5.1.7.3 RSR 197 -- Solution Heat Treated, Quenched,
 and aged at 870 C for 1 Hour, Furnace
 Cooled to 760 C and Aged for 100 Hours
 at 760 C.

 Even after aging at 870 C for one hour, the D022 and

Dla phases readily form when aged at a lower temperature.

The dark field images shown in Figures 5.29a and 5.29b are

B = [001] dark field images taken using both 1/4(420)

(Figure 5.29a) and 1/5(420) (Figure 5.29b) reflections.

5.1.7.4 RSR 185 -- Solution Heat Treated at 1315 C
 and Water Quenched

 The sample was only used to measure the gamma matrix

lattice parameter using the CBED technique. The sample

was chosen because it was water quenched from the solution

heat treatment temperature and consequently showed only

very weak (1, 1/2, 0) SRO reflections. A B = <114> CBED

pattern from the RSR 185 gamma phase is shown in Figures

5.30a and 5.30b. There is no asymmetry in the central

spot of the pattern shown in Figue 5.30a. Note the

absence of 110 superlattice reflections in Figure 5.30b.

 5.2 X-Ray Diffraction Measurements

 The gamma prime and gamma lattice parameters, as

measured by x-ray diffraction, are listed in Table 5.1.

The gamma prime lattice parameter is consistently larger

in the Ta containing alloy, the RSR 197 alloy, than