134
superlattice reflection. When the (1, 1/2, 0) reflections
are the result of the SRO, there will be no splitting of
the LI2 spots, since there is no overlapping spot (there
is no SRO superlattice spot at LI2 superlattice positions)
and no shifts in the positions of the (1, 1/2, 0)
reflections, as discussed in Section 5.3, for DO22
reflections. These shifts are discussed in Kersker et al.
(1980) .
After 100 hours, the DO22 phase is still present and
seems to fill most of the intercuboidal gamma prime
regions. The morphology of the DO22 after 100 hours at
this temperature is not similar to that after 100 hours at
760 C. Figure 5.15d is a B = [001], g = 1/4 (420) dark

field of the DO22 after 100 hours at 810 C.
In addition to the D022> the gamma prime, and
presumably the gamma phase, there is an additional phase
present at the interface between the grain boundaries and
the coarsened gamma prime that decorates these
boundaries. Its diffraction pattern was not recorded. It
is probably NiMo.
5.1.4.4 Solution Heat Treated, Quenched and Aged at
870 C for up to 100 Hours
One of the more noticeable features of the high
temperature aged RSR 197 is the development, after one
hours heat treatment, of an ordered dislocation array at