3
disordered FCC nickel and can contain numerous elements in
solution. Secondly, there are incoherent precipitates
which can include the carbides, nitrides, and Ni bearing
phases, phases like sigma phase (Sims and Hagel, 1972).
Thirdly, there are the coherent phases which are normally
ordered superlattices of the disordered FCC matrix. The
major FCC ordered phase in such Ni-Al alloys is N3AI, an
Ll2 superlattice also known as gamma prime. This is
normally the strengthening phase in Ni-Al alloys. When
refractory metals are added to Ni-Al alloys, other
coherent phases can also be present as either the minor
precipitate or as the major strengthening precipitate,
e.g., DO22 phase in In 718 (Quist et al., 1971; Cozar and
Pineau, 1973).
Alloys under development at Pratt and Whitney
Government Products Division in West Palm Beach, Florida,
are also based on the Ni-Al system. They are similar to
the ternary alloy WAZ-20-Ds (Sims and Hagel, 1972), but
additionally contain small quaternary additions of Ta and
W. A host of unforeseen solid state reactions proceeds
during low temperature heat treating of the Pratt and
Whitney superalloys (Aigeltinger and Kersker, 1981;
Aigeltinger, Kersker, and Hren, 1979). These reactions
are very similar to those in the Ni-Mo binary system.
Much effort in studying Ni rich, Ni-Mo binary alloys has
been devoted to describing the transition from the