superlattice reflection. When the (1, 1/2, 0) reflections

are the result of the SRO, there will be no splitting of

the L12 spots, since there is no overlapping spot (there

is no SRO superlattice spot at L12 superlattice positions)

and no shifts in the positions of the (1, 1/2, 0)

reflections, as discussed in Section 5.3, for D022

reflections. These shifts are discussed in Kersker et al.

(1980).

 After 100 hours, the D022 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 D022 after 100 hours at 810 C.

 In addition to the DO22, 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