ORNL-TM-2359.txt

 

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Contract No. W-7405-eng-26

METALS AND CERAMICS DIVISION

AN EVATUATION OF THE MOLTEN-SALT REACTOR

HASTELIOY N SURVEILLANCE SPECIMENS — SECOND GROUP

 

ORNL-TM-2359

EXPERIMENT

 

H. E, McCoy, Jr.

T LEGAL NOTICE

: This report was preparsd as an account of Government sponsored work, Neither the United
: Btates, nor the Commission, nor any person acting ok behalf of the Commission:

A. Makes any warranty or representation, exprossed or implied, with respoct to the accu=-

" racy, completeness, or usefulness of the information

"1 ‘of any information, apparatus, method, or process disclosed in this report may not infringe

-+ privately ownad rights; or -

... B, Assumes any liabilities with respect to the mre of, or for damages resultisg from the .
8

© use of any information, apparatus, method, or proces
" - As used in the sbove, “‘person acting on

 

. ployee or contractor of the Commission, or omplofln of such contractor, fo the sxtent that

: such smployes or contractor of the Commission,

"Vd!sumhntes, or provides access to, any informatios pursusnt to his employment or contract
{ with the Commission, or Lis employment with such contractor, . ’

* FEBRUARY 1969

~QAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee
. _operated by |
UNION CARBIDE CORPORATION
o for the
U.S. ATOMIC ENERGY COMMISSION

 WISTRAUTION OF THIS DOCUMENT 15 UNLWAITED

contsined in this report, or that the use

disclosed in this report,
of the Commission’ fncludes any em-

eployeo of such oontractor prepares,

 
 

 

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CONTENTS

Abstract . . . v 4 o 4 vt e e e s e e e e e e
Introduction . . & + ¢ ¢« o ¢ ¢ ¢ o 4 o s ¢ o o &
Experimental Details . . . . . ¢« ¢« ¢« v ¢ ¢ o o
Surveillance Assembly . « « « ¢+ 4« ¢ ¢ o & o
Materials . . ¢ ¢ & ¢ ¢ o o ¢ & o o s o o o »
Test Specimens . . ¢ v v ¢ ¢ o v o o o o o &
Irradiation Conditions . . . + « « v « « «
Testing Techniques . . . . « ¢« + ¢ ¢ + &
Experimental Results . . . . . . . « « « « « .

Visual and Metallographic Examination . . . .

Mechanical Property Data — Standard Hastelloy

Mechanical Property Data — Modified Hastelioy

N .

N

Metallographic Examination of Mechanical Property

Discussion of Results . & o & ¢ & o o o o « o« &

‘Summary and Conclusions . « « v ¢ v ¢ ¢« « o o &

Acknowledgments . . . . . . . ¢ o o e o . .

Specimens

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AN EVALUATION OF THE MOLTEN-SALT REACTOR EXPERIMENT
- “HASTELIOY N SURVEILLANCE SPECIMENS — SECOND GROUP

H. E. McCoy, Jr.
ABSTRACT

_ ‘We have examined the second group of Hastelloy N surveila
lance samples removed from the Molten-Salt Reactor Experiment.
Two rods of standard Hastelloy N were removed from the surveilw
lance position outside the core vessel and were exposed to the
nitrogen plus 2 to 5% 0, cell enviromnment for 11,000 hr. Metal-

lographic examingtion showed that the alloy was compatible with

this environment, showing'only superficial oxidation and no
evidence of nitriding. - These samgles were exposed to a thermal
fluence of 1.3 x 10*? neutrons/cm and the mechanical proper-
ties were altered appreciably. Both tensile and creep tests
were run that showed significant changes in the mechanical
properties, particularly the strain at fracture. These changes
are in good agreement with those observed for materials irra-
diated in a helium environment in the Osk Ridge Research Reactor.

Two rods of modified Hastelloy N‘contaifiing small additions
of titanium and zirconium.were removed from the core surveillance

 facility with a thermal fluence of 4.1 x 10%° neutrons/cm?.

These materials had not been annealed properly to put them in
their most radiation-resistant condition, but tests on these
materials indicated that they have sllghtly improved postirra-
diation mechanical propertles and that their corrosion resistance
is acceptable

- INTRODUCTION

The Molten-Salt Reactor Experiment is a single- reglon reactor '

P

that is fueled by a molten fluorlde salt (65 LiF—29 1 BeF2—5 ZrF4—O 9 UF,,
L mole %), moderated by unclad graphlte, and contalned by Hastelloy N
5 (N;—lé Mo—7 Cr—4 Fe+0.05_C,_wt_%). The details of the reactor des1gn

 
 

 

 

and construction can be found elsewhere.l We knew that the neutron
environment would produce some changes in the two structural materials —
graphite and Hastelloy N, and we were very confident of the compatibility
of these materials with the fluoride salt, However, we needed to keep
abreasfi‘of the possible development of problems within the reactor itself.
For these reasons, we developed a surveillance progfam'that would allow
us to follow any changes in properties of graphite and Hastelloy N
specimens as the reactor operated

The reactor went critical on June 1, 1965, and assumed normal opera-
tion in May 1966, The first group of surveillance specimens was in the
reactor from September 8, 1965, to July 28, 1966, and was removed after
8682 Mwhr of operation (designated "first group"). The results of our
tests on the Hastelloy N specimens were reported previously.2 A second
set of specimens was removed from the core on May 9, 1967, after an
additional 27,600 Mwhr of operation (total reactor operation was
36,247 Mwhr), These specimens were two modified alloys containing
nominal 0.5% additions of titanium and zirconium. These were inserted
on September 13, 1966, after the first group was removed to determine the
mechanical property changes of these alloys due to irradiation and to
evaluate the compatibility of these alloys with the MSRE énvironmentfl
Two rods of standard fiastelloy N located outside the core and 5 in. from
the vessel were removed on June 5, 1967. These specimens had been in
place-since the reactor began operation and were examined to defiermine
the compatibility of the material with the MSRE cell environment
(N» + 2=5% 0,) and the changes in the mechanical properties due to
irradiation.

This report will describe the results of tests on the Hastelloy N
surveillance specimens removed during May and June 1967 (designated
"second group"), which includes two rods of modified (zirconium and
titanium) alloys removed from the core and two rods of standard

Hastelloy N removed from outside the core vessel.

 

1r. c. Robinson, MSRE Des1gn and Operations Report, Pt. 1, Description

 

of Reactor Design, ORNL-T™M-728 (January 1965).

~ 2H. E. McCoy, Jr., An Evaluation of the Molten-Salt Reactor
Experiment Hastelloy N Surveillance Specimen — First Group, ORNL-TM-1997
(November 1967). ,

 

 

 

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 ORNL-3872, p. 87.

_ ORNL-4037, p. 97.

. EXPERIMENTAL DETAILS

. Surveillance Assembly

The core sfirveillahee assembly was.designed by W. H. Cook and others,
and the details have been reported 3  fThe facility is shown pictorially
and schematically in Flg. 1.  The specimens are arranged in three
stringers. Each strlnger 1s about 62 in. long and consists of two
Hastelloy N rods and a graphite section made up of various pleces that
are joined by plnnlng and tongue-and-groove joxnts. The Hastelloy N
rod is periodically reduced to 0.125 in. in dismeter and can be cut into

small tensile specimens'after it is removed from the reactor; Three

7stringers are joined tbgether_Sorthat they can be separated in a hot

cell and resssembled with one or more new stringers for reinsertion into
the reactor. The assembled;stringers fit into a perforated Hastelloy N
basket that is inserted into an axial position about 2.8 in. from the
core center line. | _' | |

When the basket was removed on July 28 1966, some of the specimens

were bent, and the entire assembly had to be replaced.4 Slight modifica-

~tions in the design were made, and the assembly was removed recently and

found to'be in excellent condition.®
A control facility is associated with the surveillance program. It

utilizes a "fuel salt" containing depleted uranium in a static pot that

is heated electrically., The temperature is controlled by the MSRE com-
- puter so that the temperature matches that of the reactor Thus, these
, specimens are exposed to condltlons ‘the same as those 1n the reactor

*p'except for the statlc salt and the absence of a neutron flux.r

 

3W. H. Cook, MSR Program' ,Semi'ann. Pregr. Rept. Aug. 31, 1965,
“W. H. Cook, MSR Prbg:}am*Semiann.' Prog'r. Rept. Aug. 31, '1966,"

°W. H. Cook, "MSRE Materials Surveillance Program," Metals and

' Cermmics DlV. Ann Progr. Rept June 30 1967, ORNL-417O PP 192—195 ‘

 

 
 

 

 

PHOTO 81671

 

 

 

 

 

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Fig. 1. Molten-Salt Reactor Experiment Core Surveillance Fixture.

There is another surveillance facility for Hastelloy N located out-
side the core in a vertical position asbout 5 in. from the vessel (Fig. 2).

These specimens are exposed to the cell environment (N, + 2—5% 03).

Materiagls

The compositions of the two heats of standard Hastelloy N are given

in Table 1. These heats were air melted by Materials Systems Division of
Union Carbide Corporation. Heat 5085 was used for making the cylindrical
portion, and heat 5065 was used for the top and bottom heads of the MSRE
vessel. These materials were given a mill anneal of 1 hr at 1177°C and
s Pinal anneal of 2 hr at 900°C at ORNL after fabrication. |

- The chemical cofipositions of the two modified alloys are given in
Table 1. The modifications in composition were made principally to

improve the alloy's resistance to radiation damage'and to bring about

 
 

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THERMAL SHIELD ——-—i_\ ’
REACTOR VESSEL—\___\
SURVEILL ANCE ST_RINGER-~—\___\
'FLOW DISTRIBUTOR——__|| |
i . \\ 113in.
/,.‘? | |
. 84in
&
' t
— ~——5 in.
I
Wl ‘TOP OF LATTICE~ .~ |-
Sl ELEVATION 8281t |2inl ~ |
1%-in. LONG NOSE PIECE,__';/’/. | _'
I 0 o8 6 —{
INCHES
= Fig. 2. Molten-Sa.lt Rea.ct.or Experiment Surveilla.nce Facility
_ OutSJ.de the Reactor Vessel
-
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- Table 1, Chemical Composition of Surveillance

Heats

 

Analysis, wt %

 

 

 

Element
Heat 5065 Heat 5085 Heat 21545 Heat 21554

Cr 7.2 7.3 7.18 7.39
Fe 3.9 3.5 0.034 0.097
‘Mo 16.5 16.7 12.0 12.4
c 0.065 0.052 0,05 0.065
si 0.60 0.58 0.015 0.010
Co 0.08 0.15 )
W 0.04 0.07
Mn 0.55 0.67 0.29 0.16
v 0.22 0.20
P 0.004 0.0043 0.001 0.004
S 0.007 0.004 < 0.002 < 0.002
Al - 0.01 0.02 0.02 0.03
Ti 0.01 < 0.01 0.49 0.003
Cu 0.01 0.01
0 0.0016 0.0093 0.0002 < 0.0001

0.011 0.013 < 0.0001 0.0005
Zr 0.35

Analysis, ppm

B 24, 37, 38 2 2

20, 10

 

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- general improvements in the fabricability, weldability, and ductility.6

These alloys were small 100-1b heats made by vacuum melting by Special

Metals Corporation. They were finished to l/2-in. plate containingr40%

cold work, We used slightly different procedures for Obtaining the

l/é-in.-dlam X 62-in.-long ~rods required for the survelllance assembly

‘as 1nd1cated by their f&brlcatlon history:

1.

