The effects of irradiation on the formation of guinier-preston zones

THE

EFFECTS

OF

IRRADIATION

ON

GUINIER-PRESTON H.

THE

FORMATION

OF

ZONES*

HERMAN?:

Resistivity measurements and small-angle scattering of X-rays were employed to study the effects of (10.5 MeV.) deuteron irradiation on the formation of spherical coherent Guinier-Preston zones (G.P. aszones) in Al-5.3 at. ‘A Zn. Specimens were irradiated at 7’7°K after different thermal treatments: quenched from 3OO”C, as-reverted from 2OO”C, and as-reaged. Irradiation of the specimen quenched from 300°C has the effect of slightly retarding the rate of zone formation. For specimens reverted at 200°C and then irradiated with 0.5 to 1.9 x 1 015 deuterons/cm 2, the initial part of the reaction is accelerated, the rate of zone formation increasing with dose. The later part of the reaction is not greatly influenced, the final zone sizes, as determined using small-angle scattering of X-rays, are only slightly larger. Irradiation of an alloy containing zones (as formed on reaging) does not result in enhanced growth. It is concluded that vacancies as generated by irradiation with deuterons can aid G.P. zone formation, but the defect distribution as obtained by quenching is different from that resulting from irradiation. For the case of the present alloy, deuteron bombardment does not give rise to enhanced nucleation. INFLUENCE

D’UNE

IRRADIATION DE

SUR

LA

FORMATION

DES

ZONES

GUINIER-PRESTON

L’auteur a utilise des mesures de resistivitb et la diffusion des rayons X aux faibles angles pour Studier l’influence d’une irradiation par deutons (10.5 MeV) sur la information de zones de GuinierPreston spheriques cohkrentes dans l’allisge Al-5.3 at. %Zn. Les Bchantillons ont BtB irradiBs B 77°K apr6s diffbrents traitements thermiques: trempe B partir de 3OO”C, r&version B 2OO”C, et vieillissement. L’irradiation d’un &hantillon tremp8, B partir de 300°C a comme effet de retarder l&g&rement la vitesse de formation des zones. Apr&s r&version B 200°C et irradiation avec 0.5 B 1.9 x 1Ol5 deutons/cm2, le debut de la r&action est acc&r& la vitesse de formation des zones augmentant en m&me temps que la dose d’irradiation. La fin de la reaction n’est que peu influencke: la dimension des zones obtenues finalement, d&erminee par diffusion des rayons X faibles angles, n’est que l&g&rement augmentbe. L’irradiation d’un alliage contenant des zones (form&es par un vieillissement) ne conduit pas B une augmentation de leur allure de croissance. L’auteur conclut que les lacunes produites par l’irradiation pars deutons peuvent aider B la formation des zones de Guinier-Preston; toutefois, la distribution de defauts qu’on obtient par une trempe diffkre dr celle qu’on obtient par une irradiation. Dans le cas de l’alliage &udiB, un bombardement par deut,ons n’acc&:re pas la germination. DER

EINFLUD

VOX

BESTRAHLUNG

AUF

DIE

BILDUNG

VON

GUINIERP

PRESTON-ZONEN Mit Hilfe van Messungen des elektrischen Widerstandes und der Kleinwinkelstreuung von RGntgenstrahlen wurde der EinfluD von 10.5 MeV-Deuteronen-Bestrahlung auf die Bildung kugelfijrmiger kohiirenter Guinier-Preston-Zonen (G.P.-Zonen) in Al-s.3 %Zn untersucht. Die Bestrahlung erfolgte bei 77°K nach verschiedenen WBrmebehandlungen: nach Abschrecken von 3OO”C, nach Riickbildungsbehandlung bei 200°C und nach erneuter Alterung. Bestrahlung der von 300°C abgeschreckten Probe fiihrt dazu, da13 die Bildung der Zonen leicht verlangsamt ist. Bei Proben, die nach einer Riickbildungsbehandlung bei 200°C mit 0.5 bis 1.9 x 10 I5 Deuteronen/cm2 bestrahlt wurden, ist der Anfangsteil der Reaktion beschleunigt; die Bildungsgeschwindigkeit der Zonen nimmt mit der Dosis zu. Der weitere Teil tier Reaktion wird nicht sehr beeinfluat, die EndgrGDen der Zonen (durch Kleinwinkelstreuung von R&tgenstrahlen bestimmt) sind nur leicht erhtiht. Bestrahlung einer Legierung, die (als Folge erneuter Alterung) Zonen enthiilt, fiihrt nicht zu verstiirktem Wachstum. Es wird geschlossen, da13 die durch Deuteronen-Bestrahlung erzeugten Leerstellen die Bildung von G.P.-Zonen fiirdern kiinnen, da0 jedoch die Fehlstellenverteilung nach Abschrecken verschieden von tier durch Bestrahlung erzeugten ist. Im Fall der vorliegenden Legierung fiihrt Deuteronen-Bestrahlung nicht zu verstiirkter Keimbildung.

