Cracking of zircaloy as a result of unusual localized texturing
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DURINGthe v i s u a l i n s p e c t i o n of cold r o l l e d
Zircaloy* s t r i p , s m a l l t r a n s v e r s e d i s c o n t i n u i t i e s w e r e ob*ZlrcaloyIs a zlrcomum-basealloycontainingI 5 wt pct Sn, 0 20 wt pct Fe, and 0.10 wt pct Cr. It has a hexagonalclosepackedcrystalstructure s e r v e d . M e t a l l o g r a p h i c e x a m i n a t i o n r e v e a l e d them to be tiny c r a c k s up to 0.010 in. deep and 0.060 in. long. P e c u l i a r i t i e s a s s o c i a t e d with these c r a c k s w e r e that they w e r e o r i e n t e d at an angle of about 35 deg to the s u r f a c e of the s t r i p , F i g s . 1 and 2, w e r e s o m e t i m e s continuous, Fig. l , or d i s c o n t i n u o u s , Fig. 2. A review of the p r o c e s s i n g indicated that the s u r f a c e c r a c k i n g was r e l a t e d to r o l l e r l e v e l i n g of the cold r o l l e d s t r i p . To v e r i f y this, cold r o l l e d Z i r c a l o y s t r i p f r o m a n o t h e r s o u r c e was r o l l e r leveled. The r e s u l t s w e r e s u r p r i s i n g b e c a u s e : 1) these cold r o l l e d s t r i p s did not exhibit any c r a c k i n g when flexed the s a m e as the e a r l i e r s t r i p s ( m a x i m u m deflection equal to the s t r i p t h i c k n e s s ) ; 2) even with m o r e s e v e r e flexing of two to t h r e e t i m e s the s t r i p t h i c k n e s s , c r a c k i n g did not occur until about 100 r o l l e r l e v e l i n g p a s s e s w e r e c o m p l e t e d ; and 3) none of the c r a c k s developed w e r e at an a n g l e - - r a t h e r , they w e r e n o r m a l to the s u r f a c e . Repeated efforts failed to y i e l d c r a c k s at an angle c h a r a c t e r i s t i c of the o r i g i n a l cracks. The i n v e s t i g a t i o n was d i r e c t e d toward d e t e r m i n i n g the d i f f e r e n c e between the m a t e r i a l with angled and s t r a i g h t c r a c k s . MetaUographic e x a m i n a t i o n of copious s p e c i m e n s e n s u e d to detect s o m e m i c r o s t r u c t u r a l f e a t u r e which could be r e l a t e d to the c r a c k morphology. A d i f f e r e n c e was detected when a s p e c i m e n viewed u n d e r p o l a r i z e d light a p p e a r e d to have groups of g r a i n s a l i g n e d with the o r i e n t a t i o n of the angled c r a c k s . W. M. EVANS is Supervisor, Quality Control and Inspection Development Engineering,R. F. GESSNER is Bettis Resident Manager (West Coast), and J. G. GOODWlNis Manager, Advanced Process Development, WestinghouseElectric Corp., Bettis Atomic Power Laboratory, West Mifflin, Pc. Manuscript submitted March 25, 1970. METALLURGICALTRANSACTIONS
Having this clue, the next step was to i s o l a t e the c a u s e of the angled banding and to develop a c o n t r o l l e d t e s t to e v a l u a t e c r a c k s u s c e p t i b i l i t y . The test e q u i p m e n t depicted in Fig. 3, t e r m e d a " R o l l Bend Fatigue T e s t e r " , was u s e d to s i m u l a t e r o l l e r l e v e l i n g , a c c u r a t e l y control and
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