HOME
HELP OAK RIDGE N A T I O N A L LABORATORY operated by
UNION CARBIDE CORPORATION NUCLEAR DIVISION for the
U.S. ATOMIC ENERGY COMMISSION
ORNL- TM- 2021, Vol. I
Q
W
s
iii EFFECT OF ALLOYING ADDITIONS ON CORROSION BEHAVIOR OF NICKEL
-
MOLYBDENUM ALLOYS IN FUSED FLUORIDE MIXTURES (Thesis) Jackson Harvey DeVan
b
This report i s a portion of a thesis submitted to the Graduate Council of the University of Tennessee i n partial fulfillment of the requirements for the degree of Master of Science.
LEGAL NOTICE T h i s report was prepaed a s an account of Government sponsored work.
Neither the United States,
nor the Commission, nor ony person octing on h h a l f of the Commission:
A. Makes ony warranty or representation, expressed or implied, w i t h respect t o the accuracy, completeness, or usefulness of the information contained i n t h i s report, or that the use o f any information. apparatus, method, or process disclosed i n t h i s report moy not infringe privately owned rights; or
6.
Assumes any l i a b i l i t i e s w i t h respect t o the use of, or for damages resulting from the use of
any information, opparatur, method, or process d i Tc1or.d
i n t h i s report.
A s used i n the above, "person octing on behalf of the Commission" controctor of the Commission. or employ.. or
contractor
of the Commission,
includes any employee or
of such contractor, to the extent thot such employee
or employee of such contractor prepares,
disseminates,
or
provides access to, any information pursuant t o h i s mmployment or contract w i t h the Commission, or h i s employment w i t h such contractor.
LEGAL
w ’
NOTICE-
.
____
This report was prepared a s an %(.Countof Government bponSOrpd work. Neither the United States, mor the Commi6Sion, nor my person acting on behalf of the Commission: A. Makes any warranty o r rexesentation, expressed or implied, with respect to the accuracy, completeness, o r usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process discloaed in this report may not infringe privately owned rights; or B. A88umes any liabilities with respect to the use of, o r for damages resuiting from Lhe use of any information, apparatus, method, or Process diacloRed in this report. As used in the above, “perlion acting on behalf of the Commlseian” includes .any employee o r contractor of the Cominlssion, or employee of such contractor, to the extent that such employee or contractor of ihe Commission, or employee of such contractor prepares, disseminates, or provides acce88 to, any information pursuant to his employment o r contract with the Commission, or his employment with such contractor.
ORNL-TM-2021 VOl. I
C o n t r a c t No. W-7405-eng-26
MET!;LS
AND CERAMICS DIVISION
EFFECT OF ALLOYING ADDITIONS ON CORROSION BEHAVIOR OF NICKELMOLYBDENUM ALLOYS I N FUSED FLUORIDE MIXTURES Jackson Harvey DeVan
MAY 1969
This r e p o r t i s a p o r t i o n o f a t h e s i s submitted t o t h e Graduate Council o f t h e U n i v e r s i t y o f Tennessee i n p a r t i a l f u l f i l l m e n t of t h e requirements f o r t h e degree of Master of Science.
OAK RIDGE NATIONAL LABORATORY c
Oak Ridge, Tennessee operated by UNION CARBIDE CORPORATION f o r the U.S. ATOMIC ENERGY COMMISSION
iii
CONTENTS
Abstract
..............................
............................ Review of Related Work . . . . . . . . . . . . . . . . . . . . . . . Corrosion by Fluoride Mixtures . . . . . . . . . . . . . . . . . Corrosion Reactions . . . . . . . . . . . . . . . . . . . . Introduction
................ Corrosion o f Nickel-Molybdenum Alloys . . . . . . . . . . . . . . M a t e r i a l s and Procedures . . . . . . . . . . . . . . . . . . . . . . Test M a t e r i a l s . . . . . . . . . . . . . . . . . . . . . . . . . Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . S a l t Preparation . . . . . . . . . . . . . . . . . . . . . . . . Operating Procedures . . . . . . . . . . . . . . . . . . . . . . Test Examination . . . . . . . . . . . . . . . . . . . . . . . . R e s u l t s and Discussion . . . . . . . . . . . . . . . . . . . . . . . Chromium . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion-Product Concentrations . . . . . . . . . . . . . . Metallographic Results . . . . . . . . . . . . . . . . . . . Aluminum . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion-Product Concentrations . . . . . . . . . . . . . . Metallographic R e s u l t s . . . . . . . . . . . . . . . . . . . Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion-Product Concentrations . . . . . . . . . . . . . . Metallographic R e s u l t s . . . . . . . . . . . . . . . . . . . Vanadium . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosian-Product Concentrations . . . . . . . . . . . . . . Metallographic Re s u l k s . . . . . . . . . . . . . . . . . . . Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion-Product Concentrations . . . . . . . . . . . . . . Metallographic R e s u l t s . . . . . . . . . . . . . . . . . . . Reduction of UF4 by Chromium
. rc
1
1
3
3 3
4 6
8 8 8 12
13 13
15 15 15 21
24
24 25
28 28 29 30
30 30 30
30 32
iv 1
Page
...,.......,................ Corrosion-Psoduct Concentrations . . . . . . . . . . . . . . Metallographic Results . . . . . . . . . . . . . . . . . . .
Niobium
Tungsten
............................
.............. Metallographic Results . . . . . . . . . . . . . . . . . . . Relative Thermodynamic S t a b i l i t i e s of Alloying C o n s t i t u e n t s . . General Discussion of Alloying E f f e c t s . . . . . . . . . . . . . Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion-Product Concentrations
32 32 33 34 34 36 36
38 40 42
V
EFFECT OF ALLOYING ADDITIONS ON CORROSION BEHAVIOR OF IIICKELMOLYBDENUM ALLOYS I N FUSED FLUORIDE MIXTURFS ABSTRACT
F
Fused f l u o r i d e mixtures containing WL+ have been developed a s f u e l s o l u t i o n s f o r hi'gh-temperature nuclear r e a c t o r s . To develop c o n t a i n e r m a t e r i a l s f o r such mixtures, we i n v e s t i g a t e d t h e c o r r o s i o n p r o p e r t i e s of nickel-molybdenum a l l o y s with v a r i ous s o l i d - s o l u t i o n strengthening a d d i t i o n s . These e v a l u a t i o n s u t i l i z e d thermal convection loops which c i r c u l a t e d s a l t mixt u r e s between a hot-zone temperature of 815째C and a cold-zone temperature of 650 "C. The a l l o y s s e l e c t e d f o r s t u d y contained 17 t o 20% Mo and Loops of v a r i o u s percentages of C r , A l , T i , V, Fe, Nb, and W. i n d i v i d u a l a l l o y s were exposed t o t h e s a l t mixture NaF-LiF-KF-UF4 (11.2-45.341.0-2.5 mole 8) f o r p e r i o d s of 500 and 1000 h r . Measurements of t h e c o n c e n t r a t i o n s o f c o r r o s i o n products i n a f t e r - t e s t s a l t samples i n d i c a t e d t h e c o r r o s i o n s u s c e p t i b i l i t y of a l l o y i n g a d d i t i o n s t o i n c r e a s e i n t h i s o r d e r : Fe, I%, V, C r , inJ, T i , and A l . However, metallographic examinations o f loop s u r f a c e s showed r e l a t i v e l y l i g h t a t t a c k f o r a l l a l l o y s except t h o s e containing combined a d d i t i o n s of aluminum and t i t a n i u m or aluminum and chromium. A nickel-base a l l o y containing 17%Mo, 7% C r , and 576 Fe, designated H a s t e l l o y N, w a s found t o a f f o r d t h e b e s t combinat i o n o f s t r e n g t h and c o r r o s i o n r e s i s t a n c e among t h e a l l o y compositions t e s t e d .
INTRODUCTION
Molten f l u o r i d e s of uranium, thorium, o r plutonium, i n combination with o t h e r f l u o r i d e compounds, have wide a p p l i c a b i l i t y a s f u e l s f o r t h e production of nuclear power.'
Because of t h e i r high b o i l i n g p o i n t s , t h e s e
mixtures can be contained a t low p r e s s u r e s even a t extremely high o p e r a t i n g temperatures. c
Their chemical and p h y s i c a l p r o p e r t i e s impart a d d i -
t i o n a l advantages such a s e x c e l l e n t s t a b i l i t y under i r r a d i a t i o n and l a r g e
'R. C . B r i a n t and A . M. Weinberg, "Molten F l u o r i d e s a s Power Reactor Fuels," Nucl. S e i . Eng. 2, 797-803 (1957).
-
s o l u b i l i t y ranges f o r both uranium and thorium.
These f a c t o r s have
prompted design s t u d i e s of molten f l u o r i d e f u e l systems i n conjunction with thorium-uranium thermal b r e e d e r s , uranium-plutonium c o n v e r t e r s , and uranium burners. The development o f r e a c t o r s which i n c o r p o r a t e a c i r c u l a t i n g f l u o r i d e s a l t i s p r e d i c a t e d on t h e a v a i l a b i l i t y of a c o n s t r u c t i o n m a t e r i a l which w i l l c o n t a i n t h e s a l t over long time p e r i o d s and a l s o a f f o r d u s e f u l
structural properties.
The c o n t a i n e r m a t e r i a l must a l s o be r e s i s t a n t t o
a i r o x i d a t i o n , be e a s i l y formed and welded i n t o r e l a t i v e l y complicated shapes, and be m e t a l l u r g i c a l l y s t a b l e over a wide temperature range. I n o r d e r t o provide a m a t e r i a l for i n i t i a l r e a c t o r s t u d i e s , s e v e r a l commercially a v a i l a b l e high-temperature a l l o y systems were evaluated with r e s p e c t t o t h e above r e q ~ r e m e n t s . A s a r e s u l t o f t h e s e s t u d i e s , Inconel,
a nickel-base a l l o y c o n t a i n i n g 15 w t ‘$ C r and 7’wt ’$ Fe, w a s found t o a f f o r d t h e b e s t combination o f d e s i r e d p r o p e r t i e s and w a s u t i l i z e d for t h e c o n s t r u c t i o n of t h e A i r c r a f t Reactor Experiment. sion tests,’’“
’
Extensive c o r r o -
as w e l l as p o s t t e s t examinations of t h e ARE,5 confirmed
t h e s u i t a b i l i t y of I n c o n e l a s a c o n t a i n e r m a t e r i a l f o r r e l a t i v e l y s h o r t term f l u o r i d e s a l t exposures.
Corrosion r a t e s encountered w i t h t h i s
a l l o y a t temperatures above 7OO0C, however, were excessive f o r long-term use w i t h most f l u o r i d e f u e l systems.
U t i l i z i n g experience gained i n c o r r o s i o n t e s t i n g o f commercial a l l o y s , we i n i t i a t e d an a l l o y development program t o provide a n advanced c o n t a i n e r m a t e r i a l for f l u o r i d e f u e l r e a c t o r systems.
The r e f e r e n c e
a l l o y system w a s composed o f n i c k e l w i t h a primary s t r e n g t h e n i n g a d d i t i o n of 15-20’$ Mo.
This composition afforded e x c e p t i o n a l r e s i s t a n c e t o f l u o -
r i d e a t t a c k b u t lacked s u f f i c i e n t mechanical s t r e n g t h and o x i d a t i o n
e.
A i r c r a f t Reactor Experiment *W. D. Manly e t A m e c t s . ORNL-2349719575.
- Metallurgical
‘ G . M. Adamson, R. S. Crouse, and W. D . Manly, I n t e r i m Report on Corrosion b y Zirconium-Base F l u o r i de s , ORNL-2338 ( 1961)
.
5W. B. C o t t r e l l et a -l . , Disassembly and P o s t o p e r a t i v e Examination of t h e A i r c r a f t Reactor Experiment, ORNL-1868 (1958).
3 r e s i s t a n c e a t d e s i r e d o p e r a t i n g temperatures.
To augment t h e s e l a t t e r
p r o p e r t i e s , a d d i t i o n s of v a r i o u s s o l i d - s o l u t i o n a l l o y i n g agents were evaluated, among them C r y Al, T i , Nb, Fe, V, and W.