INTRODUCTION

For

many

decreasing

cipitate, but the state containing

temperature,

quenching

by a free-energy

from the single to the two phase region of the equi-

0 n quenching

librium stable occurs

with diagram

pha#se. by

(G.P. zones),

syst’ems

with zones is greater than that for the equilibrium exhibiting

solubility

alloy

decreasing

results in the formation Decomposition

formation

of

at low

of a metn-

predicted

zones

clusters which are coherent with the parent matrix.(l) The shape

and morphology of the zones are controlled by strain The free-energy associated energy considerations.

ACTA

METALLURGICA,

VOL.

12,

JULY

diffusion

supports

the idea that vacancies,

librium,

are responsible

frozen

temperature

the

which

in excess of equi-

for the high rates of zone

It is thought

in during

coefficient.(n

evidence

that

quench

these vacancies and

are able

are

to aid

migration of solute atoms to the zones. Verification that vacancies play a major role in zone formation

Laboratory, Philadelphia, 1964

by the equilibrium

formation.

*

Received October 31, 1963. t Metallurgy Division, Argonne National Argonne, Illinois. resently at: University of Pennsylvania, Pai p

and aging near room

There is a great deal of experimental

solute-rich

or semi-coherent

less than the solid solution.

the zones form at rates much greater than would be

temperatures

Guinier-Preston

pre-

zones is represented

765

has

not been very direct and has depended

on

results

obtained

from

quenching

mainly

experiments.

ACTA

766

The passage

of sub-atomic

METALLURGICA,

particles

in the MeV

VOL.

12,

1964

On aging Al-5.3

at. % Zn near room temperature

results in the generation of large numbers of defects. f2) These defects are on an atomic scale, consisting of vacancies and interstitials

for several days after a quench

and

the mature zones are about 50 A dia.c4) If this alloy

range

through

their

metals

coagulation

products.

The

net

generation of the defects, their distribution, of retention of particle ation.

depend

of

and degree

for the most part on the type

employed

Defects

retained

rate

and the temperature

introduced

by

at low temperatures

of irradi-

irradiation

can

be

and are able to move

to sinks during subsequent annealing. The rate of removal of radiation-induced defects is determined by the temperature

of annealing, the energy of motion

of t,he defect, and the distribution tion,

the presence

even in extremely modify significantly

of foreign

of sinks.

atoms

In addi-

in the lattice,

small concentrations, serves annealing characteristics.

to

in which defects, as created by irradiation, zone formation.

For irradiation

of liquid nitrogen,

that approximately

the zinc becomes

associated

is reverted librium perature,

can affect

at the temperature

the major defects retained will be

with zones:

approximately

eventually

go

to

techniques;

becoming

In this case

at 200°C (which is 10°C above

the equi-

to room

tem-

20 per cent of the zinc will

zones.(4)

The

reaging near room temperature X-ray

300°C, it has 50 per cent of

solvus line) and again cooled

zones

formed

are detectable

on

using

the average diameter of the zones

no greater than about 10 A.

For both quench-aging resistivity

does

not

and reaging,

generally

vary

the electrical monotonically

with time, but shows a maximum.

This maximum

occurs much earlier for quench-aging

than for reaging.

It has been previously

In this research we have been interested in the way

from

been determined

determined

that the maxima

in both cases represent zones of approximately

10 A

dia. and are due to critical scattering of the conduction electrons. This occurs when the diameter of the zone becomes

equivalent

to the wave-length

of the

vacancies since the great majority of generated interstitials are able to move to sinks and thereby are

conduction electron.(4y6) Federighi has discussed the significance

of the peak

removed. A study has been made of the effects of irradiation with 10.5 MeV deuterons on the kinetics of formation of G.P. zones in Al-5.3 at. ‘A Zn. Speci-

in resistance from a kinetic point of view.

The greater

mens were irradiated at - 195°C after various thermal Resistivity was the major property treatments. studied,

with small-angle

employed

to determine

scattering

of X-rays

being

zone sizes.

sumably

due to the rate of reaction

by the formation

of spherical G.P. zones,

temperature

of t’he zone is not known

with certainty,

but X-ray

of aging.

Resistance measurements

taining

thickness,

to a temperature

above

the

aging

temperature but still within the equilibrium solvus line, the zones rapidly go into solution;(5) this process “reversion.”

