Banding in niobium-niobium carbide (Nb 2 C) Composites grown by zone melting and freezing
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Table I. Typical Densitiesof Greenand Sintered601AC Aluminum PowderBlend Compacts psi
Pressure MN/m2
25,000 35,000 55,000
GreenDensity gm/cc pct TD*
172.5 241.5 379.5
2.50 2.58 2.62
SinteredDensity gm/cc pet TD*
93.0 96.0 97.4
2.57 2.60 2.63
95.5 96.6 97.8
*Basedon 2.69 gm/cctheoreticaldensity. h0
I
0.8
~ ~
108
I
I
I
I
9 ALUMINUM ALLOY DATA (THIS STUDY) 0"~ = 45000psi _ 9 IRON DATA (REF. 2)"] ~162= 41000psi 9 IRON DATA IREF. 5)J
/
I
0.6 k ~ ~
r =TENSILE STRENGTH OF ~SINTERED COMPACT, PSI
b8 0 . 4 - -
9
-
--
|
d I,< n:
given heat t r e a t m e n t P = compaction pressure A, B = c o n s t a n t s In Fig. 1, a v a l u e of a ~ equal to the t e n s i l e s t r e n g t h of wrought 6061-T6 a l u m i n u m alloy, 45,000 psi (310.5 MN/m2), was used and was found to c o r r e l a t e the r e s u l t s adequately. S i m i l a r l y , a value of a.o equal to the t e n s i l e s t r e n g t h of a n n e a l e d c a s t iron, 41,000 psi (283 MN/m2), was used and was found to c o r r e l a t e the r e s u l t s on i r o n powders t a k e n f r o m two independent s t u d ies. Thus, it can be s e e n that a ~ c o r r e s p o n d s to the t e n s i l e s t r e n g t h of the wrought m e t a l . Obviously, a ~ depends on heat t r e a t m e n t ; t h e r e f o r e , the heat t r e a t m e n t s for the powdered m e t a l and the wrought m e t a l m u s t be i d e n t i c a l . The c o n s t a n t s A and B a r e r e s p e c t i v e l y the i n t e r c e p t and slope of the l i n e s shown in F i g . 1. Since t h e i r v a l u e s depend on m a n y f a c t o r s , i n c l u d i n g the c h a r a c t e r i s t i c s of the powder, they m u s t be evaluated by e x p e r i m e n t s . Neve r t h e l e s s , the f o r m of the c o r r e l a t i o n p r e s e n t e d by Eq. [1] should be useful to d e s i g n e r s and p r o c e s s o r s for e s t i m a t i n g r e q u i r e d c o m p a c t i o n p r e s s u r e s for m a n y different powders. F i n a n c i a l support for this study was provided b y U n i v e r s i t y E n g i n e e r s , Inc., of N o r m a n , Oklahoma. 1. V. V. Hathi:Universityof Oklahoma,Norman,Oklahoma,Master'sThesis, 1972. 2. C. E. Van Burenand H. H. Hirsch:Perspectives in Powder Metallurgy, H. H. Hausner,ed., vol. 1, pp. 27--64,PlenumPress,NewYork, 1967. 3. R. G. R. Sellors:Powder Met., 1970, vol. 13, No. 26, pp. 85-99.
-r I-(.9 Z w r I--
0.2
Banding in Niobium-Niobium Carbide (Nb2C) Composites Grown by Zone Melting and Freezing o.,
20
40 60 80 PRESSURE, I000 psi
I00
Fig. 1--The change in tensile strengths of sintered compacts with isostatic compacting pressure. s i n t e r i n g a c h i e v e s little i m p r o v e m e n t in d e n s i t y at the conditions d e s c r i b e d for c o m p a c t i n g p r e s s u r e s above 25,000 p s i (172.5 MN/m2). The t e n s i l e s t r e n g t h s w e r e m e a s u r e d on an I n s t r o n b y applying the load at a c r o s s h e a d speed of 0.02 i n . / m i n . (0.05 c m / m i n ) . The r e s u l t s of t h e s e t e s t s a r e s u
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