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Anomalous electrical resistivity of ordered Cu2NiZn at low temperatures
976
ACTA
METALLURGICA,
P’Q, Q’.R, R’S in Fig. l(a) are on (5i2). (The extra spots in Fig. l(b) lying on lines parallel to t, are due to double Bragg reflexion.) It can readily be shown that if the twin axis is [OZI], incoherent twin boundaries can be formed on planes of the type (h31}, {h13}, (h21) or (hi2). Incoherent twin boundaries were observed experimentally on planes of the type 15211, (013) and {121j. These observations suggest that the interfacial energy for twin formation on these planes is low. The presence of interstitial impurities may be an important factor influencing the misfit energy of these boundaries. Stacking faults were frequently observed under the same conditions as described above for a~ealing twins. Detailed study of the faults by electron microscopy and selected area diffraction showed that the faults do not in general lie on (21 l} planes although some of the faults do have this orientation. Many of the observations are consistent with the assumption that the faults are commonly on {310f planes. However, if the possibility of high index planes is admitted, it is difficult to be certain of the fault orientation. Stacking faults were observed only after a high temperature anneal. If the niobium is annealed at about BOO’%, a temperature sufficiently low for no . . appre~lable contamlnatlon to oeeur in the vacuum system used, no extended dislocations are observed. Moreover, the dislocations cross slip frequently as they move under the stresses produced by the electron beam. The dislocations then leave curved slip traces similar to those observed in R-iron, this is shown in Fig. 2. The dislocations in pure niobium are therefore not dissociated. The apparent low stacking fault energy of niobium
VOL.
9,
1961
FIG. 2. Curved slip traces in niobium, indicating frequent cross slip. x 25,000
after a high temperature anneal is presumably due to the segregation of impurities to the dislocations as suggested by Crussard(s). Segregation to the dislocations was observed in the present work and can also be seen on the micrographs of Fourdeux and Berghezano). This effect might be important in studies of yielding in body-centred cubic metals, where different grain sizes are obtained by varying the annealing temperature. Unless very pure starting material is used and heat treatments are carried out in a vacuum better than 10e5 mm Hg the conventional Petch analysis may be influenced by effects of this type. I would like to acknowledge financial support from the Wright Air Development Division and valuable discussions with Mr. J. A. Venables and Dr. P. R. Hirsch. R. L. SEGALL~ ~~~~~~l~g~~p~~~ ~b~ra~or~ Cavendish Laboratory Cambridge, England References 1. A. FOURDEUX and A. BERGHEZAN, J. I%&. Met. 99, 31
(1960). 2. D. S. HUTTON, 0. L. COLEMAWand W. C. LESLIE, Trams. Amer. Inst. Min. (~et~ZZ.) Esges 215, 680 (1959). 3. C. CRUSSARD,C. R. Acad. Sci., Pa& 252, 273 (1961). * Received April 28, 1961. t Present address: Division Melbourne, Australia.
of
Tribophysics,
CSIRO,
Anomalous electrical resistivity of ordered Cu,NiZn at low temperatures* FIG. I(b) Selected IX-B&diffraction pattern across the twin boundary.
taken
Alloys which undergo long range ordering typically have a lower electrical resistivity in the ordered state
than in the ported
disordered
the resistivity.
disordered
CuAu,
of resistivity
re-
in that ordering
had a lower temperature
that
coefficient
than ordered CuAu, in the low temperastates
crossed
Thus below about behavior
Hirabayashi@)
Sotoc3) later showed
ture region so that the curves disordered
TO
was anomalous
that CuAu,
increased
state.(l)
LETTERS
with
for the ordered
over
between
3O”K, CuAu,
the ordered
showed
state
and
30-70°K. the norma,l
having
the lower
and Jones (4) found recently
Phillips
of approximately anomalous
the CusNiZn
of previously
because it destroyed servations
been determined,
720°K
up to
was greater
Cold working decreased the ordered material, presumably
the ordering.
were in agreement The ordered
was also
from 300°K
of about
in t,he ordered condition.
that an alloy
composition
in that the resistivity
the critical temperature
Ref. 4).
Both of these ob-
with earlier work (see
structure
in CusNiZn
but the evidence
has not
that long range
purpose
temperature
of the present note is to report low
resistivity
measurements
cal CusNiZn alloy studied previously Jones(4)
anomaly
!I77
cm diameter.