An optimum a l l o y
composition was s e l e c t e d on t h e b a s i s of p a r a l l e l i n v e s t i g a t i o n s of t h e mechanical and c o r r o s i o n p r o p e r t i e s which were imparted b y each of t h e s e additions.
The composition b e s t s u i t e d t o r e a c t o r use was determined t o
be w i t h i n t h e range 15-17 w t
0.044.08 w t
%
C, balance N i .
$ Mo, 6-8
wt
$I C r , 4-6
wt
$ Fe,
Subsequent s t u d i e s of t h e a l l o y , d e s i g -
nated H a s t e l l o y N, have shown it t o be extremely w e l l s u i t e d f o r a p p l i c a t i o n s demanding long-term c o m p a t i b i l i t y with f l u o r i d e s a l t s i n t h e temperature range 650-800"C. The p r e s e n t r e s e a r c h w a s concerned with t h e c o r r o s i o n e f f e c t s r e s u l t i n g from a d d i t i o n s of a l l o y i n g elements t o t h e nickel-molybdenum system and an a n a l y s i s of t h e thermodynamics of t h e c o r r o s i o n process a s i n d i c a t e d by t h e s e a l l o y i n g e f f e c t s .
RFVIEW OF R F U I E D WORK Corrosion by Fluoride Mixtures Corrosion Reactions The c o r r o s i o n of nickel-base a l l o y s , containing i r o n and chromium, by f l u o r i d e f u e l mixtures has been found t o r e s u l t from a combination
of t h e following types of o x i d a t i o n r e a c t i o n s :
1. Reactions7 involving i m p u r i t i e s i n t h e s a l t
2HF + C r = CrF2 + NiF2 + Cr
-
=
,
-,
CrF2 + N i
FeF2 + C r = CrF2
--
H2
+Fe
.
6W. D. Manly e t a l . , " M e t a l l u r g i c a l Problems i n Molten Fluoride Systems, I' Progr. Nucl. Energy, Ser. I V 2, 164 (1960). V
-
7 S o l i d - s o l u t i o n a l l o y i n g elements a r e underlined.
4 2.
Reactions involving i m p u r i t i e s i n o r on t h e metal, f o r example 2Ni0 + ZrF4
=
ZrO2 + 2NiF2
(4)
followed by r e a c t i o n ( 2 ) . 3.
Reactions involving components i n t h e s a l t 2UF4
+C r = CrF2 + 2UF3
,
(5)
The e x t e n t of t h e f i r s t f o u r of t h e s e r e a c t i o n s , which proceed s t r o n g l y t o t h e r i g h t and t o completion r a p i d l y , can be reduced by maintaining low impurity c o n c e n t r a t i o n s Ln t h e s a l t and on t h e s u r f a c e of t h e metal. Reactions ( 5 ) and (6), on t h e o t h e r hand, a r e indigenous t o f l u o r i d e systems which d e r i v e t h e i r u s e f u l n e s s through t h e containment o f UF4. While t h e r o l e of chromium has been i n v e s t i g a t e d e x t e n s i v e l y i n connect i o n with t h e s e r e a c t i o n s , 8 c o n s i d e r a b l y l e s s information i s a v a i l a b l e regarding t h e thermodynamics of t h e s e r e a c t i o n s f o r t h e o t h e r a l l o y i n g elements which were o f i n t e r e s t i n t h e p r e s e n t study. Reduction of UF4 by Chromium The r e a c t i o n of UF4 with chromium i s found t o be s t r o n g l y i n f l u e n c e d by t h e r e a c t i o n medium employed.'
I n melts composed p r i n c i p a l l y of
NaF-ZrF4 o r NaF-BeF2, t h e r e a c t i o n produces o n l y d i v a l e n t chromium, t h a t i s ,
However, i n t h e case of NaF-KF-LiF-UF4 mixtures used f o r t h i s i n v e s t i g a t i o n , t h e r e a c t i o n between chromium and UF4 produces b o t h d i v a l e n t and
8J. D. Redman, ANI? Quart. Progr. Rept. Dec. 31, 195'7, O m - 2 4 4 0 , pp. 78-82.
5 t r i v a l e n t chromium.
A t e q u i l i b r i u m , approximately 80% of t h e t o t a l
chromium i o n s i n t h e mixtures a r e observed t o be t r i v a l e n t , g i v i n g t h e net r e a c t ion
2.8UT4
+
Cr =
0.2CrF2 + O.8CrF3
+ 2.8vF3
,
The e q u i l i b r i u m c o n s t a n t for t h i s r e a c t i o n i s given by
where
CY
r e p r e s e n t s thermodynamic a c t i v i t y .
Because of t h e r e l a t i v e l y
small c o n c e n t r a t i o n s of CrF2 and UF3 which a r e a t t a i n e d i n t h e s a l t solut i o n s a t equilibrium, t h e a c t i v i t i e s of each of t h e s e components can be c l o s e l y approximated by t h e i r mole f r a c t i o n s , i n accordance with Henry's law.
Thus, for a s a l t system of f i x e d UF4 c o n c e n t r a t i o n , assuming t h e
r e f e r e n c e s t a t e s f o r s a l t components t o be t h e i n f i n i t e l y d i l u t e s o l u t i o n ,
For a system i n i t i a l l y containing no UF3, CrF2, or CrF3, it follows t h a t
.
I n such systems where t h e change i n = 1/14Nm NCrF2 = 1/4NCrF1 3 c o n c e n t r a t i o n i s small, Eq. ( 9 ) reduces t o
where
0
UF4
6
The c o n s t a n t LiF-KF-NaF-UF4
% has
been experimentally determined f o r t h e mixture
( 11.2-41.045.3-2.5
mole $) b y e q u i l i b r a t i n g it w i t h pure
chromium (CY" = 1) a t 600 and 800째C ( r e f . 8 ) . Under t h e s e c o n d i t i o n s , Cr t h e constent i s equivalent i n value t o t h e mole f r a c t i o n of chromium ions i n t h e s a l t a t equilibrium.
The measured v a l u e s of
5 are
listed in
Table 1. a Table 1. Equilibrium Concentrations of Chromium F l u o r i d e s f o r t h e Reaction of Pure Chromium w i t h UF4
Concentration o f Chromium I o n s i n NaF-LiF -KF -UF4 (11.241.045.3-2.5 mole
E q u il i b r a t i o n Temperatwre
(
4)
"a
ppm
mole f r a c t i o n
600
1100
1.0 x
800
2600
2.4 x
a
(s-)
J. D. Redman, ANP Q u a r t . Progr. Rept. Dee. 31, 1957, pp. 78-82.
o m -2440,
Eecause t h e chromium-UF4 r e a c t i o n i s temperature dependent, chemic a l e q u i l i b r i u m between t h e s e two components i s precluded i n systems o f uniform a l l o y composition where t h e c i r c u l a t i n g s a l t c o n t i n u a l l y e x p e r i ences a temperature change.
I n such systems chromium t e n d s t o be con-
t i n u a l l y removed from h o t t e r p o r t i o n s and d e p o s i t e d i n c o o l e r p o r t i o n s . A t h e o r y r e l a t i n g t h e r a t e o f t h i s movement t o t h e o p e r a t i n g parameters of t h e c o n t a i n e r system has been formulated by Evans.
9
Corrosion o f Nickel-Molybdenum Alloys Because of t h e o x i d a t i o n of chromium by f u e l - b e a r i n g f l u o r i d e s a l t s , a l l o y s employing l a r g e percentages of t h i s element were not s a t i s f a c t o r y 'R. E. Evans, ANP Quart. Progr. Rept. Dec. 31, 1957, ORNL-2440, pp . 1-04-113.
7 a s c o n t a i n e r m a t e r i a l s except a t temperatures where d i f f u s i o n r a t e s i n t h e a l l o y s were r e l a t i v e l y low.
Accordingly, e v a l u a t i o n s were made of
s e v e r a l commercial a l l o y s i n which chromium was not employed as a major alloying addition.
Based on t h e s e t e s t s , a l l o y s of n i c k e l and molybdenum
appeared t o o f f e r t h e most promising c o n t a i n e r system f o r achieving r e l a t i v e l y high r e a c t o r o p e r a t i n g temperatures.
Unfortunately, commercially
a v a i l a b l e nickel-molybdenum a l l o y s which e x h i b i t e d e x c e l l e n t c o r r o s i o n p r o p e r t i e s were not well s u i t e d t o contemplated r e a c t o r systems because
o f t h r e e adverse c h a r a c t e r i s t i c s :
(1) poor f a b r i c a b i l i t y ; ( 2 ) a tendency
t o age-harden and e m b r i t t l e a t s e r v i c e temperatures between 650 and
815째C ( r e f . 10); and ( 3 ) poor r e s i s t a n c e t o o x i d a t i o n b y a i r a t e l e v a t e d temperatures.
The s c a l e formed on exposure of t h e s e a l l o y s t o high-
temperature a i r w a s of t h e type NiMoO4, which upon thermal c y c l i n g between 760 and 350째C underwent a phase t r a n s f o r m a t i o n and s p a l l e d as a consequence of a r e s u l t a n t volume change. 11 By means of an a l l o y development program, however, it was considered p l a u s i b l e t o e l i m i n a t e t h e u n d e s i r a b l e f e a t u r e s o f t h e commercial m a t e r i a l s while r e t a i n i n g t h e i r i n h e r e n t c o r r o s i o n r e s i s t a n c e .
The i n i t i a l objec-
t i v e of t h i s program was t o provide an a l l o y which d i d not e m b r i t t l e under t h e thermal t r e a t m e n t s imposed by r e a c t o r o p e r a t i o n .
By experimenting
with v a r i o u s compositions of b i n a r y nickel-molybdenum a l l o y s , it was determined t h a t lowering t h e molybdenum c o n c e n t r a t i o n t o a l e v e l of 1 5 1 7 % served t o avoid d e t r i m e n t a l age-hardening e f f e c t s i n t h e a l l o y system.'* Although such an a l l o y system was s a t i s f a c t o r y from t h e standpoint of c o r r o s i o n r e s i s t a n c e , it w a s n e c e s s a r y t o augment t h e o x i d a t i o n and s t r e n g t h c h a r a c t e r i s t i c s of t h e system through a d d i t i o n a l s o l i d - s o l u t i o n alloying agents.
The c o r r o s i o n e f f e c t s which r e s u l t e d from t h e s e a d d i -
t i o n s were t h e s u b j e c t s of t h e p r e s e n t study.
'OR. E. C l a w i n g , P. P a t r i a r c a , and W. D. Manly, Aging C h a r a c t e r i s t i c s of H a s t e l l o y B, ORNL-2314 (1957).
H. Inouye, p r i v a t e communication. f
1 2 D . W. S t o f f e l and E . E . Stansbury, "A Metallographic and X-ray Study of N i Alloys of 20-30 Per Cent Mo," Report No. 1 under Subcontract No. 582 under Contract No. W-7405-eng-26, Knoxville, Tenn., Dept. of Chem. Eng. of t h e Univ. of Tenn. (1955).
8 Y
MATERIALS AND PROCEDURFS
Test M a t e r i a l s The nickel-molybdenum a l l o y compositions s e l e c t e d f o r study were supplied b y t h e Metals and Ceramics Division a t ORNL and, under subcont r a c t agreements, by B a t t e l l e Memorial I n s t i t u t e and Superior Tube Company.
Alloys furnished by ORNL were induction-melted under vacuum,
while those furnished by subcontractors were induction-melted i n a i r using a p r o t e c t i v e s l a g .
Each a l l o y h e a t , which ranged i n weight from
12 t o 100 l b , was e i t h e r forged o r extruded i n t o a 3-in.-diam tube blank and was subsequently drawn i n t o 1/2-in.-OD Superior Tube Company.
seamless tubing b y t h e
The cold-drawn tubing w a s annealed a t 1120째C.
Table 2 l i s t s t h e experimental a l l o y compositions used f o r t h i s c o r r o s i o n study. Test Equipment The method s e l e c t e d t o e v a l u a t e t h e c o r r o s i o n p r o p e r t i e s of t h e s e a l l o y s was based on t h e following c o n s i d e r a t i o n s :
1. The method n e c e s s a r i l y had t o be t a i l o r e d t o t h e use o f r e l a t i v e l y small q u a n t i t i e s of m a t e r i a l , s i n c e it was p r a c t i c a l t o produce o n l y small h e a t s o f t h e many a l l o y s d e s i r e d f o r study. 2.