=~ wmtor~ W

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o W N W N

. =

0 B A m N W oN

-

_ "Heats 5065 and 5085

Materials available as 1 1/8- and 9/16-1n plate, respectively.
Mill annealed 1 hr at 1177°C.

'Segments of l/4-in.-d1am,rod-machined.

" Reduced sections'turned'in'rods

~ Segments welded together to make 62-1n.-long rods.,

Annealed 2 hr at 900°C

_ -Heat 21545
_Materlal available as plates 1/2 in, thick x 3 in. wide X 12 in, long.
iFabrlcated with 40% re81dual cold work | |
Strips 1/2 x 1/2 X 12 in. cut from plate.
Strips machined to l/4-in;-d1am rods.
Rods were annealed 100 hr at g71° C.
Rods welded together.,'
Specimens machined.,

- | | Heat 21554

Material avallable as plates 1/2 in, thick X 3 in. wide X 12 in. long.

 Fabricated with 40% re81dual cold work,

. sPlate worked at 871°C to G 3 in. thlckness
;,Strlps 0. 3 X 0. 3 x 20 in.icut '

" strips machlned to 1/4 in. -diam rods
,tRods were . annealed 100 hr at 87l°C

Rods were straightened

'Rods reannealed 100 hr- at 87l°
- Rods welded together..j;:ff.,! |

Specimens machined.

 

o

 

°H. E. McCoy, Jr},'and.J. R. Weir, Jr., Materials Development for

 

Molten-Salt Breeder Reactors, ORNL-TM-1854 (June 1967),

 
 

 

 

Both procedures resulted in a very fine grain size (ASTM grain size
7 to 9).

Test Specimens

The surveillance rods inside the core are 62 in. long and those out-
side the vessel are 81 in. long. They both are 1/4 in. in diameter with
reduced sections 1/8 in. in diameter by 1 1/8 in. long. After removal
from the reactor, the rods aré sawed into small mechanical property'
specimens having a gage seetion 1/8 in. in diaméter\by 1 1/8 ih.\lbng.

The first rods were machined in small segments_tapprox 11 1/2 in.
long) and welded together. An improvement in this technique has been_

made that allows the entire rod to be machined as a unit (see Fig. 3).

§ PHOTO 91435

 

Fig. 3. Fabrication of Hastelloy N Surveillance Rods.

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A milling machine is used with a cutter-gfound to the shape of the gage
length, including the radius vhere the gage length blends into the full
1/4 in. dismeter of the rod. The rod is held in position and rotated

. while being fed into the milling cutter. The rod then requires only ‘a

light hand polishing of the gage sections to obtain the desired surface

- finish. This procedure is quicker, cheaper, and requires less handling

of the relatlvely fraglle rods than the previous method of making the

rods from segments.

Irradiation Conditions

The irradiation conditions in the core were described in detail
previously.’ These measurements were repegted for the second group of
‘core specimens and found to be in excellent agreement. The specimens

outside the core are exposed to the cell environment of N + 2=5% 0p. )

. The pertinent temperature and flux data are summerized in Tsble 2.

| Testing Techniques

The laboratory creep-rupture tests were run in conventional creep
machines of the dead-ioad'andrlever;arm'types. The strain was measured
by a dial indicator that showed the total movement of the spec1men and
part of the load:train. The zero strain measurement was taken immedi-

ately after the load was app;ied; The temperature accuracy was +0.75%,

_the guaranteed accuracy of the Chromel-P—Alumel thermocouples used.

The postirradlatlon creep-rupture tests were run 1n lever-arm

',rmachines that were located in hot .cells, The strain was measured byvan
7extensometer with rods attached ‘to the upper and ‘lower specimen grips.
The relative movement of these two rods was measured by & linear differ-

Vential transformer, and the transformer signal was recorded, The

~ accuracy of the strain_measnrements is difficult to determlne; ‘The

 

"H. E. ‘McCoy, Jr., An Evaluation of the Molten-Salt Reactor

'1;Experiment Hastelloy N Survelllance Spec1men-— First Group, ORNL-TM-1997
'(November 1967). |

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Table 2. Surveillance Program of the MSRE At
Group 18 Group 2
~ Core Core - Vessel !
Standard Modified ~ Standard
Hastelloy N Hastelloy N Hastelloy N
Date inserted " 9/8/65 9/13/66 8/24/65
Date removed | 7/28/66 5/9/67 6/5/67
Mwhr on MSRE at 0;0066 8682 0
time of insertion |
Mwhr on MSEE at 8682 36,247 36, 247
time of removal : : :
Temperature, °C 650+ 10 650 £ 10 650 £ 10
Time at temperature, hr 4800 5500 11,000
Peak fluence, neutrons/cm®
Thermal (<0.876 ev) 1.3 x 1020 4.1 x 1070 1.3 x 10%°
Epithermal (>0.876 ev) 3.8 x 10%° 1.2 x 1024 2.5 x 10%% !
(>50 kev) 1.2 x 10%0 3.7 x 1020 2.1 x 10%? .
(>1.22 Mev) 3.1 x 1019 1.0 x 1020 5.5 x 1018 :
(>2.02 Mev) 1.6 x 10%° 0.5 x 1020 3.0 x 1018
Peak flux,-neutrons em~? sec™! mw? | , , ‘
Thermal (<0.876 ev) 4,1 X 10'%(b,e) 4.1 x 102 (b,c) 1.0 x 10'! (b)
Epithermal (>0.876 ev) 1.2 x 103 (¢) 1.2 x 10** (c) 1.9 x 10 (v,c)
(>50 kev) 3.7 x 1012 (e¢) 3.7 x 10%2 (c) 1.6 x 101 (e)
(>1.22 Mev) 1.0 x 10'? (b,c) 1.0 x 102 (b,c) 4.2 x 10%0 (b)
x 1010 (b)

(>2.02 Mev) 0.5 x 102 (b,e) 0.5 x 102 (b,ec) 2.3

 

'_aRevised for full power operation at 8 Mw.
bExperimentally determined.
Ccalculated.
 

 

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- extensometer (mechanicaleand electrical portions) produced measurements

that could be read to about +0.02% strain; however, other factors (tem-
perature changes in the cell mechanical vibratlons, etce. ) probably
combined to give an overall accuracy of 0. 1% strain, This is consid-
erably better than the speclmen-to specimen reproduc1bllity that one

would expect for relatively brittle materials. The temperature measuring

Qand control system was the same as.that used in the laboratory with only

one exception.\ In the laboratory, the control system was stabilized at

the desired temperature by use of a recorder with an expanded scale In

-the tests in the hot cells,”the control point was established by settlng ’

the controller without the aid of the expanded-scale recorder.- This error

~and the thermocouple'accuracy combine to give a temperature uncertainty

of about +1%.

The ten31le tests were run on Instron Universal Testing Machines.
The strain measurements were taken from the crosshead travel,
, The test env1ronment was air in all’ cases. Metallographic examing-
tlon showed that the depth of oxidation was small and we feel that the

env1ronment did not apprec1ably influence the test results
EXPERIMENTAL RESULTS
Visual and Metallographic Examination

W. H. Cook was in charge of the disassembly of the surveillance
fixture. Although some dlfflcultles were encountered prevmusly,8 the

design modlflcatlons were successful and the assembly was in excellent

. mechanical condition when removed The graphite and Hastelloy N
'“surfaces were very clean w1th markings such as numbers and ‘tool marks
'ir‘fvery clear.' The Hastelloy N was ‘discolored very sllghtly Represen-
| tatlve photographs are shown in Fig. 4,1 -

 

'8W H. Cook, "MSRE Materlals Surveillance Program," Metals and

 Ceramics Div. Ann, Progr.-Rept June 30, 1967, ORNL-4170, """"pp 19,-195.

 
 

 

 

 

 

 

 

 

 

 

 

 

Fig. 4. Core Surveillance Specimens Removed on May 9, 1967.
(2) Outside of protective Hastelloy N basket. (b) Close-ups of the
top and bottom of the basket. (c) Surveillance stringer after removal
from the basket (curvature due to optical system in the hot cell).
(d and e) Close-ups of the surveillance specimens showing the high
reflectivity of the metal and graphite specimens. A few beads of
salt remain on the graphite.

.
 

 

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13

‘Small pieces of the modified alloys removed from the core were
examined metallographically Photomicrographs of heat 21554 (zirconium
modified) are shown in Fig. 5. The bulk material is characterized by a
very fine grain size and small inhomogeneouS'areas that were found to be
essentially pure ‘molybdenum (probably a result of poor melting practice).

The as=polished sample shows some very slight microstructural changes

- near the surface to a depth of 1 to 2 mils., Similar micrographs_are

shown in Fig' 6 for heat 21545 (titanium modified) The grain size of
this material is slightly smaller, but the other features are quite

similar to those observed for heat 21554

A small piece of the basket that contained the surveillance assembly
was examined.metallographically ' The basket was made from perforated .
Hastelloy N sheet. The entire surface exposed to the salt is character-
ized by the photomicrographs shown in Fig. 7. Small grains appeared to

. be almost dislodged from the surface [Fig. 7(a)]. After etching, a fine

precipitate was revealed near the surface to a depth of 1 to 2 mils.