Chemical analysis showed that it (‘on-
tained
25.5at.q;
balance
being copper
zinc
and
19.0at.O;,
containing
ities 0.25wt. 9 b manganese Ref. 4 for full analysis).
which
demonstrate
that
persists at low temperatures,
The specimen
was a polycrystalline
and 0.07wt.q:
a grooved alumina tube.
ordered
by
cooling
to room
heating
and an
77°K
(liquid
(in air) to
nitrogen)
and 42°K
were measured
thermocouple
located
193°K
temperature to
gradually
boil
inside
The sample,
and
slowly
temperature.
Temperatures
nitrogen
The sample was
900°K
The resistivity was at room temperature (198’K), 193”K,
then measured
on the identi-
(liquid
inside the alumina was achieved
off and the the
helium).
using a chrome-alumel
Dewar
low
tube.
The
by allowing
sample
still on the grooved
by Phillips and the
resistivity
temperature
to
disorder
measured at 298”, 187’,
to
the
warm
temperature
up cell.
tube, was reheated
it.
temperabure.
unlike CuAu,.
several
wire of 0.0762
appreciable
Chemical
repeated
analysis
treatments
I 150
resistivity
I 200
TEMPERATURE
I 250
I 300
OK
1. Variation of electrical resistivity with temperature of an alloy of approximately Cu,NiZn composition in the ordered and disordered condition.
I 350
of the
at 6OOY
change in composition.
WATER QUENCHED DISORDERED
I 100
The
77” and 4.2”K.
\vas
The sample
regained its original resistivity on warming up to room
28-
FIG.
an outer
inner pair, spaced 127cm, across which the resistivity
COOLED FROM 900 'K TO 460°K AT ABOUT 120'K/hr. ORDERED
I 50
(see onto
Two contact leads were spot
pair through which the current was introduced
31-
260
iron
welded onto each end of the wire, namely
0
s 0 2
the
impur-
The wire was wound
32
$
nickel,
as principle
to 873”K, held for 40 min and water quenched to room
ordering occurs seems overwhelming.(4.5) The
EDITOR
was measured on a standard bridge.
resistivity.
resistivity
THE
wire showed
after no
ACTA
978
METALLURGICA,
The results (Fig. 1) showed that although the temperature coefficient of resistivity in the disordered state was less in the range from 300’ to 77°K than in the ordered state, the curves did not cross over at low temperature. The residual resistivity of the ordered material was 2.6 $&cm higher than that of the disordered material (26.4 $&m~). Below 77”K, the temperature coeffmients in the two conditions were almost identical. The observations of a higher residual resistsnce in the ordered state might be due to a decrease in the effective number of electrons associated with a splitting of the Brillouin zone during orderingc6) and to the presence of antiphase boundaries, or to the latter phenomenon alone. It does not appear likely that the manganese, iron and other trace impurities present would be responsible for the anomaly, although it would be desirable to repeat the observations on a high purity stoichiometric CusNiZn alloy. The ordered structure in the CusNiZn alloy is currently being investigated by neutron diffraction techniques”). The author is indebted to L. Riccardi who made the resistivity measurements. v. A. PHILLIPS General Electric Research Laboratory Bchenectacty,New York References 1. C. S. BARRETT,~~~c~~re of Met&
p. 289. McGraw-Hill, New York (1952). 2. &I. HIRABAYASHI, J. P&s. Sot., Japurr. 6, 129 (1951). 3.11. SATO, Phys. Rev. 106, 674 (1957). 4. V. A. PHILLIPSand R. B. JONES, Z’ran& Amer. Sot. Metab !j$, 775 (1961). 5. D. &ALAS, R. HOSEMANN,A. KURSMANN,F. MOTZICUS and H. WOLLENBERGER, NaturuGssenschaftert 47, 81 (1960). G. J. C. SLATER,Phys. Rev. 84, 179 (1951). 7. V. A. PHILLIPS and B. W. ROBERTS, unpublished results.
VOL.
