Shear along glide planes in aluminum

460

ACTA

METALLURGICA,

VOL.

Shear

-CJ& e;S

0.r 0

x4ez (k-1y

1

dx .

Using 82 = 415” and & = 280°, we obtain the results shown in Table I (fourth column). Good agreement is shown to exist from 15” to about 80°K. The latter temperature being approximately the temperature below which Barrett has shown the spontaneous phase transformation to exist in lithium. Above this temperature the data have been described by Debye’s model using an “average” BDvalue of 405” obtained from the experimental data above liquid nitrogen temperatures.* The influence of the partially transformed lithium, from body-centered cubic to face-centered cubic induced by cold work, on the specific heat has as yet not been studied experimentally. Barrett has reported significant induced partial phase transformation up to approximately 150°K. W. DESORBO General Electric Research Laboratory The Knolls Schenectady, New York, U.S.A. References 1. SIMON, F. and SWAIN, R. C. Z. phys. Chem., B28 (1935) 189. 2. FOWLER, R. H. Statistical Mechanics, second edition (Cambridge University Press, 1936), pp. 131-2. 3. LORD, R. C. J. Chem. Phys., 9 (1941) 700. Proc. Roy. Sot., Al53 (1936) 622; Al57 4. FUCHS, K. (1936) 444. 5. SEITZ, F. The Modern Theory of Solids, first edition (New York, McGraw-Hill, 1940), p. 116. 6. BARRETT, C. S. Phys. Rev., 72, 245 (1947); BARRETT, C. S. and TRAUTZ, 0. R. Metals Technol., April 1948, T.P. 2346; BARRETT, C. S. Symposium on Phase Transformations in Solids, National Research Council Committee on Solids, Cornell (1948). 7. DESORBO, W. Eighth Conference on Cryogenics, General Electric Co., Schenectady, New York, October 6-7, 1952. 8. SIMON, F. and VOHSEN, E. Z. phys. Chem., 133 (1928) 165. 9. POSNJAK, E. J. Phys. Chem., 32 (1928) 354. 10. DESORBO, W. To be published. 11. BAUGHN, E. C. Trans. Faraday Sot., 48 (1952) 121. *Baughn [II] reports a SDvalue of 418” for lithium calculated by the Lindemann formula and a value of 420” obtained by the Guggenheimer formula, which relates the force constant, the interatomic distance, and the number of outer electrons.

1,

along

1953

Glide

Planes

in

Aluminumt

Based upon the displacement of a scratch by slip lines on an alpha brass single crystal, Treuting and Brick [l] suggested that a shear on the order of 700 atom diameters occurred per active micrographically resolved slip plane. Once this shear had occurred, further slip took place elsewhere. A more direct measurement of shear along glide planes in aluminum single crystals was made by Heidenreich and Shockley [2] using the electron microscope. They found that each lamella composing a slip zone had slipped over its neighbor a distance of 2OOOA. These experiments have been repeated by Brown [3] who found that the amount of shear on glide planes in aluminum was 2OOOA at room temperature. At -180°C the shear was 16OOA and increased to 22OOA at 250°C. More recently, Wilsdorf and Kuhlmann-Wilsdorf [4] have calculated shear along glide planes from electron microscope measurements of very well documented aluminum crystals. They found that the number of glide lamellae per glide zone increased with increasing amount of deformation but that the amount of shear along each glide lamella increased only slightfy and in some cases remained essentially constant. Their values of shear along individual lamellae ranged from as low as 7OA to as high as 12OOA. The more direct method of multiple beam interferometry [5] was employed by Tolansky and Holden [6]. Using aluminum specimens cast against special optical flats, they were able to measure shears of about 9OOA in the deformed specimens. The earlier work of Holden [7] using slow strain rate established values of the order of 2OOOA for aluminum deformed at room temperature. In the experiments of Holden, and Tolansky and Holden, no correction was made as to the true shear along the planes since they did not determine the orientations of the crystals. Nor was it known how many glide lamellae contributed to the total shear of the “slip zone.” A slip line refers to slip along one plane (a glide lamella) whereas a slip band or slip zone refers to a group of glide lamellae which have not been resolved into their component lamellae. Although multiple beam interferometry is capable of resolving slip heights down to 5A [5], its resolution in the plane of the surface is no better than obtained with the ordinary light microscope. iReceived

April 20, 1953.

LETTERS

In the experiments tri-crystal long

one-half

of

reported inch

high-purity

(mechanically)

followed

density

surface

preparation

in

a bright-dip

surface grain

by

electrolytic

The

in Figure

at high The

where the

x is the

specimen

angle axis

condition

from an interferogram

of the

1.

slip

direction

X (the

axis)

grip

tween

by ends

Sharp

jogs

in the

where

they

cross

of particular dary

produce

interest,

should and

groove

various in aqua the

second The (546OA)

regia

be

shape

appearance

passing

used

through

boundary

preparation attack.

had nor

NaOH

effect

Since

this technique only,

the

*Alcoa Bright-Dip

measures

Solution

(R-5).

etch

no effect

did

a

five

at 70°C. Hg

a Cooke

a correction

of

stress

and

the

angle

(the

o( the

scratch angle

be-

and the slip direction

was the

one

of highest

to act,

the

plane

the

traces

longitudinal

axis

stereographicallyfrom

of

from

the

the

resolved

glide

specimen

after

about

(the stress

was 1000 g/mm2)

is shown

3 and

The

in

Figures

of the zones,

ured displacements, 7.