We examined the_material,used,in.fabricating the basket; the micrOStruc-,
ture is shown in Fig. 8. ‘There is some precipitate near the surface,
but not in the quantities-observed in Pig. 7. We aged'a'piece of the
materiel for 1000 hr at 650°C (basket in MSRE was exposed 5500 hr) and
found that the quantity of precipitate increased (Fig. 9) _-However,

we were not able to dislodge any grains near the surface. even after a

| very sharp cold bend.

A sample from the basket wa.s sent to N. R. Stalica, Argonne National

- Laboratory, for microprobe studies. This 1nvestigator found that the
- precipitates contained silicon and oxygen_in large concentrations and

- suggested that they were SiOg.. Our studies on the finirradiated:speCimens

showed that the precipitates are metal-silicon compounds.! We are contin-

uing to 1nvestigate this p01nt but presently feel that the. precipitates

‘iare probably related to surface contaminatlon of the basket during fabri-

- ‘cation. The 8111con-rich contaminant should be dissolved during the post-

fabrication anneal (approx 1177 C) given the basket. and subsequently

i,precipitate while in. service at 650°C

 

 
 

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Fig. 6. Photomicrographs of Titanium-Modified Hastelloy N (Heat 21545) Removed from the MSRE

after 5500 hr at 650°C. Edge exposed to flowing salt.
100X. (c) Etchant: Aqua regia. 500X.

(a) As polished. 500x. (b) Etchant: Aqua regia.

 

 

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Fig. 7. Photomicrographs of the Edge of the Surveillance Basket
Removed from the MSRE after 5500 hr at 650°C. 500X. (a) As polished.
Note the grain near the surface that seems almost dislodged. (b) Etchant:
Aqua regia. Same area as shown in (a). Note the fine precipitate near
the surface. - g

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o ' Fig. 8. Photomicrographs of the Material Used in fia.king the
Surveillance Basket. The final processing step was a l-hr ‘anneal at
1177°C. Etchant: Glyceria regia. (a) 100x. (b),?OOXV.

%
 

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Fig. 9. Photomicrograph of the Material Used to Make the
Surveillence Basket after a 1l-hr Amneal at 1177°C and Aging for
1000 hr at 650°C. 750x. Etchant: Glyceria regia.

Small pieces of the standard Hastelloy N specimens that had been
exposed to the MSRE cell enviromment for 11,000 hr were examined. Micro-
structures of heat 5085 are shown in Fig. 10. A thin oxide is present
on the surface and some changes in microstructures occur to a depth of
sbout 3 mils. The sample examined from heat 5085 was from a welded
région. As shown in Fig. 11, tpe depth of attack seemed to be some-
what greater, but the reaction layer is very shallow, Neither specimen

showed any evidence of nitrogen absorption from the cell environment.

Mechanical Property Data — Standard Hastelloy N

The postirradiation tensile properties of heat 5065 are summarized
in Table 3., The fracture strains are plotted as a function of test
temperature in Fig. 12. There are significant reductions in the
fracture strain at 25°C and above 500°C. The properties of heat 5085
are given in Table 4. The fracture strains are plotted in Fig. 13 and
are very similar to those notédrfOr heat 5065. The strain at fracture

for both heats is reduced above about 400°C by reducing the strain rate.

 

 
  

 

   

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- Fig. 10. ‘P‘hotomicrograplris‘of 8 1/4-in.-diam Rod of Standard Hastellby N (Heat 5085) Exposed
to the MSRE Cell Environment of N; + 2-5% 0, for 11,000 hr at 650°C. (a) As polished. 500x.
(b) Etchant: Aqua regia. 100X. (c) Etchant: Aqua regia. 500X. _

 
 

 

 

 

 

 

Fig. 11. Photomicrographs of a 1/4-in.-diam Rod of Standard Hastelloy N (Heat 5065) Exposed to
the MSRE Cell Enviromment of N» + 2-5% 0, for 11,000 hr at 650°C. The cross section viewed is a weld
maede in joining small segments to make the single surveillance rod. (a) As polished. 500x. |
(b) Etchant: Aqua regia. 100X. (c) Etchant: Aqua regia. -500X. |

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. Table 3. Results of Tensile Tests on MSRE Surveillance Specimens — Heat 5065
L C ' ' , ‘ . ‘ . True‘
Specimen‘ Temg:f':.tur o | -Sfizfin Stress, psi Elongation, % Riiugi:n Fracture
Number . “" 7. c) (min~!)  Yield  Ultimate Uniform  Total (%) Stf;%“
9011 25 0.050 - 58,500 110,500 34.1 34.6 26.93 31
9012 . 200 0.050 43,100 111,000 61.2 63.2 46,14 62
9014 400 0.050 - 38,900 102,300  59.0 - 63.0 43,75 58
9033 40 . 0.,002 39,100 106,000 56.6 ~  57.7 43.75 58
9015 450 0,050 @ 38,200 100,200 56.5 ~ 58.8 '35.48 4,
. 9032 . 450 0,002 38,100 102,700 52.0 56,0  38.53 49
9016 . . 500 . . 0,050 40,200 104 300,  55.5 57.7 . 31.66 . 38
9013 - . - 500 0 " 0.002  ..39,500 ¢ 98 900 48.6 50.0 39.58 50
9017~ . . 550 0.050 @ 39,800 ;100,900 51.5 52.9 34.40 42
9022 550~ .. 0.002 36, 600 | 83,000  27.3 28.0 24,75 28
9018 - 600 - . 0.050 38,100 92,000 34.8 35.8 25.93 30
9023 - . 600 . 0.002 36,200 72,900 22.7 23.0 22.02 25
9019 . 650 0,050 40,700 199,200 25.3 25.8 22.73 26
9024 650 0.002 33,600 54,200 11,1 11,4 10.89 12
9020 760 - 0.050 31,100 56,800 6.8 7.3 14.79 16
9025 760 0.002 30,600 31,400 1.3 3.6 4.7 5
9021 850 0.050 29,500 43,400 6.2 7.5 4.78 5
9026 850 0.002 25,300 25,400 1.0 2.8 3.21 3

 

T

 
 

ORNL-DWG 68-4209

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

70 i | STRAIN RATE
® = .05min”!
L 4 =002 min™!
— T —¢
A T~
60 b ® ™~
\* S
/ \\ \,
50 Vi \
2® \
> \
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N\ \\ |
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0 ' ‘ — -
0 100 200 300 400 500 600 700 - 800 900 | 1000

'TEST TEMPERATURE,®C

Fig. 12. Variation of Ductility with Temperature for MSRE Surveillance Specimens. Heat 5065.
Thermal fluence was 1.3 X 10%? neutrons/cm?®.

22

 

 
 

 

 

" ORNL-DWG 68-4208

STRAIN RATE

 

- 80f

50

o .

 

s 05min~!
4=.002 min~!

 

 

 

TOTAL ELONGATION,

'.8'_

oo

 

 

 

I~

 

 

N ' "\

-‘*__

 

 

 

 

 

 

 

 

 

 

 

| |00200 - 300 400 500 600 700 800 900

TEST TEMPERATURE, °C.

1000

Fig. 13. Variation of Ductility with Temperature for MSRE Surveillance Specimens, Heat 5085,
Thermal fluence was 1.3 X 10? neutrons/em?. | | '

€2

 
Table 4. Results of Tensile Tests on MSRE Surveillance Specimens — Heat 5085

 

 

 

 

 

| | True
Test Strain Stress., psi Eloneation Reduction
Sfiggtmen Temperature Rate 1 2R 2 ’%1 in Ares F;:ctgre
er (°¢) (min‘l) Yield Ultimate Uniform Totea (4) ’f%)n

9047a 25 0.050 64,000 114,900 42.5 42.5 24 . 14 28
9049 200 0.050 39,000 102,700 49.8 - 51.0 39.30 50
2050 400 0.050 37,600 96,800 47.9 48.7 37.03 46
2069 400 0.002 36,600 95,300 46.3 46.9 32.88 40
9052 450 0.050 36,300 95,200 50.7 51.2 33.78 41
9070 450 0.002 36,400 92,700 42.5 43,1 26.93 31
9053 500 0.050 36,100 92,600 47.5 47.5 33.48 41
9058 500 0.002 38,100 78,700 23.3 24 .4 21.31 24
9054 550 0.050 35,500 89,800 42.8 43,8 25.93 30
9060 550 0.002 34,800 75 4200 23.4 24.1 21.31 24
9055 600 0.050 34,800 77,700 28.5 29.0 26.93 31
9061 600 0.002 33,700 64,600 17.5 18.2 23.35 27
9056 650 0.050 35,400 70,600 20.9 22 .4 22.02 - 25
92062 650 0.002 32,200 43,500 11.2 12.0 5.54 6
9057 760 0.050 29,000 49,700 12.6 13.5 12.49 13
9071 760 0.002 - 29,000 32,400 1.9 4.3 1.62 2
9059 850 0.050 27,800 37,900 6.3 9.7 7.84 8
9068 850 0.002 28,800 28,900 1.1 2.7 2.41 2

 

®Failure occurred in & weld in the gage section of this specimen.

 

 
 

o

1}

£ / | N

e ‘\ 5

Z 40 e \

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@ - 30 7 , coas’,o.osmin-'——_—\—‘?" \

s N

Pl o N\ N
20 — ‘j - — N \V - —VESSEL, 0.05 min™"

 

25

Some 1dea of the rate of property deterioration with fluence can
be obtained by comparing the results for hea.t 5085 obtained this time
on specimens irradisted outmde__the vessel to a thermal fluence of
1.3 x 10'° neutrons/em? with those obtained previously® for specimens

removed from the core with a fluence of 1.3 x 102° neutrons/cm?. The

unknown effects on the properties due to different times at temperature

must be recognlzed the core specimens for 4800 hr and the vessel

spec:.mens for 11,000 hr.. The results are compared in Fig. 14.