Tubing was considered t o be a h i g h l y d e s i r a b l e form i n which t o
t e s t t h e m a t e r i a l , s i n c e production of t h e m a t e r i a l i n t h i s form was c a r r i e d out a s an adjunct t o e v a l u a t i n g t h e f a b r i c a b i l i t y of each a l l o y .
3.
Previous demonstrations o f t h e e f f e c t s of temperature g r a d i e n t
i n t h e s a l t and t h e s a l t flow r a t e on t h e c o r r o s i o n behavior o f c o n t a i n e r m a t e r i a l s i n f l u o r i d e s made it mandatory t h a t c o r r o s i o n t e s t s be conducted under dynamic c o n d i t i o n s , t h a t i s , c o n d i t i o n s which provided f o r t h e continuous flow of s a l t through a temperature g r a d i e n t . The thermal convection loop, which had been used e x t e n s i v e l y f o r Inconel c o r r o s i o n s t u d i e s and had been developed i n t o an extremely s t r a i g h t f o r w a r d and r e l i a b l e t e s t device, was judged t o be t h e b e s t form of experimental device f o r meeting t h e s e requirements.
This device con-
s i s t s o f a closed loop o f tubing, bent t o resemble t h e o u t l i n e of a harp,
W
Table
Heat Number"
2.
Compositions
Composition, Ni
MO
Cr
80.12 78.55 73.65 78.50 77.0 73.30
16.93 16.65 16.37 15.11 20.39 20.34
2.83 4.62 9.21 6.40 2.62 6.34
Fe
of Experimental
82.10 80.30 81.10 81.10 79.80 80.00 79.00 79.20 78.90 82.00 86.58
15.93 17.80 16.8 16.60 16.53 16.80 16.90 16.60 16.40 17.42 11.23
Ti
Al
Nb
W
79.93 79.53 77.74 77.65 74.07 76.13 76.30 69.19 66.95 71.50 74.42 80.86
a0R denotes Memorial Institute.
17.56 16.50 16.00 15.90 15.15 20.50 20.50 21.10 21.60 15.06 15.20 16.70 heats
V
2.09 2.23 3.68 3.22 4.10 4.18 4.71 0.53 2.19
3.65 5.69 5.01
5.07
0.95 2.45 1.12 1.16 0. 70
1.25 2.44 7.58 7.82 3.84
furnished
1.31 C!. 53 3.513 0 . 57 by the Metals
4.90 5.23
and Ceramics
MO
85.50 83.60 78.30 82.70 83.30 78.90
11.10 10.80 10.60 9.72 13.50 13.40
85.60 85.90 88.10 86.40 85.10 86.70 87.10 84.10 85.50 87.40 88.16
10.15 11.60 11.20 10.80 10.80 11.10 11.40 10.80 10.90 11.40 6.99
84.48 82.11 81.01 80.27 77.26 83.61 82.60 75.17 71.72 79.O4 83.14 85.22
11.35 10.42 10.20 l,'] . Cl5 9.66 13.77 13.20 14.00 14.2O 10.20 10.36 10.76
Cl-
Fe
Ti
$ Al
Nb
W
V
3.41 5 5.5 11:04 7.60 3.20 7.71 4.26 2.47 0.72 2.73 4.12 2.20
Division;
a
1.44 5.11 3.62 1.22 4.85
III
0.60 1.32 1.31 2.16 2.32 4.17 4.57
Ni
at.
II
1.88
1.56 1.52 1.49
Studies
I
..89
Series OR 30-13 -14 -16 -22 -33 B2897 B2898 B3276 B3277 S T23011 S T23013 S T23014
Corrosion
Composition,
Series OR 30-7 -8 -9 -10 -11 -12 -19 -20 -21 S T23012 OR 1491
Used for
wt $
Series OR 30-l -2 -4 -6 37A-1 43A-3
Alloys
4.30 6.64 5.90
2.02 1.92 1.90 5.56
2.18 5.51 2.54 2.61 1.59
1.68 3.24 9.32 9.47 4.79
S T by Superior
2.71 Tube Company;
3.06 1.27 1.40 1.30
0.39 0.92 0.90 1.48 1.57 2.91 3.23
1.72 1.85
and B by Battelle
10 W
two l e g s of which a r e heated and two of which a r e exposed t o t h e cooling e f f e c t s of ambient a i r .
Flow r e s u l t s from t h e d i f f e r e n c e i n d e n s i t y of
t h e s a l t i n t h e hot and cold p o r t i o n s of t h e loop. The c o n f i g u r a t i o n and dimensions of t h e loop d e s i g n a r e presented i n Fig. 1. A l l loops were f a b r i c a t e d of seamless t u b i n g having an o u t s i d e diameter o f 0.500 i n . and a w a l l t h i c k n e s s of 0.035 i n .
The tubing
w a s assembled b y t h e Heliarc welding technique using an i n e r t g a s backing. During o p e r a t i o n t h e l o o p s were heated b y a s e r i e s o f c l a m s h e l l r e s i s t a n c e h e a t i n g elements l o c a t e d as shown i n Fig. 1. To f i l l t h e loop required t h a t we apply h e a t t o b o t h t h e cold- and hot-leg s e c t i o n s . A u x i l i a r y heating f o r t h i s purpose was provided b y passage of e l e c t r i c c u r r e n t d i r e c t l y through t h e tube w a l l .
When t h e loop w a s f i l l e d , a s
determined b y an e l e c t r i c a l s h o r t i n g probe near t h e t o p of t h e loop, t h e a u x i l i a r y h e a t source was turned off a d t h e h e a t i n g elements were turned on.
I n s u l a t i o n was t h e n removed from t h e cold l e g t o whatever amount
w a s r e q u i r e d t o e s t a b l i s h a predetermined temperature g r a d i e n t .
Loop temperatitre s were measured w i t h Chromel-P-Alumel l o c a t e d a s shown i n Fig. 1.
thermocouples
The thermocouple j u n c t i o n s , i n t h e form of
s m a l l beads, were welded t o t h e o u t s i d e tube w a l l w i t h a condenser d i s -
charge welder and covered b y a l a y e r of q u a r t z t a p e , which i n t u r n w a s covered w i t h s t a i n l e s s s t e e l shim stock.
A l l t e s t s were operated so as
t o achieve a maximum mixed-mean s a l t temperature of 815째C and a minimum s a l t temperature of 65C"C.
The maximum s a l t - m e t a l i n t e r f a c e temperature,
which w a s a t t a i n e d near t h e t o p of t h e v e r t i c a l heated s e c t i o n , exceeded t h e maximum b u l k s a l t temperature b y approximately 95째C ( r e f . 1 3 ) .
l'he
s a l t - f l o w r a t e under t h e s e temperature c o n d i t i o n s w a s e s t a b l i s h e d from h e a t balance c a l c u l a t i o n s t o be i n t h e range of 5 t o 7 ft/min. 13Measurements of t h e maximum i n s i d e wall temperature could not p r a c t i c a l l y be made i n each loop t e s t ; however, values of t h i s temperat u r e were recorded by means of h e a t balance c a l c u l a t i o n s and imbedded thermocouples using a s p e c i a l l y instrumented t e s t loop which e x a c t l y simul a t e d t h e geometry and temperature p r o f i l e used i n t h e c o r r o s i o n experiment.
11 V ORNL-LA-DWG
6-in. C L A M SHELL HEATERS
750/
27228R
\
7 1
CONTROL 8 NO. 2 T.C. NO. 5'
-t-
METALLOGRAPHIC SAMPLES THERMOCOUPLE LOCATIONS
4-
T.C. NO. 6 7
c
Fig. 1. Schematic Diagram of Thermal Convection Loop Used for Evaluations of Experimental Nickel-Molybdenum Alloys. The locations of thermocouples and test samples are shown.
12 Y
S a l t Preparation
The f u e l mixture used i n t h e s e s t u d i e s was of t h e composition shown
i n Table 3.
We s e l e c t e d t h e LiF-KF-NaF-UF4 composition ( S a l t 107) on
t h e b a s i s t h a t t h e o x i d a t i o n of c o n t a i n e r c o n s t i t u e n t s by a given conc e n t r a t i o n o f UF4 tended t o be g r e a t e r f o r t h i s mixture t h a n f o r o t h e r mixtures of p r a c t i c a l importance.
Thus, achievement of s a t i s f a c t o r y
c o m p a t i b i l i t y with t h i s mixture i n e f f e c t provided a c o n t a i n e r m a t e r i a l
of u l t i m a t e v e r s a t i l i t y with r e s p e c t t o a l l f u e l mixtures. Table 3. Composition of Fluoride Mixture Used t o Evaluate Experimental Nickel-Molybdenum Alloys S a l t Number: 137 Liquidcs Temperature:
490째C
Component
&Tole %
NaF
11.2
LiF
45.3
24.4
KF
41. C
49.4
m4
2.5
16.3
%
Weight 9.79
The f l u o r i d e mixtures were prepared from reagent-grade m a t e r i a l s and were p u r i f i e d by t h e Fluoride Processing Group of t h e Reactor Chemistry Division.
I n general, t h e procedure f o r p u r i f i c a t i o n was a s follows:
(1)t h e dry i n g r e d i e n t s , except f o r U F 4 , were mixed, evacuated s e v e r a l times f o r moisture removal, and then melted under an atmosphere of helium;
( 2 ) t h e molten mixture was held a t 815OC and t r e a t e d with hydrogen f o r 4 h r t o pmge h y d r o f l u o r i c a c i d from t h e mixture; ( 3 ) t h e mixture was cooled t:, 205째C under a helium atmosphere and UF4 was admitted.
Upon t h e a d d i t i o n
of t h e UF4, t h e mixture was remelted, heated t o 815"C, and then t r e a t e d again with hydrogen t o purge t h e excess h y d r o f l u o r i c a c i d . A l l mixtures were prepared i n 303-lb q u a n t i t i e s and apportioned i n t o
50-lb c o n t a i n e r s , a f t e r which samples were submitted for a n a l y s i s of N i , Fe, and C r .
It was required t h a t each of t h e s e elements be p r e s e n t
I
i n amounts l e s s t h a n 500 ppm a s determined from i n d i v i d u a l b a t c h analyses. A second b e f o r e - t e s t a n a l y s i s of each s a l t mixture w a s obtained from a
sample of t h e s a l t t a k e n as it was being admitted t o t h e t e s t loop. Operating Procedures Each loop w a s thoroughly degreased with acetone and checked f o r l e a k s using a helium mass spectrometer.
A f t e r thermocouples and h e a t e r s
were assembled and i n s u l a t i o n was a p p l i e d , t h e loop was placed i n a t e s t stand, a s shown i n Fig. 2. The s a l t charging pot was connected t o t h e loop with n i c k e l or Inconel tubing, and both t h e loop and t h e charging pot were heated t o 650째C under a dynamic vacuum of l e s s t h a n 50 p Hg.
Helium p r e s s u r e was
t h e n a p p l i e d t o t h e charging pot i n o r d e r t o f o r c e t h e s a l t mixture from t h e pot t o t h e loop.
A f t e r f i l l i n g , s a l t was allowed t o stand i n t h e
loop a t 650째C f o r approximately 2 h r , so t h a t oxides and o t h e r impuri-
t i e s would be d i s s o l v e d from t h e c o n t a i n e r s u r f a c e i n t o t h e s a l t mixture. This mixture was t h e n removed, and a f r e s h s a l t mixture was admitted from t h e f l u o r i d e charging pot.
A helium cover g a s under s l i g h t p o s i t i v e
p r e s s u r e (approx 5 p s i g ) was maintained over t h e s a l t mixture during a l l p e r i o d s of t e s t i n g . A t t h e end of t e s t , power t o t h e loop was c u t o f f and i n s u l a t i o n
was s t r i p p e d f r o m t h e loop so as to f r e e z e t h e s a l t mixture a s r a p i d l y as possible.
