Surface segregation and interaction of oxygen and nitrogen with zirconium in Nb-1% Zr alloy
- PDF / 354,581 Bytes
- 3 Pages / 613 x 788.28 pts Page_size
- 29 Downloads / 181 Views
P R O P E R T I E S of many m e t a l l i c s y s t e m s a r e often i m p r o v e d by s m a l l additions of z i r c o n i u m . Small amounts of z i r c o n i u m (as little as 100 ppm) a r e added to liquid bismuth to p r e v e n t liquid metal c o r r o s i o n of the low alloy s t e e l c o n t a i n e r s . Zirconium is b e l i e v e d to inhibit c o r r o s i o n by forming p r o t e c t i v e l a y e r s of ZrN or ZrC on the s t e e l surface, the carbon and nitrogen being p r o vided by the s t e e l . 1 P r e f e r e n t i a l c o r r o s i o n of Nb grain b o u n d a r i e s by lithium has been a t t r i b u t e d 2 to oxygen s e g r e g a t i o n , It has been found that the c o r r o s i o n could be r e t a r d e d by adding 1 pct Zr to niobium to p r e c i p i tate the oxygen as ZrO2 upon p r o p e r heat t r e a t m e n t . ~ The most common niobium alloy used is Nb-1 pct Zr b e c a u s e of its b e t t e r mechanical p r o p e r t i e s and w e l d a b i l i t y , s F a b r i c a t i o n of rf superconducting c a v i t i e s is contemplated using N b - Z r a l l o y s . Zirconium additions to Nb a r e also made to r e s t r i c t grain growth in some niobium compounds. 4 In most of these c a s e s the advantages of Zr a d d i tions is b e l i e v e d to a r i s e f r o m its r e a c t i v i t y with c a r b o n , nitrogen and oxygen and the s t a b i l i t y of these c o m pounds. The p r e s e n t investigation on a c o m m e r c i a l Nb1 pct Zr alloy was undertaken to study the surface s e g r e g a t i o n and interaction of zirconium, oxygen and n i t r o g e n utilizing the technique of Auger E l e c t r o n Spect r o s c o p y (AES). EXPERIMENTS AND RESULTS The s t a r t i n g m a t e r i a l was a c o m m e r c i a l Nb-1 pct Zr alloy cold r o l l e d to 10 rail thickness, cut to 2 in. by 1/8 in. and mounted on 60 mil diam Nb s u p p o r t s . All the e x p e r i m e n t s were done in an u l t r a - h i g h v a c uum s y s t e m capable of achieving p r e s s u r e s ~ 1 • 10 -~ torr or better. The s p e c i m e n s were heated by p a s s i n g d i r e c t c u r r e n t and the t e m p e r a t u r e s were m e a s u r e d by an optical p y r o m e t e r . The t e m p e r a t u r e s below the optical range a r e e s t i m a t e d f r o m the r e s i s t a n c e values and hence a r e subject to l a r g e e r r o r s . E r r o r s of the o r d e r of +75~ a r e not inconceivable in this range. A A. JOSHI, is Assistant Metallurgist,M. N. VARMA,is Associate Scientist, and M. STRONGIN,is Physicistat Brookhaven National Laboratory, Upton, New York 11973. Manuscript submitted September 26, 1973. METALLURGICALTRANSACTIONS
c y l i n d r i c a l m i r r o r a n a l y z e r with an i n t e g r a l e l e c t r o n gun was used to obtain the AES data. AES is a highly s e n s i t i v e technique 5 for s u r f a c e chemical a n a l y s i s . In this technique one o b s e r v e s the i n e l a s t i c a l l y s c a t t e r e d e l e c t r o n s a f t e r b o m b a r d i n g the s a m p l e with e l e
Data Loading...