Alloy with small change of electric resistance over wide temperature range and method of producing the same

The disclosed alloy has a temperature coefficient of electric resistance with an absolute value smaller than 100 ppm/.degree.C. in a temperature range between the order-disorder transformation point and melting point thereof, which alloy is made by molding an alloy consisting of 59.0-88.0 wt. % of palladium and the remainder of iron with a small amount of impurities, quenching the molded alloy from a temperature between the above-mentioned order-disorder transformation point and melting point to room temperature, cold working the quenched alloy for shaping, and annealing the shaped alloy.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electric resistance alloy consisting 
essentially of palladium and iron with a small amount of impurities, which 
alloy is stable at very high temperatures. More particularly, the 
invention relates to an alloy material for electric resistive elements 
having a small change of electric resistance over a wide temperature range 
of 490.degree.-1340.degree. C. and yet being easily workable at room 
temperature by forging, rolling, drawing, winding, shaping, and the like. 
2. Description of the Prior Art 
The need for measurement at high temperatures under very stringent 
conditions has been increasing these years in various industries, such as 
iron manufacturing industry, chemical industry, nuclear industry, 
space-related industry, and the like. 
For instance, in the continuous casting process, the top surface of molten 
metal in a tundish or mold must be continuously controlled at a desired 
level, so as to ensure continuous production of iron or steel goods of 
high quality with a high yield through an uninterrupted casting process. 
Conventional level meters for molten metal which use .gamma.-ray, X-ray, 
or other radioactive ray, have a shortcoming in that they are bulky and 
have safety problem. To overcome this shortcoming, the use of an 
eddy-current type displacement meter (to be referred to as "the 
displacement meter" hereinafter) of small size has been contemplated 
recently. 
The performance of the displacement meter depends on the material of sensor 
coils assembled therein, so that the properties of the sensor coil 
material, such as electric characteristics, response to ambient conditions 
during use, and stability, are very important. For example, in the case of 
the continuous casting, the temperature of the molten metal can be as high 
as 1,500.degree. C., and the sensor coils which are located immediately 
above the molten metal are required not only to withstand high 
temperatures of about 1,000.degree. C. but also to maintain their utmost 
performance with a high stability over a long period of time as essential 
quality thereof. 
The inventors disclosed a palladium-silver alloy (to be referred to as "the 
Pd-Ag alloy" hereinafter) consisting essentially of 55.5 to 60.6 wt.% of 
palladium and 44.5 to 39.4 wt.% of silver for the sensor coils of the 
displacement meter for use at high temperatures (see Japanese Patent 
Laying-open Publication No. 122,839/80). The Pd-Ag alloy has excellent 
corrosion-resistances and acid-resistances and good workability at high 
temperatures, and furthermore, the alloy is characterized by its very 
small temperature coefficient of electric resistance of less than +20 
ppm/.degree.C. over a wide temperature range of -50.degree. C. to 
+600.degree. C. (as shown by a curve for the reference alloy in FIG. 1). 
However, at the very high temperatures of 600.degree.-1,000.degree. C., 
the Pd-Ag alloy shows a large temperature coefficient of electric 
resistance of +133 ppm/.degree.C., so that the sensor coils made of the 
Pd-Ag alloy are susceptible to large drifts at the very high temperatures 
such as those experienced in the above-mentioned continuous molding, and 
the accuracy of the displacement meter using such sensor coils is rapidly 
reduced at such very high temperatures and accurate measurement of level 
cannot be ensured. Accordingly, there has been a pressing need in various 
industries for novel material of sensor coils which ensures high accuracy 
of measurement in a very stable fashion at the very high temperatures in 
excess of 600.degree. C. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to meet such pressing need 
and to obviate the above-mentioned shortcoming of the prior art. After 
elaborate studies, the inventors have found that a binary alloy consisting 
essentially of 59.0-88.0 wt.% of palladium and 41.0-12.0 wt.% of iron with 
a small amount of impurities has not only a very small change of electric 
resistance over a wide temperature range between its order-disorder 
transformation point (490.degree. C.) and its melting point (1,340.degree. 
