The hardness and grain size of consolidated fine tungsten powder
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g r a i n d i a m e t e r was m e a s u r e d at 500X, using the optical m e t a l l o g r a p h , and at m a g n i f i c a t i o n s to 20,000X, u s i n g a r e p l i c a t i o n technique and the e l e c t r o n m i c r o scope. Fig. l(a) and (b) shows t y p i c a l m i c r o g r a p h s of the s a m e g r a i n size as o b s e r v e d with the optical m i c r o s c o p e and the e l e c t r o n m i c r o s c o p e . H a r d n e s s m e a s u r e m e n t s of a s - c o n s o l i d a t e d ingots were m a d e p r i o r to giving the m a t e r i a l any m e t a l l o graphic m o u n t i n g or polishing t r e a t m e n t and the data showed c o n s i d e r a b l e s c a t t e r . The m e a s u r e d h a r d n e s s v a l u e s were g e n e r a l l y equal to or g r e a t e r than the m e a s u r e m e n t s obtained on the m e t a l l o g r a p h i c a l l y p r e p a r e d s p e c i m e n s u r f a c e s . Loads r a n g i n g between 50 g a n d 2 kg were e m p l o y e d to m a k e the m e a s u r e m e n t s . It was found that the h a r d n e s s of this fine
Fig. l(a)--Optical micrograph of consolidated polycrystalline tungsten. Magnification 460 times.
Fig. l(b)--Electron replica mierograph of same specimen. Magnification 5100 times. VOLUME 1,JUNE 1970-1769
g r a i n e d m a t e r i a l was e s s e n t i a l l y independent of the lo ad , a s shown in F i g . 2. T h i s r e s u l t is in a g r e e m e n t with p r e v i o u s m e a s u r e m e n t s on d i f f e r e n t t u n g s t e n m a t e r i a l . 7 Table I g i v e s f o r v a r i o u s g r a i n s i z e s a v e r age m e a s u r e m e n t s of the h a r d n e s s at lo a d s of 200, 300, and 2000 g. F i g . 3 shows the D i a m o n d P y r a m i d H a r d n e s s (Dph) m e a s u r e m e n t s vs the r e c i p r o c a l s q u a r e r o o t of the a v e r a g e g r a i n d i a m e t e r , 1-1/2, of the m a t e r i a l . At l -~/2 = 0, a data point is p lo tt e d f o r the r e p o r t e d h a r d n e s s of s i n g l e c r y s t a l l i n e m a t e r i a l of 99.98 wt p ct p u r i t y . 8 In the v i c i n i t y of l -~/2 = 50 cm -~/2, a c l u s t e r of data points is shown within which each h a r d n e s s v a l u e o c c u r s at two g r a i n s i z e s . In each c a s e , the two
2.0
TUNGSTEN
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DIAMOND PYRAMID jt-i/2
TEST
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1.5
A
1.0
0.5
g r a i n s i z e s w e r e m e a s u r e d on the s a m e s p e c i m e n , but one g r a i n s i z e v al u e was o b t a i n e d by c o n v e n t i o n a l opt i c a l m e t a l l o g r a p h y at 460X, a s shown in Fig. l(a), while the o t h e r was m e a s u r e d on e l e c t r o n p h o t o m i c r o g r a p h s p r o d u c e d by r e p l i c a t i o n of the e t c h e d s u r f a c e , a s shown in F i g . l(b). The c o n v e n t i o n a l o p t i c a l photom i c r o g r a p h s gave l a r g e r g r a i n s i z e s in each c a s e . It is p r o p o s e d that this o c c u r s in t h i s p a r t i c u l a r study b e c a u s e t h e s e g r a i n s i z e s a r e l a r g e enough that n u m e r o u s
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