THE DISORDERIKG O F BRASS BY COLD WORK
By R. W. K. HONEYCONBE*
[Manuscript received N a r c h 2, 19481
Summary
The electrical resistivities of a n
M - P brass, some cr brasses of various zinc contents, and an aluminium bronze have been measured after various deformations by wire drawing. The resistivity of the duplex alloy increases steeply after about 80 per cent. reduction in area. This increase is shown to be due to the resistivity change of the
P phase which probably becomes disordered on deformation. A recovery effect is observed in the duplex alloy on aging a t room temperature, indicating that the disordered state is not stable. No recovery has been observed in single phase wires. Unusually large increases in resistivity of some a phase alloys with deformation hare been observed and may indicate that even these alloys are not completely disordered.
I. INTRODUCTIOX
The /3-P' transformation in brass has been the subject of many investigations in recent years. I n no case has the disordered state been preserved a t room temperature by quenching. This is shown by the fact t h a t the electrical resistivity of quenched /3 brass is very close to that of slowly cooled P brass.
Smith(1) attempted to produce the disordered state by cold work, but reported that the resistivity changes less than 1 per cent. after wire drawing t o 9 . 5 per cent. reduction in area. However, these experiments afford little possibility of producing the disordered structure because of the very small amount of deforma- tion which could be imposed on the /3 brass before rupture.
The authors have shown that an sr-p brass containing up t o 80 per cent,
/3 phase can be deformed t o 90 per cent. reduction in area by wire drawing, during which process severe deformation occurs in both phases(%). The use of a duplex alloy in which crystals of a hard phase are embedded in crystals of a ductile phase may thus afford a general means of heavily deforming the hard phase without rupture. If in consequence of such a deformation the order in the alloy is destroyed, a marked increase in electrical resistivity occurs. ]For example, ordered single phase copper-gold and iron-nickel a l l o y have been cold worked and the establishment of the disordered state has been followed in this manner(3). I n a brass where both kinds of atoms have nearly the same scattering factor for X-rays, the measurement of the electrical resistivity is the most
This paper describes the changes in specific resistivity of deformed in an attempt to produce the disordered state in the cc-P brass wires
P phase. Some single phase copper alloys have also been examined.
*
Division of Tribophysics, C.B.I.R.

DISORDERING OF p
BRASS BY COLD WORK 191
11. EXPERIMENTAL
The materials used in the experiments were an a-p brass wire, 0.187 in. in diameter, and wires of single phase a solid solutions 0.192 in. in diameter.
The chemical analyses are contained in Table 1.
All the wires were annealed for 30 minutes at 800' C. and then slowly cooled in the furnace, taking approximately 12 hours to reach room temperature.
The wires were then drawn through a set of carbide dies using a mechanized wire drawing machine. The speed of drawing was about 4 ft./min. and stearic acid was used as a lubricant.
The electrical resistivity was measured within two hours of drawing on
20 cm. lengths of wire using a Kelvin double bridge. The temperature in each series was constant to within k 2 . 5 " 0.
0 - 5 per cent.
COMPOSITIONS
O F COPPER ALLOYS cSED I N THE
INVESTIGATION
Brass 2 Brass 3 Brass 4
(a)
Aluminium
Bronze
(4
Copper
Zinc
Aluminium
Iron
Lead
Tin
Nickel
Others
. . . . . .
. . .
.
. . .
. . . .
. . . . .
. . . . . .
. .
.
. . . .
. . . . .
. . . . . .
*
By difference.
I
1
Trace
Trace
Trace
Trace
1
0 0 5 i
111. RESULTS
( a ) Duplex Brass Wires
After the annealing treatment the a-p brass wires consisted of a very coarse distribution of a crystals in the p matrix, the phases being present in approxi- mately equal proportions. Their specific resistivities after various reductions in area by drawing are shown in Figure 1A. The specific resistivity increases almost linearly a t first, but more steeply at higher deformations. After 95 per cent. reduction in area the specific resistivity had changed from 6 x ~ O - ~
8 x ~ O - ~ cent. reduction in area the resistivity decreased slightly.

