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National Advisory Committee for Aeronautics, Technical Notes - Investigation of Nickel-Aluminum Alloys Containing from 14 to 34 Percent Aluminum

As part of a study of the properties of intermetallics, an inves—
tigation was made of nickel-aluminum alloys which were from 14 to 54
percent aluminum by weight. It is in this range that the Ni3Al and NiAl
intermetallics are found. These alloys were prepared by casting. As
the aluminum content was increased, more difficulty was encountered in
the preparation of sound, nonporous castings, apparently because of the
increasingly exothermic nature of the reaction between the nickel and
the aluminum. However, except for the alloys containing 54 percent
aluminum and the stoichiometric NiAl (51.5 percent Al), all castings
were sound and free from excessive porosity.

The NisAl intermetallic compound had a room-temperature tensile
strength of 48,450 pounds per square inch with 2.5- to 6.5-percent
elongation. The NiAl cast alloys whose strength properties were de-
termined ranged in composition from 25 to 50 percent aluminum. The
maximum room-temperature tensile strength was 24,100 pounds per
square inch for the 25—percent—aluminum alloy.

A mixture of phases NisAl and NiAl occurred in the 17.5-percent-
aluminum alloy. Of those investigated, this alloy had the most out-
standing properties and was studied in greatest detail. The strength.of
the as-cast 17.5—percent-aluminum alloy at room temperature was 79,600
pounds per square inch with l.2-percent elongation. At 15000 F, the
tensile strength was 50,000 pounds per square inch. The 17.5-percent-
aluminum alloy was readily rollable at 24000 F, resisted thermal shock,
possessed outstanding oxidation resistance, and had a moderate impact
strength. In creep—rupture at 15500 F, the lOO—hour strength was 14,000
pounds per square inch. Compared with conventional high—temperature
alloys, creep rates for this alloy were high. The effect of thermal
treatment on microstructure was determined. It was found that a
martensite-like transformation takes place during cooling at tempera-
tures of 22000 F and above. The martensite-like transformation may be
very useful for precipitationrhardening of the alloy.