 

°H. E. McCoy, Jr., An Evaluatlon of the Molten-Salt Reactor
Experiment Hastelloy N Survelllance Specimen — First Group, ORNL-TM-1997
(November 1967). _

ORNL-DWG 68~ 4207R

. 1 T T T |

 

 

 

 

- LOCATION | THERMAL FLUENCE(neutrons/cm? ) ISTRAIN RATE (min™1)
70 : & - VESSEL 30 x1019 ‘ 0.05 .
1 ~ -a = VESSEL 30 x 109 0.002
® - CORE 1.3 x {020 005
» - CORE - 1.3 x 1020 0.002
60

 

 

* / : 5_“"_-5'.' \ ‘

 

 

 

 

 

CORE, 0:002 min™—"N\ \Q\\h\\ |
. : ' . s - . - - ’
o _ - S .\\\\ . ~N
| - ' | VESSEL,0002 min~'— T o
T SIS
0 0 200 300 400 500 600 700 800 900 1000
' o TEST TEMPERATURE (°c) ' ' a

 

 

 

 

 

 

 

 

 

 

 

 

 

'Flg. 4. A Comparison of the Ductility of Survelllance Specimens

- of Heat 5085 Exposed in the Core and Outside the Core Vessel,

 
 

 

 

26

1, the fracture strain is decreased

At a strain rate of 0.05 min~
appreciably as the thermal fluence increased from 1.3 X 101_9 to

1.3 X 1029 neutrons/cm®. At a slower strain rate of 0.002 min~!, the o
same trend holds, but the change is much smaller, If this same trend

persists to lower strain rates, the fracture strain in creep tests may

not be influenced significantly by fluence over the small range studied.

 

Our previous studies showed that the tensile properties of‘materials
irradiated in the MSRE and those irradiated in the ORR and ETR in a |
helium environment were similar, the only significant_differenée being
the reduction in fracture strain observed® at 25°C. The present results
are in good agreement with this conclusion. Our present studies also -
support previous observations® that the yield stress was unaffected by
irradiation and that the ultimate tensile stress was reduced sbout 10%
at low temperatures and progressively reduced further above 500°C to a
maximum of 30% at 850°C,

The results of several creep-rupture tests on the standard
Hastelloy N surveillance specimens from the second group are given in

Table 5. The stress-rupture properties are compared in Fig. 15 with

Table 5. Creep-Rupture Properties of Surveillance
Specimens of Standard Hastelloy N

 

 

i Stress Rupture Rupture Minimum
N:E;gr Sfii;figin Level Life ‘Strain Creep Rate
| (ps1)  (hr) (%) (%/nr)
Heat 5065
R-320 9030 47,000 23.0 2.10 0.081
R-313 9027 40, 000 39.7 2.12 0.034
R-315 9029 32,400 122.3 2.06 0.0078
R-326 9031 27,000 290.2 1.47 0.0035
| Heat 5085
R-321 9066 47,000 23,2 2,39 0.061 |
R-312 9063 40,000 6.7 2.28 0.029 ’
R-327 9067 32,400 336.6 2.25 - 0.0032
2.4 0.0063 - | .

 

R-418 9072 30,000 323.4
 

 

44

%)

T

27

 

ORNL—-DWG 68~6576R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

wo! 2. 10°

RUPTURE TIME (hr}

70
N,
60
\ ,
N, | | | L -UNIRRADIATED
\("
50 1 ;
11 N
| {114 « ‘
SN \
_ TN .
-8 40 s lolh
o N \
S IRRADIATED L~ - N
Pt (AVERAGE)/ M N
8 - R ORR o | (o)A | N
g 30 EXPER&MENTS NN N,
n bt \\~h.~ \‘
"\ \
50 ' MSRE SURVEILLANGE =~
VESSEL  CORE - ~ HEAT
o : 5065
o - u - 5085
: A - -s081
10 19 20
4 £3X10 3x10%Y THERMAL FLUENCE (neutrons/cm?)
' (000 4800  TIME AT 650°C (hr)- '
. HIIII I I|IIHII ||
o' 2 5 102 2 5 0% 2 104

Flg 15, Postirradlation Creep-Rupture Properties of MSRE Surveillance

Specimens at 650°C

those obtained previously on surveillance specimens from the core.

Standard Hastelloy N.

The

results on heat 5085 show clearly that the rupture life is less for the

rspecimens from the core tha.n for those from outside the vessel.

for this behavior.

compared in Fig. 16.

by irradiation.

- The fracture strains are shown as a functlon of stra:.n rate in

Heat 5085 seems to have _the_ poorest

This is
~ probesbly due to the thermal fluence of the material from the core being
'ihigher.by a factor of abdfit 10.
‘rupture life and”heat_5081'ffie'beSt;*there is no abparentiexPlanation )

The minimum creep rates for these Same materials are

ThlS parameter is not s:Lgn:.ucantly different for

The sca.tterband in this flgure was determined from results

~ the three heats of materlal 1nvolved a.nd is not influenced apprec:.ably

‘obtained on these same- materials irradiated to a thermal fluence of about

2 X 10?0 neutrons/cm? in the ORR.

The fracture strains are significantly

 
 

28

~_ORNL—DWG 68-6577R oW
70

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A

; 60

: ’,/

IRRADIATED AND /

'UNIRRADIATED 7/

f 50 L

/Jy 4

%

; = "

o 40

o

: o )

= Y

a h a7

o y

i & 30

i @ & / ol :

| ”//, MSRE SURVEILLANGE

i ) VESSEL CORE HEAT

| 20 Y \ o 5065

| v o . , 5085

| L/ . 4 5081

’ A 13%10'°  13%102% THERMAL FLUENGE (neutrons/cm?)

Y 11,000 4800  TIME AT 650°C (hr)

; 10
Y -4 -3 -2 -1 0O q
10 2. 5 40 2 5 10 2 5 {0 2 5 10 2 5 {0

 

MINIMUM CREEP RATE (%/hr)

Fig. 16. Variation of Minimum Creep Rate of Hastelloy N MSRE
Surveillance Samples in Postirradiation Creep Tests at 650°C.

higher for the specimens irradiated outside the vessel to a thermal
fluence of 1.3 x 10° neutrons/em® when tested at high strain rates (12
to 300%/hr). At lower strain rates most of the fracture strains are in
the range of 1.5 to 2.5%. Comparison of the results for the two sets of
specimens shows the fracture strains to be slightly lower for the specimens
exposed to the higher fluence in the core. These results do not indicate
! the very pronounced ductility minimum at a strain rate of about 0.1%/hr

| that is noted for these same materials when irradiated in the ORR. The
very long thermal exposures involved may be responsible for this behavior;
thatris, about 5000 hr in the MSRE compared with only 1000 hr in the ORR.
Heat 5081 shows unusually high strains and exhibits the trend of

increasing strain with decreasing strain rate.

 
 

 

W

.

n

 

29

o ' ORNL-DWG 68-6578R

5 . 25.8
, 224

MSRE SURVEILLANCE

| VESSEL. CORE HEAT
" e . . 5065
) o _ . l_ S 5085
") : : A 50814
t3x00 !3x!02° THERMAL
14,000 4800 TIME AT 650°C (hr)
g ° ‘
z
g 8
b=
w
&
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'—
Q
<
a
v o6

4 . SCATTERBAND FOR SEVERAL
AIR MELTS IRRADIATED
IN THE ORR

 

1073 02 o 10° 10' 102 10°
STRAIN RATE (%/hr)

- Fig, 17. Variation of Fracture Strain with Straln Ra.te for MSRE
Surveillance.Specimen at 650°C, Scatterband is for samples irradiated

~to a thermal fluence of 3 x 1020 neutrons/cm in the ORR -

1'Mecha.ni'cal ,Property :'D'a.t_a'—- 'Modified' Ha.stelloy N

Specimens of two modified Ha,stelloy N alloys were removed from the

o core surveilla.nce a.ssembly for examination and mechanical testing. Control
'specimens of these same- alloys were exposed to a static vessel of barren |
) _salt to duplicate the therma.l history of the sPec:imens in the reactor.,

, 'I'he tensne properties of the control specimens of heat 21554 (mrconium -

modlfied) are given in Table 6 the total strain to fracture is shown

in Fig. 18. The behavior is similar to that observed for sta.ndard

 
 

- Table 6. Results of Tensile Tests on MSRE Surveillance Control Specimens — Heat 21554

 

 

 

 

Specimen Test S.Ibtr:in Stress, psi Elongation, % Rgdu::ion Frzz}cl:re
Number Temperature ave, Yield Ultimete  Uniform  Total in Area Strain
(°c) (min=?) (%) (4)
5543 25 0.050 67,700 128,700 42.3 47,0 56.33 83
5544 200 0.050 60,000 115,900 39.9 42.9 59.80 91
5545 400 0.050 54,700 109,200 40.7 bk 46,82 63
5553 400 0.002 54,200 111,800 45.8 48.3 - 53.59 77
5546 450 0.050 53,000 107,200 41.3  44.3 54,56 79
5554 450 0.002 55,900 110,500 42.7 48.1 48.26 66
5547 500 0.050 51,400 106,900 42.5 4, 8 49.79 69
5555 500 0.002 58,600 111,400 39.9 45.3 43.69 57
5548 550 0.050 58,700 106,900 38.7 43.2 42.73 56
5556 550 0.002 59,800 101,300 - 26.4 28.0 24.70 28
5549 600 0.050 53,400 102,000 37.0 30.3 31.44 38
5557 600 0.002 56,800 91,000 22.7 25.0 24.18 28
5550 650 0.050 46,400 87,500 27.6 30.4 31.88 38
5558 650 0.002 55,800 - 75,500 13.3 46.6 63.15 100
5551 760 0.050 43,700 59,000 4.0 g.1 64 .27 103
5559 760 0.002 37,900 37,900 1.6 47.4 69.45 119
5552 850 0.050 36,900 37,700 7.5 56.5 69.70 119
5560 850 0.002 22,000 22,000 100.0 46.9 60.94 94

 

oe

 
 

 

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*

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31

ORNL-DWG 68-7761

 

 

 

 

 

 

 

 

 

 

60
!
50 : !
T — ]
< ._—--—_-_—_‘--_1l‘-¢': - -’_
g ' > |
Z 40 I
2 I
éao ' \ f\ 7 i
o . STRAIN RATE 3\ /
@ (min™1) \j \ "
3 20 * 005 vt
o s 0002 \ ;

 

5
4

 

 

 

 

 

 

 

 

 

 

 

0 .
0 100 200 300 400 500 600 700 800 900

TEST TEMPERATURE (°C)

Fig. 18. Variation of the Ductllity with Temperature for Control
Specimens of erconlum-Modlfied Hastelloy N (Heat 21554).