192 R. W. K. HONEYCOMBE AXD W. BOAS
Measurements made one day after drawing showed (Fig. 2 ) that the resistivity decreased with time. After six days, in the more heavily deformed wires, this recovery was between 1 2 and 25 per cent. of the total change in resistivity produced by cold drawing. Recovery had almost ceased after 27 days ; the further decrease in resistivity after this period up t o 79 days was just above the limit of accuracy of the measurements.
After aging for 42 days, one set of wires was annealed in hydrogen for 30 minutes a t 800" C. and furnace cooled, i.e. the wires were subjected t o the same treatment as they had received prior to dra~-ing. Thus no difference in the
75
7 0
6 5
9 0
8 5
8 0
A 60/40 BRASS
C C a l c u l a t e d Curve f o r b PHASE
Fig. 1.-Specific resistivity of cold drawn %,and brass wires. distribution of the two phases should have occurred. The results of resistivity measurements on these wires are also plotted in Figure 2. This shows that all the annealed wires h a r e approximately the same resistivity
TT hatever the amount of previous cold work.
( b ) of 35 Per Cent. Zinc
To separate the behaviour of the a and (3 phases in the duplex wire, resistivity measurements \vere made on a single phase a brass wire (35 per cent. zinc), the composition of which approximated to that of the a phase i n the duplex brass.
The measurements showed that the specific resistivity of the a brass wire also a change from 6 . 5 x t o 8 - 6 X ohm-cm. (Fig. 1B). However, here the increase was uniform u p t o high deformations.

DISORDERING O F
P
BRASS BY COLD WORK 193
This is in contrast to the behaviour of the duplex brass wires, as is also the fact that practically no recovery occurs. This was established by measure- ments made on the single phase wires after periods of one and six days after
B As drawn
C
A l t e r l day
D A f t e r 42 d a y 5
A After anneai~ne
0 10 20 30 40 53 60 70 80 9C 103
% R e d u c t ~ o n in Area
Fig. 2.-Effect of recovery on the specific resistivity of cold drawn duplex brass mires. drawing to different degrees (Table 2). Although the changes are of the order of the experimental error it should be noted that in no case is there an increase in resistivity with time.
SPEOIFIC RESISTIVITY O F
35
PER CENT. ZINC BRASS
1
I
Specific Resistivity (ohm-cm.)
Per Cent.
Reduction in Area
Immediately after
Drawing
One Day after
Drawing
Six Days after
Drawing

*I94 R. W. K. HOKEYCOMBE AND W. BOAS
(c) Single Phase Wires of Various Compositions
The behaviour of the 35 per cent. zinc brass wire in the above experiments was contrary to that expected from the literature. It is generally thought that severe cold work changes the specific resistivity of most pure metals by less than
5 per cent. and that solid solutions behave in a similar manner(4). However, the above results indicate that the specific resistivity of brass containing 35 per cent. zinc has increased by about 30 per cent. after 90 per cent. reduction in area.
0 10 20 30 40 50
X Reduchon rr Area
60 70 80 90 I00
Fig. 3.-Specific resistivity of cold drawn copper base alloys.
To determine whether copper alloys of other compositions behave similarlg, the brasses 3 and 4 and an aluminium bronze were investigated. As a check, pure copper wire v a s also examined.
The results obtained are plotted in Figure 3. I t is clear that pure copper undergoes only a slight increase in electrical resistivity, the change amounting to only 3 per cent. after 90 per cen.t. reduction in area. With the 8 . 6 per cent. zinc brass, again only a small increase in resistivity occurred, the change after
90 per cent. reduction being approximately 6 per cent. However, an increase of
22 per cent. was observed in the 20 per cent. zinc wire after 90 per cent. reduction in area and of 30 per cent. in the aluminium bronze. Thus the effect is not specific to the addition of zinc to the copper.
The measurements were repeated on the 20 p& cent. zinc alloy after 12 days and as in the 35 per cent. zinc alloy, the recovery observed was very small.

