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National Advisory Committee for Aeronautics, Technical Notes - Effects of an Aging Treatment on Life of Small Cast Vitallium Gas Turbine Blades

An investigation was conducted to determine the effects of
an aging treatment on the life of small cast Vitallium gas-turbine
blades operated at a blade temperature of approximately 1500° F
and a stress of 20,000 pounds per square inch at the blade-failure
plane. Twenty blades that were aged for 48 hours at 15000 F were
compared with 35 unaged blades.

Aging, which has been reported to harden cast Vitallium and -
to improve stress-rupture life, apparently improved the time for
initial blade failure, the average life, and the uniformity of
life of the blades used in this investigation. The lives of the
last blades to fail were not appreciably affected by the aging
treatment. Statistical analysis of the blade -life data did not
indicate a significant improvement in mean life or uniformity of
life of the blades. This fact, however, does not necessarily prove
that aging is without beneficial effects, but rather indicates that
further investigation is desirable to obtain more conclusive results.

A comparison of the lives of unaged Vitallium blades with stress-
rupture data for cast Vitallium bars evaluated at substantially the
same conditions indicated a relation between stress-rupture life and
blade life.

Both samples were progressively hardened by precipitation
during operation. After about 55 hours of operation, they were at
the same hardness, which increased slightly thereafter.

A possible method of improving the times for initial failure
of gas-turbine blades is heat treatment of the material in order
to increase the average life, unifomity of life, or both. Investi-
gation of the effects of aging certain high-temperature alloys has
shown that in several instances improved stress-rupture properties
may be obtained by such treatment (reference 1) . Cast Vitallium,
an alloy currently used as a. turbine-blade material, has shown
appreciable improvement in stress-rupture strength when aged
(reference 1) . Aging strengthens the alloy structure through the
fomation of a precipitate in the crystal matrix.