Gold solubility in cobalt-rich Co-Fe-Au alloys
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ing to s i n z0 = 1. The a c c u r a c y of the lattice p a r a m e t e r d e t e r m i n a t i o n was e n h a n c e d by the p r e s e n c e of {400}K/3 l i n e s whose sin 20 v a l u e s w e r e slightly g r e a t e r than 0.95. The s o l u b i l i t y l i m i t of gold in the y was e s t a b l i s h e d by the p a r a m e t r i c method 4 in which the discontinuity in the plot of lattice p a r a m e t e r of the solvent vs p e r c e n t solute for a p a r t i c u l a r t e m p e r a t u r e i s taken a s the l i m i t of s o l u b i l i t y at that t e m p e r a t u r e . The plot of lattice p a r a m e t e r s vs p e r c e n t gold is shown in Fig. 1, and the s o l u b i l i t y l i m i t as a function of t e m p e r a t u r e is p r e s e n t e d in Fig. 2. The solid p o r t i o n of the solu~ 3.57 -
E
356
~
-
1100~ 1050~
o
900 C
A
o 750=C
=o
1
5 55
I
2
I
4
I
6
t
~
8 IO Wt % Au
t
i2
I
14
I
16
18
Fig. 1--Lattice parameter vs percent gold for temperatures indicated. Open circles represent points determined after heating at both 900~ and 1050~ Solid circles are points determined after heating at 1050~ only.
\
7"+h
\ i
X+Au+b
7+Au
4--
=o
Table I. Chemical Composition of the Alloys
Wt Pct Au
Wt Pet Fe
Wt Pct Co
0.5 1.0 1.5 2.0 4.0 6.0 10.0 14.0 18.0
12.4 12.3 12.2 12.2 12.0 11.8 11.2 10.8 10.2
87.1 86.7 86.3 85.8 84.0 82.2 78.8 75.2 71.8
LARRY LYNCH and P. S. VENKATESANare Graduate Engineering Education Instructor and Member of the Research Staff, respectively, Western Electric Company, Inc., Princeton, N.J. GEORGE KRAUSS is Associate Professor, Lehigh University, Bethlehem, Pa. Manuscript submitted January 7, 1970. METALLURGICALTRANSACTIONS
-
E
,
I
I
I
I
I
I
I
I
I
0
2
4
6
8
I0
12
14
16
18
Wt % Au
Fig. 2--Portion of equilibrium phase diagram along constant Co-Fe ratio of 7. VOLUME 1, MAY 1970-1471
Fig. 3--2 pct Au alloy heated at 900~ times.
Fig. 4---4 pct Au alloy heated at 900~ times.
Magnification 810
Magnification 820
b i l i t y l i m i t r e p r e s e n t s the r a n g e of t e m p e r a t u r e s c o n s i d e r e d . Fig. 1 shows that the slope of the c u r v e r e p r e s e n t i n g the b o u n d a r y b e t w e e n the y and the + Au r e g i o n s is f a i r l y s t e e p below 1000~ but d e c r e a s e s at higher t e m p e r a t u r e s . T h i s m a k e s a c c u r a t e location of the s o l i d u s p o r t i o n of the b o u n d a r y of the s i n g l e - p h a s e y r e g i o n m o r e difficult s i n c e a s m a l l e r r o r in l a t t i c e p a r a m e t e r would r e s u l t in a l a r g e r e r r o r in gold s o l u b i l i t y . A m i n i m u m of two d i f f r a c t i o n p a t t e r n s was m a d e for each a l l o y - t e m p e r a t u r e c o m b i n a t i o n , and both points a r e plotted in F i g . 1 for those s a m p l e p a i r s for which s i g n i f i c a n t d i f f e r e n c e s w e r e obtained. The d i f f r a c t i o n p a t t e r n s showed no e v i d e n c e of e i t h e r a bcc ~ phase or an o r d e
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