C.), but also excellent workability, so that the binary alloy has 
excellent stability of electric resistance at very high temperatures and 
serves as a good electric resistance alloy for sensor coils to be used at 
the very high temperatures. 
Another object of the present invention is to provide an electric resitance 
alloy consisting essentially of 59.0-88.0 wt.% of palladium and 41.0-12.0 
wt.% of iron with a small amount of impurities, which alloy has a 
temperature coefficient of electric resistance between -100 ppm/.degree.C. 
and +100 ppm/.degree.C. over a wide temperature range of 
490.degree.-1,340.degree. C. 
Another object of the present invention is to provide an electric 
resistance alloy consisting essentially of 72.0-86.5 wt.% of palladium and 
28.0-13.5 wt.% of iron with a small amount of impurities, which alloy has 
a temperature coefficient of electric resistance between -50 
ppm/.degree.C. and +50 ppm/.degree.C. over a wide temperature range of 
570.degree.-1,335.degree. C. 
The electric resistance alloys of the invention are suitable for sensor 
coils to be used at the very high temperatures. 
A further object of the present invention is to provide a method of 
producing an electric resistance alloy comprising steps of molding an 
alloy consisting of 59.0-88.0 wt.% of palladium and the remainder of iron 
with a small amount of impurities, and quenching the molded alloy from a 
temperature higher than an order-disorder transformation point thereof but 
lower than a melting point thereof to room temperature, the alloy thus 
quenched is easy to forge, roll, draw, wind, and shape, so as to provide a 
sensor coil to be used at the very high temperatures. 
A still other object of the invention is to provide a method of producing 
an electric resistance alloy by thoroughly annealing the above-mentioned 
quenched alloy at a temperature higher than the order-disorder 
transformation point thereof but lower than the melting point thereof, so 
as to render excellent stability of electric characteristics to the alloy. 
The use of the electric resistance alloy of the invention is not restricted 
to the sensor coils for very high temperatures, but the alloy is suitable 
for various sensors and electric resistive elements of precision type 
measuring instruments which are exposed to very high temperatures in 
excess of 490.degree. C. so as to effectively utilize the characteristics 
of the alloy. Besides, the alloy of the invention can be used in composite 
devices having such sensors or elements as constituent parts thereof.

In FIG. 1, Tc shows a magnetic transformation point, T.sub.o-d shows a 
order-disorder transformation point. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A method of producing an electric resistance alloy according to the present 
invention will be described in detail now. 
To produce the alloy of the invention, a suitable amount of starting 
material mixture consisting of 59.0-88.0 wt.% of palladium and 41.0-12.0 
wt.% of iron is melted at first in a non-oxidizing atmosphere or in vacuo 
by using a suitable melting furnace, and homogeneous molten alloy with a 
uniform composition is prepared by thoroughly agitating the thus molten 
alloy. A sound ingot is formed by pouring the molten alloy into an iron 
mold of suitale shape and size, and the ingot is worked at room 
temperature by forging or the like so as to prepare a suitably shaped 
alloy such as a bar or a plate. The shaped alloy is processed by cold 
working, such as swaging, drawing, rolling, or flatening, so as to form 
goods of desired shape such as a fine wire of a thin sheet. If the 
cold-worked goods such as the fine wire or thin sheet is going to be used 
as an electric resistive element, such cold-worked goods must be 
stabilized by thorough annealing, which annealing is effected by heating 
in vacuo or in a non-oxidizing atmosphere at a temperature higher than its 
order-disorder transformation point but lower than its melting point, 
preferably higher than a measuring temperature or a temperature at which 
the cold-worked goods is to be used. e.g., at 1,050.degree. C. or higher 
for a goods whose highest possible temperature of use is 1,000.degree. C., 
keeping it at the heating temperature for 2 seconds to 100 hours, more 
preferably 5 minutes to 50 hours, and cooling it at a rate of 
5.degree.-300.degree. C./hour. The method described above provides 
excellent products. 
