Resistometric investigation on SAP alloys neutron irradiated at 100 °k

JOURNAL

OF NUCLEAR

R~ISTO~ETRI~

37 (1970) 125-132. 0

MATERIALS

NORTH-HOLLAND

Received

of a resistometric compositions,

fast neutrons resistivity depends

and isothermal

recovered

spectrum

at

the

irr~di&tion

content

introduced

on SAP

alloys

were irradiated

room

temperature resoluble

of

Italy

ambiante,

en deux

d’activation

et

stades

de 0,60 f

le spectre 11-b

0,02

et III.

obtenu Une

Btait

Bnergie

eV a et& mesuree pour

la migration des defauts du stade III. Las consequences de ces r&ult&s,

of each alloy.

anneulings.

vis-rli-vis des mod&les de restaumtion

proposes jusqu’ici

by iso-

sont discutees.

All the damage

temperature,

which is resolved

of

strongly

were investigated

(Varese),

4 Mcby 1970

with

show that the amount

by

on the impurity

chronal was

at 100 “K,

introduced

The defects

study

which

AT 100 “K

and C. BASSANI

Solid State Physics, CCR Euratom, Iepra

different

CO., AMSTERDAM

INVESTIGATION ON SAP ALLOYS NEUTRON IRRADIATED S. AUDOLY

Results

PUBLISHING

through

in stages II-b

a Ergebnisse

and III.

der Untersuehungen,

die an SAP-Legie-

An activation energy of 0.60 rt: 0.02 CV w&s determined

rungen versehiedener Konzentrationen

for the defects migrating in stage III. The implications

st~d~messungen

of

Bestrahlung mit schnellen Neutronen bei 100 “K, dass

these

results

on

existing

recovery

models

are

durchgefiihrt

die Hohe des Widerstands,

discussed.

durch Wider-

wurden,

zeigen nach

der durch die Bestrahlung

hervorgerufen wird, stark von der Verunreinigung Legierung Les

result&s

d’une

etude

rOsistom&rique

slliages SAP de differentes compositions

sur

les

qui ont 6th

abh8ngt.

Die

naeh isochroner und isothermer

rmteraus,

que la valeur

IX1 aufgelost.

introduite

par l’ir-

de

chaque

etudies Tout

1.

alliage.

au tours le

Les

dtjfauts

introduits

ont

M

de recuits isochrone et isotherme,

dommage

structural

&sit

restaure

Fiir

die Wanderung

der Defekte

in

von 0,60 &

0,02

&us

eV

bestimmt.

Die

Folgerungen

werden in Verbindung

Erholun~modellen

Introduction

wurde in die Stufen IIb und

Stufe III wurde eine Aktivierungsenergie Ergebnissen

it la

der

wurden

Behandlung

das Erholungsspektrum

de la resistivite

Defekte

sucht, Alle Schkden heilten bei Raumtem~rat~

irradies avec des neutrons rapides it 100 “K, montrent radiation, depend fortement de la teneur en impuretes

erzeugten

diesen

mit vorhandenen

diskutiert.

at - 195 “C 314) indicate that lattice defects can

Quenching experiments in SAP 132) (a sintered

be introduced

in SAP;

their recovery

stages

alloy of Al with dispersed Al&s) have shown that no recovery in electrical resistivity is observed below 100 “Ct. This is in contrast with

correspond roughly to those observed AI. The aim of the present work

quenched Al, which shows a large recovery stage below 0 “C: the extra-resistivity introduced in SAP by quenching could not be interpreted in terms of vacancy-type defects, but was attributed to impurities frozen in the matrix by the quenching. The absence of vacancies in quenched SAP was accounted for by the presence of a large density of sinks (dislocations and interfaces between the matrix and the oxide particles) which cause vacancies to be lost during the quenching. On the other hand, cold work experiments

SAP by neutron irradiation, their activation energy and the influence of composition and impurities on the recovery stages.

