Interaction of vacancies with Sn atoms and the rate of G-P zone formation in an AlCuSn alloy

ACTA

1076 possibly

of the type

METALLURGICA,

described

by Seegerc4).

would

correlation

diffuse out of the surface of very thin

to any great extent as fact that no loops were

reason for the slo,wer disappearance

traces is not clear.

Further investigation

the other observations

of the slip of this and

is being made.

Atomic Energy of Canada Ltd.

W. R. THOMAS J. L. WHITTON

4. 5.

and Al-Zn.(a) microscopy

dislocations

Therefore,

to accept.

may

out

not

be ruled

Moreover, showed

and the G-P

by the

quenched-in

such a small amount

of Sn (of order of 0.01 at. %)

to collect the majority

of Cu atoms of about 2 at.%.

to explain

zone formation the

quenched-in

atoms

are

the suppression

by addition excess

considered

vacancy to

mechanism.

attract

quenched-in

temperature

the rate of G-P zone formation Al-Cu-Sn

(>99.99

per cent).

position

of 3.8 wt.%

Pronounced

effects of addition

Sn, Cd or In (0.05% of Al-Cu Hardy

and

others.(l)

examined

Hardy@)

addition

cause of the rapid

of Sn, Cd or In:

binary Al-Cu

stresses are supposed rate of G-P

alloys.

three

of G-P zone

ternary elements may reduce the quenching Here the quenching

by Heal,

suggested

for the marked suppression by

of

on the ageing processes

alloys were extensively

mechanisms formation

to 0.1%)

of small amount

(1) The

Sn atoms

of excess treatment

and

The following

cannot

experiment

Chemical analysis gave the comCu and 0.025

wt.%

mens were wire of 0.4 mm in diameter furnace

Quenching

extracting

furnace

and immersing it in water.

the specimen quickly

bath,

quickly into

resistivity

treatment

was carried out in a

from 550°C.

well represented by the equation as in Al-Cu increase

binary

alloy.t3)

in resistivity

a liquid

measurements

Figure 1 shows the change in resistivity ing at 14°C after quenching

due to ageThe curve is

ApIp = In (a + bt)/b Here, ApIp is the

and a and

6 are constants.

stresses. to be the

zone formation

(2) The ternary elements

in may

be attached to dislocations to form obstacles against the pipe diffusion of copper atoms along dislocations. Here, the pipe diffusion

is supposed

of the rapid rate of GP

zone formation.

to be the cause

(3) Because Sn atoms (as well as Cd and In atoms) are larger than Al atoms, they may collect Cu atoms, smaller than Al atoms, around them so as to reduce the strain energy. Hence, the number of Cu atoms available to the G-P zone formation is reduced. Now it is almost certain that the excess vacancies quenched-in from solution treatment temperatures are responsible for the rapid rate of clustering of solute atoms

or G-P

zone

formation

in some

aluminum

0

I

I

2

3

4 TIME

5

by

out of the

After quenching,

transferred

in which

were done. Ageing silicon oil bath.

Speci-

was performed

merely

were

Sn.

and heated in

at 550°C for 30 min for the

treatment.

nitrogen

alloy *

to

a solution

more

was performed to support this proposal. An alloy was made from high purity Al, Cu and Sn

specimens

in an

bound

enhance the Cu clustering.

solution

and

are

from

Sn

vacancies

a horizontal

vacancies

of G-P

of the third element with

* Received August 4, 1961.

with Sn atoms

excess

vacancy mechanism, but it is hard to see, as pointed out by Hardy himself, how it could be possible for

strongly than Cu atoms, so that the majority

of vacancies

by

The third suggestion

References F. W. C. BOSXNELL and E. SMITH, Symposium on Advances in Electron Metallography p. 245. American Society for Metals, Cleveland) (1958). 1,. G. COOK and R. L. GUSHING, Acta Met. 1,p.539 (1953). H. 0. F. WILSDORF, Structure and properties of thin $lms p. 151. John Wiley, New York (1959). A. K. SEEGER, in Proc. 2nd. Int. Conf. Peaceful Uses Atomic Energy, Geneva, 1958. Vo16, p. 250. United Nations, New York (1958). H. G. F. WILSDORF and D. KUHLMAN-WILSDORF, Phys. Rev. Letters 3, p. 170 (1959).

Interaction

no zone

the first two suggestions

Hardy are difficult

It is possible

Chalk River, Ontario

Al-Ag electron

between

formation.‘4) defects do not appear

observed.

