14-MeV neutron irradiation of copper alloys

449

Journal of Nuclear Materials 122 & 123 (1984) 449454 North-Holland, Amsterdam

14-MeV NEUTRON

IRRADIATION

OF COPPER ALLOYS

S.J. ZINKLE and G.L. KULCINSKI Department

University

of Nuclear Engineering,

of Wisconsin-Madison,

Madison,

WI 53706

Copper and copper alloys with 5 atomic percent of either alumiyym, nickel or manganese were n/m . Resistivity, microirradiated at 25°C with 14-MeV neutrons to a fluence of 3 x 10 Using a loghardness and electron microscopy were used to characterize the radiation damage. normal distribution to describe the defect cluster size distribution, good agreement was found At least between resistivity estimates of the cluster density and the observed (TEM) density. 11% of the defects created during the irradiation escape correlated recombination.

1. INTRODUCTION

irradiated 70%

investigation1

copper

alloys

of the defect

the

of 14-MeV neutron

estimated

clusters

normal

microscope

nature This

to

made

be

these

of

of

three

an

the

In

size

relative

appropriate

yields

the frac-

tion of defects which escape correlated This

radiation

quantity

is

recom-

important

for

damage modeling.

II

National sisted

four

of

pure

alloyed

either

aluminum, Hanford

(99.99+ with nickel

and

these

foils,

and

irradiated

at

air

room

and

irradiation fluences

procedure

in

with

the

foil

standard

resistance

sensitivity

copper

had

sample

an

initial

microhardness

Vickers

using

performed3

tester

a

been

the

periphery

for each

resis-

of 380.

loads

four

were

materials

micro-

of

5g and

were made

different

at every

conditions

The pure

residual

indentations of

metal

mea-

equipment

Micromet@

indenter

of 60

were

measurements

Buehler

at

A minimum

disks

a

Details

= 10 nV1.

tivity ratio (RRR = P298/P4.2°K)

around

to

have

resistivity

(potentiometer

hardness

con-

up

described.2

Changes sured

of

in cool.

Laboraof

were

The

temperature

(TEM)

cut

high-purity metals using

0022-3 11S/84/$03.00 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)

Figures

from

argon, were 14-MeV

B.V.

1

fluence

and

properties

of

the

TEM

level.

metals

inves-

RESULTS and

2

irradiation-induced pure

microscope

foils

3. EXPERIMENTAL

obtained

Development

electron

annealed to

copper percent

to a thickness

resistivity

allowed

%)

atom

or manganese

Engineering

25 urn. Transmission

atom

five

toryI were cold-rolled

disks

The

experimental

previously

log.

Neutron Livermore

tigated are given in Table 1.

copper

from

Target

Lawrence

level of about 3 x 1021 n/m2.

irradiation

Foils

at

incremental

Pre-irradiation

2. EXPERIMENTAL

Rotating

Laboratory.

the

of

the

(RTNS-II)

of

maximum

of

at low neutron

using

analysis

distribu-

a comparison

sensitivity

tools

addition,

Source

smaller

to character-

also allows

experimental

bination.

than

electron

to these

the cluster

resistivity

models,

of

in an attempt

analysis

fluences.

smaller

along with TEM and microhard-

ness measurements ize the

limit

are sensitive

clusters,

tion.

were

in copper

We have used resistivity

(- 1 nm). which

methods, defect

resolution

that about

produced

:Irutron irrddiation

during

from

neutrons

A previous

for

copper the

and

pure

show

the

resistivity the

copper

copper sample

vious

dependence

is

in

scales

The

for data

linearly

fluence.

agreement

work for both electron

diation at temperatures

changes

alloys.

