THE EFFECT OF LOW MELTING POINT
IMPURITIES ON THE PROPERTIES OF Al-Li
ALLOYS
D. Webster
To cite this version:
D. Webster. THE EFFECT OF LOW MELTING POINT IMPURITIES ON THE PROPERTIES OF Al-Li ALLOYS. Journal de Physique Colloques, 1987, 48 (C3), pp.C3-685-C3-691.
<10.1051/jphyscol:1987379>. <jpa-00226610>
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Submitted on 1 Jan 1987
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JOURNAL DE PHYSIQUE
C o l l o q u e C 3 , s u p p l 6 m e n t au n 0 9 , Tome 48, s e p t e m b r e 1 9 8 7
THE EFFECT OF LOW MELTING POINT IMPURITIES ON THE PROPERTIES OF A1-Li
ALLOYS
D
. WEBSTER
K a i s e r Aluminum a n d C h e m i c a l C o r p o r a t i o n , P.O.
P l e a s a n t o n , C A 94566, U . S . A .
Box 877,
Abstract
The e f f e c t of low m e l t i n g p o i n t i m p u r i t i e s ,
s u c h a s sodium a n d
p o t a s s i u m , o n t h e p r o p e r t i e s a n d m i c r o s t r u c t u r e o f A1-Li a l l o y s h a s
been i n v e s t i g a t e d .
T h e s e i m p u r i t i e s have b e e n shown t o o c c u r a s
d i s c r e t e l e n t i c u l a r p a r t i c l e s along g r a i n boundaries.
I n underaged
a n d peak-aged c o n d i t i o n s ,
t h e impurity p a r t i c l e s a r e l i q u i d and t h e
t o u g h n e s s a n d d u c t i l i t y o f a l l o y s i n t h i s c o n d i t i o n were found t o be
improved by l o w e r i n g t h e t e s t t e m p e r a t u r e below t h e f r e e z i n g p o i n t o f
t h e impurity.
I n t h e overaged c o n d i t i o n ,
t h e sodium a n d p o t a s s i u m
o c c u r a s a s o l i d p h a s e a n d m a t e r i a l s i n t h i s c o n d i t i o n were f o u n d t o
f o l l o w t h e p a t t e r n o f most aluminum a l l o y s a n d show a d e c r e a s e i n
C h a r p y i m p a c t t o u g h n e s s a s t h e t e s t i n g t e m p e r a t u r e was l o w e r e d .
The
a d d i t i o n o f sodium a n d p o t a s s i u m t o A1-Li a l l o y s r e d u c e d t o u g h n e s s
a n d d u c t i l i t y a t room t e m p e r a t u r e i n t h e r a n g e o f c o m p o s i t i o n s
Low m e l t i n g
i n v e s t i g a t e d ( u p t o 476 ppm Na a n d up t o 23 ppm K ) .
p o i n t i m p u r i t i e s were found t o have l i t t l e e f f e c t on t h e t o u g h n e s s o r
d u c t i l i t y of h i g h p u r i t y aluminum.
Introduction
A t t h e p r e s e n t s t a g e of
t h e i r development,
A1-Li
alloys
g e n e r a l l y compare u n f a v o r a b l y w i t h c o n v e n t i o n a l aluminum a l l o y s i n
terms of t o u g h n e s s a n d d u c t i l i t y a t e q u i v a l e n t s t r e n g t h l e v e l s .
For
e x a m p l e , A 1 7075 a n d A 1 2024 e x t r u s i o n s made from c o m m e r c i a l i n g o t s
times) i m p a c t t o u g h n e s s
than
have
s i g n i f i c a n t l y g r e a t e r (2-3
i d e n t i c a l A 1 8090 a n d A 1 2090 e x t r u s i o n s .
T h e r e is e v i d e n c e i n t h e
l i t e r a t u r e t h a t t h i s d i f f e r e n c e i n t o u g h n e s s may b e r e l a t e d t o low
m e l t i n g p o i n t i m p u r i t i e s s u c h a sodium a n d p o t a s s i u m .
Payne a n d
Eynon, i n 1957 B r i t i s h P a t e n t 787665, s u g g e s t e d t h a t e m b r i t t l e m e n t o f
A1-Li
a l l o y s o c c u r r e d i f t h e sodium c o n t e n t w a s o v e r 5 0 ppm.
et al,
(Ref.