One of the very important factors in the process of effecting the 
above-mentioned method or producing the electric resistance alloy of the 
invention is that the alloy has such a strong affinity with air or oxygen 
that exposure of the molten alloy to air causes not only considerable 
deterioration of the electric resistance as shown in FIG. 2 but also 
adverse effects to cold-working of the manufacturing process. Therefore, 
careful treatment of the molten alloy is necessary. More particularly, in 
the melting operation, the contact of the alloy with air or oxygen must be 
avoided by all means, and in addition, due care must be paid to the 
above-mentioned factor during various heat treatments in the manufacturing 
process after the melting and during the use of the alloy as a sensing 
device. 
Apart from the above-mentioned oxidation, the alloy of the invention is 
susceptible to transformation into hard and brittle alloy of the ordered 
state (.gamma..sub.1 phase and .gamma..sub.2 phase) such as intermetallic 
compounds depending on the manner of the heat treatments, and such 
transformation tends to deteriorate the workability of the alloy. To 
further improve the workability, the disordered state (.gamma.-phase) of 
the alloy can be ensured by quenching it during the working from a 
temperature higher than its order-disorder transformation point but lower 
than its melting point through suitable means, such as high-speed blowing 
of a non-oxidizing gas to it, quick cooling of it in an oil, and vacuum 
sealing of it in a quartz tube followed by dipping of it in ice water 
containing salt, so as to render good workability at room temperature. The 
fine wires or thin sheets of the alloy of the invention which are quenched 
in the above manner before the working are very soft and can be easily 
wound in the form of coils and spirals. 
The above-mentioned treatment for rendering the good workability is an 
embodiment of the method of the invention. 
The following three methods of insulating the alloy of the invention are 
possible. 
(A) Wires, sheets, or other suitably shaped goods of the alloy of the 
invention prepared by such working as casting, forging, rolling, or 
drawing are fastened to one or more insulating material members; for 
instance, by embedding them in a heat-resisting insulating material such 
as high-purity ceramic paste, by directly adhering them to heat-resisting 
insulating member with alumina adhesive, by winding them on a cylindrical 
ceramic member, or by sandwiching them between two insulating plates. 
(B) To improve the space factor of the sensor coils in instruments, 
heat-resisting inorganic insulating films are adhered to the surfaces of 
the suitably shaped goods of the alloy of the invention formed by casting, 
forging, rolling, or drawing, and the shaped goods with the insulating 
films are worked so as to produce products of desired form such as 
windings or the like. Examples of the heat-resisting inorganic insulating 
films are silica, alumina, magnesia, fluorides, borides, and nitrides, and 
examples of the method of adhering the insulating films to the surfaces of 
the shaped goods are electrodeposition, vacuum evaporation, plating, and 
sputtering. 
(C) Heat-resisting inorganic insulating films are adhered to the surfaces 
of the suitably shaped goods of the alloy of the invention, and then the 
shaped goods with the insulating films are worked so as to produce 
products of desired form by etching, punching, or trimming. Examples of 
the method of the above-mentioned adhering of the insulating films to the 
surfaces of the shaped goods are electrodeposition, vacuum evaporation, 
plating, and sputtering. 
Although the products finished by the above-mentioned insulating method are 
ready for practical application, if necessary the annealing may be applied 
to the insulated products in the above-mentioned manner, so as to 
stabilize the alloy material thereof. Whereby, the characteristics of the 
electric resistance alloy can be fully utilized to provide excellent 
sensors or resistive elements to be used at the very high temperatures. 
The invention will be described in further detail by referring to examples. 
