NATIONAL BUREAU OF STANDARDS REPORT

3901

THEML CONDUCTIVITIES OF THREE INCONEL ALLOYS

AT TENPERATURES FROM 100 TO 700°C

by

H. E. Robinson

Silas Katz

Report To

The

National Advisory Committee

For Aeronautics

Washington 25, D.C,

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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^Office of Basic Instrumentation ^Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-30-1015 January 19, 1955 3901

THERFJX CONDUCTIVITIES OF THREE INCONEL ALLOYS

AT TEMPERATURES FROM 100 TO 700°C

by

H, R, Robinson

Silas Katz

Heating and Air Conditioning Section

Building Technology Division

to

National Advisory Committee

For Aeronautics

Washington 25, D.C,

<^BS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re

unless permission Is

25, D, C. Such per

cally prepared If ti

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

In part, is prohibited

andards, Washington

port has been speclfieport for Its own use.

THERMAL CONDUCTIVITIES OF THREE INCONEL ALLOYS

AT TEI^TERATURES FROM 100 TO 700 °C 1.

INTRODUCTION

Three Inconel alloys were submitted by the National

Advisory Committee for Aeronautics for measurements of

their thermal conductivities in the temperature range from

100° to 700°C. Three specimens of each alloy were furnished

these being designated as NX9519 (1,2,3); NX592 ( 4 , 5 , 6 );

NX656 (7,^,9)«

This report presents the results of measurements made

on two specimens of each of the three allo^^s (Specimiens 2, 3

5, 6 ; 9).

2,

DESCRIPTION OF THE ALLOYS AND SPECIMENS

According to information furnished by the International

Nickel Company, the compositions of the alloys were as follows ; NX 9519 NX 592 NX 656

c .02 ,07 .11

Mn 0 2S .26 .33

Fe 7.89 8.17

Si ol? .19 .21

Cu .22 .15 0I9

Ni 15.99 76.45 75.64

Cr 1Z(, , 42 14.96 15.32

S .007 .007 .007

The specimens were cylindrical bars, niachined to a

length of 37.^ cm and a uniformi diameter of 2,42 cmi. An

axial hole, 1,3 cm. in diameter, was drilled to a depth of*

5 ,^ cm in each end of the bar.

According to information obtained from the NACA, the

specimens after machining were subjected to heat treatment

by being placed in an oven at 1120°C, left there for 9-1/4

minutes, and then removed and allowed to cool in quiescent

air.

3

.

TEST METHOD AND PREPARATION OF SPECIMENS

The general arrangement of the test apparatus vath a

specimen installed is shown in Figure 1, The test specimen

was heated at the bottom by means of the internal electric
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heater, and held at a constant temperature at the top by

the circulating coolant. The guard cylinder was similarly

heated at the bottom and cooled at the top.

Seven th erm*ocouples , spaced about U cm apart along the

measuring section of the specimen, indicated the temperature at the ends of six 4-cm spans of the bar, thus enabling

calculation of six values of the thermal conductivity of the

metal, corresponding to six progressively lower mean temperatures, for each temperature regime at which the apparatus

was operated.

The internal bar heater was energized with constant

voltage direct current, the power input being determined

by measurements of the current and potential drop in the

heater using standard resistors and a high-precision potentiometer. The guard heater was energized with voltage-stabilized a.c., adjusted to yield a minimal average temperature

difference between the bar and the guard as indicated by thermocouples » in corresponding longitudinal positions on the bar

and guard. Other thermocouples on the bar and guard provided

additional temperature data needed to calculate corrections

for small heat interchanges betv^een guard and bar. The

space between specimen and guard was filled with a freeflowing powder insulation of which the thermal conductivity

at various temperatures was known; the guard cylinder was

suspended within the outer cylindrical container, and similarly insulated.

Thermocouples on the specimen were made of No. 26 AWG

chromel and alumel wires, welded with an oxygen-gas torch to

yield small bead-like junctions. These were inserted in

i mm diameter holes drilled 2 mm deep radially in the side

of the specimen, and fastened tightly by punch-pricking

the metal around the hole. The thermocouple wires were separately insulated with fine woven glass tubing; and wrapped

at least one-half turn around the specimen, in the transverse plane of the junction, before being led away to the

top of the apparatus through the powder insulation. The

guard thermocouples were similarly installed. All thermocouple emfs were measured against a reference junction at

0°C, using a high-precision potentiometer.

