close

Вход

Забыли?

вход по аккаунту

?

PREFERRED ORIENTATIONS IN ROLLED AND RECRYSTALLIZED ALUMINUM

код для вставкиСкачать
The Pennsylvania State College
The Graduate School
Department of Chemistry
PREFERRED ORIENTATIONS IN ROLLED AND
RECRYSTALLIZED ALUMINUM
A Thesis
by
James Vv. Ford
Submitted in partial fulfillment
of the reauirements for the degree of
Doctor of Philosophy
August, 1940
Approved^^S^&^c^u
Head of Department
Major Professor
/y
Date of Aooroval
1
Introduction
Since the classical work of Taylor and E l a m ^ ^ o n the deformation
of aluminum single crystals, preferred orientations ("deformation” or
"fiber" textures) have "been found to have a marked effect on such
properties of single and polycrystal materials as hardness
size
(2 )grain
(3 )
(a)
and recrystallization
,
It is the purpose of the present work to present new data con­
firming the accepted texture of cold-rolled, high purity aluminum and
to show the relationship "between initial deformation texture and the
texture present after recrystallization.
Apparatus and Technique
The material used in this study was high purity aluminum furnished
by the Aluminum Coirpany of America, through the courtesy of Mr. J. A.
Nock, Jr.
Its chemical analysis was as follows:
Si .......... . .0.004$
Fe
.........0.003$
C u .............0.004$
A1 ............99.989$
The original pieces (12x2x0.3 cm.) were rolled to strip approximately
0.05 cm. thick with two-high, four r.p.m. rolls.
The same relative
position of sample and rolls was maintained throughout and a slow rolling
speed avoided any local heating of the sample.
Samples 8x2x0.05 cm. were cut from the rolled strip for invest­
igation.
A preliminary examination indicated that the rolled surface
2
.contained large, flat crystals differing considerably from those in
/
the main body of the material. Consequently, all samples were etched
in a 10 per cent NaOE solution (aqueous) to remove this surface layer
before further treatment or examination.
Recrystallization was brought
about by annealing in a tubular electric furnace with a quartz insert
through which passed a stream of dry, Og free hydrogen.
A schedule
of rolling and annealing is given in Table 1.
Table 1
Monochromatic pin hole X-Ray photograms were taken using ZrO£
filtered Mo radiation from a G.E., water cooled Coolidge (type CA2)
tube operated at 42 k.v. peak and 25 milllamperes.
outfit (1937) was used.
A G.E. diffraction
Double coated Agfa film with "FluorazuKe"
back intensifying screens shortened exposure times to about one hour.
During exposure the sanples were held in a scanning device and
moved continuously in their own plane at constant linear speeds of
five inches per minute longitudinally and three-fourths inches per
hour laterally.
Suitable adjustments were provided to set and re­
produce desired angular relationships between the X-Ray beam and
sample face.
The scanning device is illustrated in figure 6.
Rig. 6
Stereo graphic projections (pole figures) of ^100} , (llOf a*1*3-
families were plotted, with the aid of the McLachlan pole figure
(5 )
machine
, using data taken directly from the diffraction patterns.
Because of the importance of (ill) planes in the deformation of face-
centered metals
(l)
3
additional (ill) poles were plotted by inference ;
from known (100) and
(110) pole positions.
Experimental Results
Stereographic projections of the X-Rays diffraction patterns
are shown in figures 1-5.
Eigs. 1, 2, 3, 4, 5
Only the upper half of each pole figure has been plotted.
The
lower part is a mirror image because of symmetry in the rolling
operation about the rolling direction.
These projections show
concentrations of (ill} poles located from both direct and indirect
information.
The contours of fig. 1 are determined according to the
following plan.
Any group of crystallites having orientations within
certain limits will diffract X-Ray energy into a corresponding limited
area on the film.
Thus diffraction - spot blackness (more specif ically-
density), being determined by the diffracted energy, is proportional
to the number of contributing crystallites.
Although the same pro­
portionality may not hold from one diffraction spot to another because
of absorption, angle effects, etc., it does hold sufficiently well
over any single spot.
Each diffraction spot, therefore, is compared