Te st Examination Each loop was sectioned with a t u b i n g c u t t e r i n t o approximately 6-in.
lengths.
Five 2-in.
s e c t i o n s were t h e n removed from t h e loop p o s i -
t i o n s i n d i c a t e d i n Fig. 1 f o r metallographic examination.
Two of t h e
remaining 6-in. s e c t i o n s , one from t h e h o t t e s t s e c t i o n of t h e loop (specimen H) and one from t h e c o l d e s t s e c t i o n (specimen C ) , were obtained f o r s a l t chemistry s t u d i e s , and t h e remaining loop segments were held i n s t o r a g e u n t i l a l l examinations of t h e loop were completed. S a l t removal was accomplished by h e a t i n g each s e c t i o n i n a small t u b e furnace a t 600째C i n helium.
The s a l t was c o l l e c t e d i n a g r a p h i t e
ig. 2.
-_
Photograph o
ermal Convection Lo
15 c r u c i b l e l o c a t e d below t h e furnace windings.
The f i v e 2-in.
s e c t i o n s of
tubing were examined m e t a l l o g r a p h i c a l l y , and t h e s a l t samples were submitted i n d i v i d u a l l y f o r petrographic and chemical analyses.
If layers
of c o r r o s i o n products were discovered on t h e tube w a l l , samples of t h e tubing and s a l t contained i n t h a t s e c t i o n were a l s o submitted f o r x-ray d i f f r a c t i o n examination.
RESULTS AND DISCUSSION Alloying e f f e c t s were evaluated i n terms of both t h e c o r r o s i o n products e n t e r i n g t h e s a l t mixtures and t h e metallographic appearance of the alloy a f t e r t e s t .
Results have been grouped i n t h i s s e c t i o n
according t o t h e a l l o y i n g element s t u d i e d . chromium Corrosion-Product Concentrations E f f e c t s of chromium a d d i t i o n s were examined i n s i x t e r n a r y a l l o y s with chromium c o n t e n t s of 3.2 t o 11.0 a t . $.
One loop of each of t h e s e
compositions w a s operated with S a l t 107 f o r 500 h r under t h e t e s t condit i o n s described above.
The compositions i n v e s t i g a t e d and t h e a t t e n d a n t
c o n c e n t r a t i o n s of chromium i o n s i n s a l t samples taken a t t h e conclusion of t h e s e t e s t s a r e shown i n Table 4.
The e x t e n t of r e a c t i o n between
chromium and f l u o r i d e c o n s t i t u e n t s , a s i n d i c a t e d by t h e chromium ion conc e n t r a t i o n s , increased w i t h t h e amount of chromium i n t h e a l l o y .
This
i n c r e a s e i s i l l u s t r a t e d g r a p h i c a l l y i n Fig. 3, where t h e d a t a a r e compared with data f o r Inconel14 and f o r pure chromium.15
It may be noted
t h a t t h e chromium c o n c e n t r a t i o n s of t h e s a l t s were l e s s t h a n t h o s e for Inconel loops operated under i d e n t i c a l temperature c o n d i t i o n s .
A hori-
z o n t a l l i n e , which r e p r e s e n t s t h e chromium i o n c o n c e n t r a t i o n a t 1 4 G . M. Adamson, R. S. Crouse, and W. D. Manly, I n t e r i m Report on Corrosion b y Alkali-Metal F l u o r i d e s : Work t o May 1, 1953, ORNL-2337 (1959).
"J. D. Redman, A pp . 7842.
5 ORNL-2440,
16 Table 4.
W
Corrosion-Product Concentrations of S a l t s Tested w i t h Nickel-Molybdenum-Chromium Alloys
Alloy Composition Heat Number
(at.
Test Duration
$1
Other Components
Cr
Chromium Concentration i n S a l t Samples" (mole $1
(hr)
Sample H
Sample C
Other
OR 37A-1 OR 30-1 OR 30-2
3.20 13.5 Mo, b a l N i 3.41 11.1Mo, b a l N i
520
3.3194
0.0180
0.0213
500
3.0222
0.0365
0.0291
5.55
10.8 Mo, b a l N i
5C0
3.3375
0.0352
0.0376
OR 30-2
5.55
10.8 Mo, b a l N i
1300
0.0509
0.0509
0.0543
OR 30-6
7.60
500
0.0606
0.0606
0.0566
500
0.0453
0.0476
0.0425
520
0.0819
0.0814
0.0699
9.72 Mo, b a l N i
OR 43A-3 7.71 13.4 Mo, b a l N i OR 30-4 11.04 10.6 Mo, b a l N i a
Sample d e s i g n a t i o n s "H" and "C" a r e discussed on page 13; "other" d e s i g n a t e s s a l t samples obtained f r o m metallographic specimens. equilibrium w i t h pure chromium a t GOO"C, i s seen i n Fig. 3 t o be above t h e measured chromium i o n concentrations for a l l a l l o y s t e s t e d .
Thus,
t h e observed concentrations were l e s s t h a n t h o s e required f o r t h e format i o n of pure chromium c r y s t a l s i n t h e c o l d e s t p o r t i o n of t h e loops (approx 650 " C )
.
A s discussed previously, t h e concentration o f chromium i o n s under t h e c o n d i t i o n s of t h e s e t e s t s should be governed by t h e r e l a t i o n rEq.
(1111
where NCr ions i s t h e mole f r a c t i o n of chromium i o n s i n S a l t 107 a t If we assume Cr' t h e r e s u 1 G n t chromium ion
e q u i l i b r i u m w i t h an a l l o y o f given chromium a c t i v i t y , t h a t NCr g i v e s an approximate measure of
aC r '
Q
c o n c e n G a t i o n s for t h e s e a l l o y s should l i e w i t h i n a r e g i o n which i s bounded above b y t h e f u n c t i o n determined a t a temperature e q u i v a l e n t t o t h e maximum loop temperature and below by t h e f u n c t i o n determined a t t h e minimum loop temperature.
Bounds using experimental v a l u e s of K2
W
17 ORNL-LR-DWG
46946
3000
200 2000
450
4600 c
5 n =0 G
E
(200
400 I
1000
I
l
I
l
0
I
x
Z W V
5
80 800
E
V
z 0
55n
I V
s-" -
400p-
60
600
~-~ ~-
I
i
j
/ I /
200
40
.
RANGE OF CHEMISTRY SAMPLES H AND C - 500 hr TESTS AVERAGE CONCENTRATIONS I N METALLOGRAPHIC SAMPLES -500 hr TESTS
x ,
RANGE OF CHEMISTRY SAMPLES H AND C -io00 hr TESTS AVERAGE CONCENTRATIONS I N METALLOGRAPHIC SAMPLES - 1000 hr TESTS
I
- 20 -
I 0.03
0.04
0.06
0.2 ATOM FRACTION OF CHROMIUM I N ALLOY
0.08 0.10
0.4
0.6
0.8
4.0
F i g . 3. Concentration of Chromium Ions i n S a l t 107 a s a Function of Chromium Content i n Nickel-Molybdenum-Chromium Alloys. measured a t 800 and 600 "C (Table 1), which reasonably approximate t h e maximum and minimum loop temperatures, a r e p l o t t e d i n Fig. 3 and a r e seen t o include o n l y two of t h e observed loop c o n c e n t r a t i o n s , both c o r r e sponding t o chromium compositions g r e a t e r t h a n 7 a t .
%. However,
except
for t h e a l l o y w i t h l e a s t chromium c o n t e n t , a l l c o n c e n t r a t i o n s l i e r e l a t i v e l y c l o s e t o t h e lower bound and roughly approximate t h e slope of t h i s bound. The d e v i a t i o n o f measured corrosion-product c o n c e n t r a t i o n s i n t h e s e t e s t s from t h e p r e d i c t e d c o n c e n t r a t i o n ranges may have r e s u l t e d p r i m a r i l y equals Cy However, assuming from inaccuracy i n t h e assumption t h a t N Cr Cr' t o be a c c u r a t e l y known, t h e c o r r o s i o K p r o d u c t c o n c e n t r a t i o n s i n t h e s e cy Cr t z t s would n e v e r t h e l e s s have been lower than t h o s e p r e d i c t e d , s i n c e corr o s i v e a t t a c k would n e c e s s a r i l y reduce t h e chromium content and hence t h e
18 chromium a c t i v i t y a t t h e s u r f a c e o f t h e a l l o y s r e l a t i v e t o t h e o r i g i n a l chromium a c t i v i t y .
We a l s o examined t h e p o s s i b i l i t y t h a t t h e t e s t times
were not s u f f i c i e n t l y long f o r t h e chromium c o n c e n t r a t i o n of t h e s a l t t o have completely a t t a i n e d t h e maximum or s t e a d y - s t a t e l e v e l .
To e v a l u a t e
t h i s l a t t e r p o i n t , s u f f i c i e n t m a t e r i a l of one of t h e a l l o y compositions, h e a t OR 30-2, was obtained t o permit t h e o p e r a t i o n o f a 1000-hr t e s t . R e s u l t s of t h i s t e s t , which are shown i n Table 4 and F i g . 3, i n d i c a t e d t h a t only a small i n c r e a s e i n chromium c o n c e n t r a t i o n occurred between t h e
500- and 1000-hr i n t e r v a l s .
It was concluded, t h e r e f o r e , t h a t t h e 500-hr
t e s t provided a reasonably c l o s e e s t i m a t e of t h e l i m i t i n g c o r r o s i o n product c o n c e n t r a t i o n s a s s o c i a t e d with t h e temperature c o n d i t i o n s of t h e s e experiments. A d d i t i o n a l data on t h e e f f e c t s of chromium i n nickel-molybdenum a l l o y s
were afforded by t e s t s of f i v e a l l o y s which contained chromium i n combinat i o n w i t h one o r more o t h e r alloying e l e m e n t s , as shown i n Table 5.
Not-
withstanding t h e a d d i t i o n a l a l l o y i n g agen+,s, t h e c o n c e n t r a t i o n s of chromium-containing c o r r o s i o n prodncts following 500-hr t e s t s o f t h e s e a l l o y s i n S a l t 1C7, as shown i n Table 5: were comparable t o t h e concent r a t i o n s a s s o c i a t e d with t h e simple t e r n a r y chromium-containing a l l o y s . The corrosion-product c o n c e n t r a t i o n s f o r t h e a l l o y s with m u l t i p l e a d d i t i o n s a r e p l o t t e d i n F i g . 4 , and a r e seen t o show t h e same g e n e r a l v a r i a t i o n w i t h chromium c o n t e n t as t h e t e r n a r y a l l o y s ( s e e F i g . 3 ) .
Also shown i n Table 5 and F i g . 4 a r e t h e r e s u l t s of 1000-hr t e s t s of f o m o f t h e a l l o y s c o n t a i n i n g m x l t i p l e a d d i t i o n s . A f t e r a l l b u t one of t h e s e t e s t s , t h e chromium i o n c o n c e n t r a t i o n s i n t h e s a l t s were s l i g h t l y h i g h e r t h a n f o r 500-hr t e s t s of t h e same a l l o y s ; i n one t e s t , t h e chromium i o n c o n c e n t r a t i o n was unaccountably lower.
The chromium i o n concentra-
t i o n s of t h e s e multicomponent a l l o y s a g a i n f e l l n e a r t h o s e p r e d i c t e d on t h e b a s i s o f e q u i l i b r i u m d a t a f o r pure chromium a t 600째C and were cons i d e r a b l y l e s s t h a n t h e c o n c e n t r a t i o n needed t o d e p o s i t pure chromium a t
600 "C. The chromium a c t i v i t i e s i n a l l of t h e a l l o y s t e s t e d would appear on t h e b a s i s of corresponding corrosion-product c o n c e n t r a t i o n s t o be lower t h a n t h e a c t i v i t y o f chromium i n I n c o n e l .
However, it i s important t o
note i n F i g s . 3 o r 4 t h a t any a l l o y I n which t h e chromium a c t i v i t y
Y
Table
5.
Corrosion-Product Concentrations of Containing Chromium in Combination
Alloy
Heat Number
Composition,
Chromium
Other
at.
