Recovery of cold worked body-centered cubic metal

LETTERS

TO

THE

The case for

width of the denuded zone on one side of the boundary and a the lattice parameter.

In the present

ments, there is approximately

one vacancy

experi-

absorbed

119

EDITOR

extrapolation in f.c.c.

vacancy

metals

to b.c.c.

for every five boundary atoms. The stacking sequence across a twin, in the usual

defects produced

notation,

with

the

is ABCACBA.

boundary

vacancies, of part moves

plane,

Although A,

by

is energetically

removing

inserting

unfavourable,

of one of the adjoining the

boundary

boundary plane

direction

moved

an atomic

C, simply

Thus,

if the

distance

in one

in some parts and a similar distance

other

direction

in some

could

be accommodated

other

parts,

that a platelet of vacancies

readily

at the twin boundary

as elsewhere, possibility segregation

than in the adjoining

there would be no denuded

boundary,

zone.

One

cluster preferentially

by analogy

of impurities

likely explanation

it is not

would form more

at

with the suggested

to stacking

faults.

A more

is that there are pre-existing

mon-

is based

on an

of experimental

metals.

by quenching,

results

In f.c.c.

metals,

irradiation,

and cold

work anneal out at about the same temperature about

the

same

activation

it is reasonable

they are also produced

and

energy.(l)

excess vacancies are likely to be produced ing and irradiation,

Since

by quench-

to conclude

that

by cold work.

In the ease of b.c.c. metals, excess vacancies not been produced

by quenching,

they

can be (a calculation

that

this is possible,

overlooks

in solution

have

nor is it likely t#hat

by Gregory,@)

showing

the likelihood

interstitial

atoms

will act

vacancies).

Indeed, the main recovery

that

as sinks for process occur-

ring after quenching of iron is second phase precipitation, i.e. quench aging. It is likely that irradiation

were as difficult at the boundary

is that vacancies

the twin

the vacancies

However,

obvious

If nucleation

in the

with a very small increase

in energy of the twin boundary.

matrix.

of

the removal

planes,

locally.

plane

part of

a sheet

migration

of explanations

b.c.c.

metals,

that vacancy recovery

however migration

is a controlling

of irradiation

some experimen~l stitial impurity

produces

vacancies

in

it has not been established dama,ge.

evidence

migration

process in the

Indeed,

to indicate

controls.

there

is

tha.t inter-

Wagenblast

and

boundaries

and

Damaskt3) have shown, by means of internal friction, solid solution

during

I would like to thank Dr. L. M. Clarebrough

and

annealing of irradiated iron with an activation

energy

atomic

steps in the coherent

that these act as vacancy

twin

that carbon

sinks.

Mr. J. F. Nicholas for valuable

discussions. R. L. SEGALL

Division of Tribophysics Commonwealth Scienti$c and Industrial .&search Organization

equal to the activation energy for diffusion of carbon in unirradiated iron. However, the absolute rate of carbon

was more rapid in irradiated

removal

irradiation

produces

and

and aged iron.

sites for trapping

Thus,

carbon atoms,

and the kinetics of the process depend on the distance

References 1. P. B. HIRSCH, 3. SILCOX,R. E. S~~L~~N WESTMACOTT, Phil. &fag. 3, 897 (1958). SILCOX

from

aged iron than in quenched

University of Melbourne

2. J.

is removed

and P. B. HIRSCH, Phil.Mag.

carbon atoms travel before encountering and K. H.

4, 72 (1959).

* Received Suly 11, 1963.

one of these

sites. From the above

discussion,

evidence concerning of quenched

it is evident

that the

the role of vacancies in annealing

and irradiated

b.c.c. metals is not nearly

as conclusive Recovery

b.c.c. metals as a result

offered

as to the

different controlling

experiments: (a) vacancy stitial impurity migration.

process

is removal

(T,

= melting

suggestions

have been

of Thomas

mechanism

in such

migration and (b) interDespite this divergency

there appears to have been little attempt

to assess the relative merits of each viewpoint.