with test strips of film which have received known exposures and
angular values for points of one-fourth, one-half and three— fourths
maximum blackness are obtained.
These angles are plotted in stereo-
graphic projection to give the outlines shown,
^hus seventy-five
per cent of the crystallites have an orientation within the limits of
4
the outmost contour, fifty per cent within the second contour and
twenty-five per cent within the innermost contour.
Within the limits usually imposed on such projections a (110),
£L12l texture
direction
^(llO) in the rolling plane, [1121 in the rolling
satisfactorily represents the condition of the plastically
deformed sample.
Solid black squares show the ideal locations of
(ill) poles in this texture.
For reasons to "be discussed in the following section, the
annealed samples (figs. 2, 3, 4, 5) can also he represented by this
same texture.
However, because of the nature of their diffraction
patterns (many small spots) it was impossible to detect any variation
in blackness over individual spot areas.
Figures 2, 3, 4, and 5,
therefore, show in stereographic projection only the angular spread
of apparently uniform blackness,
contours cannot be set up.
since, in such cases, definite
,
The outlines of the original rolling
texture from fig. 1 are included for comparison.
The lack of symmetry
about the rolling direction found in all of the projections is associated
with a lack of perfection in the rolling process.
It is not a true
compression, but a compression-extrusion method and thus introduces
assymetrles.
Discussion
The results mentioned briefly in the preceding section - and shown
by the projections — are in accord with previous work.
E, Schmid
(6)
and C. S, Barrett^^have worked with aluminum under similar conditions
and find a definite similarity between rolling and recrystallization
textures.
(It might be well to note that this correspondence doe3
not exist in single crystals similarly treated
of the literature shows that the (110) Ill2|
(?). An examination 5
texture occurs more
often than any other in plastically deformed face-centered metals*
Theoretical work hy Pickus and Mathewson
gives that texture as
the most probable although others may arise because of peculiarities
in treatment or past history.
The transition from a highly stressed to a recrystallized
condition in metals can be thought of as a solid-solid phase change
(9,10
The reaction is presumably initiated through the presence of re­
crystallization •'nuclei*' - potential centers of growth — which exist
in the deformed material.
open to question.
How these nuclei originate is a matter
Burgers and Louwerse
(7)
, for example, assume that
they are "local distortions" caused when crystal fragments are caught
and rotated during the slipping process.
Barrett
this viewpoint but gives no alternate suggestion.
(4)
takes exception to
Regardless of the
origin of these nuclei, however, it seems to the present writer that
such transitions can be quite reasonably explained on the basis of
their presence and the reaction rate kinetics associated with such
"germinated" processes.
During the annealing process three factors are operative! (l)
elastic recovery, (2) recrystallization and (3)g*nain growth, in that
order in time.
strain.
The term "recovery" signifies release of internal
"Recrystallization" denotes the beginnings of self-diffusion
and crystallite growth.
Grain growth, as distinguished from crystallite
growth, is merely a matter of magnitude in rate and size.
By suitable
control the growth of large grains can be kept to a minimum.
It is
6
an experimental fact well known to metallurgists that increasingly
higher plastic strain is associated with lower and lower annealing
temperatures or with shorter annealing times.
Thus, a sample consist­
ing of portions having different degrees of strain, when held at a
constant temperature, will anneal (recover and recrystallize) more
rapidly in the regions of most intense strain.
These same regions,
consisting as they do of tiny fragments, are able to absorb the
energy released on recovery without sensibly changing their overall
extent or configuration.
It is to be assumed, then, that with
sufficiently high annealing temperatures, recrystallization could
take place without changing the original texture more than a slight
amount.
At lower temperatures, with more time for diffusion to occur,