The

grains

is given

on the grain

The

curves

plotted

whose

shown

through

are drawn

in Figures

since

microscope

and

ratio

of

between

the

lines

are the

and the dashed

of

a fringe

the

fringes

ranges

best

curves

It is not known one.

as determined

width

by

8.

5, 6, 7, and 10 are

solid

the

two were

is shown

is the “correct”

the resolution

5, 6, and

in Figure

all the points.

curves

meas-

Measurements

circles

The

along

the

betIveen

orientation

the data

through

of these

8.

of great

in two ways.

fit curves

shear

from

difference

in Figure

the filled sections

4.

calculated

are shown in Figures

orientation

ever,

in order

The

5 per cent elongation

line

the perpendicular

x

and

between

a reference

specimen

scratch

mean

angles

from the initial

angle

and

slip direction

green

is needed

the

of the

rotation. The appearance

which

glass.

noting

the

slip direction

To insure that the slip system shear

made

Con-

through a half-silvered microscope cover Initial magnification used was 200 X. or 2 height

to

to

is known).

segments

fringe.

A 30 second

temperature

interferometer

are

expected

of the

was conducted.

points

the boun-

of a grain

survey

in 10 per cent

at

in the

chemical

to

customarily

of the specimen with

at room

ledge etch

the

would

a preliminary etchants

due

surface.

patterns

indicate

than

the profile

vary

Such

discontinuity

be a function

sequently,

are

be seen

for they

which

that

should

can

rather

a V-shaped

It is realized

on

fringes

to be a ledge

visualized

fringes

the boundary.

and

between

The

of the crystal.

the reference

was determined or hills in the specimen

the

are determined

of observation

on the

normal

between

orientations

position

the

on the slip plane.

angle

is determined

FIGURE 1. Interferogram of grain boundary. Orientation difference of the grains are shown in projection in Fig. 8. 935 X, reduced to 6/7 in reproduction.

and

projected

and final

the

angle

FIGURE 2. Relation of measure step height, 2, to calculated shear, D, on slip plane. x is the angle between the specimen axis and the slip plane.

the specimen

in

the slip plane

a: is the

_--

at a

and

undulations

between

and

final

taken

may be seen in Figure

depressions

cos a

x

immersion

surface

Gentle

2. The

& sm

D =

the

slight

D. (.‘onsider the scheshear, D, is

the true shear,

drawing

was

polishing

(2:l)

a 30 minute

solution.*

boundary

HNOs

amperes/dm2).

included

as judged

(99.9975)

matic

method. The surface etching and polishing

and

(1000

to determine

by six inches

aluminum

of CH,OH

current

a cylindrical

in diameter

grown by the strain-anneal was prepared by alternate in a solution

here,

TO

to

from

the

90A

How-

from

the

distance

(Figure

9)

to about 15OA (Figures 5, 6, 7) and the circles about 8OA units in diameter, the dashed curves

are are

probably the more accurate representation of the true amount of shear along the slip zones concerned. If it is assumed

that

the amount

of shear

on a

462

-ACTA

METALLURGICA,

plane or group of planes constituting a slip zone is a function of the time that the line is active, it can be said that when the curves of shear versus distance along the line have maxima, these maxima are the points where the slip planes have first intersected the surface. The directions of propaga-

VOL.

1,

1953

tion of the slip lines in these cases would be in both the positive and negative directions from these points. This is in keeping with the model of slip line formation recently discussed by Chen and Pond [8]. In the cases where no maxima appear, it can be said that the direction of propagation is towards the direction of lowest shear along any one line. Values of shear as much as 5OOOA and as little as 15OA have been observed. Along any one line a gradient of shear from as much as 4OOOAto almost 1OOA was measured.

FIGURE 3. Interferogram of the grain boundary (approximately) shown in Fig. 1, but after about 5 per cent elongation. Note short zone which has greatest amount of shear near the boundary (curve 5 in Fig. 5). Position of the boundary is at position 0 microns. 1350 X, reduced to 5/6 in reproduction.

L”

N

DISTANCE1 MICRONS) FIGURE 5. Shear, D, versus distance along slip zones away from the grain boundary (at position 0) shown in Fig. 3. Note curve’ 5 when shear is greatest near the boundary.

FIGURE 4. Interferogram showing shear along slip zones. The curves of shear versus distance are shown in Fig. 6. Note steep shear gradient in some of the lines. 1600 X, reduced to 5/6 in reproduction.