EXAMPLE 1 
Preparation of alloy No. FP-18 (86.5% of Pd and 13.5% of Fe) 
As starting materials, palladium with a purity of higher than 99.9% and 
iron with a purity of higher than 99.9% were used. Specimens were prepared 
by placing 100 g in total of the starting materials in a high-purity 
alumina crucible, melting them in a high-frequency induction furnace while 
blowing high-purity argon gas to the surface of the contents of the 
crucible to prevent oxidation of the starting materials, thoroughly 
agitating the molten materials so as to produce homogeneous molten alloy, 
and molding by pouring the molten alloy in an iron mold with an inner 
diameter of 7 mm and a height of 180 mm. Surface unevenness of the ingot 
thus molded was removed, and the ingot was cold worked by swagging so as 
to reduce the ingot diameter to 5 mm. The swaged ingot was homogenized by 
heating at 1,150.degree. C. in vacuo and then water quenched from 
1,000.degree. C. which is above the order-disorder transformation point 
(570.degree. C.) thereof. Fine wires with a diameter of 0.5 mm were 
prepared by repeating the swaging and cold drawing while applying several 
water quenching in between. Lengths of about 10 cm were cut off from the 
fine wires for use as the desired specimens for the measurement of the 
electric resistivity thereof in vacuo at a temperature between the room 
temperature and 1,300.degree. C. The result is shown in the curve FP-18 of 
FIG. 1. In FIG. 1, T.sub.c shows a magnetic transformation point and 
T.sub.o-d shows an order-disorder transformation point. The alloy show 
non-magnetic property in the temperature more than said magnetic 
transformation point T.sub.c, and is ferromagnetic in the temperature of 
less than said T.sub.c. In FIG. 1, dashed lines represent the electric 
resistance of the specimens as worked while the solid lines represent that 
of the specimens after the annealing. Since the structure of the alloy as 
worked was not stable, if the alloy was cooled from an intermediate 
temperature during the heating, such as the point a (350.degree. C.) or b 
(450.degree. C.) which are temperatures lower than the order-disorder 
transformation point T.sub.o-d, the locus of the reduction of the electric 
resistances differed from that of the increase thereof during the heating, 
as shown by the loci a--a' and b--b' of FIG. 1. Thus, without the 
annealing, the variation of the electric resistance of the specimen showed 
hysteresis. On the other hand, the specimen which was annealed at a 
temperature above the order-disorder transformation point T.sub.o-d 
(=570.degree. C.) showed substantially the same locus of the electric 
resistance variation even after repeated heatings and coolings, except a 
small hysteresis loop in the vicinity of the order-disorder transformation 
point T.sub.o-d, as shown by the solid line of FIG. 1. It was found that 
the variation of the electric resistance at temperatures above the point 
T.sub.o-d was very small as compared with that at temperatures below the 
point T.sub.o-d. Table 1 and FIG. 1 show the variation of the electric 
resistance characteristics of the specimens for different heat treatments. 
Average temperature coefficients of electric resistance in the temperature 
ranges 800.degree.-900.degree. C., 900.degree.-1,000.degree. C., and 
800.degree.-1,000.degree. C. are shown in items 1, 2, and 3 of Table 1. 
When the differences among values in the items 1 through 3 are small, the 
second order derivative of the electric resistance variation is small and 
the electric resistance varies linearly. It was confirmed that even if the 
specimens were heated to 1,300.degree. C. and then cooled to keep them at 
1,000.degree. C. for 50 days and at 1,100.degree. C. for 20 days, the 
electric resistance of the specimens did not show any change. 
TABLE 1 
__________________________________________________________________________ 
Properties of Alloy No. FP-18 
Item 
1 2 3 
Temperature 
Temperature 
Temperature 
coefficient 
coefficient 
coefficient 
4 
of electric 
of electric 
of electric 
Specific 
resistance 
resistance 
resistance 
resistivity 
at 800-900.degree. C. 
at 900-1,000.degree. C. 
at 800-1,000.degree. C. 
at 900.degree. C. 
Heat treatment (ppm/.degree.C.) 
(ppm/.degree.C.) 
(ppm/.degree.C.) 