1 ) i n 1976 found a 16% d r o p i n t o u g h n e s s o f
Vaynblat,
A1-2
Li-0.13 Z r a l l o y s when t h e sodium c o n t e n t was i n c r e a s e d from 3 1
i n 1982 ( R e f .
2)
t o 7 6 ppm.
More r e c e n t l y , Vasudevan, e t a l ,
o b s e r v e d l i n e a r d e c r e a s e s i n t o u g h n e s s i n A1-Li a l l o y s c o n t a i n i n g up
t o 480 ppm sodium, a n d W e b s t e r ( R e f . 3 ) o b s e r v e d t o u g h n e s s d e c r e a s e s
i n A1-Li a l l o y s c o n t a i n i n g up t o 434 ppm sodium a n d 23 ppm p o t a s s i u m .
The a d d i t i o n o f sodium a n d p o t a s s i u m p r o m o t e s t h e g r a i n b o u n d a r y
2 ) a n d t h e s e e l e m e n t s have b e e n
f r a c t u r e mode i n A1-Li a l l o y s ( R e f .
f o u n d by s u r f a c e a n a l y s i s t o s e g r e g a t e t o t h e g r a i n b o u n d a r i e s
(Refs.
2,
3 , 4 , , 5 ) . t h e aim o f t h e p r e s e n t work i s t o i d e n t i f y t h e
n a t u r e of t h e g r a i n b o u n d a r y s e g r e g a t i o n a n d t h e c h a n g e s l t u n d e r g o e s
during aging.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987379
JOURNAL DE PHYSIQUE
Experimental Technique
Most of t h e a l l o y s e v a l u a t e d i n t h i s work were from a l l o y s c a s t
i n t o 1 2 7 mm d i a m e t e r i n g o t s and e x t r u d e d t o f l a t b a r 5 8 x 14 mm.
Four a l l o y s w i t h a d d e d Na a n d K were c a s t a s b o t h 127 mm d i a m e t e r
i n g o t s , e x t r u d e d t o f l a t b a r and a s 100 mm x 25 mm i n g o t s which were
The a l l o y s were m e l t e d u n d e r a n a r g o n
h o t r o l l e d t o 6.4 mm p l a t e .
atmosphere.
Results
When l i t h i u m m e t a l i s a d d e d t o a m o l t e n aluminum a l l o y , t h e r e is
a n i n c r e a s e i n sodium, p o t a s s i u m and hydrogen l e v e l s i n t h e a l l o y .
22ppm K
T h e s e e l e m e n t s a r e p r e s e n t i n t h e l i t h i u m m e t a l ( 5 3 ppm Na,
a n d 280 ppm H). A d d i t i o n s of sodium, p o t a s s i u m a n d l i t h i u m g r e a t l y
i n c r e a s e t h e hydrogen c o n t e n t o f aluminum a l l o y s .
This is n o t
s u r p r i s i n g s i n c e hydrogen h a s a h i g h s o l u b i l i t y i n a l l t h r e e a l k a l i
metals When t h e d a t a a r e measured a s a t o m i c p e r c e n t a g e s t h e hydrogen
c o n t e n t i s e q u a l t o t h e cube r o o t o f t h e sum o f t h e a l k a l i m e t a l s .
I n a l l t h e a l l o y s examined t h e r e i s a n e x c e s s of a l k a l i m e t a l s above
t h a t r e q u i r e d t o form h y d r i d e s , e v e n b e f o r e t h e a l l o y s a r e d e g a s s e d .
S m a l l p a r t i c l e s r i c h i n Na a n d K were o b s e r v e d i n t r a h s m i s s i o n
e l e c t r o n m i c r o s c o p y i n a l l t h e a l l o y s examined w i t h a d d e d amounts o f
t h e s e elements.
The p a r t i c l e s were l e n t i c u l a r i n s h a p e w i t h t h e i r
l o n g e s t d i m e n s i o n (0.3-1.7 pm) a l o n g t h e g r a i n boundary.
I n many
c a s e s t h e r e was a s m a l l p a r t i c l e , r i c h i n Pb w i t h i n of t h e l e n t i c u l a r
Na-K p a r t i c l e ,
s u g g e s t i n g t h a t t h i s was a c t i n g a s a n u c l e a t i n g a g e n t
f o r sodium a n d p o t a s s i u m s e g r e g a t i o n .