$
Salts with
Tested Other
with Nickel-Molybdenum Alloying Elements
Alloys
Chromium Concentration Salt Samples," mole
in
Test Duration (hr)
Sample
MO,
500
0.0227
0.0236
0.0204
500
0.0490
0.0490
0.0426
1000
0.0689
0.0731
0.0620
Components
H
Sample
C
$ Other
OR 30-16
4.30
2.54 bal
S T23011
4.79
1.27 Al, 2.91 10.2 MO, bal
N-b, 1.72 Ni
W,
OR 30-33
5.90
1.59 bal
Fe,
9.66
MO,
OR 30-22
6.64
0.43 Fe, 0.39 Nb, 10.05 MO, bal Ni
2.61
Al,
500
0.0583
0.0555
0.0490
OR 30-22
6.64
0.43 Fe, 0.39 Nb, 10.05 MO, bal Ni
2.61
Al,
1000
0.0416
0.0402
0.0370
B3276
9.32
1.48
Nb,
500
0.0615
0.0615
0.0578
B3277
9.47
1.57 bal
N-b, 3.06 Ni
Al,
14.2
MO,
500
0.0698
0.0700
0.0624
B3277
9.47
1.57 bal
Nb, Ni
Al,
14.2
MO,
1000
0.0731
0.0657
0.0740
'Sample designations obtained from metallographic
'Hfl
Al, Ni
Al, Ni
1.90
5.56
14.0
3.06
Ti,
10.2
MO, bal
and "C" are specimens.
Ni
discussed
on page
13;
"other"
designates
samples
20 UNCLASSIFIED ORNL-LR-DWG 46945
W
3000
200 2000
-
(50
1600
: Q
z
0
1200
5
4000
slr
100
W 0
80
z
8
10
800
z
0 x
c
0
60
2 0
E
F CHEMISTRY SAMPLES - 500 hr TESTS
4 00
40
CONCENTRATIONS I N GRAPHIC SAMPLES - 500 hr TES
.
H AND C -1000 hr TESTS
AVERAGE CONCENTRATIONS IN METALLOGRAPHIC SAMPLES -1000 hr TESTS
20 200
0.03
0.04
0.06
0.00
0.40
0.2
0.4
0.6
0.8
j.0
ATOM FRACTION OF CHROMIUM IN ALLOY
Fig. 4 . Concentration 01’Chroniun I o n s i n S a l t 107 as a Function o f Chromium Contents i n Nickel-Molybdenum Alloys Containing M u l t i p l e Alloy Additions.
exceeded a value of 3.935 would support t h e formation o f pure chromium
a t 600°C i n any case where t h e c o n c e n t r a t i o n of CrF2 and CrF3 approached e q u i l i b r i u m w i t h t h e a l l o y a t temperatures of 800°C o r above.
Thus,
u n l e s s t h e a c t i v i t y c o e f f i c i e n t s f o r chromium i n t h e s e a l l o y s a r e much smaller t h a n u n i t y , t h e p o s s i b i l i t y for t h e d e p o s i t i o n o f pure chromium i n cold-leg r e g i o n s cannot be completely excluded f o r any of t h e a l l o y s tested
.
I n t h e case of ZrF4- o r EeF2-base s a l t mixtures, t h e temperature dependence o f t h e Cr-UF4 r e a c t i o n i s much l e s s t h a n f o r S a l t 107.
It
has been shown16 t h a t i n t h e s e mixtures, a l l o y s having a chromium
I6W. R. Grimes, ANP Quart. Progr. Rept. March 10, 1956, ORNL-2106,
pp. 96-99.
W
21 a c t i v i t y e q u i v a l e n t t o or l e s s t h a n t h a t f o r Inconel cannot support chromium i o n c o n c e n t r a t i o n s a t 800째C which a r e s u f f i c i e n t l y high t o maint a i n pure chromium a t 600째C.
Consequently, mass t r a n s f e r of chromium
by d e p o s i t i o n o f pure chromium c r y s t a l s i n t h e l a t t e r s a l t mixtures t
should not be p o s s i b l e f o r any of t h e a l l o y s l i s t e d i n Tables 4 and 5. MetalloaraDhic R e s u l t s Metallographic examinations o f t h e t e r n a r y a l l o y s shown i n Table 4 showed l i t t l e evidence of c o r r o s i v e a t t a c k o t h e r t h a n shallow surface roughening.
Void formation, which c h a r a c t e r i s t i c a l l y had been found i n
nickel-chromium a l l o y s under s i m i l a r t e s t c o n d i t i o n s , l7 was not d e t e c t e d i n any of t h e s e a l l o y s .
The r e l a t i v e depths of a t t a c k which occurred
f o r t h e a l l o y containing 5.55 a t .
'$
C r ( h e a t OR 30-2) a f t e r 500- and
1000-hr t e s t s , r e s p e c t i v e l y , a r e compared i n Fig. 5 .
Although t h e depth
of a t t a c k w a s s i m i l a r a t both time i n t e r v a l s , t h e i n t e n s i t y of surface p i t t i n g was somewhat g r e a t e r a f t e r t h e 1000-hr exposure.
The i n t e n s i t y
of s u r f a c e roughening was a l s o found t o i n c r e a s e with i n c r e a s i n g chro-
m i u m concentration.
.
This i s seen i n Fig. 6 which compares photomicro-
graphs of two a l l o y s containing d i f f e r e n t chromium c o n t e n t s .
Cold-leg
s e c t i o n s of t h e s e loops showed no evidence of c o r r o s i o n and contained no v i s i b l e d e p o s i t s of c o r r o s i o n products. The depths of a t t a c k observed m e t a l l o g r a p h i c a l l y f o r a l l o y s cont a i n i n g chromium i n combination with o t h e r a d d i t i o n s a r e shown g r a p h i c a l l y i n Fig, 7.
Attack i n t h e s e a l l o y s was manifested as surface
roughening af'ter 500 h r and a s a combination of s u r f a c e p i t t i n g and shallow void formation a f t e r 1000 h r .
Depths of c o r r o s i o n were i n gen-
e r a l h i g h e r t h a n f o r t h e t e r n a r y chromium-containing a l l o y s , p a r t i c u l a r l y i n a l l o y s which contained aluminum a d d i t i o n s .
1 7 L . S. Richardson, D. C . Vreeland, and W. D. Manly, Corrosion by Molten F l u o r i d e s , ORNL-1491 (Sept . 1 9 5 2 ) .
22
.
Appearance of inin? 5.55 at. Heat OR 30-2. a) After 50
f Ternary N i c xposure to Salt fter 1000 hr.
m
i
23
i
a
b.
Fig. 6. Hot-Leg Se Convection Loops Followin (a) 3.2 (3-13.5 Mo-bal
f Nickel-Molybdenum-Chromium Thermal hr Exposure to Salt 107. 1, (b) 11.0 CI-10.6 Mo-bal Ni (at. $1.
24 ORNL- LR- DWG 46944
5 I
10
500 hr
9
-
SALT 107
F S
x
._ 6
4 1000 hr - SALT 107
2
2 cn
3
0 Lz
n 8
2
LL
0
E ' a
W
D
0 Mo
-
Cr
2 z
Fe
I
0
11.35
I
AI
1.40 15.61 12.18
I
0
a
&J
I
I
10.36 12.89
I
10.76
1
1.30
I
I
I
I
I
I
I
I
I
I
I
10.2
10.2
(3.77 14.20 10.42
9.66
10.0:
9.32
4.30
4.79
9.47
5.90
6.64
5.56
0.43
I
I
I
14.00
12.54
I
1
1.27
I
13.06 15.51
I
I
I
I
1 1.59 12.61 I
I
I
I
Ti
1
a
I
Nb
3.23
w
1.85
0.07
I
1.48
I
I
2.91
I
0.92
I
1.57
0.39
1.72
F i g . 7. Depths o f Corrosion Observed f o r Nickel-Molybdenum Alloys with Multiple Alloy Additions Following Exposure t o S a l t 107. Bars d e s i g n a t i n g c o r r o s i o n depths appear d i r e c t l y above t h e a l l o y compositions vhick t h e y r e p r e s e n t . (Wkere b a r s have b o t h p o s i t i v e l y sloped and n e g a t i v e l y sloped cross-hatching, t h e h e i g h t of p o s i t i v e l y sloped c r o s s h a t c h i n g i n d i c a t e s depth of c o r r o s i o n a f t e r 500 h r and combined h e i g h t of both t m e s i n d i c a t e s depth a f t e r 1323 h r . )
Aluminum Corrosion-Product Concentrations Table 6 l i s t s t h e c o n c e n t r a t i o n s o f aluminum which w e r e a n a l y t i c a l l y determined i n f l u o r i d e mixtures operated f o r 500- and 1000-hr p e r i o d s w i t h nickel-molybdenum a l l o y s c o n t a i n i n g s i n g l e a d d i t i o n s of aluminum. I n t h e case o f a l l o y s c o n t a i n i n g g r e a t e r t h a n 2 a t . '$ A l , t h e c o r r e sponding aluminum c o n c e n t r a t i o n s i n t h e s a l t mixture were r e l a t i v e l y high, t h a t i s , i n t h e range o f 0.15-0.37 mole
$.
Only one a l l o y composi-
t i o n was subjected t o t e s t s a t b o t h 500 and 1000 h r ; however, r e s u l t s f o r t h i s a l l o y suggest t h a t e f f e c t i v e l y s i m i l a r s a l t c o n c e n t r a t i o n s were
25 W
Table 6. Corrosion-Product Concentrations of Salts Tested with Nickel-Molybdznum-AluminumAlloys
Heat Number
S T23012 OR 30-7 OR 30-7 OR 1491
Alloy Composition (at. $1
Test Duration
Aluminum Concentration in Salt Samples" (mole $)
A1
Other Components
(hr)
Sample H
Sample C
Other
1.22 4.26 4.26 4.85
11.4 Mo, bal Ni 10.15 Mo, bal Ni 10.15 Mo, bal Ni 6.99 Mo, bal Ni
500 500 1000 1000
0.000872 0.220 0.214 0.374
0.000872 0.070 0.105 0.374
b 0.137 0.178 0.374
a
Sample designations "H" and "C" are discussed on page 13; "other" designates samples obtained from metallographic specimens. bNot determined. realized for both time intervals.
Table 7 lists the concentrations of
corrosion products which formed in salt mixtures circulated in loops containing aluminum in combination with other alloying elements.
These
concentrations were of the same general magnitudes as those observed f o r the ternary Ni -Mo-A1 alloys. The corrosion-product concentrations showed no definable correspondence with the aluminum content of the alloys.
However, the propensity
for aluminum to react with interstitial contaminants, such as nitrogen, in these alloys, makes the activity of aluminum in the alloys very dependent on composition and metallurgical history.
For this reason poor
correspondence between the corrosion-product concentration and total aluminum concentration in the alloy would not be unexpected. It is apparent from tests of both the ternary and multicomponent alloys that aluminum additions less than 2 at. $ give rise to very much lower aluminum ion concentrations than additions above 2 at.
8.
This
observation may suggest that below a concentration of 2 at. $ the bulk of the aluminum addition has formed highly stable compounds with interstitial contaminants in the alloy. Metallographic Results v
Hot-leg surfaces of ternary alloys containing aluminum in amounts greater than 2 at. $ underwent relatively severe attack by Salt 107 in
Table 7. Corrosion-Product Concentrations of Salts Tested with Nickel-Molybdenum Alloys Containing Aluminum in Combination with Other Alloying Elements
Heat Number
Alloy Composition, at.
