An indirect method for the determination of intrinsic microhardnesses of microporous and finely divided materials
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An Indirect Method for the Determination of Intrinsic Microhardnesses of Microporous and Finely Divided Materials ERHARD KLAR
of t h e v o l u m e r a t i o of t h e p h a s e s of t h e c o m p o s i t e , t h e i n t r i n s i c h a r d n e s s e s of the i n d i v i d u a l p h a s e s , a n d t h e i r g e o m e t r i c s t r u c t u r e . T h e d i s p e r s i o n of s u c h a f r e q u e n c y d i s t r i b u t i o n , i . e . , t h e s c a t t e r i n g of the v a l u e s f r o m t h e i r a v e r a g e , i s a m e a s u r e of t h e h e t e r o g e n e i t y of t h e c o m p o s i t e a n d d e p e n d s on t h e s a m e v a r i a b l e s . It d e c r e a s e s a s t h e h a r d n e s s of t h e a u x i l i a r y p h a s e a p p r o a c h e s the i n t r i n s i c h a r d n e s s of t h e m a t e r i a l u n d e r s t u d y . T h e d i s p e r s i o n of a t w o - p h a s e composite has a minimum where both phases have equal hardness. The approximate intrinsic hardness of a m a t e r i a l c a n t h e r e f o r e b e o b t a i n e d f r o m e x t r a p o l a t i o n to z e r o o r m i n i m u m d i s p e r s i o n of e x p e r i m e n t a l hardness dispersions. F o r a s u c c e s s f u l a p p l i c a t i o n of t h i s m e t h o d , t h e load on the indentor must be chosen so that the areas c o v e r e d b y the i n d e n t a t i o n s a r e s m a l l e r t h a n w h a t c a n b e c o n s i d e r e d r e p r e s e n t a t i v e of t h e e n t i r e s t r u c t u r e . I T h e m e t h o d i s i l l u s t r a t e d in t h e f o l l o w i n g two e x a m p l e s . E x a m p l e No. 1. T h e e x p e r i m e n t a l d a t a s h o w n in F i g s . 1 to 3 w e r e o b t a i n e d o n p o r o u s c o p p e r c o m p a c t s m a d e b y i s o s t a t i c c o m p a c t i o n of a c o m m e r c i a l , recently reduced, -325 mesh copper powder. The c o m p a c t s w e r e t r e a t e d u n d e r h y d r o g e n a t 1000~ f o r
g i s w iN d e l y uE s e d a sS a n o nS destrucH A Rt e s t i n D t i v e m e t h o d f o r a s s e s s i n g m e c h a n i c a l p r o p e r t i e s of m e t a l s . In m u l t i p h a s e m a t e r i a l s a s p r o d u c e d b y p o w d e r m e t a l l u r g i c a l t e c h n i q u e s , o n e of t h e p h a s e s f r e q u e n t l y i s t h e p o r e p h a s e . In s u c h p o r o u s s y s t e m s t h e m e a s u r e d h a r d n e s s i s c a l l e d a p p a r e n t h a r d n e s s if the hardness indentation covers an area large enough to b e r e p r e s e n t a t i v e of t h e e n t i r e p a r t . It i s c a l l e d t r u e m a t e r i a l o r i n t r i n s i c h a r d n e s s if t h e i n d e n t a t i o n is taken well within the solid material. For a better u n d e r s t a n d i n g of c o r r e l a t i o n s b e t w e e n h a r d n e s s a n d m e c h a n i c a l p r o p e r t i e s of p o r o u s s y s t e m s , it i s d e s i r a b l e to know b o t h a p p a r e n t a n d i n t r i n s i c h a r d n e s s . W h i l e t h e m e a s u r e m e n t of t h e a p p a r e n t h
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