Hestelloy N, but the ductility of the zirconiumemodified alloy at 760°C
is considerably lower. The strong dependence of fracture strain on
strain rate at 760°C is also quite unusual where the strain is higher
at the lower strain rate; The properties of this material after

irradiation are given in st}e 7. The total elongatien of the irradiated

. material is shown in Fig. 19 as a function of test temperatures. The

behavior is very similar to thet'shown'in Fig. 14, p. 25, for the standard
Hastelloy N exposed under similar conditions; however, the fracture strain

at 600 to 700°C is higher for the modifled alloy. The ratios of the

‘various properties in the irradlated and unirradiated conditions are

shown in Fig. 20. The yleld and ultimate strengths were not affected
appreciably by 1rradiat10n. The ratio for the elongation at fracture
drops precipltously above about 600 C for standard Hastelloy N (ref. 10),

Vbut the very low elongatlon observed for the unirradlated zirconium-
7',mod1fied material at 760°C causes the ratio to be very high at this tem-
','perature. The behavior of the ratio for the reduction 1n area is quite

normal with the exceptlon of the reduction of this parameter by about 25%

'l:,at low temperature.

 

- 10§, E. McCoy, Jr.,iAn Evaluatlon of the Molten-Salt Reactor
Experiment Hastelloy N Survelllance Spec1men-— First Group, ORNL—BM—1997

o (November 1967)

 
 

Table 7. Results of Tensile Tests on MSRE Surveillance Specimens — Heat 21554

 

 

 

ce

True
Specimen Temgzizture S;::in Stress, psi Elongation, % R;g“;fii:n_ Fracture

Number ° -1 Yield Ultimate Uniform Total Strain
. _ (°c) (min=1) (%) (%)
9110 25 0.050 64,200 122,100 bl 47.5 39.08 50
9111 200 0.050 61,000 116,100 43.7 46,0 1 51.90 73
9112 400 0.050 52,700 109,100 42.5  46.2 34,96 43
9131 400 0.002 64,600 112,600 39.5 = 45.2 36,26 45
- 9114 : 450 0.050 56,000 110,200 - 39.8 42.3 33.24 40

9132 450 0,002 57,400 107,900 41.8 45.7 33.94 41
9115 500 0.050 56,900 109,900 40.4 434 33.48 41
9113 500 0.002 50,500 119,700 43.4  45.6 25.54 29
9116 550 0.050 60,200 107,700 47.5 36.52 45
9121 550 0.002 43,600 91,700 23.0 21.15 24
9117 600 0.050 52,700 9,100 32.0 28.09 33
9122 600 0.002 50,300 80,300 16.8 18.42 20
9118 650 0.050 25.54 29
9123 650 0.002 48,100 65,600 10.9 11.2 0 12.39 13
9119 760 0.050 42,400 55,400 6.6 6.8 10.89 12
9124 760 0.002 37,600 37,900 1.7 5.4 b 7 5
9120 850 0.050 34,800 38,600 3.1 6.4 6.27 6
9125 850 0,002 3,800 12,100 5.1 10.4 13.88 15

 

 
o it

 

 

ORNL ~DWG 68-7762

 

o -
O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

50 ; : —
L L . - ‘n‘ - .
& | ] —:‘fl
= 40
& L
E It E ! - \\ \
o . Y e
g 30 | T\ ‘\
o \
‘ . ] : o\
3 20 o ‘ N
E 'STRAIN RATE s \
= o tminthy N |
10 e 0,05 ‘ ‘ L L
| o 0.002 N "\\-.37%

0 100 2000 300 400 500 600 700 800 900

TEST TEMPERATURE (°C)

Fig. 19. Variation of the Ductility with
Temperature for MSRE Surveillance Specimens of
Zirconium-Modified Hastelloy N (Heat 21554),
Thermal fluence was 4.1 X 102° neutrons/em?.

IRRADIATED PROPERTY
UNIRRADIATED PROPERTY

 

1.2
o ! } 2 % R
1-0 ( I o 4 o
. A
o8 - 1 e
* .
0.6 T —— —
o YIELD STRESS | \
04— & ULTIMATE STRESS A
I @ TOTAL ELONGATION a
® REDUCTION IN AREA \
02 —— Ny
STRAIN RATE = 0.05 min~" \ /
a
L L ™

ORNL —DWG 687763

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0
0O 400 200 300 400
TEST TEMPERATURE (°C}

Fig. 20, Comparison of the Tensile Properties

of irra.dié.ted and Unirradiated Zirconium-Modified
Hastelloy N (Heat 21554).
4.1 % 1029 neutrons/cm?.

Thermal fluence was

500 600 700 800 900

£e

 
 

 

 

34

The tensile properties of the control specimens of heat 215457
(titanium modified) aré given in Tdble 8. The total elongation is shown
in Fig. 21 as a function of the test temperature. Therproperties are
quite similar to those observed for heat 21554 (Fig. 18, p. 31, and
Table 6, p. 30). The properties of the surveillance specimens are given
in Table 9, and the total elongation at fracture is shown graphically in
Fig. 22. The fracture elongations for this material are quite similar
to those shown in Fig. 19 for heat 21554."Thé ratio of the irradiated
to the unirradiated property is shown in Fig. 23. Generally the yield
strength is increased slightly by irradiation, and the tensile stress
is decreased. The elohgation at fracture is generally decreased, but
decreases precipitously sbove 600°C. However, the ratio at 760°C is
again high due to the extremely low elongation of the unirradiated
material. The ratio for the reduction in area is reduced sbout 30% at
low temperatures and decreases rapidly above 600°C.

Several creep-rupture tests have been run on both irradiated and
unirradiated specimens of heats 21554 and 21545, The results of tests
on these materials are given in Table 10 (annealed 100 hr at 871°C),
Table 11 (annealed 100 hr at 871°C and exposed to barren salt for
5500 hr at 650 + 10°C), and Table 12 (annealed 100 hr at 871°C and
exposed to MSRE enviromment for 5500 hr at 650 + 10°C)., The stress-
rupture properties of heat 21554 are compared in Fig. 24 for the various
conditions studied. The strength is reduced slightly by the long thermal
exposure to barren salt. Exposure to the MSRE environment reduces thé
rupture life at a given stress by about a factor of 10. The creep rates
of heat 21554 are compared in Fig. 25. The minimum creep rate is
increased slightly by the 5500 hr soak at about 650°C in the barren salt;
~ the same change is noted for the specimens removed from the MSRE.

- The creep-rupture properties of heat 21545 are shown in Fig. 26
for the various conditions studied. Just as noted for the zirconium-
modified alloy in Fig. 24, the rupture life of the titanium-modified
alloy is reduced slightly by the long soak in the barren salt and the
rupture life is reduced by a factor of 10 by exposure to the MSRE
- enviromment. The minimum creeprrate was not affected significantly by Q;j

any of the variables investigated, Fig. 27.

 
 

 

Table 8. :Results,of'Tensile Tests on MSRE Surveillance Control Specimens — Heat 21545

 

 

 

 

._ o True
Test - Strain si longatio Reduction
Spgcimen - Temperature Rate Stress, P ?ong ton, in Area ‘Fracture
Number — ~7 7, - -1 Yield Ultimate Uniform Total Strain
5531 25 . 0.050 95,700 = 127,100 38.1 42.3 - 61.05 - 9%
5530 -~ 200.  0.050 49,300 112,800 - 46.9 ' 50.9 . 55,45 81
5529 . . 400 . 0.050 © 46,000 107,600 46.4' 51,1 43.75 - 58 -
5521 . 400 : ¢ 0,002 51,800 @ 111,700 445 - 50.1 0 59.30 90
5528 =+ 450 - . 0.050 - 50,000 108,700 45.3 48.8  58.14 87
5520 .. 450 .- 0.002 51,100 109,200 45.6 47.7 43.69 57
5527 - 500 - 0.050 50,400 104,900 43.7 47.9 - 51.69 73
5519 . 500 0.002 47,900 106,900 41.8 45,2 42.06 55
5526 . - 550 0.050 49,500 102,800 42.7 48.0 51.36 72
5518 - 550 0.002 .= 47,800 93,500 24.9 26.5 31.51 38
5525 600 0.050 43,100 93,300 - 32.7 34.6 37.67 47
5517 600 0.002 48,000 84,600 - 23.5 24 .6 21.27 2%
5524 650 0.050 44,400 84,600 31.0 33.8 28.64 34
5516 650 - 0.002 45,200 68,500 16.5 - 40.8 43.84 58
5523 760 - 0.050 45,900 56,400 3.4 7.3 63.00 99
5515 - 760 - 0.002 37,900 37,900 1.3 - 43.8 63.9% 102
5522 . - 850 0.050 = 33,900 34,200 6.1 - 53.4 71.83 127
5514 . 850 0.002 20,100 20,300 0.9 44,0 - 55.77 82

Ge
 

ORNL~-DWG 68-7764
€0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. ORNL—DWG 68-T7765
| r 60
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Fd » \ " - .
z 40 STRAIN RATE \ M | ® \\\,\.
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® 0, ‘ <
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10 . \.‘.,' P " * 0002 \ \\ / &
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00 100 200 00 400 500 600 T00 80C 900 00 100 200 300 400 50 600 700 800 900
TEST TEMPERATURE (°C) TEST TEMPERATURE {*C)
Fig. 21. Variation of the Ductility with Fig., 22, Variation of the Ductility with
Temperature for Control Specimens of Titanium- Temperature for MSRE Surveillance Specimens of

Modified Hastelloy N (Heat 21545). Titanium-Modified Hastelloy N (Heat 21545},
| Thermal fluence was 4.1 X 10?0 neutrqns/cmz.

 
 

"‘Table 9. Results of Tensile Tests on MSRE Surveillance Specimens — Heat 21545

 

 

 

T \ - - : , True
Specimen 'T:::ture S;::in Stress, psi Elongation, % Rgfiufigizn Fracture
- Number - ?m?oc) 1 (min~1)  Yield Ultimate  Uniform  Total (%) Stfégn

9083. . 25  0.050 61,900 @ 145,600 46.3 50.3  45.71 61
9084% 200 .~ 0.050 80,300 111,200 38.9 411 42,53 55
9085 400 . 0.050 - 56,100 © 104,300 42.7 457 40,06 51
9105 . - 400. . . 0.002 ' 57,000 = 107,200 37.5 42,6 47.58 65
86 ' 450 0.050 54,200 - 104,300 44,5 47.0 - 37.54 47
9106 . 450 0,002 57,000 102,700 35.8 - 38.2 32.10 39
2088 500 . . 0,050 54,700 102,700 41.1 42,7 36.78 46
%089 500 0,002 53,000 86,700 32.2 35.2 29.88 35
9090 550 - 0.050 46,900 95,800 38.7 41.2 40.12 51
90%4 550 0,002 57,100 91,600 15.3 16.5 23.35 27
9091 600 - 0.050 44,500 83,600 25.2 . 26.93 31
9096 600 - 0.002 46,900 66,200 9.6 10.4 16.83 18
2092 650 - 0.050 45,200 73,700 13.4 14.6 12.79 14
9097 650, 0.002 48,900 58,900 5.4 6.2 4. 74 5
9093 = -~ 760 . - 0.050 - 39,000 46,800 5.4 - 5.8 3.98 4
9098 - 760 0,002 31,200 31,200. 1.3 5.7 5.54 6
9095 850 - 0.050 33,500 33,600 1.7 9.2 12.39 13
9104 - 850 0.002 = 8,100 10,600 1.1 20.2 19.07 21

 

‘aTest preloaded;:therefdre measured yield stress higher than normal and elongation lower.
 