The d i h e d r a l a n g l e o f t h e
l e n t i c u l a r Na-K p a r i c l e s a t t h e g r a i n b o u n d a r i e s was found t o be i n
t h e r a n g e 100-120
One o f t h e s m a l l e s t (0.3 p m ) s o d i u m - r i c h
p a r t i c l e s o b s e r v e d was found a t a g r a i n boundary t r i p l e j u n c t i o n i n
a l l o y 2BLKN a n d i s shown i n F i g u r e 1.
Inside t h i s p a r t i c l e is a
lead-rich particle.
The EDX a n a l y s i s from t h i s p a r t i c l e i n d i c a t e s i t
i s 81% Na,
1 9 % K.
A TEM e x a m i n a t i o n o f a l l o y 2BLK,
which c o n t a i n s
s l i g h t l y more p o t a s s i u m t h a n 2BLKN, b u t o n l y 6% a s much sodium, shows
s i m i l a r g r a i n boundary p a r t i c l e s r i c h i n Na and K which a l s o a p p e a r
t o have n u c l e a t e d on l e a d p a r t i c l e s .
EDX a n a l y s e s t a k e n from t h e
g r a i n b o u n d a r i e s a d j a c e n t t o t h e Na-K
p a r t i c l e s show o n l y t h e
p r e s e n c e o f aluminum, i n d i c a t i n g t h a t t h e sodium and p o t a s s i u m a r e
n o t p r e s e n t a s a u n i f o r m g r a i n boundary f i l m b u t a r e c o n c e n t r a t e d i n
isolated particles.
Because o f t h e s m a l l volume of e a c h s o d i u m - r i c h
particle, a
q u a n t i t a t i v e a n a l y s i s of t h e c o m p o s i t i o n c a n n o t b e made by EDX i n t h e
STEM. However, t h e Na:K r a t i o c a n be o b t a i n e d , a n d i f t h e a s s u m p t i o n
i s made t h a t a p a r t from o c c a s i o n a l n u c l e a t i n g p a r t i c l e s t h e sodiumr i c h p a r t i c l e c o n t a i n s o n l y sodium p l u s p o t a s s i u m ,
then
the
c o m p o s i t i o n o f e a c h p a r t i c l e and t h e r e f o r e i t s l i q u i d u s a n d s o l i d u s
temperature can be estimated.
T h i s h a s been done f o r a l l o y s
2BLK(llppmNa, 23ppm K ) , 2BLKN(476ppm Na,
15ppm K and 2BLKNC( lloppm
Na) F i g u r e 2.
The c o m p o s i t i o n of e a c h p a r t i c l e i s p l o t t e d o n t h e NaK p h a s e d i a g r a m a t t h e l o w e s t t e m p e r a t u r e a t which a l i q u i d p h a s e c a n
I t c a n be s e e n t h a t a
e x i s t i n a p a r t i c l e of t h a t composition.
l i q u i d p h a s e would b e e x p e c t e d a t room t e m p e r a t u r e i n a l l t h r e e
a l l o y s a n d t h a t p o t a s s i u m was i d e n t i f i e d i n t h e g r a i n boundary
p a r t i c l e s e v e n when t h e amount was t o o low t o b e d e t e c t e d by b u l k
a n a l y s i s (2BLKNC).
I n most o f t h e s o d i u m - r i c h p a r t i c l e s o b s e r v e d a f t e r a g i n g a t
394K,
s m a l l b u b b l e s were o b s e r v e d moving s l o w l y j u s t i n s i d e t h e
p e r i m e t e r of t h e p a r t i c l e i n d i c a t i n g t h a t t h e p h a s e i s i n d e e d l i q u i d
<Ref. 6>.
6
.
Figure 1. TEM of Na-K particle in grain boundary triple
junction of alloy 2BLKN.Dark particle contains Pb.
FIG. 2 . Na-K PHASE DIAGRAM SHOWING
RELATIVE CONCENTRATIONS OF Na-K
ElEASURED BY EDX FROM PHASES OBSFBVED
BY 'TI31
WEIGHT PCT. SODlL?l
C3-688
JOURNAL DE PHYSIQUE
I n o r d e r t o show t h e a l k a l i m e t a l d i s t r i b u t i o n i n a l l o y s w i t h
o n l y r e s i d u a l amounts, a more s e n s i t i v e m i c r o - a n a l y t i c a l
technique,
Rb
t h e Cameca I o n Microprobe was used.