Test Dura tion (hr)
Aluminum Concentration of Salt Samples," mole $ Sample H
Sample C
Other
<O .0009 0.0606
<O .0009
500
<O. 0009 0.160
9.7 Mo, 5.9 Cr, 5.6 Fe, bal Ni
1000
0.0660
0.0820
0.124
2.54
10.2 Mo, 4.3 Cr, 1.9 Ti, bal Ni
500
0.358
0.326
0.334
OR 30-22
2.61
10.0 Mo, 6.6 Cr, 0.4 Fe, 0.4 Nb, 2.6 W, bal Ni
500
0.382
0.570
0.244
OR 30-22
2.61
10.0 Mo, 6.6 Cr, 0.4 Fe, 0.4 Nb, 2.6 W, bal Ni
1000
0.249
0.259
B32 77
3.06
14.2 Mo, 9.5 Cr, 1.6 Nb, 3.1 W, bal Ni
500
0.502
0.525
0.481
B32 77
3.06
1000
0.473
0.394
0.374
OR 30-14 OR 30-14
5.51
14.2 Mo, 9.5 Cr, 1.6 Nb, 3.1 W, bal Ni 10.4 Mo, 1.9 Ti, bal Ni 10.4 Mo, 1.9 Ti, bal Ni
500
0.394
0.434
0.499
1000
0.250
0.174
0.0960
Aluminum
Other Components
S T23014 S T23013
1.30
10.8 Mo, 2.7 Ti, bal Ni
500
1.40
10.4 Mo, 3.2 Nb, 1.8 W, bal Ni
OR 30-33
1.59
OR 30-16
5.51
a Sample designations "H" and "C" are discussed on page 13 ; I f other" designates samples obtained from metallographic specimens. bNot determined.
b
b
27 t h e form of surface p i t t i n g and subsurface void formation.
Void formation
was evident t o a depth of 0.002 i n . i n 500-hr t e s t s of these alloys and
t o 0.003 i n . i n 1000-hr t e s t s .
Figure 8 shows the appearance of an a l l o y
containing 4.27 a t . $I A 1 a f t e r a 1000-hr t e s t exposure.
However, an
a l l o y containing only 1.22 at. $I A 1 revealed negligible a t t a c k a f t e r a 500-hr exposure t o S a l t 107. Alloys containing aluminum combined w i t h other alloying components a l s o exhibited both surface p i t t i n g and subsurface void formation a f t e r exposure t o Salt 107.
The depths of attack f o r these alloys a r e shown
graphically i n Fig. 7.
Additions of up t o 2 a t . $, A l resulted i n only
l i g h t a t t a c k except i n alloys where chromium additions were a l s o present. Alloys which contained over 2.5 a t . $, Al i n combination w i t h chromium or titanium revealed pronounced attack i n the form of subsurface voids t o depths ranging from 0.002 t o 0.00.5.5 i n .
Cold-leg sections of a l l loops
were unattacked and contained no insoluble corrosion products.
.
.
Fig. 8. Hot-Leg Containing 4.27 a t . $,
f Ternary Nickel-Molybdenum Alloy 000-hr Exposure t o S a l t 107. Heat OR 30-7.
28 Titanium Corrosion-Product Concentrations Titanium-containing a l l o y s which were i n v e s t i g a t e d a r e l i s t e d i n 4
Table 8, t o g e t h e r w i t h a t t e n d a n t t i t a n i u m corrosion-product concentrations.
Except for t h e f i r s t composition shown, which contained
2.47 a t . $ T i , a l l o y i n g a g e n t s i n a d d i t i o n t o t i t a n i u m were p r e s e n t i n a l l o f t h e a l l o y s evaluated.
The c o r r o s i o n p r o p e r t i e s o f t h e s i n g l e
t e r n a r y a l l o y were s t u d i e d a t b o t h 500- and 1000-hr time i n t e r v a l s . Analyses of s a l t s operated i n loops of t h i s a l l o y revealed t i t a n i u m Table 8. Corrosion-Product Concentrations of S a l t s Tested with Nickel-Molybdenum Alloys Containing Titanium
Heat Number
Alloy Coxposition ( a t . $1 Ti
Test Duration
Other Components
(hr)
Titanium Concentration i n S a l t Samples" (mole $> Sample H
Sample C
Other
OR 3C-8 OR 30-8
2.47
11.6 Mo, b a l N i
5c3
0.0394
0.0386
0.0380
2.47
11.6 Mo, b a l N i
1000
0.0404
0.0495
a897
1.68
13.8 Mo, 2.9 Nb,
1020
0.0373
0.0383
G. 05C5 0.0283
0.0378
0.0348
3.0500
503
0.0449
0.0489
0.03'78
lC00
0.0373
0.053C
0.0434
5 00
0.0389
0.0404
0.@A84
500
12.018'7
0.0242
0.0187
500
0.0353
0.0252
b
bal N i
OR 30-16
1.90
10.2 Mo, 4.3 C r , 2.5 Al, b a l N1
OR 3C-14
1.92
13.4 Mo, 5.5 Al, bal N i
OR 3C-14
1.92
10.4 Mo, 5.5 A l , bal N i
OR 30-13
2.02
11.3 Mo, 2.2 Al, bal N i
S T23014
2.71
10.8 Mo, 1.3 Al, bal N i
B2898
3.24
13.2 Mo, 0.9 Nb, bal N i
a
Sample d e s i g n a t i o n "H" and "C" a r e discussed on page 13; l f o t h e r ' f d e s i g n a t e s samples obtained from metallographic specimens. bNot determined.
29 concentrations of 0.038-0.04-0 mole $ a f t e r 500 h r and 0.040-0.055 a f t e r 1000 hr.
mole $
These 'analyses correspond c l o s e l y t o t h e analyses of
s a l t s circulated i n loops constructed of the other titanium-bearing alloys, i n which titanium contents ranged from 1.68-3.24 a t . $. Only the t e s t of the 2.71 a t . $ a l l o y effected a titanium salt concentration s i g n i f i c a n t l y d i f f e r e n t from t h e t e r n a r y alloy, t h e concentration i n the former t e s t being unaccountably lower than f o r t h e other t e s t s . Metallographic Results The t e r n a r y titanium-bearing a l l o y revealed only l i g h t a t t a c k i n the form of surface p i t t i n g a f t e r both the 500- and 1000-hr t e s t i n t e r vals.
The photomicrograph i n Fig. 9 shows the appearance of a t y p i c a l
hot-leg section of t h i s a l l o y a f t e r the longer t e s t i n t e r v a l .
Depths of
a t t a c k which were observed i n the remainder of the titanium-bearing a l l o y s are graphically depicted i n Fig. 7.
Except where aluminum addi-
t i o n s were present i n these a l l o y s i n amounts g r e a t e r than 2 at. 6, depths of a t t a c k were i n a l l cases l e s s than 0.003 in. and generall-Y
*
P
b,
Fig. 9. Hot-Leg Surface of Ternary Nickel-Molybdenum Alloy C ontaining 2.47 a t . $ T i After 1000-hr Exposure t o S a l t 107. Heat OR 30-8.
30 W
were l e s s t h a n 0.002 i n .
Attack i n a l l c a s e s w a s manifested as g e n e r a l
surface p i t t i n g and shallow vi;id formation.
No a t t a c k was seen i n t h e
cold-leg s e c t i o n s of any of t h e titanium-containing loops nor were c o l d leg deposits detected. Vanadium Corrosion-Product Concentrations Loops were operated with two t e r n a r y a l l o y s containing a d d i t i o n s of 2.73 and 5.11 a t . $, r e s p e c t i v e l y .
ranadi un
A s shown i n Table 9,
t h e vanadium c o n c e n t r a t i o n d e t e c t e d i n a s a l t mixture t e s t e d w i t h t h e former a l l o y a f t e r 500-hr exposure was l e s s t h a n 0.005 mole $.
However,
s a l t s operated with t h e a l l o y of higher vanadium c o n t e n t contained 0.027 mole
%V
i n a 500-hr t e s t and 0 . 0 1 9 4 . 0 2 0 mole $ V i n a 1000-hr
test.
Metallographic Results Metallographic examination of t h e a l l o y with 2.73 a t . v e r y l i g h t a t t a c k i n t h e form of s u r f a c e roughening.
$I V revealed
Hot-leg s u r f a c e s
of t h e a l l o y with 5.11 a t . $ V e x h i b i t e d a t t a c k i n t h e form of void formation t o a depth of 0.002 i n . i n t h e 500-hr loop and 0.004 i n . i n t h e 1000-hr loop.
A photomicrograph i l l u s t r a t i n g a t t a c k i n c u r r e d by t h e
l a t t e r loop i s shown i n Fig. 10.
Iron Corrosion-Product Concentrations 3 n l y t w o loop t e s t s were completed with a l l o y s c o n t a i n i n g i r o n a s a
major a d d i t i o n .
Results of b o t h t e s t s , one of which operated f o r 500 h r
and t h e o t h e r f o r 1000 h r , a r e summarized i n Table 9.
I n t h e 500-hr
â&#x20AC;&#x2122;$ Fe, a f t e r - t e s t s a l t samples were analyzed t o c o n t a i n 0.013-0.015 mole $ Fe. I n t h e 1000-hr loop, which conloop, which contained 4.12 a t .
t a i n e d 5.56 a t .
%
Fe t o g e t h e r with aluminum and chromium a d d i t i o n s , t h e
a f t e r - t e s t s a l t samples contained an even lower i r o n c o n c e n t r a t i o n . would appear t h a t c o r r o s i o n products formed by r e a c t i o n s involving
It
Table 9.
Corrosion-Product
Concentrations Containing
Alloys
Alloy
Heat Number V
Fe
Composition MO
(at. Cr
of Salts Tested Vanadium and Iron
$> Al
Ni
Test Duration (hr)
with
Nickel-Molybdenum
Corrosion-Product Concentration in Salt Samples" (mole $1 Sample
H Vanadium
co.005
Sample
C
Other
Concentration
OR 30-10
2.73
10.8
bal
500
co. 005
OR 30-20
5.11
10.8
bal
500
0.0274
0.0274
0.0261
OR 30-20
5.11
10.8
bal
1000
0.0198
0.0194
b
Iron OR 30-11
4.12
10.8
OR 30-33
5.56
9.7
from
"Sample designation "H" and "C" metallographic specimens. b Not determined.
5.9
are
1.6
discussed
bal
500
bal
1000
on page
13;
'other"
co.005
Concentration
0.0146
0.0134
0.0152
0.00517
0.00387
0.00517
designates
samples
obtained
32
a
t
Fig. 10. Attack a t Hot-Leg Surface of Ternary Nickel-Molybdenum Alloy Containing 5.11 a t . 4 V. Alloy was exposed t o S a l t 107 f o r 1000 hr. Heat OR 30-20. chromium and aluminum i n t h i s l a t t e r t e s t served t o i n h i b i t t h e reaction with iron. Metallographic Results Metallographic examinations of specimens from the 500-hr loop showed no evidence of attack other than l i g h t surface roughening, Examinations of t h e 1000-hr t e s t , as i n d i c a t
7, showed corrosive a t t a c k t o subsurface voids.
ions were carried out with t e r nary a l l o y s containing 2.20 a i n Table 10, t h e niobium conce
$-Nb, respectively. As shown i n salts exposed t o these a l l o y s
increased from a value near 0,015 mole $ i n the 500-hr t e s t s t o values of from 0.022 t o 0.025 mole $I i n the 1000-hr tests. . S a l t s t e s t e d with
,. r
33 W
Table 10. Corrosion-Product Concentrations of S a l t s Tested with Nickel-Molybdenum-Niobium Alloys
Heat Number
Alloy Composition (at. Nb
OR OR OR OR
30-12 30-12 30-21 3C-21
2.20 2.20 3.62 3.62
Test Duration
Niobium Concentration i n S a l t Samples" (mole $)
Mo
Ni
(hr)
Sample .H
Sample C
11.1 11.1 10.9 lC.9
bal bal bal bal
5GO l0OC
0.00363 0. 0225 0.0155 2 . C244
0.02C7 0.0174 0.C228
;-\I
.,EL:
,
1CJX
b
Other
0.0135 C.G233 0.0153 0.02.59
a
Sample designations "H" and "C" are discussed on page 13; "other" d e s i g n a t e s samples obtained from metallographic spec:1 mens. bNot determined.
a l l o y s which contained niobium combined w i t h o t h e r a d d i t i o n s showed v e r y much lower niobium concentrations t h a n d i d t h e simple t e r n a r y a l l o y s . A s seen i n Table 11, c o n c e n t r a t i o n s i n t h e m u l t i p l e - a d d i t i o n t e s t s were l e s s t h a n 0.002 mole
%
f o r niobium c o n t e n t s a s high as 3.62 a t .
$I.