Reversion

occurs

at

the

the lower rate

EXPERIMENTAL APPARATUS TECHNIQUES

diffraction results indicate that the zone is highly enriched with zinc.(3T4) On heating the alloy, conzones,

For reaging,

of zone formation is thought to be due to the lower vacancy concentration that is available after reversion.

coherent with the aluminum matrix;(3) this process is referred to as “quench-aging.” The composition

termed

Again, diffusion is

a thermally activated process, and the zones will grow to the critical diameter faster, the higher the

On aging at temperatures in the approximate range of -60°C to 90°C the quenched Al-rich Zn alloy

is

being dependent

on the excess vacancy concentration frozen-in during the quench. Likewise, the higher the aging temperature, the earlier will be the peak:

The alloy

decomposes

the temperature from which the specimen is quenched, the earlier will the maximum occur:(7) This is pre-

The

specimens

were

cut

from

AND

a foil,

into strips 0.2 in. by 2.0 in.

0.004 in.

Four alumi-

num leads, 0.031 in. dia., were spot welded to the specimen giving approximately 1.5 in. between the two

inner

voltage

probes.

The

leads

were passed

temperature at which the free-energy of the solid solution is less than the free-energy of the alloy which contains zones. Reversion can result in the

through a four-hole ceramic tube before spot-welding. The standard four-probe potentiometric method was

most homogeneous condition available to the alloy at low temperatures. c4) On cooling from the temperature of reversion to the original temperature of

nique was used, resistance measurements being carried out at the temperature of liquid nitrogen (-195’C).

aging,

the

zones

rate.c4) Formation to as “reaging.”

reform,

but

at a much

reduced

of zones after reversion is referred

employed.

For measurements,

an interruption

tech-

The Al-5.3 at. % Zn alloy was supplied by Alcoa and stated to be of high purity. Aging was carried out in a thermostated bath of distilled water. The temperature of the aging bath

HERMAN:

IRRADIATION

did not vary by more than a 1/4”C during the experiments. Hea.t treatments were in molten salt, the specimen being manually quenched into water at 25% Reversion was carried out in silicone oil at 200°C for 10 min.

Small-angle scattering of X-rays was employed to determine zone sizes. The same specimens were used for t,he X-ray work and resistance measurements. This insured a reasonable comparison between the resistance data and determinations of zone size. The procedure involved removing the specimen from the annealing bath and placing it on the diffractometer at the end of an aging experiment, after no less than 10.000 min (approximately 1 week) of aging. An XRD-5 diff~ctometer was used. The apparatus employed consisted essentially of an arrangement whereby the specimen surface remained perpendicular to the beam: The 13motion of the base plate of the goniometer associated with the counter motion of 28 was eliminated.(4) A 0.1” small-angle scattering beam slit was employed in conjunction with a 0.2’ receiving slit. An adjustable slit was placed at the beam slit to limit vertical divergence. The direct beam intensity and parasitic scattering were limited by employing a copper beam-stop after the method due to Kratky.@) X-rays, as obtained from a &-tube (35 kV at 23 mA), were nlonochromatized using the balanced filter technique:@) A run was first carried out with a Ni-Al filter and then with COO, the difference in intensity yielding Cu K,. The efficiencies of these fibers were determined at Northwestern IJniversity:(4) For wavelengths below Cu K, tlhe filters were matched to 0.2 per cent and above Cu K, to 2.0 per cent. Automatic step scanning was employed, a 1000~see count! being made every 0.1’28 which was automatically registered on a digital printer. Parasitic scattering was determined using a pure aluminum specimen adjusted in thickness to give the same absorpt,ion as the alloy specimen (0.0044 in.). This parasit,e was subtracted from the scattering curve. The maximum error in the zone sizes was no more than &8 per tent.(4) Irrdintion

procedures

The 60-in. cyclotron at Argonne National Laboratory was employed for irradiation with energetic deuterons. The specimen was mounted at the targetwindow of the cyclotron. Liquid nitrogen, as supplied from a self-pressurized 250 1. Dewar, was continuously sprayed down on t,he specimen from a height of

AND

G.P.