The d i s t r i b u t i o n o f Na, K ,
a n d Cs was examined o n b o t h p o l i s h e d s a m p l e s and s a m p l e s f r a c t u r e d
i n t e r g r a n u l a r l y a l o n g t h e S-T d i r e c t i o n .
The K d i s t r i b u t i o n i n a
l5Oum d i a m e t e r c i r c l e on a f r a c t u r e s u r f a c e o f a semi commercial A 1
8091 a l l o y i n t h e peak a g e d c o n d i t i o n is shown i n F i g u r e 3.
The Na
a n d K d i s t r i b u t i o n s v a r y from p a r t i c l e t o p a r t i c l e b u t t h e l o c a t i o n
o f t h e h i g h c o n c e n t r a t i o n s o f e a c h e l e m e n t a r e t h e same a s i n d i c a t e d
by t h e TEM work a b o v e .
F o r t h e t h r e e l a r g e p a r t i c l e s shown i n F i g u r e
3 t h e a v e r a g e Na a n d K a t o m i c c o n c e n t r a t i o n s were a b o u t e q u a l .
The
Cs l e v e l s were 24 times l o w e r and t h e Rb l e v e l s were 300 times l o w e r
I n t h e c a s e o f t h e K and p e r h a p s a l s o t h e
t h a n t h e Na a n d K l e v e l s .
Cs a n d Rb t h e r e i s e n r i c h m e n t i n t h e p a r t i c l e s compared t o t h e b u l k
composition.
FIGURE 3 . PfYFASSIU? DISTRIBUTION ON SEIORT ?EWEVERSE FRACI'LJRE SURFACE
OF Al 8091 AUQY EXTRUSION AS SH@,JN BY THE ION .PUCROPROBE.
TIE DARK AREAS ARE REGIONS OF HIGH POTASSIW4 C O N ~ R A T I O N S .
N a , R b AND C s WE ALSO CONCEJTRA"D I N THE S R I E NZEAS.
Na AMD K LFVELS BY BULK ANALYSIS ARE 3 PPM AND 4 0 . 5 PPM
RESPECTIVELY. THE NUMBEPS INDICATE TEE REXATIVE POTASSIUq
C O N ~ T I O N SI N TI= YATIIIX AND I N THE PAF3ICLE CENTERS.
The t e n s i l e and Charpy i m p a c t p r o p e r t i e s of underaged 6 mm A1-Li
p l a t e w i t h v a r i o u s a d d i t i o n s ' o f sodium and p o t a s s i u m a r e a s f o l l o w s .
A t 295K t h e r e i s a s l i g h t d e c r e a s e i n y i e l d s t r e n g t h w i t h i m p u r i t y
c o n t e n t and a s i g n i f i c a n t d e c r e a s e i n d u c t i l i t y and t o u g h n e s s .
The
h i g h p o t a s s i u m a l l o y s have l o w e r t o u g h n e s s t h a n e x p e c t e d a b o v e 77K,
b a s e d o n t h e a s s u m p t i o n t h a t Na a n d K a r e of e q u a l e f f e c t i v e n e s s i n
A b e t t e r correlation is obtained
i f the
reducing toughness.
p o t a s s i u m c o n t e n t a l o n e i s assumed t o b e t h a c o n t r o l l i n g f a c t o r .
For
t h e r e s u l t s a t 295K t h i s i s a l o g i c a l a s s u m p t i o n s i n c e i n a l l t h e
a l l o y s , Na which is t h e m a j o r a l k a l i m e t a l i m p u r i t y , i s a s o l i d a t
295K.
I n t h e c o m p l e t e a b s e n c e of o t h e r a l k a l i m e t a l s t h e r e f o r e n o
e m b r i t t l e m e n t s h o u l d b e o b s e r v e d a t 295K. I n t h i s c a s e t h e amount o f
l i q u i d p r e s e n t w i l l b e c o n t r o l l e d e n t i r e l y by t h e s e c o n d m a j o r a l k a l i
p o t a s s i u m which when i n t h e p r e s e n c e of sodium
m e t a l i m p u r i t y i.e.
