Dislocation etch pits in tungsten

LETTERS

TO

THE

EDITOR

559

(b) FIG. 3. Corrosion occurring from side wall of a needle crystal. (a) and (b) are before and after the corrosion respectively, in 4 x 1O-4 mm Hg vacuum at 1100°C. x 30,000. observation

are corroded

independently.

Such

be-

haviour seems to be evidence for the bundle structure of such a crystal. When the filament was intermittently temperature suitable often

in the

range

for the growth

observed

following

that

way.

During

7OO”C-lOOO”C, which

of needle

the

heated at a

growth

is

crystals,

it was

advances

in the

the first heating

very

thin

needle crystals grew, whilst during the next heating their thickness thin needle

increased

appeared

and, simultaneously,

on its tip.

repeated

during the subsequent

cess

likely

is

formation

to

be

not

This process heatings.

incompatible

of a bundle structure,

a new was

The

pro-

with

and moreover

the gives

evidence of tip growth of this crystal. H. HASHIMOTO Physical Institute

K. TANAKA

Kyoto University

E. YODA

Sakyoleu, Kyoto, Japan

H. ARAKI

(1955).

Naturwiss. 40, 551 (1953); 2.

Met&k. Ibid.

12,

3. J. M. COWLEY, J. EZectrochem. Sm. 99, 393 (1952). 4. T. MORITA, S. USHIO and T. SEIYAMA, J. Appl. Phys. Japan 25, 70 (1956). 5. R. TAKAGI, J. Electronmicroscopy 3, 18 (1955). 6. S. M. ARNOLD and S. E. KOONCE, J. Appl. Phys. 27, 964

(1956).

8. A.

24,

K. TANAKA

6, 8 (1958). ~VAGNELI, Arkiv. Kemi.

microscopy

1998 (1952).

and E. YODA,

1,

223

have been made visible,

number

of

metals

to the knowledge observed

and

in an ever increasing

inorganic

crystals’1>2) but

of this writer have not so far been

in tungsten.

By employing an etching reagent developed by Millner and Sassc3) (2 parts 25% CuSO, solution and 1 part

concentrated

NH,OH),

subgrain

boundaries

in arc cast material and slip lines in swaged tungsten can be resolved

into individual

etch pits as shown

in Figs. 1, 2, and 3. Care has to be taken to remove The etch completely the deformed surface layer. pit pattern is then reproducible lytic polishing

of the samples.

not critical; prolonged etching not more numerous, etch pits. etch

after repeated electroThe etching produces

as well as the typical

pits

along

subgrain

time is

larger,

but

arrangement

boundaries,

very

strongly suggest that the pits are developed at dislocation sites. In arc cast material the time avail-

2. R. TAKAGI, J. Phys. Sot. Japan 9, 162 (1954); 1212 (1957).

7. h. ~ASRIMOTO,

In recent years dislocations

This feature,

References 46, 204

etch pits in tungsten

by specialized etching techniques,

of the

Received February 4, 1958.

1. G. PFEFERKORN,

Dislocation

(1949);

J.

Amlyt.

ElectronChem.

able for movement of dislocations is limited, so they This cannot attain their equilibrium positions. accounts for the etch pits scattered at random, and for such imperfect boundaries as that at lower left of Fig. 2. Generally, the spacing of dislocation etch pits along subgrain boundaries is quite irregular, the vertical boundary in Fig. 1 being an exception. It is noteworthy that not all grains exhibit etch may pits, even though the subgrain boundaries sometimes

be faintly

visible

as shallow

grooves

at

ACTA

560

METALLURGICA.

VOL.

6,

1958

FIG. 3. Tungsten rod reduced 60 per cent by swaging. Rod axis is vertical. The center grain shows dislocation pile-up x 1300. on slip lines. The left grain contains sub-boundaries. cast tungsten in slightly oblique illumination, Dislocation etch copper ammonium sulfate. pits line up at subgrain boundaries and are scattered in the bulk of the subgrains. x 2000.

FIG.

1. Arc

etched with

low

pits

magnification. have

a rough

Grains that do not develop surface

after

etching

a {loo)

plane, as mdicated

the standard stereographic

by the hatched projection,

area,s in

Fig. 4.

The tilt angle between subgrains can be calculated from

etch

the

spacing

of the

etch

pits.

The

average

110

(see right

grain in Fig. 3), while grains with etch pits are very An X-ray check of a number of grains smooth. revealed that etch pit formati~~n is orientation ent.

Etch pits are developed

depend-

only on surfaces which

form an angle of less than approximately

38” with

if0

4. Standard stereographic projection of hody-centered cubic crystal. The [llOl direction is vertical. This is also the orientation of the rod axis. The hatched areas represent those surface orientations on which dislocation etch pits are produced in tungsten. A or B is the orientation of the cemer grain in Fig. 3. Slip plane is one of the (112) planes marked. FIG.

FIG. 2. Arc cast tungsten. Subgrain boundaries at right are well formed; at lower left dislocations have been arrested in the process of migration toward the subgrain boundary. x 1000.

Ii0

LETTERS

distance

D between

of Fig.

