Au Sujet de la Mise en Evidence de la Polyǵonisation de l'Aluminium par la Methode des Rayons X et par la Microǵraphie

656

ACTA

METALLURGICA,

VOL.

4,

D’apres

lui,

diffraction

X

spon~aient cristaux

1956

les

fragmentations

obtenues

des

dans les deux

taches

pas au mQme ph~nom~ne.

d’aluminium

polygoniseraient Nous voudrions

Des mono-

t&s pur faiblement

uniquement

de

cas ne corredeform&

vers 630°C.

p&ciser exactement

notre point de

vue. 11 est d’abord

certain

que la methode

que nous

avons proposee(3)

pas&de une sensibiliti sup&ieure B celle de Guinier-Tennevin.c4) M. de Beaulieu peut

FIG. 3. Spscimen subjected to shear parallel to grain boundary. Voids have developed along grain boundary. Conditions: 600 p.s.i., 482”C, 20 hours in H,, as polished, x 150.

the boundary

for 10 hours at 1200°F.

series of specimens, parallel stress,

shear traction,

to the boundary, applied

For a third

applied

was succeeded

as above,

normal

as before by tensile

to the boundary.

The results of the tests were, that with shear alone some

voids were found

along

the

boundary.

With

tension alone, no voids were found at the boundary. With

shear, followed

found

along the boundary.

and etching

by tension,

techniques

were used.

are shown in Fig. 3. It is apparent, therefore, necessary

condition

line voids

(cracks).

were performed mechanism,

many

that boundary

shear is a

our experiments

to a knowledge

of Gifkins’s

and do not serve to distinguish

simple experiments

results

of intercrystal-

Unfortunately,

his concept,s and ours.

between

We are now performing

to so di~erentiate.

it is apparent that grain-boundary

were

polishing

Typical

for the formation

prior

voids

Both diamond

some

In any ease,

sliding is a necessary

prerequisite in order to obtain intercrystalline

cracking.

School of Mines,

C. W. CHEN

~olurnbia I.:niversity,

E. S. MACHLIN

New York 27, IV. Y.

difficilement

dans

ses aristaux

des

sous-

11 lui est done impossible ments

thermiques

de asvoir si, pour les traite-

effect&s

& des

temperatures

infdrieures B 630”, une sous-structrue pas deja presente.

pIus fine n’est

En fait, memo dans des cristaux

moins purs, nous avons trouve des stries nettes dans les taches de diffraction

enregistrees

apres une deformation avons

faible

immediatement

(quelques

pu suivre leur evolution

%) et nous

apres divers

traite-

ments thermiques. Nos observations

peuvent se resumer de la man&e

suivante. 1. En-dessous

d’une

certaine gamme

de tempera-

tures, les sous-grains form& directement a la tempgrature ordinaire (sans intervention du processus thermiquement active de Cahn) ne semblent pas croitre

d’une

man&e

Blimine progressivement a cot& des continues. identifie

importante. La matrice les courbures locales presentes

sous-grains

parfaits

et plus

ou moms

Ce mecanisme peut &ire probablement B Ia diffusion et & la r~organisation des

dislocations,

c’est-a-dire

a ee que l’on appelle generale-

ment la “polygonisation.” 2. Au-dessus de ces temperatures (variables suivant la pure% du metal, de la deformation, etc.), une croissance reguliere de certains individus se dkveloppe

References

avec conservation

1. R. D. GIFKINS Actn Met. 4, 1955. 2. C. W. CHEN and E. S. MACHLIN

On the Mechanism of Intercrystalline Fracture, to be submitted to A.S.M. 3. C. ZENER The Micro-Mechanism of Fracture. Fracturing of Metals, A.S.M. (1947), p. 3. 4. H. C. CHANQ and N. J. GRANTMechanism of Intercrystalline Fracture Journ.aEof Metals February, 1956. * This research was supported by the United States Air Force through the Wright Air Development Center. Received April 25, 1956.

chacun

des

Au Sujet de la Mise en Evidence de la Polygonisation de 1’Aluminium par la Methode des Rayons X et par la Micrograp~ie~ Xous le m&me titre, M, de Beaulieu

a recemment

obtenus au laboraavec 110s propres

dune haute perfection

interne pour

sous-grains.