9,
1961
melting in evacuated silica tubes, shaking vigorously and water quenching. Weight losses were negligible. Filings, from ingots homogenized for 2 weeks at 6OO”C, were quenched from 450°C and annealed (see Table 1). Previous work(a,Q indicates that these treatments will give equilibrium conditions. TABLE 1. Time in hours of the equilibration treatment for gold-copper alloys previously quenched from. 450°C --v -----i_‘.._
;.$?~~;.;~)~
450
65
-------
69
--
75 80
~ 300 1 250
4
2
/
4
2
4
2
4 ~____ 4 ~_____
/Ti
2
4
/
4
/ 225 1 180 1 150 / 121
500
1 1700
110
i
500 1700 -.-.-____ 94 500 1700 --‘66 1 500 1 1700
--.p_-_
Lattice parameter measurements were made in a 11.46~cm Debye-Scherrer camera with Cu-radiation when a consistency of &O.OOOlA was obtained. For domain size and degree of order measurements filtered Cu-radiation was used. To reduce air scattering the 5.73-cm Debye-Scherrer camera was evacuated to a pressure of less than 1 mm Hg. The changes in lattice parameter with equilibration temperature for the four alloys are shown in Fig. 1; T, is taken as the point of inllexion of the curves. It is possible to obtain a value of T, of -@‘C for the 80% alloy by assuming that the lattice contraction __ -3
4.0066
80%Au
60
* Received May 11, 1961.
3.9853
75% Au
3.9571
X-ray
study of order in
69%
CuAu, alloys*
Conclusive evidence for long range order at the composition CuAu, was first obtained by Hirabayashi(l), although weak superlattice lines had been observed by Johansson and Lindet2) in 1936. Recent measurements of lattice parameter@, resistivity(a-6) and the disappearance of superlattice lines as the temperature increases(‘) all give a critical temperature, T,, of 190”200%. Unlike CusAu, sharp superlattice lines cannot be obtained for CuAu, where a limiting value for the size of antiphase domains appears to be ~50 8. Alloys containing 65, 69, 75 and 80 per cent Au? were prepared from 99.95 per cent copper and gold by t AlI oompositions are in atomic percentages.
Au
3.9431
65%
Au
B---
01 100
id /
150
200
250
300 T,
350
400
450
:
0
OC
Pm. 1.Variationof lattice parameter with equilibration temperature for gold-copper alloys. Numbers at right hand side of enrves indicate lattice parameter after quenching from 450°C.
ACTA
METALLURGICA,
P’Q, Q’.R, R’S in Fig. l(a) are on (5i2). (The extra spots in Fig. l(b) lying on lines parallel to t, are due to double Bragg reflexion.) It can readily be shown that if the twin axis is [OZI], incoherent twin boundaries can be formed on planes of the type (h31}, {h13}, (h21) or (hi2). Incoherent twin boundaries were observed experimentally on planes of the type 15211, (013) and {121j. These observations suggest that the interfacial energy for twin formation on these planes is low. The presence of interstitial impurities may be an important factor influencing the misfit energy of these boundaries. Stacking faults were frequently observed under the same conditions as described above for a~ealing twins. Detailed study of the faults by electron microscopy and selected area diffraction showed that the faults do not in general lie on (21 l} planes although some of the faults do have this orientation. Many of the observations are consistent with the assumption that the faults are commonly on {310f planes. However, if the possibility of high index planes is admitted, it is difficult to be certain of the fault orientation. Stacking faults were observed only after a high temperature anneal. If the niobium is annealed at about BOO’%, a temperature sufficiently low for no . . appre~lable contamlnatlon to oeeur in the vacuum system used, no extended dislocations are observed. Moreover, the dislocations cross slip frequently as they move under the stresses produced by the electron beam. The dislocations then leave curved slip traces similar to those observed in R-iron, this is shown in Fig. 2. The dislocations in pure niobium are therefore not dissociated. The apparent low stacking fault energy of niobium
VOL.