This

of

How-

impurities

from

is the well-known

paper

and Leak,(*) w-ho sh owed that the rate of return of the yield point paralleled the rate of removal of interstitial Rosenfield of

a number

reported

impurities from solution. and Owen(5) have examined of

activation

in the literature

data could be interpreted or interstitial impurities.

impurity

paper.

is stronger.

migration.

interstitial

The best example

note discusses the background of each suggestion and suggests that the case for control by interstitial migration

by vacancy

ever, there is a large body of data concerning strain aging which can only be explained if the controlling solution.

of annealing in the range, T~~~-T*l~ Two broadly

cold work is controlled

have studied the changes

of cold-worked

point).

in approach,

concluded

of cold worked body-centered cubic metal*

A number of investigators in properties

as that in f.c.c. metals. It cannot be on this basis alone that annealing out of

The

circles

(0)

energy

the results

measurements

to determine

whether

the

as favoring either vacancies Figure 1 is taken from their represent

values

for

the

ACTA

120

25-

5 4 2

VOL.

12,

1964

Strain agelng

P 0

Recovery

X

Dlffwon

ZO-

METALLURGICA,

of

rachmon

damage

fastestmowng Interstitial of

15-

I-

a IO-

2000

3000 Meltmg

Pomt,

4ooo

K

FIG. 1. The variation of the activation energy for strain ageing, for recovery of radiation damage, and for diffusion of the fastest moving interstitial as a function of the melting point of the solvent.

activation (whether

energy for the recovery the experiment

“recovery

of deformed

is called

of cold work damage”

“strain

metals

aging”

is irrelevant),

or

while

where the details concerning

A. R. Rosenfield,‘5) preparation supported

by

the

United

States

The work was DisAir Force.

the squares (0) represent radiation damage recovery.

cussions with the staff of the Department

These

at the University

two values

agree

quite

well,

an observation

which has been cited as evidence for a vacancy annealing

cold-worked

compared

graphically

values of activation mechanisms. for recovery

are

1 with the predicted

energy based on the two possible impurities,

by diffu-

the activation

energy energy

of the fastest

which

moving

is represented by vacancy

However,

migration,

energy should be proportional

interstitial

by a cross

here is quite good.

is controlled

role in

values

should be equal to the activation

for diffusion agreement

in Fig.

These

If the annealing is controlled

sion of interstitial

purity,

metals.c6)

iin-

(X).

The

if annealing

the activation

to the activation

energy

of self diffusion, which, for these metals is proportional to the melting point.“) the

Brooks”)

proportionality

energy for vacancy

constant migration

has suggested that between

activation

and self diffusion is 0.2,

which is the lower line in Fig. 1. Clearly, does not well represent the recovery if the proportionality somewhat

constant

alone no clear distinction values for diffusion kinetics

ments presented concluded nealed

at

controlled

this line However,

is 0.3, the fit becomes

of Liverpool

at Battelle

Memorial

ofMetallurgy

and the Metal Science Institute

are gratefully

acknowledged. A. R. ROSENFIELD

Metal Science Group Battelle Memorial Institute Columbus , Ohio References

1. H. G. VAN BUEREN, Imperfections in Crystals, p. 300. Amsterdam (1960). 2. D. P. GREGORY, Acta Met. 11, 623 (1963). 3. H. WAGENBLASTand A. C. DAMASK, J. Phys. Chem. Solids 23, 221 (1962). 4. W. R. THOMASand G. M. LEAK, Proc. Phys. Sm. Lond. 6SB, 1001 (1955). 5. A. R. ROSENFIELDand W. S. OWEN, Symposium 071 the Role of Substructure in the Mechanical Behavior of Metals, p. 351. i\SD-TDR-63.324. Wright-Patterson APB (1963). 6. D. S. PEACOCK,Ph.D. Thesis, Imperial College, London (1961). 7. 0. D. SHERBYand M. T. SIMNAI), Trans. Amer. Sot. Metals 54, 227 (1961). 8. H. BROOKS, Impurities and Imperfections, p. 1. ASM ( 1955). * Received July 15, 1963.

better.

On the basis of activation

recovery

data.

Group

the

of Fig. 1 may be found,

better. above range

by migration

considerations

can be made, although

of interstitial

that recovery the

energy

impurities

fit the

In

argu-

often

When the additional are taken into account, of cold

worked

T&T,/5 of interstitial

is

On the theory

the

it is

metal

more

an-

likely

impurities.

This note is based on a report by W. S. Owen and

Turnbull’s referred

of cellular theory

of

precipitation* cellular

to as discontinuous

precipitation,

precipitation

or

nodular reaction, the growth rate of the cells is shown to be controlled atoms

along

by the rate of diffusion

the interface

cell and the matrix; addition

(boundary)

of solute

between

the

that is, the cell grows by the

of the solute atoms to lamellae edges in the