with the square root of neutron fluence

respective

with

and neutron

This preirra-

where the interstitial

450

S.J. Zinkle,

G.L. Kulcinski

/ I4-MeVNeutron

TABLE 1 Data forResistivity

Irradiation

Grain Size u

pn(n-m)

of copperalloys

irradiation

and TEM Samples

Contrjl Hardness (kg/mm 1, log Load

f vml

Maximum Fluence {n/ml!) Resistivity T&M

CU

4.48 x IO-II

13

56.7 f 4.3

2.9 x 1021

1.9 x 1021

Cu-5% Al

3.96 x 1O-B

23

53.8 f 0.9

2.9 x 1021

2.1 x IO21

Cu-5% Mn

1.08 x 1O-7

22

53.4 f 2.5

2.8 x 1021

2.0 x 1021

Cu-5% Ni

5.16 x lO-8

12

53.4 f 2.8

2.9 x 1021

2.2 x 1021

is mobile.4 produces tivity, with

initial

followed

fluence

alloys. became at a

the

greater

in

Cu-5%

resistivity than of

10 grams

resis-

14-MeV

and

Cu-5%

these

alloys

hardness

data

The

changes

in

sample at

all

remained fluence

negative the

levels

resistivity

irradiated

to be due

below

copper

to short-range

ordering.' Changes

in the Vickers

four metals obtained

200 -

I

I 25%

microhardness

of the

at an indenter loading of

I

I

nearly after the

of 5 grams evidenced

for

all

showed

in

four

period

and

3,

the

scale

li-

to the alloys.

exhibited

significantly the

other

levels

investigated.

3 have

roughly

microhardness

equal

fluence

duration

is on the order

is shorter

compared

than

The

at

similar

Fig.

metals

fluence.

of

obtained

with the fourth root of neutron

n/m2,

ening

Results

is

an incubation

incubation

1020

in Fig. 3 as a function

fluence.

loading As

value

Mn

an indenter trends.3

resis-

n/m2.

are shown

neutron

Ni

The

investigated.

are believed

alloys

in resistivity

Al of

10zl

value

observed

foil

the pre-irradiation

3 x

of the Cu-5%

unirradiated

alloys

of the copper

decrease

by an increase

for

The

fluence

tivity its

Irradiation

an

for pure

of

of 1 x

copper

as

The Cu + 5% Mn alloy larger metals

All

radiation

hard-

the

fluence

four metals

in Fig.

slopes

at

in their curve

of

vs. fluence.

I

IRRADIATION

RRR=380

AP

PO 150 (%I

(961

0.2 -

100 -

50 -

0

I

-/I 0123456

I

I

I 0

fl

I2

3

4

5

6

(i020n/m2)i'2

FIGURE 1 Resistance change vs. the square root MeV neutron fluence for pure copper

of 14-

FIGURE 2 Resistance change vs. the square root MeV neutron fluence for copper alloys

of 14-

S.J. Zinkle, G.L. &dcinski / Id-Me V Neutron irradiationof copper alloys

451

is the radfation-inducedresistivity increase.

A least squares fit to the present resistivity data yields the result f od I$ = 8.4 x 1O-32 n-m"3 . The

quantity pi depends on

(3')

the amount of

clustering which has occurred.

To obtain a

lower limit for the fraction of defects escaping correlated reco~inatjon, may be taken os to be equal to the isolated Frenkel pair specific resistivity ifl copperS7 PFp = 2.0 uncm/% F-P.

Using a dfsplacement cross-section1

of Ud = 3690 barns then gives f z 11%. A more accurate estimation of f requires a FIGURE 3 Change in Yickers mjcrohardness root of I4-MeV neutron fluence

dete~ination of the effect of clustering on

4, DATA ANALYSTS

an electron irradiation at temperatures where

Thompson et al.8 ex~erjmenta~ly investi-

n;.

gated the effect of clustering on PFp during

Early

resistivity

studies of pure metals

irradiated at temperatures above 70%

provided

support for a theoretical model known as the unsaturable trap model (UTMIS4

Eiore recent

only interstitials mSgrate and cluster. Using his result of n$'pFp =

0.8 * 0.1 along with

= 1.4 u&cm/% interstitialsand PED = 0.6

"FD &cm/%

vacancies,? the specific resistivity

developments have concentrated on examination

of trapped Frenkel defects (where both inter-

of the reciprocal damage rate (RDR) for study-

stitials and vacancies are clustered) can be

ing point defect interactions,

computed.