ZONES

767

approximately 2 in. It was observed that the specimen and leads were bathed with a thin film of liquid nitrogen. The beam current was 0.02 x low6 A/cm2 for irradiations at the temperature of liquid nitrogen and 0.01 x 1O-6 A/cm2 for the irradiation at room temperature. It was necessary to use these low beam currents to avoid heating the specimens. Preliminary experiments employing currents some forty times greater than this gave poor reproducibility of the as-irradiated resistance increment. This was attributed to specimen heating. The energy of the deuterons was 10.5 MeV as degraded by foils from 20.5 MeV. A beam stop behind the specimen, electrically connected to the targetwindow, collected the beam, and the total current was registered with a current integrator. The beam cross-section, after passing a defining slit, was approximately rectangular, 18 in. x 3 in., and the intensity distribution was rather ilat near the center of the beam, the position of the specimen. The long dimension of the beam was horizontal and parallel to the specimen length. Before the specimen was mounted a colored Cellophane foil was placed on the window of the cyclotron and exposed to a deuteron beam for a short time. The discolorat,ion of the Cellophane clearly indicated the posit.ion of the beam, and the specimen was mounted accordingly. This procedure was carried out for each experiment. The electrical resistance of the specimen wa,s measured before and after irradiation. The specimen was transported to and from the cyclotron in liquid nitrogen. After irradiation the specimen was stored in liquid nitrogen for several hours so that the activity could decay to reasonable levels. The thickness of the specimen, 0.004 in., was approximately l/4 of the range of 10.5 MeV deuteron in pure aluminum.(l”) Thus it was felt that essentially no stopping of deuterons occurred. In addition, this thickness insured an opt#imum combination of maximum damage with minimum thickness. This thickness was also perfect for the required X-ray studies and compared well to specimen dimensions employed previously to study kinetics in this system.(@ EXPERIlMENTAL

RESULTS

The damage-rate curve is plotted in Fig. 1: The as-irradiated fractional increase in resistance is plotted versus dose in units of 1015deuterons/cma (10’s dIema) for irradiations at -195°C. For dose levels of the order of 1Or5d/cm2 the curve is linear, giving a slope of 0.24 %/lOi* df cm2 as determined from a least-squares

768

ACT.4

~IETALLUR~ICA,

3.2.

VOL.

12,

analysis.

0

This

for irradiation

2.8 -

1964

be positive

value

deviations

doses (~10~~ d/om2). 2.4 -

is

of

the

order

of pure aluminum.(11~*2) from linearity Within

reported

There

may

for the higher

the limits of accumcy

possible here, there does not appear pendence of damage on the state

to be any deof the alloy.

(Table 1). m = 0.24 %/tOlsd,cm~

I.$-

Specimens Figure

1.2 -

retained

in the as-quenched

were irradiated at the temperature 3 shows

quenched

at 20°C

of a specimen

from 300°C t#o water at 25°C and brought

immediately -195°C B).

annealing

condition

of liquid nitrogen.

to -195”C,

followed

to an integrated

Curve

A is quench-aging

specimen.

by irradiation

a,t

dose of 1Ol5 d/cm2 (Curve of a non-irradiated

There does not appear to be a significantj

modification

of the reaction.

for quench-aging

normally

Some early-time

dat’a

and aft’er irradiation

are

given with a linear t,ime scale in Fig. 3. Irradiation,

DOSE IN UNITS OF 10%fpcm2 FIG. 1. Damage-rate curve. Fractional increase in resistaucu as a function of dose in units of 101” deuterons/ cm2 at -195°C. R, is the resistance prior to irradiation. +--as-quenched alloy. O-as-reverted alloy. Slope: 0.24 o/0/1O’5 d/c&.

though sistance

not importantly change,

modifying

does appear

the rate of re-

to slightly

retard the

reaction.

TABLE 1

~-

Expt.

Treatment

Dose in units of 1Ol5d/cm2

y. increase on irradiation R, = resistance prior to irradiation

o/oincrease to maximum R, = as-quenched, as-reverted, or as-irradiated

0.9

0 “5

19.0

116

19.6

150

19.0

1.50

(Time),,,. minutes to maximum in resistance

Isothermal annealing 1. 2. 3. 4. 6. ti. i. 8. ‘)* .

10. 11. 12. 13. 14.

As-reverted: 200°C for 10 min and reage 20°C after irradiation As-reverted: 200°C for 10 min and reago 20°C after irradiation As-reverted: 200°C for 10 min and reage 20°C after irradiation As-reverted: 200°C for 10 min and reage 20°C after irradiation Re-aged for 3000 min: from Expt. 3 As-reverted: 200°C for 10 min and reago at 20°C after irradiation As-reverted: 200°C for 10 min and reagt: at 20°C after irradiation As-reverted: 200°C for 10 min and reagr: at 2O’C after irradiation As-reverted: 200°C for 10 min and reagt: at 20°C after irradiation As-quenched from 300°C to 25°C water and age at 20°C after irradiation As-quenched from 300°C to 25°C water and age at 20°C after irradiation As-quenched from 300°C to 25°C wa,ter and age at 20°C after irradiation As-quenched from 300°C to 25°C water and age at 20°C after irradiation As-quenched from 300°C to 25°C water and age at 20°C after irradiation

.I

0

-

0 0.5 0.9

0.14 0.26

18.5

1%

1.9

0.56

19.7

150

9.0

3.00

2.9

0.64

13.3

2.64

0

0

li.o

1.0

0.25

16.X

1.0

0.15

18.3

0

0

17.0

2.0

0.43

1.0

0.23

0.798 x 1O-3

36

0

0

0.782 x 10-Z

58

Isoohronal annealing 15. 16.