The internal bar heater consisted of a multi-hole ceramic

cylinder 1.2? cm in diameter and 5.2 cm long, with nichrome

resistance wire threaded longitudinally through the holes.

Specimens No. 5 and ^ were tested with a heater of about 30

ohms resistance; all other tests were made with a different

heater of about 55 ohms resistance. Low resistance current

leads, and fine wire potential leads, were brought out to
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the top of the apparatus through the powder insulation.

Results were calculated using average values of data

obtained in several readings over a period of three or more

hours at a substantially steady-state condition. Temperature conditions were considered satisfactorily steady when

no thermocouple on the specimen changed temperature at an

average rate greater than 0,3 degree C per hour. Thermocouple readings were converted to degrees Centigrade using

data obtained by a calibration of the thermocouple wire.

To calculate the thermal conductivity, observed temperatures of the specimen and guard were plotted versus

longitudinal position, and smooth curves were drawn through

the points representing the specimen and guard temperatures.

Average temperature differences between specimen and guard

were determined from these curves, for various parts of the

specimen, and used, in conjunction with geometric factors

and the knovm thermal conductivity of the insulation, to

calculate heat interchanges between the specimen and the

guard. Such corrections to the measured heat input to the

specimen heater were calculated for the heat interchange

(a) between the loxver end of the specimen and the guard,

(b) between the specimen and the guard at the heater region

up to the first span thermocouple, and (c) between specimen

and guard for each of the six thermocouple spans. The

average rate of heat flow in the specimen between any two

adjacent thermocouples x*/as thus computed and used, together

with the measured distance and temperature difference between them, and the cross-sectional area of the specimens,

to calculate the average thermal conductivity at the span,

corresponding to the average or mean temperature of the span.

The maximum difference for any thermocouple span between

the corrected heat flow in the span and the measured electrical input to the heater ranged from -12 to 22 percent of

the input in the various tests, averaging S,7 percent. It

is believed that corrections to account for heat interchanges

between bar and guard were computed with an uncertainty of

less than 15 percent and consequently that the uncertainty^

in the rates of heat flow used in calculating the thermal

conductivities was not more than 3 percent, and in most cases

was considerably less.

Measurements were made on each specimen at several

different temperature regimes or gradients, each such regime

yielding six values of thermal conductivity at six corresponding values of mean temperature. For two of the alloys, the

initial test was made on one specimen at a low temperature
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and on the other specimen at a moderate or high temperature.

In the case of one specimen (No. ^) , on which the initial

test ’(/vas made at a high temperature, the specimen v/as removed

from, the apparatus, reversed end for end, and retested with

the initial test made at a low temperature.

4 . TEST RESULTS

The values of thermal conductivity obtained from each

of the tests on each specimen were plotted versus their

corresponding mean temperatures (Figures 2 through 7 )« For

each set of six values obtained in each test, a straight line

was drawn, as determined by the method of least squares. In

cases where the initial test on a specimen was made at a low

temperature, a dashed line was drawn for that test.

This method of plotting the results indicated that the

conductivity — mean temperature relationships were slightly

concave upward. Accordingly, quadratic curves were fitted

to the data for each specimen, using the theory of least

squares, as shown in Figure S. One curve sufficed for both

specimens of alloy NX 592 , and similarly for alloy NX 656, but

in the case of alloy NX 9519 the results on the two specimens

differed sufficiently to require a curve for each specimen.

The quadratic equations plotted in Figure & are given

below, together with the standard deviations of the individual

conductivity determinations from the corresponding equations.

The standard deviation given is a measure both of the errors

in individual determinations, and of how well the equation

fits the data.

Specimen

NX 9519 - No. 2 k = 0.1349

NX 9519 - No. 3 k = 0.1356

NX 592 - Nos. 5 & 6 k = 0.1342

NX 656 - Nos. g & 9 k = 0.1345

where k = thermal conductivity.

Equation Std. Dev

+ 0.0105X + 0.00090x^ 0.00301

+ 0.0134X +0.00055x^ .00325

+ 0.0144X +0.00045x^ ,00267

+ O.OI46X + 0.00046x^ .00206

watt/cm( deg C

)

o

lOOx = mean temperature, °C. (O.^^x < 7 . 0 ) Values of thermal conductivity (watt/cm deg C) calculated

from these equations, and used to plot the curves in Figure S,
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are tabulated below,

to show differences.