(.mu..OMEGA.-cm) 
__________________________________________________________________________ 
After cold drawing, heating 
+26 +45 +35 100 
at 900.degree. C. for 5 hours in vacuo 
and cooling in furnace to 
room temperature at 150.degree. C./hour 
After cold drawing, heating at 
+25 +43 +33 100 
1,000.degree. C. for 30 minutes in vacuo 
and cooling in furnace to 
room temperature at 150.degree. C./hour 
After cold drawing, heating at 
+25 +43 +33 100 
1,250.degree. C. for 5 minutes in vacuo 
and cooling in furnace to 
room temperature at 300.degree. C./hour 
__________________________________________________________________________ 
EXAMPLE 2 
Production of alloy No. FP-24 (80.2% of Pd and 19.8% of Fe) 
Palladium and iron with the same purities as those of Example 1 were used 
as the starting materials. Specimens were prepared by placing 10 g in 
total of the starting materials in a high-purity alumina crucible (SSA-H, 
No. 2), melting them in a Tammann furnace while blowing high-purity argon 
gas to the surface of the contents of the crucible to prevent oxidation of 
the starting materials, thoroughly agitating the molten materials so as to 
produce a homogeneous molten alloy, sucking the molten alloy into a quartz 
tube with an inner diameter of 2.6-2.7 mm, pouring the molten alloy into 
another quartz tube having one end closed and an inner diameter which is 
somewhat larger than a desired specimen diameter, and homogenizing the 
alloy by heating it in the quartz tube at 1,000.degree. C. for 10 minutes 
and water quenching. Fine wires with a diameter of 0.5 mm were prepared by 
swaging and cold drawing of the thus quenched alloy. Lengths of about 10 
cm were cut off from the fine wires for use as the desired specimens. The 
characteristics of the specimens thus prepared for different heat 
treatments are shown in Table 2 and FIG. 1, which characteristics showed 
similar tendencies to those of Example 1. 
TABLE 2 
__________________________________________________________________________ 
Properties of Alloy No. FP-24 
Item 
1 2 3 
Temperature 
Temperature 
Temperature 
coefficient 
coefficient 
coefficient 
4 
of electric 
of electric 
of electric 
Specific 
resistance 
resistance 
resistance 
resistivity 
at 800-900.degree. C. 
at 900-1,000.degree. C. 
at 800-1,000.degree. C. 
at 900.degree. C. 
Heat treatment (ppm/.degree.C.) 
(ppm/.degree.C.) 
(ppm/.degree.C.) 
(.mu..OMEGA.-cm) 
__________________________________________________________________________ 
After cold drawing, heating 
-105 +30 -35 120 
at 900.degree. C. for 5 hours in vacuo 
and cooling in furnace to 
room temperature at 50.degree. C./hour 
After cold drawing, heating at 
-100 +27 -38 120 
1,000.degree. C. for 30 minutes in vacuo 
and cooling in furnace to 
room temperature at 50.degree. C./hour 
After cold drawing, heating at 
-100 +27 -38 120 
1,200.degree. C. for 5 minutes in vacuo 
and cooling in furnace to 
room temperature at 150.degree. C./hour 
__________________________________________________________________________ 
EXAMPLE 3 
Production of alloy No. FP-8 (70.0% of Pd and 30.0% of Fe) 
The starting materials and the preparation of specimens were the same as 
those of Example 2. The characteristics of the specimens of Example 3 for 
different heat treatments are shown in Table 3 and in the curve FP-8 of 
FIG. 1, which characteristics showed similar tendencies as those of 
Examples 1 and 2. T2 TABLE 3Properties of Alloy No. FP-8? Item? ? 1? 2? 
3? ? ? Temperature? Temperature? Temperature? ? coefficient? coefficient? 
coefficient?4? ? of electric? of electric? of electric? Specific? ? 
resistance? resistance? resistance? resistivity? ? at 800-900.degree. C.? 
at 900-1,000.degree. C.? at 800-1,000.degree. C.? at 900.degree. C.? Heat 
treatment? (ppm/.degree.C.)? (ppm/.degree.C.)? (ppm/.degree.C.)? 