Thus,
it appears t h a t c o r r o s i o n products formed by r e a c t i o n s w i t h o t h e r components i n t h e s e a l l o y s , namely t i t a n i u m , aluminum, and chromium, were e f f e c t i v e i n i n h i b i t i n g r e a c t i o n o f t h e s a l t w i t h niobium. Metallographic R e s u l t s Neither t e r n a r y a l l o y containing niobium showed s i g n i f i c a n t a t t a c k i n metallographic examinations of 500-hr t e s t s ; however, t h e presence of v e r y s m a l l subsurface voids t o depths of approximately 0 . 0 0 1 i n . was d e t e c t e d i n examinations of t h e 1000-hr t e s t s , as i l l u s t r a t e d i n Fig. 11. Corrosion r e s u l t s determined for a l l o y s containing niobium t o g e t h e r with o t h e r a d d i t i o n s a r e summarized i n Fig. 7.
Except where aluminum and
chromium were b o t h p r e s e n t , a t t a c k i n t h e s e a l l o y s w a s l e s s t h a n 0.002 i n . i n depth.
34 Table 11. Corrosion-Product Concentrations of S a l t s Tested w i t h Nickel-Molybdenum Alloys Containing Niobium i n Combination with Other Alloying Elements
Heat Number
Alloy Composition ( a t . $1
Test Duration
Niobium Concentration i n S a l t Samples" (mole
9)
(hr)
Sample H
Sample C
10.0 Mo, 6.6 C r , 2.6 A l , bal N i
500
0.00129
0.00181
0.00207
10.0 Mo, 6.6 C r ,
1000
0.00052
0.00104
0.00052
Nb
Other Components
OR 30-22
0.39
OR 30-22
0.39
Other
2.6 A l , bal N i
<O. 0005
B2898
0.90
13.2 Mo, 3.24 T i , bal N i
500
â&#x201A;Ź2897
(3.92
13.8 Mo, 1 . 7 T i ,
1000
0.00104
0.00052
0.00129
0.00078
0.00052
0.00078
<O. 0005
b
bal N i B3276
1.48
1 4 . 0 Mo, 9 . 3 C r , bal N i
500
B3277
1.57 1 4 . 2 Mo, 9 . 5 C r ,
500
<O. 0005
<O. 0005
<O . GOO5
3.1 A l , b a l N i
B32 77
1.57
S T23Q13 3.23
1 4 . 2 Mo, 9.5 C r , 3.1 Al, bal N i
loo!:
112.4 Mo, 1 . 4 Al, 1 . 8 W, b a l N i
500
0.002 59
<O. 0005
0.00181
<O. 0005
0.00104
.
<O. 0005
a
Sample d e s i g n a t i o n s "H" and rrC" a r e discussed on page 13; " o t h e r t 1 designates saniples obtained from metallographic specimens.
bNot determined. Tungsten Corrosion-Product Concentrations Single a l l o y i n g a d d i t i o n s o f t u n g s t e n t o t h e nickel-molybdenum system were evaluated a t l e v e l s of 0.72 and 1.44 a t .
'$, r e s p e c t i v e l y .
Loop
t e s t s of both a l l o y s were conducted f o r 500 h r , a t which time t u n g s t e n c o n c e n t r a t i o n s i n t h e s a l t mixtures had reached l e v e l s of 0.029 t o 0.032 mole
4.
I n 500-hr t e s t s o f two a l l o y s which contained t u n g s t e n i n
a d d i t i o n t o chromium, niobium, o r aluminum, t h e c o n c e n t r a t i o n o f t u n g s t e n d e t e c t e d i n s a l t samples w a s below 0.010 mole
4.
Compositions of t h e s e
a l l o y s and t h e i r a t t e n d a n t s a l t corrosion-product c o n c e n t r a t i o n s a r e shown i n Table 12.
d
Y
Li
Fig.' 11. Appearance of-Voids in Nickel-Molybdenum filoy Car to Salt 107. Heat OR 30-21. 3.62 at. $ Nb after lOOO-hr Exposure _ Corrosion-Product Nickel-Molybdenum
Table 12.
Alloy~;~p;;ition
Concentrations of Salts Tested Alloys Containing Tungsten
.
W
Other Components
Test Duration b=-)
OR 30-9 OR 30-19
0.72 1.44
11.2 MO, ~bal Ni 11.4 MO,- bal Ni
ST23011
1.72
ST23013
1.85
10.2 MO, 1.3Al, 2,9'Nb, 4*8 Cr, bal Ni 10.4 iI0,~ 1.4 Al, bal Ni ~~~
Heat Number
Sample H
Sample C
Other
500 500
0.0318 0.0384
0.0287
0.0311
0.0325 0..0310
500
0.00500
0.00983
b
500
0.00223
0.00105
b
aSamples designations ~"H" and "C" are discussed on page 13; wother" designates samples obtained -from-metallographic specimens. 'bNot determined.
36 Metallographic Results,
,
Metallographic examination of loops constructed of nickel-molybdenumtungsten alloys revealed only slight surface pitting, as illustrated in Fig. 12. The addition of aluminum together with tungstenled to heavy surface pitting, while the addition of aluminum, chromium, and niobium produced subsurface voids to a depth of 0.0025 in., as shown in Fig. 7.
t
Fig. 12. Hot-Leg Surface of Nickel-Molybdenum Alloy Containing 1.44 at. $ W after 500-hr Exposure to Salt 107. Heat CR 30-19. â&#x20AC;&#x2DC; Relative ThermodynamicStabilitiesof
Alloying Constituents
Since-the salt mixtures supplied for this investigation were very uniform in composition, one.can presume that the samerelative activities It follows, therefore, of UFI, and tJF3existed at the start of each test. that the relative extent of reaction which occurred between the salt mixtures and an alloying element ~$+yuF4=MxFy+yUF3
2
37 f o r which
KCY =
should be d i r e c t l y r e l a t e d t o t h e a c t i v i t y of t h e f l u o r i d e compounds, M F i n v o l v i n g t h a t element. x Y9 An i n d i c a t i o n of t h e r e l a t i v e a c t i v i t i e s of t h e s e compounds i s provided by a c o n s i d e r a t i o n of t h e i r standard f r e e e n e r g i e s of formation, a s
derived from t h e r e a c t i c n
where
I n Table 13 a r e l i s t e d t h e standard f r e e e n e r g i e s o f formation, p e r gramatom o f f l u o r i n e , of f l u o r i d e compounds a t 800 and 600째C a s s o c i a t e d with each of t h e a l l o y i n g elements i n v e s t i g a t e d .
Values a r e given f o r t h e
most s t a b l e compounds ( t h a t i s , t h o s e w i t h most n e g a t i v e f r e e e n e r g i e s ) r e p o r t e d 1 8 f o r t h e s e elements, and a r e l i s t e d i n o r d e r o f d e c r e a s i n g stabilities.
The r e s u l t a n t o r d e r s u g g e s t s t h a t corrosion-product
c o n c e n t r a t i o n s a s s o c i a t e d with each element a t a given a c t i v i t y should have i n c r e a s e d i n t h e following order:
W, N b , Fe, C r ,
V, T i , and A l .
I n F i g . 13, t h e g e n e r a l ranges of corrosion-product c o n c e n t r a t i o n s a c t u a l l y observed f o r t h e s e components, when p r e s e n t as s i n g l e a l l o y i n g a d d i t i o n s , are p l o t t e d a s a f u n c t i o n of a l l o y c o n t e n t .
It i s seen t h a t ,
18A. Glassner, The Thermodynamic P r o p e r t i e s o f t h e Oxides, F l u o r i d e s , and C h l o r i d e s t o 2500째K, ANL-5'750.
38 Table 13. R e l a t i v e Thermodynamic S t a b i l i t i e s of F l u o r i d e Compounds Formed by Elements Employed a s Alloying Additions (Data Compiled by Glassner)"
Element
Most S t a b l e Fluoride Compound
A1
AlF3
Ti
AG i o 0 "C
YiO3OC
F)
f o '(g: : : -92
TiF3
-87 -q 5
-90
v
m2
-80
-84
Cr
C rF2
-72
-77
Fe
FeF2
-66
-66
m
mF5
-58
-60
W
wF5
-46
-48
c /
a
A. Glassner, The Thermodynamic P r o p e r t i e s of t h e Oxides, F l u o r i d e s , and C h l o r i d e s t o 253CCK,ANL-5750.
with t h e exception of niobium and t u n g s t e n , t k e c o n c e n t r a t i o n s p e r atomic p e r c e n t of a d d i t i o n do i n c r e a s e i n the e x a c t o r d e r p r e d i c t e d .
Only
t,ungsten n o t i c e a b l y d e v i a t e s from t h i s p r e d i c t e d behavior; t h e causes f o r t h i s d e v i a t i o n have n o t been e s t a b l i s h e d , although t h e number o f t e s t s completed on a l l o y s with t u n g s t e n a d d i t i o n s were q u i t e l i m i t e d .
General Discussion of Alloying E f f e c t s The corrosion-product c o n c e n t r a t i o n s a s s o c i a t e d w i t h e i t h e r i r o n , niobium, or t u n g s t e n a l l o y i n g a d d i t i o n s were much lower when t h e s e e l e ments e x i s t e d i n multicomponent a l l o y s than i n simple t e r n a r y a l l o y s . The reason f o r t h i s behavior i s undoubtedly a s s o c i a t e d with t h e presence of t h e more r e a c t i v e a l l o y i n g a d d i t i o n s i n t h e multicomponent a l l o y s . Consider, for example, a system containing comparable a d d i t i o n s o f chromium and i r o n , f o r which t h e c o r r o s i o n r e a c t i o n s a r e
39 v
O R N L - LR- DWG 46943
500
+/
400
300
200
-
/
IC)
0 X
s-â&#x20AC;? 0) -
-E
+ 400 -I
Q
m
90
Z
80
n w
70
c
0
60 W
n
0
5 c
50 Ti/
+
40
z W 0
c2
1 , / /
z 30
~
-Y
20
/
/ Fe
40 I
2
3
4
5
6
7
8
9
1
2
A L L O Y CONTENT (at. %)
Fig. 13. Comparison of Corrosion-Product Concentrations Formed in Salt 107 by Various Alloying Additions as a Function of Alloy Content.
40 Since &
I
i s considerably more negative t h a n
aII,t h e
e q u i l i b r i u m UF3
I
c o n c e n t r a t i o n produced b y t h e f i r s t r e a c t i o n i s higher t h a n t h a t which would be produced by t h e second r e a c t i o n .
According t o t h e l a w of mass
a c t i o n , t h e r e f o r e , t h e FeF2 concentration a t e q u i l i b r i u m should be reduced i n t h e presence of chromium compared t o a system containing i r o n only. While t h i s means of c o r r o s i o n i n h i b i t i o n w a s e f f e c t i v e f o r those a l l o y i n g components l e s s r e a c t i v e t h a n chromium, i t s e f f e c t was not apparent among elements of r e l a t i v e l y high r e a c t i v i t i e s .
Thus, chromium
corrosion-product concentrations were t h e same i n t h e case of a l l o y s cont a i n i n g both aluminum and chromium as i n t h e case of a l l o y s containing chromium alone.
S i m i l a r l y , t h e presence of aluminum d i d not n o t i c e a b l y
reduce t h e titanium-corrosion products a s s o c i a t e d w i t h titanium-containing alloys.
For most of t h e multicomponent a l l o y s , t h e amount of chromium and
t i t a n i u m , on an atomic percent basis, exceeded t h a t of aluminum; conse-
q u e n t l y t h e i r a c t i v i t i e s could have approached t h e a c t i v i t y of t h e aluminum component.
Nevertheless, t h e high aluminum c o n c e n t r a t i o n s of f l u o -
r i d e mixtures a f t e r t h e s e t e s t s suggest a l e v e l of UF3 higher t h a n would have been produced by e i t h e r chromium o r t i t a n i u m alone, so t h a t some i n h i b i t i v e a c t i o n would be p r e d i c t e d .
The f a c t t h a t none occurred may
suggest t h a t t h e measured aluminum c o n c e n t r a t i o n s were somewhat higher than a c t u a l l y existed.