Close examination of Figure 3 will show not only that bands exist for a very short distance but that, in one case, the amount of shear along glide planes reaches a maximum near the grain boundary. This latter observation is contrary to the expected behavior of a glide plane in the immediate vicinity of the grain boundary. It is interesting to note that for the orientation difference shown in Figure 8 and for the amount of deformation, the slip bands stop at from 4 to 10 microns from the boundary.

THE

-

--

rti3

E1~1’I‘OI;

to below\- 150,% nex

the bountlar\.

15cA to more than

i

(‘urve

2 in Figure

I;ixure

10) shows

are

slightly

in

stopped

displaced

aluminum

same amount IJoint

11 (the

and

slij)

an interesting

or overlapped

deformed

ant1 varies

from

1sOOA a\\-a>’from the boundai-).. zone

effect.

rqions The

in

bands

Ix-esenting

apllearance crystals.

shown The

t!ie

so common

on

~)lot shows

the

of shear on both bands at the meeting

the

same

amount

of increase

in shear

j / ,

-

t

I FIGCRE 8.

-

Figs. 1 and 3.

DlSTANCE’(MICRONS)

FIGURE 6. Shear, D, versus distance along slip zones, corresponding with interferogram of Fig. 4. Note steep shear gradient.

in just

of shear another

in the same manner

until just of the

the amount

a few slip zones,

prepared

distance

away from the meeting (shown

in Figure

of about

To observe

two bands

fringes along

and the

9, 10, and 11. Here,

aluminum

band

crystal

was pulled in tension

were visible. a plot

on glide planes

of the are

the shearqis

The shear,

shown shown

appearance

Orientation

Faints.

Curve

9) gives minimum

3 in Figure

11

value of shear

15OA near the boundary.

Attempts cinematography metry

difference of grains shown in

are

now

being

made

with the multil:le

in order to measure

pIanes as a function

to

incorporate

beam

interfero-

the shear along the glide

of time.

D, versus in

Figures

to decrease

FIGURE 7. Shear, D, versus distance along slip zones at position remote from the grain boundary. Here, a constancy of shear is apparent.

FIGURE 9. Interferogram showing the stopping of a slip zone. The boundary is at the left. 3200 X, reduced to 6/7 in reproduction.

462

ACTA

METALLURGICA,

VOL.

1, 1953

Bright Dip solution. This work was sponsored by the Office of Naval Research under Contract Nom 248(35). R. MADDIN, E. H. HARRISON, and R. W. GELINAS School of Engineering The Johns Hopkins University Baltimore, Maryland References

FIGG~ 10. Interferogram of the same slip zone as shown in Fig. 9, but at a position remote from the grain boundary. Note that the “zone” splits into two “zones.” Shear curves for these zones are shown as curve 2 in Fig. 11. 3500 X, reduced to 5/6 in reproduction.

1. TREUTING,R. G. and Bruce, R. M. Trans. A.I.M.E., 147 (1952) 128. 2. HEIDENREICH, R. D. and SHOCKLEY, W. Report on a Conference on the Strength of Solids, Bristol, 1947 (London, The Physical Society). 3. BROWN,A. F. Nature, 163 (1949) 961. 4. WILSDORF,H. and KVHLMANN-WILSDORF, D. Z. angew. Phys., 4 (1952) 361; 409; 418. 5. TOLANSHY,S. Multiple Beam Interferometry of Surfaces and Films (Oxford, 1948). S. and HOLDEN,J. Nature, 164 (1949) 754. 6. TOLA’~~SKY, 7. HOLDEN,J. M.Sc. Thesis, University of Manchester (1948). 8. CHEN,N. K. and POND,R. B. J. Metals, October (1952) 1085.

The Formation

DISTANCE

ihlICRON8)

FIGURE II. Shear, D, versus distance aIong slip zones. Curve 2 represents the split in the zones shown in Fig. 10.

Ackmdedgement The authors would like to thank the Aluminum Company of America for supplying the highpurity aluminum and for the use of their R-5

of Lattice Slip*

Defects during

Recent observations [I] have brought to light the existence of an elementary structure on the surface of a slightly deformed aluminum crystal, It consists of a large number of lines, with an average length of a few times 10V3 cm., and spaced some hundreds of atomic distances apart. Each line represents a slip distance between 10 and 50 atomic distances. The elementary structure should be clearly distinguished from the usual slip lines, these being much longer, more widely spaced, and showing more slip. The formation of an elementary structure may be explained in the following way. An activated Frank-Read source emits a number of dislocation rings. These rings expand and cross the ever present, randomly distributed dislocations. Jogs are formed and, as in face-centered cubic crystals, each dislocation probably has some screw character 121, further expansion of the jogged rings produces trails of vacancies or interstitial atoms. Additional expansions of a ring of radius R over a distance equal to the Burgers vector b produces % = & TUR defects per unit length, *Received April 27, 1953.

where u is the density

of