IV. DISC~SSIOK
All the annealed duplex brass wires have nearly the same resistivity. This fact alone is not sufficient to indicate that the increase in resistivity on drawing is not due to the formation of cracks. However, a microscopic examination of sections of the drawn wires failed to reveal any cracks. Further, i t is most unlikely that the wires could have been drawn t o 98.1 per cent. reduction if cracks had been present previously, and, moreover, in this case the resistivity would h a r e increased and not decreased during the last stages of drawing.
The behaviour of a wire of the pure
(Figs.
P phase can be deduced from the curves la and 1B) if i t is assumed that :
(1) The alloy consists of equal parts by volume of each phase.
(2) The crystals in the duplex alloy change their resistivities with deforma- tion in the same way as in the single phase alloys.
(3) The deforination of the a phase in the duplex alloy is the same as t h a t of this alloy.
\
Curve C (Fig. 1) has been calculated using these assumptions.
Whereas the first assumption is borne out by microscopic observation, and t h e second by the success of the rule of mixtures applied t o such alloys, indicating t h a t the interaction between crystals is negligible as far as the electrical resistivity is concerned, the last assumption is certainly not correct. We have shown earlier(2) that the x phase in the duplex brass is always deformed t o a larger extent than the p phase, i.e. its deformation is larger than indicated by the total deformation of the alloy. Hence the curve B should be compressed horizontally a t sniall and medium deformations in order t o show the change in resistivity of t h e a phase against the total deformation of the duplex alloy. On the other hand, the curve B is more nearly correct a t high deformations since both phases then deform approxiniately t o the same extent. Hence if the unequal defornia- tion of the
Y. and p phases is taken into account, the curve C of the resistivity of t h e 13 phase will be lowered a t small and medium deformations whereas a t high deformations the sharp increase will be maintained. Thus this sharp rise will be still more pronounced than in the plotted curr7e.
As a n explanation of this behaviour i t is suggested t h a t the P phase becomes disordered as a result of the cold working. This occurs only after an amount of deformation apparently larger than in other ordered alloys ; however, the actual deformation suffered by the P phase is smaller than indicated by the total deforniation of the duplex alloy. No definite explanation of the decrease in resistivity a t very high reductions will be offered. Perhaps the heat developed during drawing produces a partial annealing of the wires. The fact that recovery occurs in the duplex but not in the single phase a wires shows t h a t the disordered s t a t e into which the P phase is brought by deformation cannot be stable a t room temperature.
The change of resistivity with deformation of copper and a n 8 . 6 per cent. zinc brass is as small as reported in the literature. However, the resistivities of
20 and 35 per cent. zinc brasses and of the aluminium bronze increase consider- ably. There is, of course, the possibility of the existence of a certain degree of

196 R. w.
AND W. BOAS order also in those alloys. Guinier(5) has found that perfect disorder in a solid solution does not exist but that there is a certain extent of short range order.
It is not clear whether such a short range order affects the electrical resistivity.
According to Nix and Shockley(4) local short distance order does not affect such properties as electrical resistivity, and Muto(6) has calculated the resistivity a s a function of the long range order parameter. On the other hand, similar claims had been made by Linde(7) and Muto regarding the insensitivity of X-ray interferences t o order, if the coherent regions are small and irregular, before
Guinier showed the effect experimentally. The possibility of the short range order affecting the electrical resistivity can therefore not be exoluded.
This work forms part of the research programme of the Division of Tribo- physics, Oouncil for Scientific and Industrial Research, Australia. We wish to thank Dr. S. H. Bastow, Chief of the Division, for his interest in the work and for helpful discussions. We are grateful to Professor E. J. Hartung for laboratory facilities in the Chemistry School, University of Melbourne; t o
Professor H. K. Worner for use of equipment in the Rosenhain Memorial
Laboratory ; and to the staff of the Munitions Supply Laboratories, Maribymong, for carrying out spectrographic analyses.
( 1 ) SMITH, 8.-Trans. Amer. Inst. M i n . (Xetall.) Engrs. 152 : 144 (1943).
(2) R . W . K., and BOAS, W.-Xature 159 : 847 (1947) ; Aust. J. Sci. Res. A 1 :
'70 (1948).
(3) DAHL, 0.-2. Metallk. 28 : 133 (1936).
(4) NIX, P. C., and SHOOKLEP, Mod. Phys. 1 0 : 57 (1938).
(5) GUINIER, A. J.-Proc. Phys. Soc. 57 : 310 (1945).
( 6 ) Muro, T.-Sci. Pap. Inst. Phys. Chem. Res. Tokyo 30 : 99 (1936).
(7) LINDE, Phys., Lpz. 30 : 151 (1937).