i s m a t i c d i s l o c a t i o n loops and h e l i c e s having axes in
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