The D022 phase, as Ni3Nb, 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 D022

nucleated on the gamma prime cuboids with c axis of the

D022 perpendicular to the 100 faces of the gamma prime.
The situation is similar in the RSR 197 and RSR 209 except

that the D022 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

D022 Ni3Nb in which small smounts of Al substitute for the

Nb (Paulonis et al., 1969). Oblak et al. (1974) found

that certain D022 variants could be suppressed by

application of tensile and compressive loads. When a

tensile load of 69 Mn/m2 was applied parallel to the [100]

axis, the D022 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 D022 in the RSR 197 samples aged at 760 C. A

compressive stress along the [100] lead to precipitation

of the other two variants.