(.mu..OMEGA.-cm)? After cold drawing, heating +65 +87 +76 129 at 
900.degree. C. for 5 hours in vacuo and cooling in furnace to room 
temperature at 15.degree. C./hour After cold drawing, heating at +63 +86 
+75 129 1,000.degree. C. for 30 minutes in vacuo and cooling in furnace to 
room temperature at 15.degree. C./hour After cold drawing, heating at +63 
+86 +75 129 1,200.degree. C. for 5 minutes in vacuo and cooling in furnace 
to room temperature at 120.degree. C./hour? 
Referring to FIG. 3, experiments similar to those of Examples 1 through 3 
were carried out for full range of palladium-iron binary alloy 
composition, and the average temperature coefficient of electric 
resistance 
##EQU1## 
and the electric resistivity at 900.degree. C. (.rho..sub.900) for 
different palladium concentrations were determined as shown in the 
figures. The average temperature coefficients C.sub.f were measured in 
three different temperature ranges, namely the temperature range I 
(800.degree.-900.degree. C.), temperature range II 
(900.degree.-1,000.degree. C.), and temperature range III 
(800.degree.-1,000.degree. C.). The graph of the figure indicates that the 
desired small temperature coefficient of electric resistance C.sub.f 
between -100 ppm/.degree.C. and +100 ppm/.degree.C. can be obtained only 
when the palladium concentration is 59.0-88.0 wt.% (between the points A 
and D of FIG. 3), and the preferred smaller temperature coefficient of 
electric resistivity C.sub.f between -50 ppm/.degree.C. and +50 
ppm/.degree.C. can be obtained only when the palladium concentration is 
72.0-86.5 wt.% (between the points B and C of FIG. 3). As the differences 
among the temperature coefficients C.sub.f (I), C.sub.f (II), and C.sub.f 
(III) for the temperature ranges I, II, and III increase, the second order 
derivative of the electric resistance variation becomes larger. On the 
contrary, as the differences among the temperature coefficients C.sub.f 
(I), C.sub.f (II), and C.sub.f (III) decrease, the second order derivative 
of the electric resistance variation becomes smaller. For instance, at the 
point A of FIG. 3, the three curves for the temperature coefficients 
C.sub.f (I), C.sub.f (II), C.sub.f (III) intersect, so that the second 
derivative of the electric resistance variation is zero at this point, and 
the electric resistance varies linearly in the temperature range of 
800.degree.-1,000.degree. C. 
The electric resistivity .rho..sub.900 of the alloy of the invention 
assumes a maximum value of 130 .mu..OMEGA.-cm and varies to 92 
.mu..OMEGA.-cm at the palladium concentration of 88.0%. Such resistivity 
is about three times that of the reference alloy of FIG. 2 at the room 
temperature which is 39 .mu..OMEGA.-cm (as disclosed in Japanese Patent 
Laying-open Publication No. 122,839/80). Although the high electric 
resistivity is a negative factor which tends to reduce the sensitivity of 
a very-high-temperature displacement meter, the resistivity does not cause 
any practical difficulty because high-frequency currents of several kHz to 
several MHz flow along the surface of the alloy wire of the sensor coil 
and the surface area of the sensor coil wire can be easily increased by 
using the alloy wire having a larger diameter. 
In an iron-palladium system equilibrium diagram of FIG. 4, wide and narrow 
shaded portions indicate that the alloy of the invention consisting of 
59.0-88.0 wt.% of palladium and 41.0-12.0 wt.% of iron has a temperature 
coefficient of electric resistance C.sub.f between -100 ppm/.degree.C. and 
+100 ppm/.degree.C. and between -50 ppm/.degree.C. and +50 ppm/.degree.C. 
The above mentioned temperature coefficients are valid over a wide 
temperature range between the order-disorder transformation point and the 
melting point of the alloy, and more particularly the temperature 
coefficient C.sub.f with an absolute value of not greater than 100 
ppm/.degree.C. is valid in a temperature range of 
490.degree.-1,340.degree. C. while the temperature coefficient C.sub.f 
with an absolute value of not greater than 50 ppm/.degree.C. is valid in a 
temperature range of 570.degree.-1,335.degree. C. Referring to FIG. 1, the 
curve for the alloy No. FP-24 has a portion in the neighborhood of about 
400.degree. C. where the change of electric resistance is small, but said 
portion involves a discontinuous change at the order-disorder 
transformation point and does not satisfy the condition of small change of 
electric resistance over a wide temperature range as aimed at by the 
invention, so that said portion is not indicated in FIG. 4. 
