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Low temperature creep of rock salt single crystals
ACTA
520
METALLURGICA,
VOL.
1959
7,
the same giving support to L exp is approximately the hypothesis that the growth rate, at least below the melting
point of CuI, is primarily
controlled
by
The reason that Lexp is
the vapor pressure of Cul.
is probably due to (1) the vapor only about l/3 L,,, pressure of CuI surrounding the whiskers never quite reaches pocUI and (2) the CuI molecules have to diffuse through the H, and HI gas. The hypothesis adsorption
that whisker growth occurs by the
of CuI and its catalytic
reduction
whisker tip presumes that (1) the reduction the vapor phase is negligible
at the
of CuI in
and (2) the whisker tip
has different properties than the sides of the whisker. Sears@) has proposed that whiskers contain only axial dislocations
and hence the whisker tip would contain
permanent
surface
would
not.
steps whereas
If halide molecules
the whisker
are reduced
only at surface steps the catalytic can be understood. reduction mixture readily
of the tip
Further support(3) for the catalytic
mechanism of
activity
sides
rapidly
CuI
is that copper deposits
vapor
on a crystalline
and
hydrogen
surface
from a
much
more
than on a polished
quartz. The abrupt
increase of L at the melting
the CuI and its temperature is at present
dependence
not understood.
point of
above 590”
Gorsuch(4)
FIN. 1. Experimental
proposed
that in the case of iron where such an increase is also
the same way to the terminal
observed the surfaces of the whiskers become covered
extension
with
mirrors Mi.
liquid
whiskers.
halide
which
flows
to
It is of interest however
the
tip
of the
that at no tem-
was measured
exceed the value predicted
contact with the air.(l)
S. S. BRENNER General Electric Research Laboratory
2. R. V. COLEMAN and G. W. SEARS, Acta Met. 3. S. S. BRENNER, Thesis, R.P.I. May 1957. 4. P. GORSUCH, To he published. * Received
temperature
high
References
February
5, 131 (1957).
single The behaviour examined
creep of rock salt crystals *
The specimens were cylindric,
loads:
motion
gave
no appreciable
250,
300,
350
and
effect, 450
and
relatively
g/mm2
When the load was applied,
was observed.
been
The
time
interval
were
a jerky between
described
by
M.
the They
grown from the melt in
this laboratory. The specimens were fixed in a frame F with araldite, copper cylinders were attached in
Such a behaviour
Klassen-Nekludowa@).
After this initial period continuous
flow started, the
results are summarized
Each
indicate
were machined as shown on Fig. 1 from parallelipipeda from pure crystals
further
were negligeable.
loads
in Fig. 2.
mean between several runs.
load was
diameter 5 mm and the effective length 20 mm. cleaved
to prevent
with the set up at our disposal.
of rocksalt under constant
at 35°C.
paraffin
The oil was kept at a constant
two successive elongations was too small to be recorded
9, 1959.
temperature
the out,er
by means of a Hiippler thermostat
therefore used.
has
Low
The
the whole set up was in a room where temperature Low
1. S. S. BRENNER, Actn Met. 4, 62 (1956).
of degassed
fluctuations
Schenactady, N. Y.
1).
with the aid of
After a final etch to remove
in a bath
(2).
parts (Fig.
optically
layers of the central part, the specimen was immersed
perature does the growth rate of the copper whiskers by equation
set up.
that the process
curve is a
These curves obviously
is complex,
the different
stages are more clearly separated as the load is higher. Similar complex creep curves have recently been reported
by Van Buerent3) in the case of ger-
manium single crystals. the initial deformation
In the curves presented here, has been disregarded. One
can conclude that the process always starts with creep of the u-type followed by some P-creep after
LETTERS
TO
THE
0
t l 250 g/mm2;
Fro. 2. Results:
+ 300 g/mm2;
which a new sequence of LX-and /?-creep takes place. We believe could
that the interpretation
be given along
a-stages
may
following
consist
of
a kind
i.e. a formation
blocked
barriers
against
the effect of another
process,
This may be connected
as described
by
Friedel(*).
the different
of
non-persistent
of piled up groups
until they
are released
occurring
by
in the next
with rapid climb such The
initially
blocked
sources are freed and can give a new piling up, which results
in a further
creep
of the first type.