determine

2.

the kind

Ex~~mental

of defects

in pure

was to

introduced

in

procedure

Different kinds of SAP alloys, the composition in table 1, were employed

of which is given for the research. sheets (SO x 4 x 0.1 for 6 h at 600 “C the furnace. The irradiations 125

Samples consisted of thin mm) which were annealed and then slowly cooled in were performed

in the low

126

S. AU-DOILY

AND

C, BASSANI

TABLE Alloy

composition

and

1

radiation-induced

resistivitjy

Composition Alloy Table

Fe

AW3

(7%

/

(at%)

1

0.03

Resistivity Si

(lo-50

de (n~em)

ppm)

I ;

la

SAP ISML

3.57

SAP

ISML

7.78

SAP

ISML

0.09

10.90

Al 99.995

j

Table lb Puroxal 70R

1

0.04

/ 5.05

II

0.006

\ Mn, Zr, Ga, ; 0.07 ; 0.06 1 zn, cu, Cr, 0.06 ; Is /

i

0.02

Cn, Zn,

’ SAP

Traces

I / (at %) /

_

I

ISML

Puroxal

45R

temperature

!

4.05

’

5.90

facility

32

538

29

I

597

28

!

230

18

S

(I Mn, Ga, Zn, S

0.09

I 0.095 / /

0.006

0.15 1

I

of the Ispra-I reactor.

Ti,

465

;

cu,

Cr,

Ti

Cn, s

All

the samples were irradiated at a controlled temperature of 100 “K to a neutron dose (E> 1 MeV) of 1.2 x 1017 n/cm2. After irradiation the samples were extracted from the cryostat and transferred to the laboratory for isochronal and isothermal an-

j’ Annealed 18

462

’

401

/

irradiation

375

the

samples

10 min at temperatures

~ QLy;hed

30

37

2:

46

were

annealed

raised about

fo--

10 “K aA

time, in the range from 100 to 353 “K. The results, presented in fig. 1, show that: the curves obtained for the alloys have a shape similar to that obtained for pure Al, all the damage is recovered at room tempera-

specimen was used to account for the small variations in the temperature of the liquid bath.

ture, the different amount of alumina does not affect either the shape of the curves or the value of the radiation induced resistivity Ag, which is about the same for each alloy,

The changes in resistivity, de, were calculated with reference to the value of the specimen,

recovery

nealings. Resistance measurements were carried out at liquid nitrogen temperature by the standard potentiometric method. A dummy

annealed at 600 “C and slowly furnace by the formula:

cooled,

Ae = eo(R - fio)/Ro

R being the resistance after any treatment and Ro and ~0 the resistance and resistivity of the annealed sample, respectively. The values of ~0 are given in table 1. 3. 3.1.

Results ISOCHRONAL

AN?JEA~~~

a. A preliminary investigation was carried out by irradiating the alloys listed in table la, which contain different amounts of alumina, together with a sample of pure Al. After

the

recovery

spectrum

is resolved

stages: conventionally

in two

indi~a,ted as

stage II-b and III, oeeurring in the temperature ranges from - 170 to - 110 “C and - 100 to 0 “C, respectively. Both stages show greater amplitude in the alloys than in pure Al. b. A second investigation was carried out, on a new set of materials, listed in table lb, each material containing about the same amount of alumina but different impurity concentrations. The curves of the isochronal annealings are reported in fig. 2, together with the differential curves (scale on the right). From a,n analysis of fig. 2 one can observe that: - the extra-resistivity ,!I@ introduced by irradiation is strongly dependent on the impurities present in the alloys, its value in-

RESISTOMETRIC

-150

INVESTIGATION

-100

ON

SAP

-50

127

ALLOYS

0

'C

Fig. 1.