ORNL ~-DWG 68-7766

»

-
o

B

Elz 10

LW

ala

el

Ela 08

i

2lq 06

2lg YIELD STRESS

E|E ULTIMATE STRESS
z 04 TOTAL ELONGATION

REDUCTION IN AREA
STRAIN RATE = 0.05 min~!

o
m

 

°
o 100 200 300 400 SO0 600 7TO0 800 900

- TEST TEMPERATURE (*C)

Fig. 23. Comparison of the Tensile Properties
of Irradiated and Unirradiated Titanium-Modified
Hastelloy N (Heat 21545). Thermal fluence was
4.1 % 1029 neutrons/cm?. ‘

ORNL-DWG 88-7767

 

70 "

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N
I
b
60 N a ANNEALED
N * CONTROL
\.\ o IRRADIATED
50 N
N {\ .'\.‘\
% 40 iy \\-
o \\ \\\\
= & \\\\
[3] >\ \p:‘ &
30 e ™ \‘
E N
~
20 N
10
0
10° o' to? 10° 10

- RUPTURE TIME ({hr) -

Pig. 24, Creep-Rupture Properties of
Zirconium-Modified Hastelloy N (Heat 21554)
at 650°C. in Several Conditions; Annealed at
871°C (see p. 7); Annealed at 871°C and Aged
for 5500 hr at 650°C in Static Fluoride Salt;
and Irradiated to a Thermal Fluence of
4.1 x 10?9 neutrons/cm?,

8¢

 

 
 

© Table 10.

 

 

Creep-Rupture Properties of Heats 21545 and 21554

 

 

1768

at 650°C After Annealing 100 hr at 871°C
Test = Specimen | Rupture Rupture Reduction Minimum Fracture
- Number Number Stress Life Strain in Area Creep Rate Strain
" | Tos) () (B) (%) B)  (#)
o . |  Heat 21554 |
5862 2435 47,000 128.3 3.0 50.6 0.203 7
5857 . 2434 40,000 324.2 355 519 0.056 73
5858 2491 . 40,000 226.3 60.8 . 50.9 0.128 71
6168 2433 32,400 1390.9 = 55.1 42,4 0.0176 55
. : s Heat 21545 |
540907 1771 - 55,000 201 52,5 47.3 1.37 64
5564 1822 40,000 . 248.1 b 20.5 0.0688 23
5580 1773 40,000  242.6 59.4 56.6 0.120 84
5449 30,000 1171.5 56.7 51,5 0.0174 72

 

6¢

 
 

Table 1l1l. Creep-Rupture Properties of MSRE
Surveillance Control Specimens at 650°C

 

 

Test Specimen Rupture Rupture Reduction Minimum Frg}l;zre
Number Number Stress Life Strain in Area Creep Rate Strain
| (psi) (hr) (%) (%) (%/hr ) (%)
Heat 21554 ’ '
6399 - 5535 70, 000 3.3 60.6 48.3 8.375 67
6398 5536 63,000 8.3 50.0 50.1 3,20 70
6397 5537 55,000 28.2 55.8 45.0 1.01 | 60
6380 5538 47,000  58.1 38.3 58.3 0.365 88
6425 5540 47,000 84.1 75.1 56,0 10.363 82
6390 5539 40,000  228.7 69.5 56,6 0,120 &
6426. 5541 40,000  244.0 63.1 49.6 0.113 69
6427 5542 32,400  709.8 56,1 49.7 0.032 69
| Heat 21545

638, 5508 . 70,000 1.9 39.2 30.6 | 36
6385 5509 63,000 5.5 46.1 32.7 450 40
6386 - 5510 55,000  15.7 47.4 34.3. 2.50 42
6387 5511 47,000  50.8 43.9 bbsi 0.50 59
6388 5512 40,000  177.2 55,3 45.1 0.165 60

6428 5513 32,400 438.8 = 40.1 49.8 | 0.0398 - 69

oY%

 

 

 
 

A

 

41

Table 12, Creep-Rupture Properties of Surveillance
Specimens of Modified Hastelloy N at 650°C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Teét” Specimen - Stress 3Rupture ~ Rupture Minimum
Nasber fiumber Level Life  Strain = Creep Rate
| | - (psi) (hr) (%) ~ (%/nr)

Heat 21554 |
‘R-316 9127 47,000 11.1 4,57 0.343
R-311 | 9126 40,000 19.3 3.99 - 0.138
R-318 9128 32,400 5.4 2.36 0.013
R-322 9129 27,000 204.9 3.45 0.0088
| | Heat 21545 |
R-317 . 9100 47,000 2.8 1.59 0.455
R-314 9099 40,000 13.1 2.68 0.085
'R-319 9102 32,400  51.1 3.39 0.0180
R-323 9103 27,000 - 124.1 3.69 0.0089
ORNL-DWG 68-7768
70 “TTIH
A
1
60 © IRRADIATED /
' = ANNEALED | ;/
. - A
50 ‘/
- L
& a0 » " :
.-§.-, ' ‘ A /:/”
| E’p T
20 +
10
040"’ - so‘zr — ot 10° e
S  MINIMUM CREEP RATE Whr)

Fig. 25. Varlatlon of the Minlmum Creep Rate Wlth Stress for

f Zircon1um-Mbdified Hastelloy N (Heat 21554) at 650°C. Tested after

650°C in. static fluoride salt and 1rradiated to a thermal fluence

of 4.1 x 1020 neutrons/em?.

 
 

10 ORNL-DWG 68~T7769 ORNL-DWG 68-7770

 

 

3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"N
\\o\ H ’ m TDLOl ."
* CONTROL [
&0 1N e CONTROL % o IRRADIATED f
'§§\ o IRRADIATED 8" AS ANNEALED P

50 < K a AS ANNEALED 50 5
:§. : \‘\.‘ . \::: § //.m
8 40 .\‘\ \\3.“% § 40 L]
Q \\ Q ‘ 11
= \\ \\\ = L1
@ a o| TN @ o//o
w 30 » i i) 30 /‘—"
E \ 5 ,’a‘f

20 20

10 0

0 | 0

10° o' 102 - 10° - 0? \ 1073 102 0! 1 10’
RUPTURE TIME (h'_') ‘ MINIMUM- CREEP RATE (%/hr) .
Fig. 26, Creep-Rupture Properties of Fig, 27. Variation of the'Mihimum Creep Rate
Titanium-Modified Hastelloy N (Heat 21545) at with Stress for Titanium-Modified Hastelloy N
650°C in Several Conditions: Annealed at 871°C (Heat 21545) at 650°C. Tested after annealing at

(see p. 7), Annealed at 871°C and Aged for 5500 hr 871°C (see p. 7), annealing followed by 5500 hr at
at 650°C in Static Fluoride Sza,lté and Irradiated 650°C in static fluoride salt, and irradiated to a
to & Thermal Fluence of 4.1 X 10?C neutrons/cm?. thermal fluence of 4.1 X 10?° neutrons/em®.

c7

 

 
 

 

 

 

43

- The fracture strains of these materials in the unirradiated state

" under creep conditions are-excellent, ranging from 30 to 60% (Tables 10
- and 11). However, the fracture strains after irradiation are appreciably
less ranging from 1. 5 to 4.5% (Table 12) These Strains are generally
“higher than those obtained from standard Hastelloy N (Fig. 17 p. 29).

Metallographic Examinatien of Mechanical Property Specimens_

: Several of the fractured test specimens were examined metallograph-
| ically Typical micrographs'frcm a specimen of heat 5065 exposed to the
cell env1ronment for ll 000 hr and tested at room temperature are shown
in Fig. 28. Flgure 28(a) ‘shows the fracture region and demonstrates the

‘mixed intergranular-transgranular nature of the fracture. The edge of
the gage section is shown' in Fig. 28(b). There isivery little edge-
cracking or other indications of deleterious reactions with the MSRE
cell environment. Large:quantities of fine precipitate that formed
during the long thermal history are also obvious. A higher magnification
photomicrograph.made near the surface is shown in Fig.e28(c) Significant
features are the llmlted surface reaction and the coplous quantities of
fine pre01pitates.
| Photomicrographs of a spec1men from heat 5065 tested at 650°C are

shown in Fig. 29. The fracture shown 1n Fig. 29(a) is completely inter-
granular and typical. of'materials exhlbltlng low fracture strains.

~  The microstructure of a speclmen from heat 5065 that was tested in
{\creep at 650°C and 27,000 psi is 1llustrated in Fig 30 Flgure 30(a)
f shows that the fracture 15 entlrely intergranular with some cracklng
 near the fracture.- Flgure 30(b) and (c) shows the thin reaction layer
at the ‘surface and the large amount of fine precipitate that formed.
| _ Several photomlcrographs of the specimen of heat 5085 tested at
“;25 C. are shown in Flg.;Bl The gage portlon of this spec1men contalned

‘a weld and the fallure occurred in this reglon [Fig. 31(a)] There is
Ta very thin reglon near the surface that shows some modlflcation of

'?microstructure [Flg Bl(b) and (c)] ThlS layer is quite 51m11ar in

 
 

 

 

 

 

 

 

 

 

a)

Fig. 28. Photomicrographs of & Hastelloy N Surveillance Sample (HEat.5065) Tested at 25°C at a

| i

 

Strain Rate of 0.05 min™'. Exposed outside the core for 11,000 hr at 650°C to a thermal fluence of

1.3 x 10'% neutrons/cm®. Etchent: Aqua regia. (a) Fracture — note the mixed transgranular and inter-
granular fracture. 100x. (b) Edge of sample sbout 1/2 in. from fracture., Note the fractured precipi-
tates. 100x. (c¢) Edge of sample showing shallow surface oxidation and extensive precipitation. 500x.