The fourth digit

NX9519 NX9519

is presented merely

NX592 NX656

Mean Temp,°C Spec .

2

Spec .

3

Spec. 5,6 Spec.

8

100 0.1464 .1495 .1490 .1496

200 .1596 .1645 .164s .1656

300 .1746 .1807 .1815 .1825

400 *1914 .1980 .1990 .2004

500 .2100 .2164 .2175 .2191

600 .2304 .2358 .2369 .2388

700 .2526 .2564 .2512 .2594

5 . DISCUSSION OF RESULTS

The results, as shown in Figure S and by the tabulated

values, indicate that the three alloys, as represented by

Specimens 3 (NX 9519 ), 5 and 6 (NX 592 ) and g and 9 (NX 656),

had thermal conductivities over the range 100 to 700 C which

were the same within one percent. Specimen 2 (NX 9519 ), however, was about 3 percent lower in conductivity than its comparison specimen (No, 3 ) of the same alloy, and similarly

about 3 percent lower than the specimens of the other two

alloys, A retest of Specimen 2 was made, in view of the above,

but the results were not significantly different from those

first obtained.

Assuming that Specimen 3 , rather than Specimen 2 , properly represented alloy NX 9519 , the differences in conductivity of the three alloys are smaller than the uncertainties

in the conductivity results as indicated by the standard

deviations from the quadratic curves. If the tabulated conductivity values are taken as virtually comparable, the conductivity of the specimens appeared to increase slightly with

carbon content of the alloy, the increase being one percent

for an increase of carbon content from 0.02 percent to 0.11

percent according to the manufacturer’s composition data.

However, in viev; of the smallness of the differences, the

complexity of the allo^'-s, and the variations in their other

constituents, the conclusion must be that carbon content, in

the range covered, has little effect on the conductivity of

the alloy.

For each alloy, the conductivities obtained when the

first test of a specimen was made in the low temperature range

(see dashed curves of Figures 4 and 7 ; the same was true of

initial tests made on Specimen 2 ) were a few percent higher

than the values at the same mean temperatures obtained in tests

of the same specimen conducted at a higher range of temiperature

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or in the same low temperature range after tests had been

made at higher temperatures. When the first test of a

specimen was made in the intermediate or high temperature

range (see Figures 3> 5 and 6 ), all conductivities at the

lower mean temperatures were in good agreement. In the

case of Specimen S (NX 656 ). tested with the specimen reversed end-for-end (Figure ok) following the tests shown

in Figure 6 , the initial test, conducted at low temperatures,

yielded results in close agreement with those obtained in

later tests conducted at higher temperatures. Similarly^

the results obtained initially in a second series of tests

of Specimen 2 (NX 9519), shown in Figure 2, were not sensibly

different from those obtained in the later tests at higher

temperatures, although in the first series of tests of this

specimen the initial test, conducted at low temperatures

gave conductivities at lov/ temperatures 4 percent higher

than those obtained in later tests in this or the second

series,

A heat-treating effect on conductivity was therefore

observed consistently for each of the three alloys namely,

that when heated to only moderate temperatures, and for only

several hours, the metal had conductivities a few percent

higher than the more stable values that were obtained following longer exposure to similar temperatures, or heating to

moderately higher temperatures. The effect was obtained even

though the specimens, before submission, had been heat-treated,

as described earlier, at temperatures exceeding those reached

in these measurements. The effect is probably of little importance practically, but may be of considerable interest as

regards the nature of heat treatment effects on Inconel, which

could not be thoroughly explored within the scope of these

measurements ^

53.0

CENTIMETERS

T =1

0 5 10 15 20

CIRCULATING

COOLANT

RUBBER STOPPER

- OUTER

CONTAINER

GUARD CYLINDER

SPECIMEN (2-2.5 CM.

DIA.)

INSULATION

BAR HEATER

GUARD HEATER

SUPPORT CAP

SUPPORT PIN

NOTES

I. Dimensions in Centimeters.

2 X Indicates thermocouple positions.

APPARATUS FOR MEASURING THE THERMAL

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THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended hy Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

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