___--

Reverted at 200°C for 10 min irradiated and isochronally annealed from -70°C Reverted at 200°C for 10 min irradiated and isochronally annealed from - 70°C

irradiation c~ontinuc~din Expt. 9

16.6 (%W. (Ohms)

_-._.____x

IRRADIATION

HERMAN:

AND

G.P.

ZONES

769

(min.)

TIME FIG. 2. Quench-aging

at 20°C. (A) Quenched from 300°C and aged (Expt. 13). (B) Quenched from 3OO”C, irradiated to a dose of 1Ol6 d/cm2 and aged at 20°C (Expt. 11).

-.

16 ,2 IRRADIATED

8

v1-

0

3

2

I

4

5

(min.)

TIME

FIG. 3. Quench-aged at 20°C after quenching from 300°C. A-Expt. 13. l-Expt. 10. Quench-aged at 20°C after quenching from 300°C and irradiated at -195°C. x-Expt. O-Expt. ::-Expt.

Irradiation

of the as-reverted

specimen

to a greater effect, at least initially. the fractional

change in resistance

minutes for reaging normally various reversion

doses.

Here,

the

temperature acceleration

of liquid

the larger the dose.

Note,

versus log time in

specimens

nitrogen.

of t#he reaction,

gives rise

Figure 4 shows

and after irradiation

t#reatment and brought

11 12 14

were given

immediately

to a

to the

There is an initial

1 x lo’& d/cm2 1 x 1Ol5 d/cm2 2 x 1Ol5 d/cm2

two cases; Expts. 1 and 4, Table 1). Figure 5 shows a linear plot for early times of reaging. The rate of resistance change as determined

at 0.02 minutes from

Fig. 5 is plotted versus dose in Fig. 6. Expt.

2 for reaging

(Figs. 4 and 5) represents

non-irradiated specimen which irradiated specimen, including

was handled cooling with

a

as an liquid

this effect being greater

nitrogen

however,

the kinetics are not different from that of a specimen

that as in the

case of quench-aging, the later part of the reaction is not modified for doses of the order of 1015 d/cm2 (though the peak is shifted to slightly earlier times for

at the cyclotron

normally reaged, Expt. that plastic deformation A specimen

target-window.

Note that

3. It can thus be concluded was not a factor.

was normally

reaged

for

10,000 min

ACTA

770

METALLURGICA,

VOL.

12,

1964

16-

12-

6-

4-

1.0

0.1

woo

1000

100

IO

TIME (min.) FIG. 4. Reaging at 20°C after reversion at 200°C for 10 min. The specimens mere quenched-aged at 2O’C for 1 hr prior to reversion. Irradiation was carried out at -195°C. O-Expt. l-Expt. x-Expt. q-Expt. +-Expt. A-Expt. a::-Expt. O-Expt.

2-Unirradiated 3-Unirradiated 4- 0.5 x 1Ol5d/cm2 l0.9 x 1Ol5d/cm2 6- 1.9 x 1015d/cm2 7- 9.0 x 1015d/cm2 9-13.3 x 1Ol5d/cm2 5- 0.9 x 1Ol5d/cm2

“I IO __--

6 6 4 2 0

0

I

3

2

4

5

6

7

6

9

TIME (min.1 FIG. 5. Reaging

at 20°C after reversion.

A-Expt. B-Expt. C-Expt. D-Expt. E-Expt. F-Expt. G-Expt.

Same date as FIG. 4.

3-Unirradiated 2-Unirrediated 4- 0.5 x 1Ol6d/cm2 l0.9 x 1Ol6d/cm2 6- 1.9 x 1Ol5d/cm2 9-13.3 x 1Ol6d/cm2 7- 9.0 x 1Ol5d/cm2

H)

HERMAN:

IRRADIATION

AND

G.P.

ZONES

771

70

60-

A(gXld) 10.5 MEV DEUTERDNS

At

AT 77OK

as determined at 0.02 min, versus dose in units of 1015 deuterons/cmz.

and then irradiated

to a dose of 1Or5 d/cm2 (Expt.

Fig.

on reaging

4).

No

significance

effect

was observed.

5,

The

of this result will be discussed later.