C ' - . C

 
 

 

 

 

 

 

45

|R-11238

 

Fig. 29. Photomicrograph of the Fracture of a Standard Hastelloy N
Surveillance Sample. (Heat 5065) Tested at 650°C at a Strain Rate of
0.002 min~!, Exposed outside the core for 11,000 hr at 650°C to a
thermal fluence of 1.3 x 10%° neutrons/cm 1OOX. " Etchent: Aqua regia.

R-41542 [

 

 

 

(a)]

 

 

Fig. 30, Photomicrographs of a Standard Hastelloy N Surveillance
Semple (Heat 5065) Tested at 650°C and 27,000 psi. Failed in 290 hr
after strainlng 1.47%. Prior to testing, ‘the sample was exposed outside
the MSRE core for 11,000 hr at 650°C ‘to & thermal fluence of 1.3 X 10%°
neutrons/cm?. Etchant* Aqua regla. (a) Fracture — note the predominately
intergranular fracture 1100%, " (b) Edge of sample about 1/2 in. from
fracture. 100x. (e¢) Edge of sample showing shallow oxldation and
extensive precipitation. - 500%.

 
 

 

 

46

 

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N
v u...flht“,l.
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1lance Sample (Heat 5085) Tested at -

 

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47

 

appearance to that noted préviously'® for this material when exposed to
the core enviromment, However, this layer seems to have only minor
effects on the deformation as evidenced by the very limited surface
cracking shown in Fig. 31(ec).
The fracture of a SPecimen from heat 5085 that was tested at 650°C

is shown in Fig. 32. The fracture is completely'ihtergranfilar and shows

little evidence of plastic_defdrmation.' A comparison.of'Figs. 32 and

31(b) gives an indication of the wide variation in the grain size of

this material.

 

“1lH, E. McCoy, Jr., An Evaluation of the Molten-Salt Reactor

Experiment Hastelloy N Surveillance Specimen — First Group, ORNL-TM-1997

(November 1967)

R-1129 |

 

Fig. 32. Photomicrograph'of'therFracture'of'a Standard Hastelloy N
Survelllance Semple (Heat 5085) Tested at 650°C at a Strain Rate of
0.002 min~!, Exposed outside the core for 11,000 hr at 650°C to a

:thermal fluence of 1.3 X 1019 neutrons/cm2 100x. Etchant: Aqua regia.

 
 

 

 

48

Photomicrographs of a specimen of heat 5085 that was tested in
creep at 650°C are shown in Fig. 33. The fracture is entirely inter- .
granular with a few cracks near the fracture. The thin reaction layer
near the surface is apparent in Fig. 33(b) and (c).

Both the control and the irradiated specimens from heats 21554 and
21545 were exposed to salt for 5500 hr. The microstructures of thesé
alloys before'stressing were shown in Figs. 5 and 6, pp. 14 and 15. The
microstructure of a specimen from heat 21554 that was tested at 25°C is
shown in Fig. 34. The fracture was predominately transgranular., There
was a layer near the surface of the specimen that showed.eXten§;ve
intergranular cracking [Fig. 34(b) and (c)]. A typical phbtamicrografih'
of the control sample is shown in Fig. 35. The fracture is a typical
ductile shear type and there is no appreciable edge cracking.

The microstructure of a specimen of heat 21554 tested at 650°C is
illustrated in Fig. 36. rThe fracture is intérgranular and ielatively_
brittle in appearance [Fig. 36(a)]. The edge cracking is quite extensive
at this temperature also. The fracture of the control specimeh'(Fig.;37)
is mixed intergranular-transgranular. There.is some edge crécking,\but
not at the frequency noted for the irradiated sample [Fig. 36(b)].

At a test temperature of 850°C, the fracture strain for heat 21554
after irradiation was higher than at 650°C. The microstructures shown in
Fig. 38 for the specimen tested at 850°C support this obser?ation. The
fracture is entirely intergranular with extensive intergranular cracking
throughout the sample. The edge cracking is not quite aé severe at this
temperature [Fig. 38(b) and (¢)]. The fracture of the control sample
is shown in Fig. 39. The original grain structure has been fragmented
completely because of the very high mobility of the grain boundaries
at this temperature. |

" The microstructural features of heat 21545 were quite similar to
those for heat 21554, Typical photomicrographs for heat 21545 are shown
in Figs. 40 through 45 for fensile test temperatures of 25, 650, and 850°C.
Significaht features are the shear fracture at 25°C in the irradiated

and unirradiated conditibns,-the extensive edge cracking in the

 
 

 

   

 

 

 

 

 

Fig. 33. : Photomicrographs of a Standard Hastelloy N Surveillance Sample (Heat 5085) Tested at
650°C and 30,000 psi. Failed in 323.4 hr after straining 2.4%. Prior to testing, the sample was
‘exposed outside the MSRE core for 11,000 hr at 650°C to a thermal fluence of 1.3 X 10° neutrons/cm?,
Etchant: Aqua regia. (a) Fracture, 100x. (b) Edge of sample about 1/2 in. from fracture. 100x."

(c) Edge of semple showing shallow surface oxidation and extensive precipitation, 500x.

 

6Y

 
 

 

 

 

 

N R=l 1 UBH

““ -
A2 T |

 

qnn;,\'“‘ e

 

 

 

Fig., 34. Photomicrographs of a Zirconium-Modified Hastelloy N Surveillance Sample (Heat 21554)
Tested at 25°C at a Strain Rate of 0,05 min~!., Exposed in the MSRE core for 5500 hr at 650°C to a

thermal fluence of 4.1 X 1020 neutrons/cm?. Etchant: Aqua regia. (&) Fracture. 100x. (b) Edge of
sample sbout 1/2 in. from fracture. 100x. (c¢) Edge of sample showing edge cracking. 500X.

13+ %

 

0s

 
 

 

 

TFig. 35, Photomicrograph of the ¥racture of a Zirconium-Modified Hastelloy N Samplé (Heat 21554)
Tested at 25°C at a Strain Rate of 0,05 min™!, Exposed to a static fluoride salt for 5500 hr at 650°C
before testing. Note the shear fracture and the absence of edge cracking. 100x. Etchant: Glyceria
regia. ~ | 2 S - ' _ . .

   

 

ERRE

15
 

 

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| Fig. 36, Photomicrographs of a Zirconium-Modified Hastelloy N Surveillance Sample (Heat 21554)
Tested at 650°C at a Strain Rate of 0.002 min™!, Exposed in the MSRE core for 5500 hr at 650°C to &
thermal fluence of 4.1 x 10°° neutrons/ecm?. Etchant: Aqua regia. (a) Fracture. 100x. (b) Edge of
sample about 1/2 in. from fracture. 100x. (c¢) Edge of sample showing edge cracking, Oxide formed

during the tensile test. 500x,

cs

 
 

 

",

 

n

 

 

. Fig. 37.  Photomicrograph Showing a Portion of the Fracture of a
ZirconiumpModified.Hastellog‘N\Sample (Heat 21554) Tested at 650°C at -
& Strain Rate of 0.002 min~", Exposed to static fluoride salt for

5500 hr at 650°C before testing. 100X. Etchant: Glyceria regia.

 

£S

 

 
 

 

 

 

 

 

 

Fig. 38. Photomicrographs of a Zirconium-Modified Hastelloy N Surveillance Sample (Heat 21554 )
Tested at 850°C at a Strain Rate of 0.002 min-!, Exposed in the MSRE core for 5500 hr at 650°C to a
thermal fluence of 4.1 X 1020 neutrons/cm®. Etchant: Aqua regia. (a) Fracture. 100X. (b) Edge of
sample about 1/2 in. from fracture, 100x. (c) Edge of sample showing edge cracking. Oxide formed
‘during the tensile test, 500x. | o | | -

e

 
i_r

 

W Y-53585

 

’jFig}”39"‘Phbtdmiérograph Showing the Fracture of*a;Ziréonifim;

“37Modified Hastelloy N Sample (Heat 21554) Tested at 850°C at e Strain
' Rate of 0,002 min~!

 650°C before testing.
100x. - Etchant Glyceria regia.

Exposed to static fluoride salt for 5500 hr at
Note the extensive grain boundary migration.

 

o

Gs
 

 

 

 

 

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‘3 . -
E
.
e 1
srieeL
T
* L
F Y .
bt
]

Yt s

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=TS

-

e
(™

 

 

Fig. 40. Photomicrographs of a Titanium-Modified Hastelloy N Surveillance Sample (Heat 21545)
Tested at 25°C at a Strain Rate of 0.05 min~!., Exposed in the MSRE core for 5500 hr at 650°C to a
thermal fluence of 4.1 X 10?0 neutrons/cm?®. Etchant: Aqua regia. (a) Fracture. 100x. (b) Edge of
sample about 1/2 in, from fracture, 100x. (c) Edge of sample showing edge cracking. 500x.

 

9¢

 
  

     

 

 

 

Y-83570

 

   

   

LS

 

Pig. 41, Photomicrograph of the Fracture of a Titéhium;Mbdifiéd
" Hastelloy N Surveillance Sample (Heat 21545) Tested at 25°C at a Strain )
N .Rate of 0,05 min=!, Exposed to a static fluoride salt for 5500 hr at

 

 

- 650°C before testing Note the shear fracture and the absence of edge
cracking. 100x, Etchant- Glyceria regia, -
 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 42. Photomicrographs of a Titanium-Modified Hastelloy N Surveillance Sample (Heat 21545)
" Tested at 650°C at a Strain Rate of 0,002 min~!, Exposed in the MSRE core for 5500 hr at 650°C to
‘& thermal fluence of 4,1 X 10?C neutrons/cm®. Etchant: Aqua regia, (a) Fracture. 100x. (b) Edge
of sample about 1/2 in. from fracture. 100x. (c) Edge of sample showing edge cracking. Oxide
formed during the tensile test. 500X, ; ‘ - o o

8¢

 
 

fpre L

mmY-83573

  
     

Fig. 43. Photomicrograph Showing a Portion of the Fracture of a
Titanium-Modified Hastelloy N Surveillance Sample (Heat 21545) Tested at

- 650°C at a Strain Rate of 0,002 min~!, Exposed to static fluoride salt
for 5500 hr at 650°C before testing. 100x. Etchant: Glyceria regia.

