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The DC>22 phase, as Ni^Nb, has been observed in
preferential orientation with gamma prime phase in other
alloy systems (Cozar and Pineau, 1973). In the Inconel
(In) 718 type alloys that they characterized, the DO22
nucleated on the gamma prime cuboids with c axis of the
DO22 perpendicular to the 100 faces of the gamma prime.
The situation is similar in the R.SR 197 and RSR 209 except
that the DO22 does not nucleate on the gamma prime. It
nucleates throughout the intercuboidal gamma matrix, as
shown in Section 5.4.
Oblak et al. (1974) studied the aging, under tensile
and compressive stresses, of single 100 crystals of In
718. The primary strengthening phase in this alloy is
DO22 Ni3Nb in which small smounts of Al substitute for the
Nb (Paulonis et al., 1969). Oblak et al. (1974) found
that certain DO22 variants could be suppressed by
application of tensile and compressive loads. When a
tensile load of 69 Mn/m^ was applied parallel to the [100]
axis, the DO22 variant with c axis parallel to the stress
axis was observed. The morphology of the DO22 in this
alloy is an ellipsoidal plate with the c axis
perpendicular to the plate axis, clearly different from
the DO22 in the RSR 197 samples aged at 760 C. A
compressive stress along the [100] lead to precipitation
of the other two variants.