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February, 1925
Forging-Stamping-Heat Treating
P r o p e r t i e s o f H i g h R e s i s t a n c e
*
A l l o y s
This Paper Contains a Summary of the Important Physical Con­
stants of the Well Known High Resistance Alloys
T H E recent advances in the art of electrical heating
have stimulated research in the field of high-resistance
alloys. In the last 10 years many new
combinations of the metals have been suggested as
resistor materials and some of them have rendered
very satisfactory service. The new alloys are for the
most part binary and ternary mixtures of the more
common metals. A review of the literature discloses a
considerable amount of information on the specific resistances
of these alloys and also on their temperature
coefficients between room temperature and 100 deg. C.
Little information will be found, however, on the same
electrical properties at the high temperatures at which
the material is required to operate.
The present paper gives, in an attempt to supply
this need, a summary of these important physical constants
for some of the well-known high-resistance alloys.
The attempt to use ,the high-resistance alloys as
elements in base-metal thermocouples for the measurement
of temperature was only a natural ste2 in the
development. In the second division of the paper
some old and some new information has therefore been
included on the electromotive forces which may be expected
from various combinations of these materials.
Theoretical Considerations.
It has already been stated that high-resistance alloys
are produced by alloying metals with one another
in binary or ternary combinations. It does not follow,
however, that all such combinations give materials of
high specific resistance.
When two or more metals are melted together they
may behave on freezing in two characteristically different
ways. When in the molten state the constituents
of the alloy are of course minutely dispersed in
one another. On freezing they may remain minutely
dispersed so that even in a microscopic section the constituents
cannot be differentiated. These combinations
are known as "solid solutions." The second class of
alloys comprises those which on freezing permit the
two or more constituents to freeze separately from one
another. They no longer remain in solution in the
solid state. The microscope can distinguish the separate
constituents. These alloys form what is known
as "eutectic mixtures" with one another. The metals
may, however, in certain concentrations form intermetallic
compounds with one another and the compound
thus formed may dissolve and subsequently
freeze either as a solid solution or as a eutectic mixture
with the pure metal which is present. Since these
intermetallic compounds are in general hard and brittle
materials no great concentrations can be carried
*A paper presented at the Twenty-seventh Annual Meeting of
the American Society for Testing Materials, held at Atlantic
City, N. J., June, 1924.
tRussell Sage Laboratory, Rensselaer Polytechnic Institute;
also Research Division, Driver Harris Co.
tRussell Sage Laboratory, Rensselaer Polytechnic Institute.
That Are Used for High Temperatures
By M. A. HUNTERf and A. JONES*
in any alloy which has subsequently to be reduced to
wire.
The electrical properties of these two classes of
alloys are very different from one another. In a solid
solution the electrical resistance of the resulting alloy
bears no relation to the resistances of the components.
It is in all cases very materially higher than either.
The temperature coefficient of electrical resistance is
also changed. Whereas the individual constituents
have temperature coefficients approximately equal to
0.004 per deg. C, the temperature coefficient of the
solid solutions drops very rapidly with increasing con-
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200 400 600 800 1000
Temperature, deg. Cent.
FIG. 1 — Showing the variation of Electrical resistance of
nickel and certain nickel alloys at various temperatures.
Values plotted are given in Table I, chemical compositions in
Table II.
centrations of the added component. In some cases
it drops to zero and may even in special cases become
negative. In eutectic mixtures, however, no such radical
variations are produced. The electrical resistances
of these alloys approximate in the main to the mean of
the electrical resistances of the components while the
temperature coefficient, if it drops at all, does so to
only a slight degree.
It is therefore evident that high-resistance alloys
belong in the class of solid solutions. It is further to
be noted that such combinations will yield alloys with
temperature coefficients which are considerably lower
than the pure metals from which they are made.
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