Using the

Assuming an equivalent number of

analysis of Oworschak et. al.6, the following

vacancy and interstitial clusters leads to a

result is obtained:

prediction

of

Pi = 1.4 f 0.25 nn-cm/% F.P.

With this value, f s 16%. Rrager et a1.l irradiated identical metals with 14-MeV neutrons up to a maximun fluence of 7.5 x 10zl n/g

This may be rewritten in the form

TEM,

m

1

-=-+I+

AP

where 8

Ap

]

2 pftCtrt/rv

f'd 'f

is the neutron fluence, f

12) is the

and examined

ble defect cluster size distrfbution can be fitted very well by a log-normal distribution' with do = 2.25 nm:

fraction of defects escaping correlated recom bination, section,

bd

displacement cross is the specific resistivity of iS

the

the foils with

We have found that their reported visi-

N(d) =

QG

1

fm an Q

@XP [-

d/do?

2 (rn aI*

1 a (41

pft trapped Frenkel defects, rt and rv are the

In anticipation that a large number of maIf

capture radii of impurity traps and vacancies,

defects might be invisible to TEM methods, we

ct Is the concentration of impurities, and AR

also fit the distribution

larger

defects

to a log-normal

of

the

observed

distribution

452

S.J. Zinkle, G.L. Kulcinski

I 14-Me V Neutron irradiation of copper alloys

too -

AuY I

TEM data fram et al.

I

40

(MPa) 80 -

Brapar

60 -

40 Trend Lina (Mitchell &al.)

-

20 -

CLUSTER DIAMETER (nm)

D20

102’

+t (n/m’1 FIGURE 4 Log-normal curve (Eq. 41 fitted to observed TEM clus r da a at a 14-MeV neutron fluence of 3 x I$? n/3

with

smaller values of do.

butions per

are compared

TEM

data

Applying

the

resistivity

b

Brager

w;NC, b

the

et

a1.l

in

Fig.

distribution

to

4. the

similar

sile data tron al.l"

analysis

vector

can

of

microhardness

to

tensile

(51

of the defect

be applied

copper

by

to ten-

14-MeV

neu-

Mitchell

due to dislocation

et

loops

be valid copper obtained pure

alloys.

As

3.0.

correin

the

A re-

(kg/mm2).

log

copper

in Fig.

data

of

and

also

we

have

5,

correlation

tensile the

pure

seen

a reasonable

and

be

found

found the result K = 3.27 to

irradiated

three metals

can

results

for

copper

al.I"

data

data

Aoy (MPa) = K AH, 1

from a room temperature

The hardening

Vickers lated

cent correlation1

d2 e2 (in oJ2 o

Burgers

irradiation

14-MeV

(71

literature,

cluster and NC, is the cluster density. A

vs.

The fitted distri-

data gives the result,2

is

FIGURE 5 strength change

yield

to the reported pure cop-

log-normal

"P=-~ where

of

Correlated fluence

between

the

Mitchell

et

microhardness

data

for

(Cu, Cu-5% Al, Cu-5% Nil with K =

The Cu-5%

Mn microhardness

data

do not

agree well with the tensile data.

is given byll 5. DISCUSSION

(6)

The

general

radiation-induced where T = shear stress, P = shear modulus, Using

B is a constant. rion to relate yield A0y=flA~, normal

cluster

and

the Von Mises

and

crite-

strength to shear stress,

once

again

assuming

size distribution,

solved for the cluster density:

a log-

Eq. 6 can be

microhardness retical

fluence

is in good

models.

dependence

change

in

scale

14-MeV

neutron

linearly

with

cluster

density NCll _ w

fluence,

the and

agreement

Resistivity

copper

of

resistivity

theo-

for pure

the square

indicating

.