' S L W R Y AND CONCLUSIONS
The c o r r o s i o n p r o p e r t i e s of s o l i d - s o l u t i o n a l l o y i n g elements i n t h e Ni-17$ Mo system were i n v e s t i g a t e d i n molten mixtures of NaF-LiF-KF-UFL
( 11.2-41.0-45.3-2.5 mole
5).
The c o r r o s i o n s u s c e p t i b i l i t y of alloying
a d d i t i o n s was found t o i n c r e a s e i n t h e following o r d e r :
W, T i , and A l .
Fe, Nb, V, Cr,
With t h e exception of tungsten, t h e s u s c e p t i b i l i t y of
"Considerable d i f f i c u l t y was i n f a c t encountered i n a n a l y s e s of t h i s element by wet chemical methods. Analyses of a l i m i t e d number of samples were consequently made using s e m i q u a n t i t a t i v e spectrographic techniques. Concentrations obtained by t h e l a t t e r technique were lower by a f a c t o r of approximately 2/3 t h a n t h e values t h a t were reported i n Tables 6 and 7.
Y
41 t h e s e elements t o corrosion increased i n approximately t h e same order a s t h e s t a b i l i t i e s of f l u o r i d e compounds of t h e elements. The corrosion-product concentrations produced by e i t h e r i r o n , n i o bium or t u n g s t e n a l l o y i n g a d d i t i o n s i n t h e above s a l t mixture were much
lower when t h e s e elements e x i s t e d i n combination with chromium, t i t a n i u m ,
or aluminum t h a n when t h e y e x i s t e d a s s i n g l e a l l o y i n g a d d i t i o n s .
I n con-
t r a s t , corrosion-product c o n c e n t r a t i o n s a s s o c i a t e d w i t h chromium, t i t a nium, or aluminum were unchanged by t h e presence of o t h e r a l l o y i n g constituents. The metallographic examinations of a l l a l l o y s i n v e s t i g a t e d under t h i s program showed considerably l e s s c o r r o s i o n t h a n Inconel under equiva l e n t conditions.
Surface roughening or shallow p i t t i n g was manifested
i n hot-leg s e c t i o n s of a l l t h e loops t e s t e d .
Shallow subsurface voids
were a l s o seen i n aluminum- and niobium-containing systems.
Alloys con-
t a i n i n g more t h a n one a l l o y i n g a d d i t i o n i n v a r i a b l y were a t t a c k e d t o depths g r e a t e r t h a n a l l o y s containing each of t h e a d d i t i o n s i n d i v i d u a l l y . The g r e a t e s t depths of a t t a c k , which ranged from 0.003 t o 0.0045 i n . i n 1000-hr exposures, were incurred i n a l l o y s which contained combined a d d i t i o n s of aluminum and chromium or aluminum and t i t a n i u m .
Alloys without
e i t h e r aluminum or t i t a n i u m i n no case e x h i b i t e d a t t a c k t o depths of more t h a n 0.002 i n . and g e n e r a l l y showed a t t a c k i n t h e range from
0.001 t o 0.002 i n . I n t h e case of t h e m a j o r i t y of a l l o y s t e s t e d , t h e depth of a t t a c k increased a t a g r e a t e r r a t e between 0 and 500 h r t h a n between 500 and
1000 h r .
This f i n d i n g i s i n agreement w i t h t h e concentrations of c o r r o -
s i o n products, which i n g e n e r a l increased o n l y s l i g h t l y between t h e p e r i ods of 500 and 1000 h r .
Both r e s u l t s suggest t h a t n e a r l y s t e a d y - s t a t e
c o n d i t i o n s were e s t a b l i s h e d w i t h i n t h e f i r s t 500 h r of t e s t o p e r a t i o n . I n view of t h e g e n e r a l l y favorable r e s u l t s of t h e s e t e s t s , one h a s considerable freedom i n t h e choice of p o t e n t i a l a l l o y i n g components f o r nickel-molybdenum a l l o y s f o r molten salt s e r v i c e .
Only t i t a n i u m and
aluminum appear t o a f f o r d p o t e n t i a l c o r r o s i o n problems, p a r t i c u l a r l y i f used as combined a d d i t i o n s o r i n combination w i t h chromium.
Thus, t h e
choice of an optimum a l l o y composition f o r any given a p p l i c a t i o n can be judged mainly on t h e basis of s t r e n g t h and f a b r i c a t i o n requirement.
42 ACKNOWLEDGMENTS
V
The many loop experiments r e p o r t e d h e r e were c a r r i e d out under t h e s k i l l e d hand of M. A. Redden.
The author i s a l s o indebted t o W. 0. Harms
f o r h i s e d i t o r i a l a s s i s t a n c e and guidance a s t h e s i s advisor.
.
43 ORNL-TM-2021 VOl.
INTERNAL DISTRIBUTION
1-3.
C e n t r a l Research L i b r a r y
4-5. ORNL Y - 1 2 Technical L i b r a r y Document Reference Section
6-15. Laboratory Records 16. Laboratory Records, ORNL-RC 17. ORNL Patent O f f i c e 18. R. K. Adams 19. G. M. Adamson 20. R. G. A f f e l 21. J. L. Anderson 22. R. F. Apple 23. C. F. Baes 24. J. M. Baker 25. S. J. B a l l 26. C. E. Bamberger 27. C. J. Barton 28. H. F. Bauman 29. S. E. B e a l l 30. R. L. B e a t t y 31. M. J . B e l l 32. M. Bender 33. C. E. B e t t i s 34. E. S. B e t t i s 35. D. S. E i l l i n g t o n 36. R. E. Blanco 37. F. F. Blankenship 38. J. 0. Blomeke 39. R. Blumberg 40. E. G . Bohlmann 41. C. J. Borkowski 42. G. E. Boyd 43. J. Braunstein
4
44. M. A. Bredig 45. R. B. Briggs 46. H. R. Bronstein
47. G. D. Brunton 48. D. A. Canonico S. W. G. 0. A. 54. J. 55. F. 56. W. 57. H.
49. 50. 51. 52. 53. i
v
Cantor L. C a r t e r I. Cathers B. Cavin Cepolina M. Chandler H. Clark R. Cobb D. Cochran
58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71-80.
81. 82. 83. %4.
85. 86.
87. 88. 89. 90. 91. 92. 93. 94. 95. 96.
97 * 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110* 111. 112.
C. W. C o l l i n s L. Compere V. Cook H. Cook T. Corbin B. Cox J. L. Crowley F. L. C u l l e r D. R. Cuneo J. E. Cunningham J. M. Dale D. G. Davis R. J. DeBakker J. H. DeVan S. J. D i t t o A. S. Dworkin I. T. Dudley D. A. Dyslin W. P. E a t h e r l y J. R. Engel E. P. Epler R. B. Evans I11 D. E. Ferguson L . M. F e r r i s A . P. Fraas H. A. Friedman J. H Frye, Jr. W. K. Furlong C. H. Gabbard R. B. Gallaher R. E. Gehlbach J. H. Gibbons L. 0. G i l p a t r i c k W. R. Grimes A. G. G r i n d e l l R. W. Gunkel R. H. Guymon J. P. Hammond B. A. Hannaford P. H. Harley D. G. Harman W. 0. Harms C. S. H a r r i l l P. N. Haubenreich R. E. Helms P. G. Herndon
E. K. W. L.
I
44 113. 114. 115-11'7. 118. 119. 120. 121. 122. 123. 124. 125. 126. 12'7. 128* 129. 130. 131. 132. 133. 134. 135. 136. 13'7. 138. 139. 140. 141. 142. 143.
D. J. M. H. D. P. R. A. T. W. H. W. P. R. M. M. C. T. H. J. D. S. J. R. A. T. J. C. J.
144. c. 145. 146. 147. 148. 149. 153. 151. 152. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 165. 166.
J. M. R. A. G. E. A. M. R. R. H.
R. J. D. C. W. H. T. H. R. H. D.
N. Hess R. Hightower R. H i l l W. Hoffman K. Holmes P. Holz W. Horton Hout z e e l L. Hudson R. Huntley Inouye H. Jordan R. Kasten J. Ked1 T. Kelley J. Kelly R. Kennedy W. K e r l i n T. Kerr J. Keyes V. Kiplinger S. K i r s l i s W. Koger B. Korsmeyer I. Krakoviak S. Kress W. Krewson E. Lamb A. Lane E. Larson J. Lawrence S. Lin B. Lindauer P. Litman H. Llewellyn L. Long, Jr. L. L o t t s I. Lundin N. Lyon L. Macklin G. MacPherson E. MacPherson C. Mailen L. Manning D. 5iartin R. Martin V. Mateer H. Mauney Mc C l a i n W. McClung E. McCoy L. McElroy
167. 168. 169. 1'70. 1'71. 1'72. 1'73. 174. 175. 1'76. 17'7. 178. 1'79. 180. 181. 182. 183.
184. 185. 186. 187. 188. 189. 190.
191. 192. 193.
194. 195.
1%. 197. 198. 199.
200. 201. 202. 203. 204. 205. 206. 207. 238. 209. 210. 211. 212. 213. 214. 215. 216. 21'7. 218.
K. McGlothlan J. McHargue E. McNeese R. McWherter J. Metz S. Meyer L. Moore M. Moulton W. Mueller A . Nelms H. Nichol P. Nichols L. Nicholson C. Oakes P. P a t r i a r c a A. M. Perry T. W. P i c k e l H. E. Piper B. E. Prince G. L. Ragan J. L. Redford M. Richardson G. D. Robbins R. C . Robertson K. A . Romberger R. C . Ross H. C. Savage W. F. Schaffer C. E. S c h i l l i n g Dunlap S c o t t J. L. S c o t t H. E. Seagren C. E. Sessions J. H. S h a f f e r W. H. Sides G. M. Slaughter A. N. Smith F. J. Smith G. P. Smith 0. L. Smith P. G. Smith 1. Spiewak R. C. S t e f f y W. C. Stoddart H. H. Stone R. A. Strehlow D. A. Sundberg J. R. Tallackson E. H. Taylor W. Terry R. E. Thoma P. F. Thomason
C. C. L. J. H. A. R. D. T. H. H. J. E. L.
45 219. 220. 221. 222. 223. 224. 225. 226. 227. 228. 229.
L. D. W. G. J. H. C. B. A. J. W.
M. Toth E. Trauger E. Unger M. Watson s. Watson L. Watts F. Weaver H. Webster M. Weinberg R. Weir J. Werner
230. 231. 232. 233. 234. 235. 236. 237. 238. 239.
K. W. West M. E. Whatley J. C. White R. P. Wichner L. V. Wilson Gale Young H. C. Young J. P. Young E. L. Youngblood F. C . Zapp
EXTERNAL DISTRIBUTION
240. 241. 242. 243. 244. 245. 246. 247. 248. 249. 250-251. 252. 253. 254. 255. 256. 257. 258. 259. 260.
261. 262. 263. 264. 265. 266-280.
G. J. D. C.
G. Allaria, Atomics I n t e r n a t i o n a l G. Asquith, Atomics I n t e r n a t i o n a l F. Cope, RDT, SSR, AEC, Oak Ridge National Laboratory B. Deering, AEC, OSR, Oak Ridge National Laboratory
H. M. Dieckamp, Atomics I n t e r n a t i o n a l A. Giambusso, AEC, Washington F. D. Haines, AEC, Washington C. E. Johnson, AEC, Washington W. L. Kitterman, AEC, Washington W. J. Larkin, AEC, Oak Ridge Operations T. W. McIntosh, AEC, Washington A. B. Martin, Atomics I n t e r n a t i o n a l D. G. Mason, Atomics I n t e r n a t i o n a l G. W. Meyers, Atomics I n t e r n a t i o n a l D. E. Reardon, AEC, Canoga Park Area Office H. M. Roth, AEC, Oak Ridge Operations M. Shaw, AEC, Washington J. M. Simmons, AEC, Washington W. L. Smalley, AEC, Washington S. R. Stamp, AEC, Canoga Park Area Office E. E. Stansbury, t h e University of Tennessee R. F. Sweek, AEC, Washington A. Taboada, AEC, Washington R. F. Wilson, Atomics I n t e r n a t i o n a l Laboratory and U n i v e r s i t y Division, AEC, Oak Ridge Operations Division of Technical Information Extension