As described in the foregoing by referring to Examples 1 through 3, the 
alloy of the invention has a small change of electric resistance for 
different temperatures. Especially, the alloy No. FP-18 of Example 1 has a 
comparatively large electric resistivity .rho..sub.900 of 100 
.mu..OMEGA.-cm, but its electric resistance varies only very little over a 
wide temperature range of 570.degree.-1,335.degree. C., and such small 
change of electric resistance of this alloy of the invention is fully 
reproducible, so that this alloy of the invention can provide a high 
stability in final products. None of individual materials of the prior art 
provides such low temperature coefficient of electric resistance between 
-50 ppm/.degree.C. and +50 ppm/.degree.C. over the wide temperature range 
of 570.degree.-1,335.degree. C., so that the alloy of the present 
invention fully meets the characteristics which are required for the 
alloys of very-high-temperature sensor coils. 
The reasons for limiting the palladium concentration to 59.0-88.0 wt.% in 
the alloy of the invention is in that the palladium concentration outside 
of this limitation is not suitable for providing the alloy having a small 
change of electric resistance over a wide temperature range, because the 
alloy composition outside of the above-mentioned limitation has a larger 
temperature coefficient of electric resistance than between -100 
ppm/.degree.C. and +100 ppm/.degree.C. over a temperature range of 
490.degree.-1,340.degree. C., as can be seen from the above Examples 1 
through 3 and the curves of FIG. 1, FIG. 3, and FIG. 4. 
The reason for using the quenching from a temperature higher than the 
order-disorder transformation point (490.degree. C.) but lower than the 
melting point (1,340.degree. C.) before the annealing in the method of 
producing the alloy of the invention is that the quenching from the 
temperature in the above-mentioned range results in .gamma.-single-phase 
(disordered state) which renders excellent workability at room temperature 
as can be seen from Examples 1 through 3 and the curves of FIG. 1, FIG. 2, 
and FIG. 4. On the other hand, quenching from a temperature below the 
order-disorder transformation point is not suitable for producing the 
alloy of the invention because such quenching makes alloys so brittle and 
hard that the thus produced alloys are hard to work at room temperature 
and difficult to form the desired coils or the like. It should be noted 
that if the sequence of the quenching and the annealing is reversed in the 
method of the invention, the annealing tends to render the alloy so 
brittle and hard that the alloy becomes hard to form the desired coils, so 
that such reversing of the sequence is not suitable for producing the 
alloy of the invention. 
In short, the alloy of the present invention is characterized in that the 
alloy has a very small change of electric resistance, i.e., a temperature 
coefficient with an absolute value of less than 100 ppm/.degree.C. over a 
wide temperature range higher than the order-disorder transformation point 
thereof (490.degree. C.) but lower than the melting point thereof 
(1,340.degree. C.), that the alloy is very stable over a long period of 
time at a very high temperature such as 1,100.degree. C., and that the 
workability of the alloy can be further improved by quenching from a 
temperature higher than the order-disorder transformation point thereof 
(490.degree. C.) but lower than the melting point thereof (1,340.degree. 
C.), preferably in a range of 570.degree.-1,335.degree. C. Thus, the alloy 
of the invention is suitable for electric resistive elements of precision 
type measuring instruments, such as very-high-temperature sensor coils and 
standard resistance elements to be used over a wide temperature range of 
490.degree.-1,340.degree. C. The excellent characteristics of the alloy of 
the invention can be fully utilized in sensor coils and electric resistive 
elements which are combined with other functional elements in forming 
various industrial devices such as composite sensors like position 
sensors, three-dimensional sensors, displacement sensors, pressure 
sensors, weight sensors, acceleration sensors, vibration sensors, torque 
sensors, level sensors, or composite switches like float switches, limit 
switches, proximity switches, and the like.