This
process can go on as long as the applied load produces enough
stresses
to overcome
the energy
necessary
for it.
by I.R.S.I.A.
ment de la Recherche l’agriculture)
(Institut Scientifique
(Brussels,
pour
(C.E.S.)
l’encourage-
dans 1’Industrie et
Belgium)
to
which
the
authors are greatly indebted. C.X.h’., Nol,
Belgium
Laboratorium, uoor Kristalkunde
Thermal
etching of silver surfaces to (110) planes*
It has been shown recently that thermal etching of is nearly parallel to a (110) plane, whereas for other orientations on etching(l)
(111) and (100) facets may be revealed The range
around
(110)
fore thermal etching provides a sensitive indicator the flatness of the surface.
The purpose
in for
of this note
is to illustrate this and to show that the waviness of a surface polished electrolytically
is sufficient to change
its etching behaviour. specimen of silver of about 2 mm
grain size was electropolished air for 15 min at 900°C.
and thermally etched in
Several crystals had a (110)
plane nearly parallel to the surface and these showed etch
patterns
Fig.
2 gives
with
ridges
a typical
lying
example
in Owe directlions. of such a surface.
each region of the surface only one direction
W.
crystal is shown at P in Fig. 1.
The average orientation
of the
The angle between the two sets of ridges shown by References
Janwwy
1).
(Fig.
which etching does not take place is small, and there-
of the ridges appears.
DEKEYSER
parallel
single crystals of silver will not occur if their surface
Within
E. AERTS and \V. DEKEYSER, Acta Met. 4, 557 (1956). &I. KLASS~~‘-SA~~LT~D~W~. 8. Phys. 55, 555 (19%). H. G. VAN BUEREK, Ph?/siccl, 24, 831 (1958). J. FIWCDN+ Lrs Disloccrtions, p. 63. Gauthier Villnrd, Paris, (1955). * Rweived
x~g/mmz.
1%. STRUMANE
Rozier 6, Gent, Belgium
1. 2. 3. 4.
minutes
350 g/mm2;
A polycrystalline
This work is part of a research program sponsored
0
of the process
lines:
work-hardening,
stage.
521
EDITOR
18. I!)59
the lines A and B is 30” and the angle between traces of the (ill) and (111) planes calculated from the stereographic projection for point P is also 30”. For crystal oriented at Q in Fig. 1 the angle between the sets of ridges was 16” and the angle between the (111) planes was calculated to be 15i”.
This correspondence
520
METALLURGICA,
VOL.
1959
7,
the same giving support to L exp is approximately the hypothesis that the growth rate, at least below the melting
point of CuI, is primarily
controlled
by
The reason that Lexp is
the vapor pressure of Cul.
is probably due to (1) the vapor only about l/3 L,,, pressure of CuI surrounding the whiskers never quite reaches pocUI and (2) the CuI molecules have to diffuse through the H, and HI gas. The hypothesis adsorption
that whisker growth occurs by the
of CuI and its catalytic
reduction
whisker tip presumes that (1) the reduction the vapor phase is negligible
at the
of CuI in
and (2) the whisker tip
has different properties than the sides of the whisker. Sears@) has proposed that whiskers contain only axial dislocations
and hence the whisker tip would contain
permanent
surface
would
not.
steps whereas
If halide molecules
the whisker
are reduced
only at surface steps the catalytic can be understood. reduction mixture readily
of the tip
Further support(3) for the catalytic
mechanism of
activity
sides
rapidly
CuI
is that copper deposits
vapor
on a crystalline
and
hydrogen
surface
from a
much
more
than on a polished
quartz. The abrupt
increase of L at the melting
the CuI and its temperature is at present
dependence
not understood.
point of
above 590”
Gorsuch(4)
FIN. 1. Experimental
proposed
that in the case of iron where such an increase is also
the same way to the terminal
observed the surfaces of the whiskers become covered
extension
with
mirrors Mi.
liquid
whiskers.
halide
which
flows
to
It is of interest however
the
tip
of the
that at no tem-
was measured
exceed the value predicted
contact with the air.(l)
S. S. BRENNER General Electric Research Laboratory
2. R. V. COLEMAN and G. W. SEARS, Acta Met. 3. S. S. BRENNER, Thesis, R.P.I. May 1957. 4. P. GORSUCH, To he published. * Received
temperature
high
References
February
5, 131 (1957).
single The behaviour examined
creep of rock salt crystals *
The specimens were cylindric,
loads:
motion
gave
no appreciable
250,
300,
350
and
effect, 450
and
relatively
g/mm2
When the load was applied,
was observed.
been
The
time
interval
were
a jerky between
described
by
M.
the They
grown from the melt in
this laboratory. The specimens were fixed in a frame F with araldite, copper cylinders were attached in
Such a behaviour
Klassen-Nekludowa@).