To b e c o n s i s t e n t t h e
f o r m s p h a s e s which a r e l i q u i d below 295K.
c h a r p y d a t a f o r 373K s h o u l d b e p l o t t e d a g a i n s t t h e sum o f Na+K s i n c e
When t h i s i s d o n e
t h i s t e m p e r a t u r e i s a b o v e t h e m e l t i n g p o i n t o f Na.
t h e number o f l i n e s on t h e p l o t is r e d u c e d t o two s i n c e t h e 373K d a t a
4).
In order t o
becomes a n e x t e n s i o n o f t h e 295K d a t a <Fig.
FIG.4.EFFECT OF LIQUID IMPURITY LEVELS ,K AT 77K AND Na+K AT
3733 ON CHARPY VALUES OF Al-Li ALLOYS WITH ADDED Na+K.
f u l l y e v a l u a t e t h e e f f e c t o f Na a n d K on t h e t o u g h n e s s o f A1-Li
a l l o y s , i t i s d e s i r a b l e t o b e a b l e t o e v a l u a t e a n a l l o y where t h e s e
e l e m e n t s a r e e x t r e m e l y low.
T h i s i s n o t e a s y t o d o by i n g o t
metallurgy,
however, t h i s c o n d i t i o n c a n b e a p p r o a c h e d i n a l l o y s made
by powder m e t a l l u r g y .
Two a l l o y s 1 6 1 1 a n d 1614 were a t o m i z e d a t
1200K i n t o -100 mesh [ < I 4 9 p m ] p a r t i c l e s .
The h i g h t e m p e r a t u r e a n d
t h e s m a l l p a r t i c l e s i z e would b e e x p e c t e d t o e n a b l e a l m o s t a l l t h e
sodium
and
potassium t o evaporate.
Specimens were aged
a t
t e m p e r a t u r e s u p t o 533K a n d t e s t e d a t room t e m p e r a t u r e a n d 77K.
The
temperature dependence of toughness f o r t h e s e a l l o y s was q u i t e
d i f f e r e n t from i n g o t m e t a l l u r g y a l l o y s c o n t a i n i n g h i g h e r Na a n d K.
The powder a l l o y s showed a d e c r e a s e i n t o u g h n e s s a t 77K u n d e r a l l
a g i n g c o n d i t i o n s < F i g . 5>.
Discussion
The a b o v e r e s u l t s show t h a t t h e a d d i t i o n o f l i t h i u m t o aluminum
K and H.
r e s u l t s i n a n i n c r e a s e i n t h e u n d e r s i r a b l e i m p u r i t i e s Na,
A l l t h r e e of t h e s e e l e m e n t s a r e c o n c e n t r a t e d i n t h e g r a i n b o u n d a r i e s
reduce t h e
<Ref. 3 > , a n d t h e K a n d t o a lesser e x t e n t t h e Na,
t o u g h n e s s o f A1-Li a l l o y s a t t e m p e r a t u r e s a b o v e a p p r o x i m a t e l y 200K.
The t e m p e r a t u r e d e p e n d e n c e o f i m p a c t t o u q h n e s s a n d d u c t i l i t y , o f
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FIG.5 TOUGHNESS AS A FUNCTION OF AGING TEMPERATURE FOR POWDER
METALLURGY EXTRUSIONS 1611 AND 1612 TESTED AT 295K and 77K.
a l l o y s w i t h a d d e d Na and K ,
and a l l o y s w i t h o n l y r e s i d u a l amounts of
these elements,
d i f f e r o n l y i n t h e m a g n i t u d e o f t h e e f f e c t <Ref. 3 ) .
I t h a s b e e n shown t h a t t h e s e e l e m e n t s o c c u r a s i s o l a t e d g r a i n
boundary p a r t i c l e s r a t h e r t h a n c o n t i n u o u s g r a i n boundary f i l m s .
T h e s e l i q u i d p h a s e s c a n a c t a s g r a i n boundary c r a c k s , w h i c h c a u s e
extensive
local
deformation i n the
grain
boundary
region.
I m p u r i t y p a r t i c l e s c o n t a i n i n g o n l y Na a n d K a r e l i q u i d down t o 260K
a c c o r d i n g t o t h e phase diagram.
The a l l o y s i n v e s t i g a t e d i n t h i s work
show a n i n c r e a s e i n t o u g h n e s s down t o a t l e a s t 200K.