For doses of the order of 1016 d/cm2 the reaction after reversion

is greatly

Figs. 4 and 5):

affected

The resistance

go through a maximum

(Expts.

7 and 9,

in this case does not

to times of 10,000 min.

Again,

in resistance (Curve A).

to a dose of 1015 d/cm2 (Expt. significant -7O”C,

increase and

the

as can be seen from Fig. 5.

occurs is specimen.

version

had been

was isochronally

irradiated

annealed.

after re-

Figure

annealing

for increasing

temperatures

to 190°C.

For the case of the unirradiated

with holding

higher

shifted

the

22°C

-70°C

specimen

there

In

maximum

lower

for

at

is an

above that

addition,

the

in resistance the

irradiated

increase

Small-angle sca,ttering of X-rays Small-angle determine

scattering

zone size.

RX

o.721 -70 -50 -30 -io -195

for one minute

temperatures

specimen.

at which

irradiated

15, Curve B) there is a

7 shows

from

there does not appear to be any significant

at

unirradiated

temperature

which

greater than -50°C

increase in resistance which is significantly for

however, the early part of the reaction is accelerated, A specimen

until temperatures

In the case of the specimen

IO 30 50 70 90 II0 130 150 170 190 210

TEMPERATURE (“Cl

FIG. 7. Isochronal annealing. Quenched and aged for 1 hr, followed by reversion at 200°C. Curve A (Expt. 16) is for the unirradiated specimen. Curve B (Expt. 15) is for a specimen irradiated to a dose of 1 x 1016d/cm2.

of X-rays

was employed

to

The data for the small-angle

ACTA

772

scat)tering plot”

is presented

in Fig. 8.

plotted

in the form

Here, log intensity

VOL.

METALLURGICA,

12,

1964

of a “Guinier in counts/set

versus .?, where E is 28 expressed

is

in radians.

Below is Guinier’s equation for the scattered intensity as a function

of scattering

angle:

I = Nn21e exp where I, is the intensity

-

Rg2c2

scattered

small angles, N is the number

(1)

1

g

by an electron at

of scattering

particles

and n is the difference between the number of electrons contained

in the particle

the homogeneous the radiation linear

and in an equal volume of

material.

1 is the wave-length

(1.54 A for Cu K,).

portion

of the

scattering

curves

determine the radius of gyration, particles. density

The

radius

analog

chanics,

of

is used

to

R,, of the scattering

gyration

is the

of the mass density

and for spherical

of

The slope of the

electron

as used in me-

particles

we have for the

radius. 11=&R, The curvature linear

region

(2)

in the scattering indicates

a range

curves

beyond

the

of zone

size.

The

and

these

contribute Any

more

to

reasonable

the

zone

would thus yield an average size, R,, Figure

8 shows

the results

irradiated

with

1015 d/cm2

at

experiments.

specimen 20°C

reaged for

reverted and

and

-195”C,

respectively, followed by reaging for 1 week. Curve D represents a specimen reverted, irradiated at -195°C for

to a dose of 13.3

1 week.

specimens

The

average

intensity

1015 d/cm2, and reaged zone

size is larger

which have been irradiated

the zone size increasing irradiated

x

with dose.

of the peak in scattering specimens,

able dependence

for

before reaging, In addition,

the

is higher for the

and here too, there is a notice-

on dose.

The maximum,

shifts to smaller angles with dose. summarized in Table 2.

I

I

I

80

100

120

scattered

= ;R.

B and C are for specimens

I

60

likewise,

These results are

DISCUSSION

The present results support the idea that vacancies play a major

role in the formation

When the initial vacancy

A B

DC% (d/cm? Nonirradiated 1 x 10’5 1 x 10’5 13.3 x 10’6

of G.P.

in the alloy

is low, as for the case after reversion,

the reaction

can be accelerated

by irradiation,

In the case of quench-aging, initially

a vacancy

generated noted.

however, there is present

concentration

by the irradiation,

In the latter

retardation

of

vacancies

the

are

at least initially. comparable

case, though, reaction

reduced

in

- 195°C 20°C - 195°C

to that

and no amplification a slight

would their

is

initial

indicate

capacity

to

that aid

diffusion of zinc, at least initially. The maximum

number of single thermal vacancies,

C,, available after the quench or following reversion can be calculated from the following equation: C,; = exp (S,.“/k) exp (--E,.“/kT)

Temperature of irradiation

zones.

concentration

TABLE 2

ChVe (Fig. 8)

I 3

x 104-

FIG. 8. Small-angle scattering of X-rays. Counts/set versus (c)2 x 104. See Table 2 for details.

distribution

of four

Curve A is for an un-irradiated 1 week.

net

size

I

40 (Ef

linear region gives the size of the largest zones present, intensity.