 

 
 

 

 

 

LLEY

N

LT Rl A

5.4
-
. Vi
el

 

 

 

Fig. 44. Photomicrographs of a Titanium-Modified Hastelloy N Surveillance Sample (Heat 21545)
Tested at 850°C at a Strain Rate of 0.002 min~!. Exposed in the MSRE core for 5500 hr at 650°C to
a thermal fluence of 4.1 X 1020 neutrons/cm?. Etchant: Aqua regia. (a) Fracture. 100X. (b) Edge
of sample about 1/2 in. from fracture. 100X, (c) Edge of sample showing edge cracking. Oxide
formed during the tensile test. 500x. - R | T

09

 
 

Rate of 0.05 min~ .
650°C before test

 

o i b A Ao a5

 

-  FigJ 45.Phgtdmicrographof the Fracture of a Titaniumerdified
(Heat 21545) Tested at 25°C at a Strain

Hastelloy N Surveillance Sample _
1, Exposed to a static fluoride salt for 5500 hr at
ing., Note the shear fracture and the gbsence of edge

cracking. 100x. Etchant: Glyceria regla.

 

 

19

 
 

 

62

irradiated material, a completely intergranular fracture of the irradiated
material at 650°C compared with a mixed transgranular and intergranular
fracture in the unirradiated material, and grain boundary migration at a

test temperature of 850°C.

DISCUSSION OF RESULTS

The stendard Hastelloy N used in constructing the MSRE continuee to
show excellent compatlblllty W1th the fluorlde salt environment and ‘the
| cell env1ronment con51st1ng of NQ-Q to 5% 02.‘ There was no evidence of
n1tr1d1ng, and the depth of oxidation in 11,000 hr was only a fEW'mllS.‘
We knew from prev1ous studies that the mechanlcal propert;es of Hastelloy N
would detericrate due to irrediation damage.lz‘17 Our examination of.the
first group of surveillance specimens18 showed that the property changes
fiere as-predicted, the only exception being & reduction in- the ductility
at 25°C. Extraction replicas showed. that-extensive'carbide'brecipitatien
occurred along the grain boundaries durlng irradiation at 650°C, and. thls
probably accounts for the reduction in ductlllty at 25°C, oo

Our primary purpose in this program is to contlnually assess the?

condition of the MSRE core vessel. The surveillance facility in the core

 

124, E. McCoy, Jr., and J. R Weir, Jr., Materlals Development for’
Molten-Salt Breeder Reactors, ORNL-TM-1854 (June 1967). .

13y. R. Martin and J. R. Weir, "Effect of Elevated Temperatfire
Irradiation on the Strength and Ductility of the Nickel-Base Alloy,
Hastelloy N," Nucl, Appl. 1(2), 160-167 (1965).

l4w. R. ‘Martin and J. R. Weir, "Postirradiation Creep and Stress-__
Rupture of Hastelloy N," Nucl, Appl 3(3), 167 (1967). g

154, E. McCoy, Jr., and J. R. Weir, Jr., "Stress-Rupture Properties
of Irradiated and Unirradiated Hastelloy N Tubes," Nucl. Appl. 4(2),- "
96 (1968). . i.fi»

16y, E, McCoy, Jr.; Effects of: Irradlatlon on the Mechanlcal
Properties of Two Vacuum-Melted Heats of Hastelloy N, ORNL-EM-2043
(January 1968). |

174, E. McCoy, Jr., and J. R, Weir, Jr.; In- and Ex-Reactor Stress-
Rupture Properties of Hastelloy N Tubing, ORNL-TM-1906 (September 1967).

184, E. McCoy, Jr., An Evaluation of the Molten-Salt Reactor
Experiment Hastelloy N Surveillance Specimen — First Group, ORNL-TM-1997
(November 1967).

¥

 
 

 

63

receives a thermal flux about a factor of 40 higher than that received
by the vessel. The first surveillance specimens removed from the core
received a thermal fluence’of 1.3 x 1020 neutrons/cm? while being heated
for 4800 hr. The surveillance specimens of standard Hastelloy N removed
with the second group were located outside the core and received a thermal
fluence of 1.3 x 101° neutrons/cm while being heated for 11,000 hr. The
. latter group should indicate more closely the properties of the vessel,
but a comparison of the properties of both groups is important in trying
to estimate the future properties. The fracture strain in tensile tests
- (Fig. 14, p. 25) is reduced'even more by the.higher‘fluence. In creep-
rupture tests at 650°C (Fig. 15, p. 27), the rupture life is also slightly
shorter and the strain at fracture (Fig. 17, p. 29) slightly less for the
specimen irradiated to the higher fluence. In the unirradiated condition,
| heat 5085 exhibited fracturepstralns of 20 to 40% in creep-rupturetests
cqmpared with fracture strains of about 2.2 and l.fi% after irradiation to
‘thermal fluences of 1.3 x 10° neutrons/cm® and 1.3 x 102° neutrons/cm?,
respectively.‘ Thus; even though-the properties continue'to change
slightly with increasing flnence, the rate oflchange has decreased
_markedly I ' | o
- Another encouraging observation is that the MSRE materials do not
seem to have as low minimum fracture strains after irradiation as we
have noted for the same materials after irradiation to the same fluences-
in the ORR (Fig. 17, p. 29). ‘This may be due to the more extensive
carbide precipitation in the materials irradiated in the MSRE for long
.periods of time. _ o
- The modified alloys, heats 21554 (zirconlum.modlfied) and 21545
(titanium.modified), were annealed to produce a.small grain size.
~_Since these samples were placed in the MSRE we have found that material
"'annealed ‘to produce & coarser grain size has better properties after

_1rradiation.19 Thus we were not surprised that the postirradlation |

 

_ 1°H, E, McCoy and J R Weir, "Development of a, TitaniumsModified

g Hastelloy with Improved Resistance to Radiation Damage,” paper presented
.at the Symposium on Effects of Rediation on Structural Metals, American

Society for Testing and Materials, San Francisco, Califbrnia, June 23-28,

1968. To be published in the proceedings.

 
64

properties of the modified alloys were not much better than those observed
for the standard Hastelloy N. However, two encouraging observations were
‘made that demonstrate the sbsence of embrittling aging reactions: (1) the
mechanical properties of the control specimens exposed,to'salt for 5500 hr
vere only slightly different from those of the as-annealed material

(Figs. 24 and 25, pp. 38 and 41) and (2) the strain at fracture in tensile
tests at 25°C fias not reduced by irradiation. The most disturbing obser-
vation is the infergranular cracking near the surface of specimens that
were removed from the reactor.. Our measurements?? of the lattice diffusion
of titanium in the modified alloy indicate that the gradients in these
samples should extend to a depth of ouly about 0.15 mil (based on a
lattice diffusion coefficient of 1 X 10”1’ cm?/sec and 5500 hr exposure

at 650°C)..waever, titanium can diffuse more rapidly along the graiu
boundaries and we can approximate‘this'depth-of removal by_the Fisher
model.?l Assuming that the grain boundary diffusion rate is 10% times
that for the lattice,2? significant depletion of the titanium should
ocecur along the grain boundaries to depths of about 4 mils. This is in
reasonable agreement with the depth of the surface cracks observed in fhe
surveillance specimens (Figs. 34 and 40, pp. 50 and 56). However, the
control specimens (Figs. 35 and 41, pp. 51 and 57) were exposed to static
salt but did exhibit edge cracking when tested. It is possible that
corrosion in the static vessel proceeds more slowly than in the flowing
reactor circuit or that the grain boundary cracking may be a result of

the loss or ingress of some element besides titanium.

SUMMARY AND CONCLUSIONS

We have examlned the second group of survelllance samples removed

from the MSRE Two rods of standard Hastelloy N were removed from the

 

200, E. Sessions and T. S. Lundy, "Diffusion of Titanium in Modified
- Hastelloy N," Molten-Salt Reactor Program,Semlann Progr. Rept Feb. 29,
1968, ORNL- 4254, Pp. 213— 215.

213, C. Fisher, "Calculation of Diffusion Penetration Curves for
Surface and Grain Boundary Diffusion," J. Appl. Phys. 22, 74 (1951),

22y R. Upthegrove and M. J. Sinnott, "Grain Boundary ‘Self-Diffusion
of Nickel," Trans. Am. Soc. Metals 50, 1031 (1958).

 

 

 

 
 

- study.

 

65

surveillance position outside the core after 11,000 hr at temperature
with a thermal fluehce-of 1.3 x 1019 neutrons/cm2 The compatibility
of the material with the cell environment of nltrogen plus 2 to 5% O,
seems excellent with no ev1dence of nitriding and only superficial

oxidation. Mechanlcal property tests show that the fracture strain at

25°C and above 500°C was reduced markedly by irradiation. Creep-

rupture tests at 650°C_show a reduction in rupture life and ductility..

. A comparison with results from the first group of surveillance specimens

exposed to the core envirenment to a fluence of 1.3 x 10?° neutrons/em?
indlcated that the mechanlcal properties deteriorated only sllghtly
with 1ncreasing fluence. o

Two heats of modified Hastelloy N containing 0.5% Ti and O. 5% Zr were
removed from the core w1th a thermal fluence of 4.1 X 1020 neutrons/cm
They had not been annealed to obtain the optimum properties and their

postirr&diation'mechenical properties were only slightly better than those

observed for the stsndard alloy. waever, these alloys did not seem to

age and their corrosion re51stance seems acceptable,

ACKNOWLEDGMENTS

‘The author is indebted to numerous persons for assistance in fhis

W. H. Cook and A. Taboada — Design of surveillance assembly and insertion
, i of speclmens
W. H. Cook and R. C. Steffy-— Flux measurements

g R. Weir, Jr., and W. H Cook'— Rev1ew of the manuscrlpt
','E° J. Lawrence and J L Grifflth'— Assembled survelllance and control

 specimens in fixture.

- P@ Haubenreich and MSRE Operatlon Staff — Exercised extreme care in

insertlng and remov1ng the

surveillance specimens,

 
 

 

H.
V.

R.

C.

66

King and Hot Cell Operation Staff — Developed techniques for
cutting long rods into individ-
ual specimens, determined
specimen straightness, and
offered assistance in running

| _ creep and tensile tests.
Williams, B. McNabb, N, O. Pleasant — Ran tensile and creep tests
on surveillance and control
specimens.

Thomas and J. Feltner - Pi'ocessed test data.

Snyder and R. H. Jones — Developed technique for making Hastelloy N

surveillance rods. _
Tinch and E. Lee — Metallography on control and surveillance specimens.

Colwell, Jr., and Graphite Arts — Preparation of drawings. )

Thelma Reedy and Meredith Hill, Metals and Ceramics Division Reports

Office — Preparation of report.

-

 

 
 

 

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