2. 3.

e.g. Al-Cu,

the transmission

to have clustered evidenced by the

1.

alloys,

9, 1961

This is contrary to a suggestion(5) that vacancies foils. (iii) The irradiation-produced

The

VOL.

6 7 (min.)

6

9

IO

FIG. 1. Increase in resistance of an Al-Cu-Sn alloy during ageing.

LETTERS

40

“G

25

TO THE EDITOR

1077

than in an Al-Cu 0

14

vacancies

binary alloy.

The concentration

of

bound to Cu atoms, CcUv, is given by

c cuv

=

c 2! c Sll

GSnv exp

-

(

k;

(1)

1

where Co, and Cs, are the atomic fraction of Cu and Sn, respectively, Csnv the concentration of vacancies bound

to Sn atoms and hB

binding

the difference

energies of a vacancy

that with a Cu atom, i.e. BSnv supposed

Bcur,. Here, BSnv is

to be larger than B,,,.

of free vacancies compared

is found

The concentration

to

be negligibly

with the concentration

at near room

between

with a Sn atom and

temperature,

small

of bound vacancies

if Bcur

and

BSnv are

greater than 0.1 eV. The initial rate of clustttring, which is reasonably considered to be proportional to 3.2

3.4

3.3 +x lo”

3.5

(T,

3.6

3

inoK)

A

the initial rate of resistivity

ing results from the temperature

FIG. 2. Dependence of the initial rate of resistivity change, l/R,(dR/dt):=o, on the ageing temperature. (A oircle represents the mean value of three measurements for each temperature. R, means the resistance as quenched. The activation energy is determined to be 0.7 + 0.1 ev.)

and of the mobility. and ~nde~ndent

alloy

the activation energy of this resistivity increase, isothermal ageing curves were evaluated for various ageing

temperatures

after

quenching

from

lated

to

be

(0.7 -& 0.1)

eV,

which

is considerably

higher than that in a binary alloy, i.e. 0.5 eV. Although the resistivity change in an Al-Cu Al-Cu-Sn

or an

alloy occurs in a much earlier stage ofageing

than the hardening due to G-P zone formation, a quite similar effect of Sn addition is observed in both resistivity

change and hardening.

to consider the clustering

Hence, it is natural

of Cu atoms, which causes

the resistivity change, to be the early stage of G-P zone formation responsible for the hardening, and the following explanation for the effect of Sn addition on the resistivity change may be taken as an explanation for the suppression of G-P zone formation due to Sn (Cd or In) addition. If vacancies are attracted more strongly by Sn atoms than by Cu atoms, smaller numbers of vacancies are available for the enhancement

of quenched-in

vacancies equation

c $Q&exp Ccuv =

of Cu atom diffusion

(

Sn 1 + exp

(

-g

-

i_

g

>

If AB is larger than 0.1 eV, CoUv may be approximated for ~mperatures

C

550%

The initial rates of changes are plotted against l/TA The in Fig. 2, where TA is ageing temperature. activation energy of the resistivity change is calcu-

of Ccuy

of the ageing ~mperature,

to that in a binary

alloy (3.8 wt.% Cu) quenched from the same temperature is found to be about lo-*. In order to obtain

dependence

(1) becomes

change is much less than that in an Al-Cu binary alloy. The ratio of the initial rates in the ternary

is proportional

Since CcUv + CSnV = C,, where

C, is the total concentration

The rate of resistivity of change

increase,

to Ccuv and to the mobility of Cu atoms, and the tem~rature dependence of the initial rate of cluster-

below 80% by

cuT,

=

$

C, exp

-

g

(

2%

. J

In equation (2) C,,, Csn and C, are independent of the ageing temperature. Therefore, the activation energy of clustering is given by the sum of AB and the activation 0.5 eV.

energy

for

the

mobility

Since the activation

in the Al-Cu-Sn

of

Cu atoms,

energy of the clustering

alloy was found to be (0.7 -& 0.1) eV,

AB is determined as (0.2 zt: 0.1) eV. The value of AB can also be evaluated ratio, that

.P, of the initial rate in an Al-Cu-Sn in an Al-Cu

alloy,

provided

both

from the alloy to alloys

are

quenched from the same temperature. Neglecting small differences in the total vacancy eon~entrat~on in both alloys due to the presence of Sn, we can consider the ratio P is equal to the ratio, P,, of Ccuv in the ternary alloy to that in the binary alloy, C&r, because the mobility of a Cu atom should be the same in both alloys.