1 is 1.1 p.

approximate

pits in the vertical From

TO

boundary

D = b/O we obtain

tilt angle of B = 50 seconds of arc when

b is taken ss the interatomic spacing direction. Since the grain orientation

in the (111) with respect

to the sample surface is not taken into account, calculated

at this particular

boundary.

boundaries

indicating

misfit.

the

value is the lower limit of the tilt angle

most subgrain density

an

As seen in the pictures, have a higher dislocation

a considerably

In preliminary

X-ray

larger

angle

of the order of 200 seconds.

This is in good agreement

with

from

angle

considering

calculated

pit spacings,

the different modes of measurement.

In swaged

material,

accumulation

on slip planes has been observed, The

etch

left

grain

constitutes

boundary

a barrier against

have piled up.

of dislocations

as shown in Fig. 3.

in the

figure

lating discussions greatly X-ray

were made,

obviously

Certain

using the fact

of any grain in a longitudinal an orientation

orientations

URSULA E.

Lamp

projection,

between

A and B will show patch

lower

of grain

left of the middle

orientation

(110).

These

by the horizontal

line

Fig. 4. As mentioned etch pits.

surface grain.

Presumably,

system is operative

in tungsten.{@

surface.

of (112)

etching.

In Fig.

is observed

3,

at the

Consequently, the

(112)(111)

the slip

Slip lines would,

planes

on the sample

The four (112) planes

marked in Fig. 4 fulfill this condition. It has generally been found that dislocations

is necessary The

etching

& Phosphors

Department

Cmpany

Ohio

Received December 5, 1957; 1958.

revised version March 3,

Sur le processus de germination et de croissance de la phase CuO au tours de l’oxydation superficielle du cuivre dans l’air dans l’intervalle 970*-1025”C*

tungsten

has not yet been investigated.

probable,

however, that decoration

temperature

decoration

of

operative

in

It appears

of some kind takes

place. The amount of impurities present (in the order of magnitude of 0.01 wt. %) is certainly sufficient and the swaging temperature (around 950%) is high enough to move atoms to the new dislocation sites. It is hoped that further investigations of slip in tungsten will benefit from the etch pit technique described. Work is continuing along this line. Stimu-

communication(l)

de l’essai de Cu,O

duree d’oxydation. la

temperature

par 2 couches

et de CuO quelle

nous avons

continues

et

que soit la

II n’en est plus de mdme quand depasse

on realise une s&e b une temperature

970°C.

d’essais

Effectivement,

d’oxydation

comprise

si

isotherme

entre 970°C et 1025’C

termines par une trempe & l’eau on constate que pour les courtes stituee

durees d’oxydation

exclusivement

demontre

la couleur

son examen d’oxydation

in order to reveal them by mechanism

Dans une precedente

montre que dans l’intervalle 600-970°C la pellicuie d’oxydation du cuivre dans l’air est constituee a la compactes

In Fig. 3 an angle of 35” between rod axis

and slip lines was measured.

WOLFF

Laboratory

References

deformed

of this grain can be assumed to be very

be traces

the

1. A. 5. FORTY, Rdwxw. Physics 5, 1 (1954). 2. J. J. GILMAN and W. J. JOHNSTON.J. Avvl. Phw. 27.I __ ” 1018 (1956). 3. T. MILLNER and L. SASS, Alumi&m (Budapest) 5, 214 (1953); also Henry Rrutcher Translation No. 3281. 4. P. A. JACQUET,A&z .iiet. 2, 752 and 770 (1964). 5. E. ETTISCH,M. POLANVI and K. WEISSENBERCI,2. phys. Chem. 99, 332 (1921). 6. COUCHER,PhiE. &fag. 49, 800 (1924).

will therefore

from

close to A or B. therefore,

Wire

Cleve~nd,

The surface

above, only grains with surface normals approximately a rough

Metals

General Ekctric

deductions

that

section

90” away

can be represented

in the stereographic

The latter also performed

~vestigations.

have been made

tungsten tends toward a (110) texture.15) have

di~action

which the dislo~tions

Similar observations

could not be measured.

however

with J. W. Pugh and S. Leber are

appreciated.

Refractory

by Jacquet(*) on brass. Because of the small grain size, the orientation of individual grains in the sample surface

561

EDITOR

of

studies, using a double

crystal X-ray spectrometer, average angles of misalignment between subgrains have been found to be the

THE

rouge

au microscope atteint

la pellicule

d’oxyde

Cu,O

fonce

est con-

eomme

de sa surface

(Fig. 1).

le et

Quand la duree

t,

apparaissent les premiers germes de la phase CuO. A mesure que cette duree augmente

de nouveaux

germes apparaissent

croissant

en general de fapon isotrope, suivant le plan de la surface, de sorte qu’ils conservent la forme ciroulaire jusqu’L

leur

contact

reciproque.

Les micrographics

des Fig. Z(a) et Z(b) montrent un tel germe sous deux grossissements. La Fig. 2(b) prouve en particulier que le front, de croissance du germe ne semble par ittre beaucoup influence par les joints de grains de la phase support C&O. Pour la duree t, la totalite de la, surface de l’dchantillon esf recouverte d’une couche continue de CuO.