with

results

root of

that

The microhard-

the

S.J. Zinkle,

G.L. Kulciwki

/ 14-Me V Neu tron irradiation

TABLE 2 Calcul ed D feet Cluster Densities Assuming 3 x 12'1 n/S

Visible

Cluster Density Microhardness*

0.4

2.0

0.7

9

2.25

1.0

10.5

*Extrapolation to $t = 3 x 1021 n/m2 from AH, vs. assumes Auy (MPal = 3.0 AHv (kg/mm21

(1022/m31 Tensile* 7

7

8

1.5

453

alloys

in Copper at a Fluence of

Predicted Resistivity

Fraction of Clusters Which are Visible (Fig. 4)

d, (nml

of copper

($t)li4

9

9

12

12

curve (Fig. 3);

TABLE 3 Comparison of Calculated afl Obs n,x ved Defect Cluster Densities in Assuming All Clusters are Visible Copper at a Fluence of 3 x 10

Type of Analysis Calculation

Resistivity

Calculation

Microhardness

Calculation

Tensile"

Observed

TEM1

+Assumed

ness

stacking

data

of

fluence, there

to

(again

is

found the

of

damage

production

data power

experiments

four

change

there in

are

the initial transition

fects

which

escape

(16%)

agrees

of

the

well with

literature

to

in

fourth

recombination

electron-irradiated

copper.13 The sities

obtained

Mitchell's

reported

visible from

tensile

defect

resistivity

data

(Eq.

cluster

den-

(Eq. 5) and

7) may

be com-

summarized

a cluster

$ = 2.7

x

diated

actually

results

agreement

1.05 x l023/m3 (tensile), fect

clusters

loops were

and

than

cluster

number

the

density

observed

MeV

neutron

searchers ences.10p15

higher

who One

asstaning perall

of

the

small

defect

a

smaller

value

21, then the calcumuch

Bragerl

cluster

smaller observed

densities

copper

possible

of

of

becomes

irradiated

good

If one assunes

(i.e.

value.

irradiated

irra-

in

densities

that

visible.

invisible

is

at

and 1.2 x 1023/m3

obtained

of do in Eq. 4 and Table lated

et al.

neutron

calculated

were

substantial are

were pi = Brager

value

(resistivityl

which

clusters a

This

the

dislocation

defect

2 and 3.

density of 1.3 x 1023/m3

copper.

with

ob-

of this

in Tables

n/m2 for 14-MeV

1021

pure

significantly

calculated

was

The

1.4 Do-cm/% F.P. and 6 = 3.711.

that de-

the value of 15% found

for

which

methods.

used in the calculation

period.

correlated

density

Parameters

The

of

the

by TEM

to

materials

fraction

to

are

equivalent

these

pared served

comparison

have

metals vs.

18 18

but

law

fluence.12

all

be

(Fig. 3) may be taken

rates

estimate

the

for

that

best

in

actual

the

fluence

indication

Our

of

microhardness

an

following

high-fluence

slopes

root of neutron as

that NC, Y ml

the

12 12

PSF = 2.5 x 10 -17 o-m2 C141.

neutron

stress is proportional

power

equal

to

of

11+

.. .. .. ... ... .. . .... .. ... ..13.........................

appears

root

previous

that the yield

curve

metals

fourth

indicating

Most

one-third

roughly the

four

the

determine

dependence.

DAFS LLNL/Cominco DAFS

insufficient

conclusively

10.5

DAFS

fault specific resistivity

all

proportional

Visible Cluster Density (lO22/d) Perfect Loops lb = aJJ2l Faulted Loops (b = a,,/m

Copper Type

Method

to

than

in 14-

other

similar

explanation

reflu-

for the

S.J. Zinkle,

454

discrepancy

is that

Brager

gated defect clusters nm.

The

carefully

size limit of the other TEM is uncertain.

appears

that

it is possible

tially

all

of

clusters

by

is

investi-

to observe

surviving

methods

undertaken,

down to diameters

of 1.0

From this analysis,

the

TEM

/ 14-MeV Neutron

investi-

down to diameters

gations

study

G.L. Kulcinski

if

point a

it

essen-

1.

