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f i l e f r o m the s a m p l e fatigued in o x y g en - 1 8 r e p r e s e n t s oxidation, diffusion, and any additional oxygen t r a n s p o r t m e c h a n i s m o c c u r r i n g d u r i n g the fatigue c r a c k p r o p a g a t i o n . Oxidation and diffusion that o c c u r r e d d u r i n g t r a n s f e r f r o m the fatigue c h a m b e r to the a n a l y s i s c h a m b e r is in p r e d o m i n a n t l y o x y g e n - 1 6 . R e s u l t s of the fatigue c r a c k growth e x p e r i m e n t s showed an i n c r e a s e d c r a c k g r o w t h r a t e in the oxygen e n v i r o n m e n t by a f a c t o r of 5 and 2 f o r Monel and t i t an i u m , r e s p e c t i v e l y , with little o r no i n c r e a s e app a r e n t f o r the a l u m i n u m a l l o y s . Th e p e n e t r a t i o n depth of the oxygen in e a c h c a s e as m e a s u r e d by AES and SIMS is shown in F i g s . 1 t h r o u g h 8. It was g r e a t e r in Monel 404 Auger (Normalized) Sample 7

1.0

10' Pa 0 2 '~ 1.3 X 10 "6 P a

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*Registeredtrademark, The International NickelCompany,Inc. c o m m e r c i a l l y p u r e t i t a n i u m , and a l u m i n u m 2219-T87 and 7075-T651 a l l o y s (see T a b l e I f o r c o m p o s i t i o n s ) . F o l l o w i n g the fatigue e x p e r i m e n t s , s a m p l e s of the f a tigue s u r f a c e s w e r e a n a l y z e d with A u g e r E l e c t r o n S p e c t r o s c o p y (AES) and S e c o n d a r y Ion M a s s S p e c t r o s copy (SIMS) to d e t e r m i n e if oxygen had b e e n t r a n s p o r t e d into the m a t e r i a l d u r i n g c r a c k p r o p a g a t i o n . The AES m e a s u r e m e n t s w e r e used due to the b e t t e r s p a t i a l r e s o l u t i o n and c o n s i s t e n t s u r f a c e c h e m i c a l s e n s i t i v i t y . T h e SIMS a l l o w e d i s o t o p e d i s c r i m i n a t i o n d u r i n g the s p u t t e r p r o f i l i n g of oxygen into the bulk. C o m p a c t t e n s i o n s p e c i m e n s w e r e f a ti g u e c y c l e d t h r o u g h m e t a l b e l l o w s in an i o n - p u m p e d v a c u u m c h a m b e r . At a p r e s s u r e of 1,3 /~Pa (10-8 T o r r ) , the c r a c k was grown 0.8 c m with load shedding a c c o m p l i s h e d e a c h 0.16 c m of growth to m a i n t a i n the AK r e l a t i v e l y constant at the va l u e given in T a b l e I. Growth r a t e was thus e s t a b l i s h e d f o r a v a c u u m e n v i r o n m e n t . U n d er constant AK conditions, c r a c k growth r a t e should be constant e x c e p t f o r e n v i r o n m e n t a l e f f e c t s , if p r e s e n t . T h e i s o t o p e o x y g e n - 1 8 of 99.9 pct p u r i t y was i n t r o duced into the c h a m b e r , b a c k f i l l i n g to a p r e s s u r e of 10 k P a (1 k P a fo r a l u m i n u m 2219 due to a l i m i t e d supply of the i s o t o p e) . T h e c r a c k was extended a n o t h e r 0.8 c m at the fixed A/f and growth r a t e in the o x y g e n - 1 8 d e t e r m i n e d . Th e s p e c i m e n s w e r e cut and t r a n s f e r r e d to the A E S / S