ORNL-1771 - Oak Ridge National Laboratory

alloys for use in fabricating the radiator, ond the
fabrication of radiators for service testing.
Investigations of Fin Materials
J. H. Coobs H. lnouye
Meta I I urgy Division
Stress-rupture and creep tests of type-310 stain-
less-steel-clad copper fins that were 8 mils thick
were made at 1500°F at stresses between 500 and
2000 psi. The material was obtained from the
General Plate Div. of Metals & Controls Corp. and
had an average cladding thickness of 1.87 mils per
side. The maximum cladding thickness was 2.3
mils per side. The results of the several tests
mode show that some alteration of the copper OC-
curs even though the specimen does not fracture.
This was indicated by the brittleness of the normally
ductile composite. For long-time exposures (1000
hours), stresses greater than 500 psi and less than
1000 psi are tolerable and there is no indication of
brittleness in the core or oxidation due to cladding
failure. In all the specimens which ruptured, oxi-
dation of the copper at the point ot fracture was
complete, and the copper which did not appear to
be oxidized was brittle. It was also noted that
when the strain in 2.5 in. was lo%, the copper re-
mained ductile, while strains above 20% (regardless
of exposure time) produced brittleness. The data
obtained are given in Table 7.1.
The aluminum bronzes are among the materials
being considered as cladding for copper fins. Al-
though extensive diffusion occurs between these
alloys and copper, increases in the thermal con-
ductivity of the fin can be realized by cladding the
copper with these alloys. The composition gradient
existing in a diffused composite results in an in-
crease in the conductivity of the cladding material
(because of the outward diffusion of aluminum) and
a decrease in the conductivity of the copper core.
Thermal conductivity measurements of two alumi-
num bronzes were made by the Solid State Division
and are reported in Table 7.2. The values given
for measurements at temperatures up to 392°F com-
pare favorably with the datu of Smith and Palmer,2
but for temperatures above 392°F they exceed the
values extrapolated from their data. Also, the
2C. S. Smith and E. W. Palmer, Am. Inst. Mining Met.
Engrs., Metals Technol. Tech. Pub. No. 648, 1-21
( 1935).
PERIOD ENDING SEPTEMBER IO, 1954
TABLE 7.1. STRESSRUPTURE PROPERTIES OF
TYP E-310 STAINLESLSTE EL-CLAD
COPPER FINS AT 15OO0F
&mil cladding on each side of 4-mil copper sheet
Rupture Elongation
Stress
Time in 2.5 in. Remarks
(Psi) (hF)
(%I
2000
1800
1650
1500
1400
1000
1000
5 00
500
96
336
52 8
887
1220
39 Capper embrittled
50 Copper embri ttled
40 Copper embrittled
Copper embrittled
In progress
27.5 Test terminated at 1000
hr; specimen oxidized
throughout
20 Test terminated at 500 hr;
oxide stringers on
surface of specimen
10 Test terminated at 1000
hr; no indication of
failure
5 Test terminated at 500 hr;
no indication of failure
TABLE 7.2. THERMAL CONDUCTIVITY OF
ALUMINUM f3RONZESATVARlOUS TEMPERATURES
Temperature
The rma I Conductivity
[col/sec.cm2 ("C/C"S1
.................................................
(OF) For For
6.2% A1-93.8% Cu 8.4% AI-91.6% Cu
.......... ~
212 0.178 0.176
30 2 0.240 0.210
3 92 0.280 0.250
1156 0.55
1562 0.77
estimated value of six times the thermal conductivity
of stainless steel at 1500°F was exce=ded by the
experimental value for the &2% AI-93.8% Cu alloy,
The values given in Table 7.2 were not corrected
for the volume expansion of the alloy with temper-
ature and are therefore accurate only to within
*5%.
117