creases

with

an increase

content, - the differential

curves,

in the

impurity

corresponding

to

stage III, show a peak which shifts to lower temperatures with an increase in the impurity content: all of them present a “shoulder” before the peak. c. In order to emphasize the effect due to impurities, a series of samples taken from the materials listed in table lb was water-quenched from 600 “C and irradiated together with samples annealed at the same temperature and slowly cooled down to room temperature. The experimental curves are presented in fig. 3,

their differential

form in fig. 4. The value of

the extra resistivity introduced by irradiation in quenched materials depends in a linear way on the Si content of the alloys (see the date reported in table 1). Fe content, which is relevant in SAP, does not affect the value of extra-resistivity introduced by irradiation, probably because of its small solubility in solid Al at 600 “C 5). 3.2.

ISOTHERMAL

ANNEALINGS

The main recovery stage (stage III) was investigated by the isothermal annealing procedure in each alloy listed in table lb. The

128

S.

AUDOLY

AND

C.

BASSANI

I

.

SAP

I

ISML

x Puroxrl

45

R (0.15%

o Puroxal

70 R (0.02%

Si) Si )

72

64

-140

-100

- 60 Fig.

isothermal curves obtained for puroxal 45R are reported in fig. 5. The activation energy was evaluated by plotting the logarithms of the times required to obtain a certain fraction of recovery, vs the reciprocal of the annealing temperatures, as shown in fig. 6. For each alloy a constant value of 0.60 i 0.02 eV was found. The value of 0.58 f 0.02 eV was obtained by comparing the isochronal with the isothermal curves [method of Meechan and Brinkman6)]. Similar results have been measured by different authors in pure Al after quenchingy), cold work s$9), neutron 10311) and electron 12) irradiation.

-20

‘C

2.

As far as the kinetics of the recovery process is concerned, it was possible to fit the isothermal curves with a second order kinetics (a deviation from second order occurring in the first lo-20 y0 of the curves). 4.

Discussion

The resistivity measurements reported in section 3.1 have shown that the defects introduced in SAP alloys by neutron irradiation at 100 “K recover with a spectrum the shape of which is typical of pure Al 10). The presence of alumina in different concentrations does not influence the recovery spectrum of the defects:

RESISTOMETRIC

-150

INVESTIOATION

- 100

ON

- 50

SAP

129

ALLOYS

0

‘C

Fig. 3.

in fact, our measurements are related to the defects created and migrating inside the matrix (Al), where the amount of radiation induced resistivity is affected by the presence of impurities. Swanson and Piercy is) reported that the damage rate, as detected by electrical resistivity in Al neutron-irradiated at 1.74 “K, is not affected by impurity concentrations of less than 0.5% at. The fact that the radiation-induced resistivity in SAP alloys after irradiation at 100 “K increases with the imp~ity content, could be explained by assuming that at 100 “K interstitials migrate and are trapped and

nucleated by the imp~ities present in the matrix, giving origin to interstitial clusters. This interpretation was formulated by Federighi et a1.14) to explain similar results obtained in Al-Si alloys neutron-irradiated at 78 “K. According to this model (vacancy model) the number of in~rstitial-vacancy recombinations, taking place during irradiation, will be reduced : therefore, after irradiation, there will be a greater concentration of vacancies (which means a higher value of radiation-induced resistivity) in the alloys with a higher impnrity content. During stage III vacancies become mobile and annihilate to interstitial clusters. The second

130

S.

AUDOLY

AND

C.

