A study of layered green ferrous powder compacts
- PDF / 803,633 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 5 Downloads / 197 Views
S E V E R A L
of the m o s t i m p o r t a n t l i m i t a t i o n s of the conventional powder m e t a l l u r g y p r o c e s s a r e a s s o c i ated with obtaining a g r e e n ( a s - c o m p a c t e d ) m a t e r i a l of sufficient s t r e n g t h and i n t e g r i t y . C o n v e n t i o n a l r e f e r s to u n i a x i a l compaction of powder within a rigid die at a m b i e n t t e m p e r a t u r e followed by a s i n t e r i n g operation. Inadequate g r e e n s t r e n g t h may be e v i d e n c e d by s p a l l e d , c r a c k e d , or f r a c t u r e d c o m p a c t s produced upon e j e c t i o n f r o m the die, or by c o m p a c t s that undergo such f a i l u r e d u r i n g n o r m a l handling for i n s p e c t i o n and t r a n s p o r t to the s i n t e r i n g f u r n a c e . Such a situation may r e s u l t f r o m : a) the use of p r e alloyed or i m p u r e powders that do not u n d e r g o sufficient plastic d e f o r m a t i o n and i n t e r p a r t i c l e s u r f a c e i n t e r l o c k i n g d u r i n g c o m p a c t i o n ; b) the use of a m e t a l powder whose p a r t i c l e s have c h a r a c t e r i s t i c s , such as s p h e r i c a l shape or smooth s u r f a c e s , that inhibit i n t e r p a r t i c l e bonding; c) the a t t e m p t to produce v e r y l a r g e c o m p a c t s for which i n s u f f i c i e n t c o m p a c t i o n p r e s s u r e is a t t a i n e d to achieve a g r e a t enough g r e e n density. E j e c t i o n s t r e s s e s a r e s o m e t i m e s induced with the c o m p a c t that exceed its s t r e n g t h , o r e x c e s s i v e s t r e s s e s a r e developed d u r i n g handling s i m p l y b e c a u s e of its weight and size. The purpose of the p r e s e n t study is to d e t e r m i n e the f e a s i b i l i t y of u s i n g l a m i n a r c o m p o s i t e s to achieve i m p r o v e m e n t s in g r e e n s t r e n g t h that could a l l e v i a t e the above noted p r o b l e m s . T h i s approach may a l s o be used to reduce the die fill depth and, h e n c e , facilitate the f a b r i c a t i o n of r a t h e r thick c o m p a c t s . The e m phasis is on e l u c i d a t i n g the potential a d v a n t a g e s of this approach and the g u i d e l i n e s for i t s optimum app l i c a t i o n , r a t h e r than the d e v e l o p m e n t of u s e a b l e m a t e r i a l s . It should be noted at the outset that the p r e s ent study differs f r o m p r e v i o u s work on l a m i n a r c o m p o s i t e s b e c a u s e the i n d i v i d u a l l a y e r s behave as b r i t t l e m a t e r i a l s and there is no s i g n i f i c a n t c h e m i c a l or m e t a l l u r g i c a l bonding b e t w e e n or within the l a y e r s (except for within the p a r t i c l e s ) .
EXPERIMENTAL
PROCEDURES
Materials. The powders used were commercial grades of the pure elemental or preblended form. Table I contains a summary of the powders used, including type number used throughout the text, together with apparent density and flow time data used to char
Data Loading...