The ratio P, is given by

ACTA

1078

METALLURGICA,

here the small number of free vacancies in the binary

Al-Cu alloy 1s neglected and CcuV is taken to be C,. At 0°C P was found to be 10p4, and AB is evaluated to be (0.35 f

0.05) eV taking

uncertainties Since

in determining

the values

independent stronger

of

ways

binding

AB

agree

into consideration

the

P. determined well,

of vacancies

the

Sn atoms

of than

with Cu atoms is considered to be true and AB is evaluated to lie between 0.2 and 0.4 eV. The binding

energy

atom is estimated

between

9,

1981

4. G. THOMAS, Phil. Mug. 4, 1213 (1959); R. B. NICHOLSON, G. THOMAS and J. NUTTING. J. 1lnst. Metals 87., 429 f~195% 59). 5. H. KIMURA, lished.

A. KIMURA

and R. R. HASICXJTI, to be pub-

* Received

July 29, 1961.

Porosity

in plastically deformed Al single crystals*

in the two hypothesis

with

VOL.

a vacancy

to be 0.2 eV in Al-Cu

Rosi and Abraham@

and a Cu

cally deformed

allays,(5)

single crystals.

and the binding

observed

porosity

was (1) to determine if this phenomenon

ancy and a Sn atom in an Al-Sn

activated

performed.

alloy is now being

In the present discussion,

the association

of Sn atoms and Cu atoms is not considered.

It is

crystals stated,

and a Sn atom estimated the binding The binding

here should be regarded as

energy of a vacancy energy,

equal to the binding

with a Sn-Cu

then, would

not necessarily

energy between

a vacancy

a Sn atom which would be estimated ment

with an Al-Sn

of interpreting

alloy.

pair. be and

alloys,

All

at.% and

basic

is also found

(2) to determine

formation

tests

is a thermally

were performed

Al(99.996)

are reported crystals

and

with

single crystals.

testing

procedure

elsewhere.t2)

of

The these

Unless otherwise

were tested at a strain rate of 5 x

1O-4 see-l. After

deforming

temperature

a specimen

and electrolytically

phoric acid solution,

porosity

to fracture etching

at room

in a phos-

was observed,

(Fig. la)

from the experi-

There is the possibility

effects of ternary addition on any pro-

cesses involving present

a vacancy

process.

preparation

quite possible that Sn atoms exist in the form of Sn-Cu energy between

(Al)

whether or not the porosity

pairs.

If so, the binding

solute

Cu(99.999)-10

in plasti-

(to failure) Ag, Cu and Cu-0.1% Al The object of the present investigation

energy between a vacancy and a Sn atom is estimated to be 0.4 to 0.6 eV. An independent deterntination of the binding energy between a vac-

in higher

Cu-10 at. %

vacancy

mechanism,

migration

i.e. vacancy

in terms of the ternary

elements

interaction. The authors wish to thank Professors and J. Takamura

for their helpful

chemical

was

Denko

analysis Co.,

Dr. Tarora

the

kindly

authors’

and Professor

done

thanks Mishima

Y. Mishima

discussion. by

The

Furukawa

are extended

to

for arranging it.

They also thank Mr. Ooi for his efforts in performing the experiment. H. KIMURA R. R. HASIGUTI

Rikagaku Kenkyusho The. Institute of Physical and Chemical Research Komqome,

Bunkyo-ku,

Tokyo, Japan

References 1

A. H. SULLY, H. K. HARDY and T. J. HEAL, J. Inst. Metals 76, 267 (1949-50); I. J. POLMEAR and H. K. HARDY, ibid. 81, 427 (1952-53); H. K. HARDY, ibid. 82, 236 (1953-54); I. J. POLMEAR and H. K. HARDY, ibid, 88,393 (1954-55), J. M. SILCOCK, T. J. HEAL and H. K. HARDY,

ibid. 84, 23 (1955-56).

2. H. K. HARDY, J. Inst. Metals 80, 483 (1951-52). 3. D. TURNBULL and H. N. TREAFTIS, Acta Met. 5, 534 (1957); W. DESORBO, H. N. TREAFTIS and D. TURNBULL, ibid. 6, 401 (1958); T. FEDERI~HI and L. PASSARI, ibid. 7, 422 (1959); C. PANSERI and T. FEDERIOHI, ibid. 8, 217 (1960); D. TURNBULL, H. S. ROSENBAUM and H. N. TREAFTIS, ibid. 8, 277 (1960).

FIG. 1. Porosity in electrolytically etched Cu-10 et.% Al single crystals fractured at loom temperature with strain rate of (a) 5 x 10e4 sew’; (b) 5 x lOma set-1. The horizontal direction is parallel t,o the tensile axis in both figures. x 15