I

20

I Inax. (counts/set)

2&n,,. (Den)

(2)

%.V. (A)

3.15 3.4 3.2 3.6

2.0 1.75 1.75 1.60

9.0 10.4 9.6 11.2

4.5 5.2 4.8 5.6

(3)

HERMAN:

The energy of formation, M-4.4

IRRADIATION

EVF, was determined

for an

XvF/k, for pure aluminum

in resistance

for

the

higher

x IO-7 -1OF

Fig.

1

may

be

specimen: enough

The effects observed

centration estimate

due to irradiation of the resistivity

verted) very

alloy

approximate

to that Thus,

for

vacancy

by

On

is present

below

with

1015 d/cm2. gives no

2OO”C, there

of about two orders of magnitude due

alloy.

to irradiation

is a

between and

that

unirradiated isochronal

scattering of X-rays,

after irradiation. Of importance, time results, resistance

and not consistent

is the fact

with the early

that the maximum

is not shifted to significantly

for reaging

after irradiation.

in the

earlier times

The maximum

is not,

holding

at

about

--50°C

the

will attempt

-70°C

alloy

for

1 per cent. and, within

specimen. curves

abion is affecting enhanced is

Small-angle

larger sizes.

of the reverted

to

1 min

causing

the

the sensitivity

irradiated

zone formation:

curves,

nucleation

because

and it is known

maximum

is dependent

zones.(4’7)

Normally

magnitude

un-

that irradiand not to

that irradiation

irradiation

maxima

is

not

in the isothermal

that, the magr&ude on the number

of the

of growing

the same effect occurs after the

quench and after reversion: on isochronal

in the and

and it is felt that

diffusivity

It is unlikely

the resistance

the

This increase

The large difference

between

nucleation.

after

of zone

does not appear for the

this is due to an increased

influencing

increases wit.h dose.

so that

towards

irradiated specimens gives clear indication

An acceleration

likewise, indicat’es that the zones grow to larger sizes

present

studies

of the present measurements,

retained on cooling from the t’emperature of reversion. of t’he reaging reaction is noted which

un-

with higher doses are not easily

annealing

increases

con-

for the

gives rise to an early enhancement

resistance

that irradiation from

Isochronal reversion formation.

single vacancy

zones

9.0 A

In this case, there

clarify t’lie situat,ion.

(reA

2.

and subsequent

fraction

irradiation

In the case of reverting fraction

An

explained,

to the higher dose

with

will be biased

is then 10-5/1015

effect in the case of the quenched

vacancy

of

con-

from 300°C is closely similar

it is not surprising

difference the

the

bombardment

on quenching

important

case

is 1.4 x 10e6 ohm-cm.

value

generated

the

can be determined.

Note that the maximum

centration

for

for the vacancy

of the homogeneous

at -195°C

created by deuteron d/cm2.

vacancy

slope

scattering

For 13.3 x 1Ol5 d/cm2

Table

large

ohm-cm/atomic

limit

irradiated

R is 11.2 _& as compared

observed

fraction

small-angle

that a larger zone finally

(of the order of 1016 d/cm2).

for the alloy from

an upper

The

indicate

(0.24 %/1015 d/cm2), and assuming a value of 2 x 1O-4 aluminum,‘l5)

but a

for annealing

Fig. 4. It would thus appear

results for specimens

irradiated Using the damage-rate

rate of growth,

is not attained

doses.

results, however,

C, (atom fraction)

-3

d/cm2) result in an increased

that the later part of the reaging reaction is retarded

TABLE 3

200 300

773

ZONES

up to one week at 20°C:

is 2.4.(14)

Table 3 lists C, for 200°C and 300°C.

T I:“c)

G.P.

maximum

at. y/oZn alloy to be 0.70 eV,(‘) and the entropy

of activation,

AND

annealing

the resistivity

for the specimen

than for t’he specimen

maximum

is considerably quenched

reverted

greater from

at 200°C

in

300°C

(data not

shifted by more t’han an average of 30 min (see Expts.

shown), but isothermal annealing gives approximately

14,

the same magnitude.

last column of Table 1). As discussed previously,

enhanced

diffusion

would

be expected

peak to much earlier times.

to shift the

That this is not the case

Irradiation reaged

of a specimen

would indicate t,hat a significant fraction of the excess

growth (Expt.

vacancies

reagnd normally

available ture.

introduced for ext’ended

It would

vacancies

by

irradiation

reaging

thus appear

are not

made

near room-tempera-

that the distribution

irradiated of

is very different in the irradiated alloy than

in the quenched

alloy.