This suggest
t h a t o t h e r i m p u r i t y e l e m e n t s , s u c h a s t h e Cs a n d Rb o b s e r v e d a b o v e i n
t h e i o n m i c r o p r o b e , a r e a s s o c i a t e d w i t h Na a n d K.
In the ternary
s y s t e m , Na-K-Cs,
a l i q u i d p h a s e c a n e x i s t down t o 195K a n d t h e
s o l i d u s is l o w e r e d f u r t h e r i n t h e p r e s e n c e of m e r c u r y .
I n most A1-Li
a l l o y s , a c o n t i n u o u s i n c r e a s e o f t o u g h n e s s would b e e x p e c t e d between
t h e f r e e z i n g p o i n t o f Na a n d t h e Na-K-Cs
eutectic.
T h i s would
p r o d u c e a marked s i m i l a r i t y t o t h e a c t u a l t o u g h n e s s - t e m p e r a t u r e
3,5>.
The t o u g h n e s s o f A1-Li
r e l a t i o n s h i p s o b s e r v e d <Refs.
a l l o y s i n c r e a s e s markedly a s t h e t e s t temperature is d e c r e a s e d , w h i l e
t h e t o u g h n e s s of c o n v e n t i o n a l h i g h s t r e n g t h aluminum a l l o y s d e c r e a s e s
a t low t e s t t e m p e r a t u r e s .
The r e s u l t o f t h i s i s t h a t t h e s t r e n g t h t o u g h n e s s c o m b i n a t i o n of A1-Li a l l o y s a t c r y o g e n i c t e m p e r a t u r e s i s
e q u a l t o , o r i n many c a s e s s u p e r i o r t o , t h a t o f c o n v e n t i o n a l aluminum
alloys.
T h i s a p p e a r s t o c r e a t e a problem f o r a l t e r n a t e t h e o r i e s f o r
t h e e m b r i t t l e m e n t o f A1-Li a l l o y s s u c h a s s t r a i n l o c a l i z a t i o n d u e t o
S t r a i n localization theories do not predict
t h e o r d e r e d A 1 Li phase.
a n i n c r e a s e i n toughness a t cryogenic temperatures n o r a n absence of
embrittlement a t these temperatures.
Conclusions
1. The a d d i t i o n of u p t o 4 7 6 ppm Na a n d 23 ppm K t o A1-Li a l l o y s
reduces t h e i r impact toughness and d u c t i l i t y b u t h a s l i t t l e i n f l u e n c e
on strength.
2. Na a n d K r e d u c e t o u g h n e s s a n d d u c t i l i t y by f o r m i n g d i s c r e t e
l e n t i c u l a r g r a i n b o u n d a r y p a r t i c l e s w h i c h a r e l i q u i d a t room
temperature.
These l i q u i d p h a s e s promote i n t e r g r a n u l a r f a i l u r e .
The
s o l i d i f i c a t i o n o f t h e l i q u i d p h a s e s a t t e m p e r a t u r e s down t o a b o u t
200K r e s u l t s i n a n i n c r e a s e i n t o u g h n e s s a n d d u c t i l i t y .
Acknowledgements.
The a u t h o r would l i k e t o t h a n k t h e f o l l o w i n g
p e r s o n n e l o f K a i s e r Aluminum & C h e m i c a l C o r p o r a t i o n l s C e n t e r f o r
Technology i n P l e a s a n t o n , C a l i f o r n i a ;
D.A.
Nguyen f o r o u t s t a n d i n g
t r a n s m i s s i o n m i c r o s c o p y , R.
H i n t z e f o r t h e development of improved
Wentz, R.C.
a n a l y t i c a l t e c h n i q u e s f o r a l k a l i m e t a l s a n d a l s o D.
D i c k i n s o n a n d K.S.
Dayton.
I n a d d i t i o n t h e e x p e r t i s e of C h a r l e s
E v a n s a n d Ron F l e m i n g o f C h a r l e s E v a n s a n d A s s o c i a t e s i n Redwood
C i t y , C a l i f o r n i a was i n v a l u a b l e when u s i n g t h e i o n m i c r o p r o b e .
The a u t h o r i s a c o n s u l t a n t f o r Advanced M a t e r i a l
D e v e l o p m e n t a t 20565 Verde V i s t a Lane, S a r a t o g a ,
C a l i f o r n i a 95070, USA.
( 4 0 8 ) 867-6017
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