H.R. Brager et al., and 104 (1981) 995.

2.

Zinkle and G.L Kulcinski Guiiterly Progress Report DOE/ER~OO~~?~ ;:;;3119821, P. 93 and DOE/ER-0046/14

3.

S.J. Zinkle and G.L. Kulcinski, Proceedings of the Sympositnn on the Use of Nonstandard Subsired Specimens for Irradiated Testing, Albuquerque, NM, Sept. 23, 1983.

clusters

4.

R.M. Walker in "Radiation Damage to Solids", Proceedings of the International School of Physics (Enrico Fermi) Course XVIII, D.S. Billington (Ed.), p. 594 (1962).

5.

and H. Wollenberger, R. Poerschke Nucl. Mater. 74 (1978) 48.

6.

F. Dworschak (19751 400.

7.

R.C. Birtcher and T.H. Mater. 98 (1981) 63.

8.

L.

9.

F. Schuckher, Quantitative (McGraw-Hill, NY, 1968) R.T. F.N. Rhines (Eds.), p. 205.

of 1.0 nm.

copper

during

irradiation

16% of the defects

room

temperature

escape

created

14-MeV

correlated

in

neutron

recombination

events. Good agreement observed

(TEMI

tions

to

this

fitted

cluster

a

defect

and

with

pears

that

TEM

essentially duced

if

data

of defect

been

be

capable defect

microscopy

resis-

found

Hence,

the

of

to

it ap-

observing

clusters

is

indicate

tensile,IO

performed

and

proon

microhardness

that, for a room temperature irradiation,

the

defect

Analysis neutron

irradiation

sistent

with

defect

reduction

of copper

previous clustering

a

(- 30%) in the Frenkel

indicate

This

work

the Magnetic ship

Program

performed Fusion and

under

Energy

with

appointment

Technology

funds

supplied

Office of Fusion Energy, Depar~ent

to

Fellowby

the

of Energy.

al.,

J.

Physics

Blewitt,

Rad.

F

5

J. Nucl.

Effects

20

Microscopy DeHoff and

Arsenault, Koppenaal and R.J. 3.5. Metallurgical Reviews 16 (1971) 175.

13.

U. Theis and W. Wallenberger, Mater. 88 (1980) 121.

14.

3. Polak, Phys. Stat. Sol. 11 (1965) 673.

15.

J.B. Roberto et al. in "Radiation Effects and Tritium Technology for Fusion Reactors," J.S. Watson and F.W. Wiffen TN (19751 Vol. II, (Eds.1, Gatlinburg, 159.

resistivity.

ACKNOWLEDGEMENT

et

al.,

12.

substantial

pair specific

Thompson

(1973) 111.

et

J.

N.M. Ghoniem et al., Proc. of Eleventh International Symposium on Effects of Radiation on Materials, ASTM STP 782, Scottsdale, AZ, (1982) 1054.

during 14-MeV

which

causes

IO3

11.

at 25'C is con-

results8

Mater.

J.B. Mitchell et al. in "Radiation Effects and Tritium Technology for Fusion Reactors," J.S. Watson and F.W. Wiffen TN (1975) Vol. II, (Eds.), Gatlinburg, 172.

14-

n/m2.

of the data obtained

Nucl.

10.

cluster

is linear with the square root of flu-

ence up to Q,= 7 x 10zl

that

Using

down to sizes of _ I nm.

neutron

density

have

results.

of

careful

distribu-

utilizing

may

all

Resistivity,

MeV

by

data

TEM

size

estimates

obtained

tensile

well

by fitting

distribution.

distribution,

agree

clusters

cluster

log-normal

density

tivity

has been obtained

J.

careful

investigating

6. CONCLUSIONS Approximately

of copperalloys

REFERENCES

defect

very

irradiation

J.

Nucl.