9,
1961
FIG. 2. Curved slip traces in niobium, indicating frequent cross slip. x 25,000
after a high temperature anneal is presumably due to the segregation of impurities to the dislocations as suggested by Crussard(s). Segregation to the dislocations was observed in the present work and can also be seen on the micrographs of Fourdeux and Berghezano). This effect might be important in studies of yielding in body-centred cubic metals, where different grain sizes are obtained by varying the annealing temperature. Unless very pure starting material is used and heat treatments are carried out in a vacuum better than 10e5 mm Hg the conventional Petch analysis may be influenced by effects of this type. I would like to acknowledge financial support from the Wright Air Development Division and valuable discussions with Mr. J. A. Venables and Dr. P. R. Hirsch. R. L. SEGALL~ ~~~~~~l~g~~p~~~ ~b~ra~or~ Cavendish Laboratory Cambridge, England References 1. A. FOURDEUX and A. BERGHEZAN, J. I%&. Met. 99, 31
(1960). 2. D. S. HUTTON, 0. L. COLEMAWand W. C. LESLIE, Trams. Amer. Inst. Min. (~et~ZZ.) Esges 215, 680 (1959). 3. C. CRUSSARD,C. R. Acad. Sci., Pa& 252, 273 (1961). * Received April 28, 1961. t Present address: Division Melbourne, Australia.
of
Tribophysics,
CSIRO,
Anomalous electrical resistivity of ordered Cu,NiZn at low temperatures* FIG. I(b) Selected IX-B&diffraction pattern across the twin boundary.
taken
Alloys which undergo long range ordering typically have a lower electrical resistivity in the ordered state
than in the ported
disordered
the resistivity.
disordered
CuAu,
of resistivity
re-
in that ordering
had a lower temperature
that
coefficient
than ordered CuAu, in the low temperastates
crossed
Thus below about behavior
Hirabayashi@)
Sotoc3) later showed
ture region so that the curves disordered
TO
was anomalous
that CuAu,
increased
state.(l)
LETTERS
with
for the ordered
over
between
3O”K, CuAu,
the ordered
showed
state
and
30-70°K. the norma,l
having
the lower
and Jones (4) found recently
Phillips
of approximately anomalous
the CusNiZn
of previously
because it destroyed servations
been determined,
720°K
up to
was greater
Cold working decreased the ordered material, presumably
the ordering.
were in agreement The ordered
was also
from 300°K
of about
in t,he ordered condition.
that an alloy
composition
in that the resistivity
the critical temperature
Ref. 4).
Both of these ob-
with earlier work (see
structure
in CusNiZn
but the evidence
has not
that long range
purpose
temperature
of the present note is to report low
resistivity
measurements
cal CusNiZn alloy studied previously Jones(4)
anomaly
!I77
cm diameter.
Chemical analysis showed that it (‘on-
tained
25.5at.q;
balance
being copper
zinc
and
19.0at.O;,
containing
ities 0.25wt. 9 b manganese Ref. 4 for full analysis).
which
demonstrate
that
persists at low temperatures,
The specimen
was a polycrystalline
and 0.07wt.q:
a grooved alumina tube.
ordered
by
cooling
to room
heating
and an
77°K
(liquid
(in air) to
nitrogen)
and 42°K
were measured
thermocouple
located
193°K
temperature to
gradually
boil
inside
The sample,
and
slowly
temperature.
Temperatures
nitrogen
The sample was
900°K
The resistivity was at room temperature (198’K), 193”K,
then measured
on the identi-
(liquid
inside the alumina was achieved
off and the the
helium).
using a chrome-alumel
Dewar
low
tube.
The
by allowing
sample
still on the grooved
by Phillips and the
resistivity
temperature
to
disorder
measured at 298”, 187’,
to
the
warm
temperature
up cell.
tube, was reheated
it.
temperabure.
unlike CuAu,.
several
wire of 0.0762
appreciable
Chemical
repeated
analysis
treatments
I 150
resistivity
I 200
TEMPERATURE
I 250
I 300
OK
1. Variation of electrical resistivity with temperature of an alloy of approximately Cu,NiZn composition in the ordered and disordered condition.
I 350
of the
at 6OOY
change in composition.
WATER QUENCHED DISORDERED
I 100
The
77” and 4.2”K.
