Relation of engine turbine-blade life to stress-rupture properties of the alloys, Stellite 21, Hastelloy B, Cast S-816, Forged S-816, X-40, Nimonic 80, Refractory 26, N-155, and Iconel X Page: 4 of 61

                                
NACA RM E51G13

through a slip-ring pickup mounted on the front of the engine. The
slip-ring pickup circuit for measuring the temperature is described in
reference 3. In order to prevent failure of these blades because of the
weakening effect of the hole drilled for the thermocouple, the airfoil
section was reduced to one-half the original length to reduce centrifugal
stresses in the weakened portion. The thermocouple mounted in the blade
is shown in figure 1. The junction of the thermocouple is located
2 inches above the base of the half blades or at the midpoint of a full-
length blade. This region is the zone of maximum blade temperature
(reference 3). In order to relate the temperature of the half blade to
the temperature of a full-length blade, a preliminary investigation was
conducted in which temperature measurements were made 2 inches from the
base of both half and full-length blades. The results of this survey
indicated that at rated speed (11,500 rpm) the temperature of the full-
length blade was approximately 250 F higher than that of the half blade.
Turbine blades. - The blade alloys investigated and their chemical
compositions are listed in table I. Turbine blades were fabricated from
these alloys by commerical methods. The blades were given the following
commercial heat-treatments by the fabricator:

Alloy               Heat treatment
Stellite 21      None
Hastelloy B      2 hr at 19000 F, air cooled;
4 hr at 15000 F, air cooled
Cast S-816       None
Forged S-816     1 hr at 21500 F, air cooled;
16 hr at 14000 F, air cooled
X-4O             None
Nimonic 80       8 hr at 19250 F, air cooled;
16 hr at 1300 F., air cooled
Refractaloy 26   1 hr at 21000 F, air cooled;
20 hr at 15000 F, air cooled;
20 hr at 13500 F, air cooled
N-155            1 hr at 22500 F, air cooled;
20 hr at 13500 F, air cooled
Inconel X        2 hr at 21000 F, air cooled;
24 hr at 15500 F, air cooled;
20 hr at 13000 F, air cooled

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