Dans les cas observes, cette &ape se deroule dans une matrice deja entierement polygonisee et peut 6tre citracterisee simple processus de croisssnce.

par un

3. Par contre, an voisinage du point de fusion, une sous-structure b larges domaines moins parfaits se forme

quelquefois

l’aluminium);

compare les importants resultats toire du Professeur Chaudron observations.(2)

detector

grains d’une taille inferieure au dixieme de millimetre.

(aussi bien dans le fer que dans

Cet &at

nous parait

correspondre

B

ce que Crussardc5) a appele “recristallisation in situ.” 11 est probable due les observations de M. de Beaulieu se rapportent b cet &at. Quoi qu’il en soit, nous n’avons jamais observe la formation de ces grands sous-grains imparfaits directement & partir de cristaux ne contenant pas au prealable une sousstructure L caractere parfait. 11 importe de remarquer

LETTERS

qu’une

telle

observation

requiert

TO

une technique

THE

657

EDITOR

a

haute sensibilite. Enfin

le

caractitre

peut Btre clairement

stable

de

l’etat

polygonis

illustre par le fait queles

cristaux que nous avons examines pas L l’etat solide.

mono-

ne recristallisent H. LAMBOT.

Laboratoire de Cristallographie UniversitC de Likge (Belgique) et Centre National de Recherches Metallurgiques

(LiLge) REFERENCES

1. C. DE BEAULIEU Acta Met. 4, 100 (1956). 2. H. LAMBOT, L. VASSAMILLET, et J. DEJACE Acta

Mel.

3, 157 (1955). 3. H. LAMBOT. L. VASSAMILLET. et J. DEJACE Acta Met. 1, 711 (i953j. 4. A. GUINIER et J. TENNEVIN Acta CT@. 2, 133 (1949).

FIG. 1. Pure iron lightly etched.

8,000 x .

5. C. CRUSSARL) Rev. MetaZZ. 45, 317 (1944). * Received

tungsten oxide, generally under an angle of 45”. The electron microscope used was that of the E.M.

April 27, 1956.

Division

Investigation of Pure Iron and Soft Steel with the Electron Microscope*

T.N.O.

of

the

Technical

and

T.H.

at Delft.

Physics We

Department

thank

Dr.

J. B.

le Poole for his kind help.

Introduction Experimental

The Research on pure metals is of great theoretical importance.

The two most interesting

the verification of slip.

advantage

kindly the

marks, The

Physical

a pure

purity. by Prof.

etching,

clearly

the crystallites effect

could

Laboratory showing

at

the

on soft

of

Eindhoven. a method

substructure

and to see whether

be obtained

is

Samples were J. D. Fast

The scope of this research was to develop of

metal

arise from precipitates dissolved atoms. The

is of 99.99%

put at our disposal

Philips

The method

theory and the mechanism

obvious, as no complications and less complications from iron investigated

are

of using

dislocation

The

subjects

of

the same etch

steel,

Moreover,

etched specimens were deformed to examine the effect

of etching

Results

used gives as a rule etch

which are protruding from the surface. subboundaries in the ferrite crystallites form

small dikes, and this makes it reasonable to suppose that, though generally etch pits mark the location of dislocations, indicate

the etch

marks

found

in our case

the site of dislocations.

A reason for the etch figures being hills rather than holes might be that

there

are

concentrate of attack,

still

interstitial

atoms

around the dislocations as Dr. J. Nutting

present,

which

and lower the rate

of ‘Cambridge,

U.K.,

suggested to us. Figs. 1 and 2 show the result of a light etching, that

of slip. Experimental After preliminary

Method

experiments,

we decided

to use

an electrolytic polish etch, which has the advantage that no deformation results from preparation. A commercial

apparatus,

the Disa Electropol,

with a bath on a perchloric-acid by which aluminum The

method

of

was used

base (Electrolyte

A-2),

was etched beforehand. replication

used

is as follows.

First, a negative silver replica is made by evaporation of silver in vaccum onto the specimen. This replica, of about 7-,a thickness, is easily removed from the specimen. A second positive replica is deposited on the first by evaporation of carbon in vacuum. After dissolving the silver in nitric acid, washing and drying of the carbon replica, the replica is shadowed with

FIG. 2. Pure iron lightly etched.

16,000 x .

!