This is not surprising

since

it would be expected that less long range vacancy motion is available after irradiation than following the quench: The vacancies, as introduced by irradiation are probably deuteron, whereas homogeneous High

doses

clustered near the path of the the quench would yield a more

distribution

of vacancies.

(9.0 x 1015 d/cm2

and

13.3 Y 10’”

which

has been

does not result in an enhancement

at

zones formed 10 B dia.,

5).

In this case, a specimen which was for almost

-195°C

with

3000 min (Expt.

3) was

0.9 x 1015 d/cm2.

The

on normal reaging were approximately

and about

segregated.c4)

well

of zone

20 per cent

For this case, then,

present and the concentration has been decreased

of the zinc was when

zones are

of solute in the matrix

considerably,

the vacancies,

as

generated by irradiation, are not able to importantly further the process of zone growth. This would appear to be inconsist’ent

with the acceleration

of zone for-

mation which was observed

after reversion

solute atoms were at zones.

It may be that the zones

when few

774

ACTA

can act

as very

thereby

quickly

mobility.

effective

traps

diminish

Another

the zone-forming

for

METALLURGICA,

vacancies

their ability

factor

is limited

If

solely by solute

atom mobility, it would be expected that the introduction of vacancies by irradiation would result in additional observed cease

simply

suggested also

segregation would

be

of solute.

indicate because

saturation

important being

of a kinetic

does not

limitation.

et aZ.,t4)thermodynamics

by Herman an

That this was not

that the reaction

factor,

the major

in terms

driving

force

of

As may

super-

for zone

growth.

low,

the concentration

of thermal

as is the case after reversion, the zone-forming

employed

here,

early times.

irradiation

reaction.

the influence

vacancies

can

For the doses

is noticeable

only

at

the final sizes of the zones on reaging are greater in nucleation

of zones

specimens.

in the Al-rich

It is felt that Zn alloy

effect’ed by irradiation

with deuterons.

It can be concluded

that vacancies,

by bombardment aid the

growth

as introduced

with 10.5 MeV deuterons, of

G.P.

zones.

is not

Thus,

are able thermal

are probably responsible for the normally rates of zone growth solution treatment,

but vacancies, tributed

Blewitt

of Argonne

National

Laboratory

fessor M. E. Fine of Northwestern continued Professor

interest

enlightening

discussion

The assistance

as generated

differently

the quench.

from

by irradiation, vacancies

are dis-

available

after

for their

suggestions,

University

to

for an

of the data, and to Professor

Northwestern

lent the small-angle Cyclotron

of Harvard

and Pro-

University

and very helpful

D. Turnbull

J. B. Cohen,

University,

who kindly

scattering equipment.

extended

by Milan Oselka and the

Group at Argonne

National

Laboratory

is

greatly appreciated. under the auspices of

Energy Commission.

REFERENCES

is

The effect is clearly seen through X-rays:

the case of the irradiated

vacancies observed

ACKNOWLEDGMENTS

The author wishes to express thanks to Dr. T. H.

This research was performed

accelerate

to

1964

the United States Atomic

CONCLUSIONS

When

12,

and

to aid solute

may be of importance:

reaction

VOL.

1. A. GUINIER, Progress in Solid State Physics, Vol. 9, p. 293. Academic Press, New York (1959). 2. G. J. DIENES and G. H. VINEYARD, Radiation Effects in Solids. Interscience, New York (1957). 3. A. GUINIER, MBtauz Corros-Usure17,209 (1943). 4. H. HERMAN, J. B. COHEN and M. E. FINE, Acta Met. 11, 43 -_ I1963\. 5. R. GRAF, C.R. Acad. Sci. Paris 246, 1544 (1958). 6. N. F. MOTT, J. Inst. Met. 60. 267 (1937). 7. C. PANSERI and T. FEDERI~HI, Akn Met. 8, 217 (1960). 8. 0. KRATKY. G. POROD and L. KAHOVEK. Z. Electrochem. 55, 53 (195i). 9. P. KIRKPATRICK, Rev. Sci. Instrwm. 10, 186 (1939). 10. D. S. BILLINGTON and J. H. CRAWFORD, Jr., Radiation Damnae in Solids. Princeton Universitv Press, Princeton, N.J. (i961). 11. K. HERSCHBACH,Phys. Rev. 130, 554 (1963). 12. H. P. YOCKEY et al., SR-NAA-186. 13. A. GU~NIER and G. FOURNET, Small-Angle Scattering qf X-rays. Wiley, New York (1955). 14. R. 0. SIMMONS, J. S. KOEHLER and R. W. BALLUFFI, Radiation Damage in Solids-I, IAEA, Vienna, 1962, p. 155. 15. T. H. BLEWITT, private communication. \----1.