BASSANI

..- A 600 ‘C + 1 Q 600 ‘Gel l SAP ISML

-

150

- 100

Fig.

order kinetics is justified by supposing that single vacancies migrate directly to very small interstitial clusters or combine with one another forming di-vacancies, which quickly disappear to interstitial clusters. Stage II-b is attributed to the annealing of interstitials released from impurity atoms. A different interpretation of stage III is given by assuming that the defects introduced by

X

Purox

45R

0

Purox

70R

- 50 4.

irradiation annihilate according to the “conversion-two-interstitial” model 15). It is postulated that the kind of defect which migrates at a temperature lower than 100 “K is an interstitial configuration (crowdion), metastable with respect to a second type of interstitial (dumbbell), which migrates in stage III. According to this model the increase of radiation-induced resistivity in SAP alloys with

RESISTOMETRIC

INVESTIGATION

ON

SAP

131

ALLOYS

.6 -

.4

.2

the impurity content could be explained by supposing that, for increasing impurity concentrations, an increasing fraction of m&a&able interstitials are converted, during irradiation,

peratures with increasing irradiation doses until it overlaps with the shoulder. Our measurements

into normal ones, the impurity atoms as defocusing centers for crowdions.

irradiations at higher doses. The hypothesis of an initial non-homogeneous

The substructure

acting

we noticed in stage III was

observed also in pure Al after neutron irradiation 111lo), but never after electron irradiation. This fact can be explained, according to the vacancy model, by thinking that, after neutrol~ irradiation, vacancies are not homogeneously distributed but rather, they are concentrated in regions, called depleted zonesr7). It is likely that a fraction of vacancies inside the depleted zones are correlated, so that their annealing (kinetics indepe~ldent of the concentration) can be responsible for the “shoulder”. Ceresara et a1.f”) determined that the position of the shoulder in Al is dose independent and is centered at - 75 “C, whereas the position of the normal peak shifts towards lower tem-

showed (fig. 4) that an increase in the Si content in SAP alloys produces an effect equivalent to

distribution

of defects may also account for the

deviation from the second order in the initial part of the isothermal curves of stage III. References 1) T.

Federighi,

Acta

Met.

2) S. Ceresara, Mater.

S.

Ceresara

T.

Sci. Eng.

Federighi 2 (1967/68)

3) G. Fiorito and W. (1967)

9

S.

D.

~ualandi,

and

D.

Gualandi,

303

Schtile, J. Nucl.

Mater.

21

61

Ceresara,

Mater.

and

15 (1965’) 399

T.

Sci. Eng.

Federighi 2 (1967/68)

and

D.

Gualandi,

309

5) J. K. Edgar, Trans. AIME 180 (1949) 225 9 C. 5. Meechan and J. A. Brinkman, Phys. Rev. 103 (1956)

7)

1193

T. Federighi,

(Academic

Lattice defects in quenched metals

Press Inc.,

New York,

1965) p. 217

132

S.

1

AUDOLY

AND

C.

BASSANI

o3

c ._

E .

o*

1

10’

1

0.1

E

5.0

Fig.

8, 0. Dimitrov, MBm. Sci. Rev. Met. 57 (1960) 787,

6.

13)

C. Panseri, S. Ceresara and T. Federighi, Nuovo Cimento

19

1

11)

)

W.

Franp. de Metall., Bauer,

Int.

stitials in Metals,

14)

D. Gelli and F. Piera-

Conf.

12-16

Octobre

on Vacancies

Jiilich (Sept.

1968)

Stat.

Federighi

and

Sol. 11 (1965)

T.

7’79

F.

Pieragostini,

15)

W. Bauer, A. Soeger and A. Sosin, Phys. Letters

10)

2411 (1967) 195 S. Ceresara, H.

(1964)

and Inter-

1605

S. Ceresara, Phys.

1223

gostini, Nuovo Cimento 29 (1963) 1244 C. Frois et 0. Dimitrov, Journees d’ilutomne Sot.

12

29 (1963)

S. Ceresara, T. Federighi,

M. L. Swanson and G. R. Piercy, Can. J. Phys. 42 (1964)

852

g,

,000

-y-

4.1

L.4

17)

F. Pieragostini, A.

Elkhoiy, Phys.

Seeger, Radiation

(IAEA,

Vienna,

T.

Federighi

and

Letters

16 (1965)

8

damage

in solids,

Vol.

1962) p. 101

I