After this initial period continuous
flow started, the
results are summarized
Each
indicate
were machined as shown on Fig. 1 from parallelipipeda from pure crystals
further
were negligeable.
loads
in Fig. 2.
mean between several runs.
load was
diameter 5 mm and the effective length 20 mm. cleaved
to prevent
with the set up at our disposal.
of rocksalt under constant
at 35°C.
paraffin
The oil was kept at a constant
two successive elongations was too small to be recorded
9, 1959.
temperature
the out,er
by means of a Hiippler thermostat
therefore used.
has
Low
The
the whole set up was in a room where temperature Low
1. S. S. BRENNER, Actn Met. 4, 62 (1956).
of degassed
fluctuations
Schenactady, N. Y.
1).
with the aid of
After a final etch to remove
in a bath
(2).
parts (Fig.
optically
layers of the central part, the specimen was immersed
perature does the growth rate of the copper whiskers by equation
set up.
that the process
curve is a
These curves obviously
is complex,
the different
stages are more clearly separated as the load is higher. Similar complex creep curves have recently been reported
by Van Buerent3) in the case of ger-
manium single crystals. the initial deformation
In the curves presented here, has been disregarded. One
can conclude that the process always starts with creep of the u-type followed by some P-creep after
LETTERS
TO
THE
0
t l 250 g/mm2;
Fro. 2. Results:
+ 300 g/mm2;
which a new sequence of LX-and /?-creep takes place. We believe could
that the interpretation
be given along
a-stages
may
following
consist
of
a kind
i.e. a formation
blocked
barriers
against
the effect of another
process,
This may be connected
as described
by
Friedel(*).
the different
of
non-persistent
of piled up groups
until they
are released
occurring
by
in the next
with rapid climb such The
initially
blocked
sources are freed and can give a new piling up, which results
in a further
creep
of the first type.
This
process can go on as long as the applied load produces enough
stresses
to overcome
the energy
necessary
for it.
by I.R.S.I.A.
ment de la Recherche l’agriculture)
(Institut Scientifique
(Brussels,
pour
(C.E.S.)
l’encourage-
dans 1’Industrie et
Belgium)
to
which
the
authors are greatly indebted. C.X.h’., Nol,
Belgium
Laboratorium, uoor Kristalkunde
Thermal
etching of silver surfaces to (110) planes*
It has been shown recently that thermal etching of is nearly parallel to a (110) plane, whereas for other orientations on etching(l)
(111) and (100) facets may be revealed The range
around
(110)
fore thermal etching provides a sensitive indicator the flatness of the surface.
The purpose
in for
of this note
is to illustrate this and to show that the waviness of a surface polished electrolytically
is sufficient to change
its etching behaviour. specimen of silver of about 2 mm
grain size was electropolished air for 15 min at 900°C.
and thermally etched in
Several crystals had a (110)
plane nearly parallel to the surface and these showed etch
patterns
Fig.
2 gives
with
ridges
a typical
lying
example
in Owe directlions. of such a surface.
each region of the surface only one direction
W.
crystal is shown at P in Fig. 1.
The average orientation
of the
The angle between the two sets of ridges shown by References
Janwwy
1).
(Fig.
which etching does not take place is small, and there-
of the ridges appears.
DEKEYSER
parallel
single crystals of silver will not occur if their surface
Within
E. AERTS and \V. DEKEYSER, Acta Met. 4, 557 (1956). &I. KLASS~~‘-SA~~LT~D~W~. 8. Phys. 55, 555 (19%). H. G. VAN BUEREK, Ph?/siccl, 24, 831 (1958). J. FIWCDN+ Lrs Disloccrtions, p. 63. Gauthier Villnrd, Paris, (1955). * Rweived
x~g/mmz.
1%. STRUMANE
Rozier 6, Gent, Belgium
1. 2. 3. 4.
minutes
350 g/mm2;
A polycrystalline
This work is part of a research program sponsored
0
of the process
lines:
work-hardening,
stage.
521
EDITOR
18. I!)59
the lines A and B is 30” and the angle between traces of the (ill) and (111) planes calculated from the stereographic projection for point P is also 30”. For crystal oriented at Q in Fig. 1 the angle between the sets of ridges was 16” and the angle between the (111) planes was calculated to be 15i”.
This correspondence