the recrystallization texture might not be so marked, and over long
periods of time an almost complete randomness of orientation would
occur.
This is brought out in Figs. 2, 3, 4, 5, which show for
similarly rolled specimens a series of heat treatments at progressingly higher temperatures and shorter times.
Figs. 2 and 5 show
definitely (a) that with a low temperature, long-time anneal the crystals
show only a suggestion of the pole figure of Fig. 1, and (b) that with
a high-temperature, short-time anneal, the crystal orientations fall
very closely within the boundaries set by Fig. 1.
Figs. 3 and 4 show
that there is no critical combination of temperature and time for pre­
serving the unannealed orientation limits, but that the effect of
temperature and time is progressive.
7
Summary
Samples of high purity aluminum have "been cold-rolled to atrip,
annealed and examined by X-Ray diffraction,
A (110), [ll2l rolling
texture was found and recrystallization textures appeared to have
very nearly the same orientation.
Experimental results confirmed
an assumption of differential reaction rate between regions of high
and low stress, which leads to the retention of the original texture,
especially at high-temperature — ~ short-time anneals.
Ackno wledgement
The writer wishes to express his appreciation to Dr. W. P. Davey
for his valuable guidance and co-operation and to Mr. Thomas P . Hahn
for his assistance in construction of the scanning device used in
this study.
TABLE 1
ROLLING AND ANNEALING SCHEDULE
THICKNESS
AFTER
ETCHING (CM.)
ANNEAL TIME
AND TEMPERATURE
PROJECTION
ON FIG.
RE­
DUCTION
PER PASS
85
4.9
0.041
4.7
0.040
6 hrs. - 300°C
2
SAMPLE NO.
2-5
0.341
0.051
4-7
ii
0.049
ii
4-5
n
n
ii
ti
0.039
3 hrs. - 368°C
3
4-5
n
ii
it
ii
0.038
2 hrs. - 440°C
4
ii
n
ii
ti
0.040
1 hr.
5
4-9
THICKNESS
AFTER
ROLLING (CM.)
TOTAL
RE­
DUCTION
ORIGINAL
THICKNESS
(CM.)
None
- 521°C
1
03
9
Bibliography
(1)
—
G-. J. Taylor and E. P. Elam
Proc. Roy. Soc.
(2)
(1923), vol. 102-A, p. 643.
W. G. Burgers and J. J. Ploos van Amstel
Ztsch. f. Physik (1933), vol. 81, p. 43.
(3)
R„ H. Randall, P. C. Rose and C. Zener
Phys. Rev. (1939), vol. 56, p. 343.
(4)
C. W. Barrett
A. I. M. E. Tech. Pub. #1141
(5 )
v
(6)
Metals Technology, Jan. 1940.
D. McLachlan, Jr.
Zeit. f. Kristallog.
(1936), vol. 94-A, p. 500.
E. Schmid
Zeit. f. Metallkun.de (1928), vol. 20, p. 370.
(7)
W. G. Burgers and P. C. Louwerse
Ztsch. f. Physik (1931), vol. 67, p. 605.
(8)
M. R. Pickus and C. H. Mathewson
J. Inst. Met. (1938), vol. 5,p. 555.
(9 )
M. Avrami
J. Chem. Phys.
(10)
(Dec. 1939 - Jan. 1940)
R. P. Mehl
A. I. M. E. Tech. Pub # n o 6
Met. Tech. Sept. 1939.
List of Tables and Illustrations
Page
Table 1
Rolling and annealing schedule
rig. 1
Stereographic projection of (ill) planes of
unannealed sample 2-5.
Fig. 2
3.14
Stereographic projection of (ill) planes of
sample 4-8 annealed one hour at 521°C
rig. 6
3.13
Stereographic projection of (ill) planes of
sample 4-6 annealed two hours at 440°C
rig. 5
3.12
Stereographic projection of (ill) planes of
sample 4-5 annealed three hours at 368°C.
rig. 4
3.11
Stereographic projection of (ill) planes of
sample annealed six hours at 300°C.
rig. 3
2,8
3.15
Photograph of scanning device showing driving
motors and gearing arrangements.
2.16
F
1N T H I S
AMD
FIGURES,
THE
PROTECTION
THE
SUCCEEDING
PLANE
I
stereographic
OF
CONTAINS
POLLING
A N D SAMPLE
DIRECTIONS.
n o r m a l
ig .
OF
0")
p l a n e s
5QOARES
pro jection
,
SHOW
IN A(lio),[l'Z]
solid
0 " )
POLES
TEXTORE.
SAMPLE L J .N J O A M N E A L .
M.D.
R.. O.
F"IQ. Cl
Ci»o projection ot5A M PL E4-/, AN NEA LED
51 \ H O O R 5 A T 3 0 0 ° C .
ROLLING TEXTURE
SHOW N by d o t t e d
OUTLINE .
N. O.
- /
' s/
•
— —*
g-D-1
F iGi. m
t il l ] P R O J E C T I O N
o f
SAMPLE 4-5. ANNEALED
T H R E E H O U R S A T 3 6 6 °C.
RO LLIN G T EX TU R E
SH O W W J BY D O T T E D
Ou t l i n e .
KJ.O.
Fia.iy
Cm) P R O T E C T I O I M
OF
S A M P L E 4-6, AimM E ALE 0
"TW O H O U R S A T 4 4 0 “C.
ROLLIN6 T E x T U C E
5 H O W M BY D O T T E O
O U T LIN E .
M. O.
R.D.
f’i&.'C
O'O p r o j e c t i o n
o r
Sa mpl e 4- s , a n n e a l e d
orse HOUR AT 5Zl “C.
ROLHN & TEX.TLIRE
5H O W N 5V DOTTED
OUT UfME_.
Fig. 6
Scanning device
to hold and move
samples
Документ
Категория
Без категории
Просмотров
0
Размер файла
777 Кб
Теги
sdewsdweddes
1/--страниц
Пожаловаться на содержимое документа