Redetermination of the invariant compositions in the Co-Coal eutectic
- PDF / 891,868 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 175 Views
8A,
A U G U S T
1977
1oy c o n f i r m that, on an o p t i c a l m i c r o s c o p i c level. the Co p h a s e is the m a j o r phase by v o l u m e when observed after directional solidification. F u r t h e r more, transmission electron microscopic observations a l s o i n d i c a t e an e x t e n s i v e p r e c i p i t a t i o n of the Co solid s o l u t i o n within the CoAl p h a s e v in a g r e e m e n t with the o b s e r v a t i o n of Cline. M o r e o v e r , our eutectic alloy was r e h e a t e d to 1623 K for 3 h (T E 1673 K) and quenched f r o m this t e m p e r a t u r e . The m e a s u r e d v o l u m e f r a c t i o n of CoAl in the alloy a f t e r this t r e a t m e n t (27.7 + 3.2 pct) was unchanged f r o m that o b s e r v e d p r i o r to heat t r e a t m e n t . It should be noted that the c h a r a c t e r i s t i c value of Dt for the above heat t r e a t m e n t exceeded that of the a l l o y following d i r e c t i o n a l s o l i d i f i c a t i o n . Thus if epita,xial growth were to o c c u r following d i r e c t i o n a l s o l i d i f i c a tion, it would a l s o have o c c u r r e d d u r i n g this heat t r e a t m e n t . It t h e r e f o r e a p p e a r s l o g i c a l to conclude that the s t r u c t u r e , a s o b s e r v e d on an optical m i c r o scopic level, is s i m u l a t i v e of the s t r u c t u r e i m m e d i -
." 1~4 ~
.~:~2-~--~:.~ ~. 7;
~,
- @ [ @ ' ~
~ *
-
....
~ ~. ~
9
~ ~
~
'[~'.,~'"
~" ~ . - ~ *
.:".
-
"
9 .
2.~'- -,d .*
,
~
~
9 =l~,--
r
~
'
(b) Fig. 1--(a) Photomicrograph taken from lower portion of ingot illustrating primary cobalt and eutectic microstructure. The nital etchant yields a mottled appearance in the cobalt rich phase which is related to subeutectic precipitate within it. (b) Photomicrograph taken from portion of ingot at which steady state eutectic growth was attained. As before, the mottled appearance of the cobalt phase ks due to subeutectic precipitation within it. METALLURGICALTRANSACTIONSA
0 05 /
004
/
L2~-~:-~,~-~-~ 003 I*_~L
''~-
-~:-'-x~'~x-.~-cx\\,. \ ~\:.k~_
/ / /
002
/ /
,/
001
4
8
12
16
20
84
80
wi% A1--
92 88 -* wt% r Fig. 2--Calibration curve relating aluminum (IA) to cobalt Ka intensity (IC) as a function sition, Specific details of the calibration are text. 96
K a intensity of alloy componoted in the
a t e l y s u b s e q u e n t to the e u t e c t i c r e a c t i o n and we a c c o r d i n g l y u n d e r t o o k a p r o g r a m to r e e s t a b l i s h the c o m p o s i t i o n s at the i n v a r i a n t t e m p e r a t u r e . T h e s a m p l e u t i l i z e d in t h i s study was a s l i g h t l y off e u t e c t i c a l l o y c o n s o l i d a t e d f r o m high p u r i t y s t a r t i n g m a t e r i a l s (99.999 p c t A1; 99.995+ pct Co). F o l l o w ing a r c m e l t i n g and inductive r e m e l t i n g , this a l l o y was d i r e c t i o n a l l y s o l i d i f i e d at a r a t e of 2 c m / h u t i l i z i n g a t e m p e r a t u r e g r a d i e n t of a p p r o x
Data Loading...
