Progress in the Development of a Mechanical Properties Microprobe
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a t e r i a l ; h e n c e , it m u s t m e a s u r e b o t h t h e elastic and plastic mechanical p r o p e r t i e s . T o d o this r e p r o d u c i b l y , t h e s y s t e m m u s t c o n t r o l o r m e a s u r e all t h e p a r a m e t e r s affecting such p r o p e r t i e s . T h e s e p a r a m e t e r s include t h e s t r a i n , strain rate, t e m p e r a t u r e , stress, and the e n v i r o n m e n t . Finally, t h e s y s t e m m u s t m a k e t h e s e m e a s u r e m e n t s w i t h r e a s o n a b l e precision and w i t h a r e a s o n a b l e i n v e s t m e n t of t i m e and effort. T h e need for such a s y s t e m is o b v i o u s . First, t h e scale of technologically i m p o r t a n t s t r u c t u r e s is c o n s t a n t l y r e d u c i n g ( t h e s e m i c o n d u c t o r i n d u s t r y is a s t r i k i n g exa m p l e ) . S e c o n d , thin film and c o a t i n g s t e c h n o l o g i e s a r e i m p o r t a n t to m a n y ind u s t r i e s ; and, third, small v o l u m e s of m a t e r i a l s a r e t h e building blocks used to p r o d u c e rapidly solidified metal alloys and a d v a n c e d c e r a m i c s . In all t h e s e t e c h n o l o g i e s , c h a r a c t e r i z i n g small v o l u m e s of m a t e r i a l s is e s s e n t i a l to u n d e r s t a n d i n g t h e overall p e r f o r m a n c e of t h e final p r o d u c t . A mechanical p r o p e r t i e s m i c r o p r o b e will also a d v a n c e o u r u n d e r s t a n d i n g of m a c r o scopic p r o p e r t i e s in t h e s a m e way t h a t t h e chemical microprobe has improved o u r u n d e r s t a n d i n g of t h e c h e m i s t r y of t h e m a t e r i a l s and t h a t t h e t r a n s m i s s i o n elect r o n microscope (TEM) h a s i m p r o v e d o u r u n d e r s t a n d i n g of s t r u c t u r e s . T w o o b v i o u s e x a m p l e s a r e t h e s a m p l i n g of t h e s e p a r a t e p h a s e s in a m u l t i p l e - p h a s e alloy and t h e m e a s u r e m e n t o f p r o p e r t i e s affected by n o n h o m o g e n e o u s a r r a n g e m e n t s of dislocations. O n l y o n e type of mechanical test can p o t e n t i a l l y satisfy all of t h e s e r e q u i r e ments. Properly instrumented and controlled, a m i c r o i n d e n t a t i o n t e s t c a n accomplish m a n y of t h e s e goals. D u r i n g an i n d e n t a t i o n t e s t , b o t h elastic and plastic s t r a i n s a r e g e n e r a t e d . For m a n y m a t e r i a l s t h e s t r a i n s from both fields a r e of sufficient m a g n i t u d e to be m e a s u r e d . T h e t e s t can be scaled d o w n so t h a t s u b m i c r o n v o l u m e s of material a r e sampled. M i c r o i n d e n t a t i o n t e s t s h a v e b e e n used to m e a s u r e an e x t r e m e l y wide v a r i e t y of m a t e r i a l p r o p e r t i e s : yield s t r e n g t h , 2 c r e e p resistance, 3 ' 4 s t r e s s r e l a x a t i o n , 5 m o d u l u s , 6 fracture t o u g h n e s s ' and even fatigue t e s t s . 9 In addition, b e c a u s e t h e m a
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