\vas
The sample
regained its original resistivity on warming up to room
28-
FIG.
an outer
inner pair, spaced 127cm, across which the resistivity
COOLED FROM 900 'K TO 460°K AT ABOUT 120'K/hr. ORDERED
I 50
(see onto
Two contact leads were spot
pair through which the current was introduced
31-
260
iron
welded onto each end of the wire, namely
0
s 0 2
the
impur-
The wire was wound
32
$
nickel,
as principle
to 873”K, held for 40 min and water quenched to room
ordering occurs seems overwhelming.(4.5) The
EDITOR
was measured on a standard bridge.
resistivity.
resistivity
THE
wire showed
after no
ACTA
978
METALLURGICA,
The results (Fig. 1) showed that although the temperature coefficient of resistivity in the disordered state was less in the range from 300’ to 77°K than in the ordered state, the curves did not cross over at low temperature. The residual resistivity of the ordered material was 2.6 $&cm higher than that of the disordered material (26.4 $&m~). Below 77”K, the temperature coeffmients in the two conditions were almost identical. The observations of a higher residual resistsnce in the ordered state might be due to a decrease in the effective number of electrons associated with a splitting of the Brillouin zone during orderingc6) and to the presence of antiphase boundaries, or to the latter phenomenon alone. It does not appear likely that the manganese, iron and other trace impurities present would be responsible for the anomaly, although it would be desirable to repeat the observations on a high purity stoichiometric CusNiZn alloy. The ordered structure in the CusNiZn alloy is currently being investigated by neutron diffraction techniques”). The author is indebted to L. Riccardi who made the resistivity measurements. v. A. PHILLIPS General Electric Research Laboratory Bchenectacty,New York References 1. C. S. BARRETT,~~~c~~re of Met&
p. 289. McGraw-Hill, New York (1952). 2. &I. HIRABAYASHI, J. P&s. Sot., Japurr. 6, 129 (1951). 3.11. SATO, Phys. Rev. 106, 674 (1957). 4. V. A. PHILLIPSand R. B. JONES, Z’ran& Amer. Sot. Metab !j$, 775 (1961). 5. D. &ALAS, R. HOSEMANN,A. KURSMANN,F. MOTZICUS and H. WOLLENBERGER, NaturuGssenschaftert 47, 81 (1960). G. J. C. SLATER,Phys. Rev. 84, 179 (1951). 7. V. A. PHILLIPS and B. W. ROBERTS, unpublished results.
VOL.
9,
1961
melting in evacuated silica tubes, shaking vigorously and water quenching. Weight losses were negligible. Filings, from ingots homogenized for 2 weeks at 6OO”C, were quenched from 450°C and annealed (see Table 1). Previous work(a,Q indicates that these treatments will give equilibrium conditions. TABLE 1. Time in hours of the equilibration treatment for gold-copper alloys previously quenched from. 450°C --v -----i_‘.._
;.$?~~;.;~)~
450
65
-------
69
--
75 80
~ 300 1 250
4
2
/
4
2
4
2
4 ~____ 4 ~_____
/Ti
2
4
/
4
/ 225 1 180 1 150 / 121
500
1 1700
110
i
500 1700 -.-.-____ 94 500 1700 --‘66 1 500 1 1700
--.p_-_
Lattice parameter measurements were made in a 11.46~cm Debye-Scherrer camera with Cu-radiation when a consistency of &O.OOOlA was obtained. For domain size and degree of order measurements filtered Cu-radiation was used. To reduce air scattering the 5.73-cm Debye-Scherrer camera was evacuated to a pressure of less than 1 mm Hg. The changes in lattice parameter with equilibration temperature for the four alloys are shown in Fig. 1; T, is taken as the point of inllexion of the curves. It is possible to obtain a value of T, of -@‘C for the 80% alloy by assuming that the lattice contraction __ -3
4.0066
80%Au
60
* Received May 11, 1961.
3.9853
75% Au
3.9571
X-ray
study of order in
69%
CuAu, alloys*
Conclusive evidence for long range order at the composition CuAu, was first obtained by Hirabayashi(l), although weak superlattice lines had been observed by Johansson and Lindet2) in 1936. Recent measurements of lattice parameter@, resistivity(a-6) and the disappearance of superlattice lines as the temperature increases(‘) all give a critical temperature, T,, of 190”200%. Unlike CusAu, sharp superlattice lines cannot be obtained for CuAu, where a limiting value for the size of antiphase domains appears to be ~50 8. Alloys containing 65, 69, 75 and 80 per cent Au? were prepared from 99.95 per cent copper and gold by t AlI oompositions are in atomic percentages.
Au
3.9431
65%
Au
B---
01 100
id /
150
200
250
300 T,
350
400
450
:
0
OC
Pm. 1.Variationof lattice parameter with equilibration temperature for gold-copper alloys. Numbers at right hand side of enrves indicate lattice parameter after quenching from 450°C.