Figure 5.31a is a B = <114> CBED pattern from the

gamma phase in the RSR 197 as solution heat treated and

quenched sample. The gamma phase contains a very fine

distribution of the D022 precipitate, as described in

Section 5.1.2. The pattern represents either diffraction

from the gamma phase strained due to the influence of the

D022, or from the D022 itself. There would be no

superlattice from the DO22 in the zero order zone, and

hence no {110) reflections. None were observed.

 The pattern in Figure 5.31a was taken from an

intercuboidal area such that the gamma lattice can be

shown to be expanded in the direction of the c axis of the

D022 phase. This direction is perpendicular to a (100)
face of the gamma prime.

 The a/b ratio used to measure the lattice parameters

in the gamma prime phase can still be used to measure the

lattice parameters from this assymetric pattern. The

values of a/b will be negative (see Appendix A) because of

the line shift algorithm used for the calculation. The

ratio is negative when the intersection of the 193 and 391

lines crosses the 10 0 2 line. This pattern has an R1

value of -5.3 and an R2 value of 0.5. The lattice

parameters corresponding to these R values are a = 3.575

Angstroms and b = 3.645 Angstroms, assuming that c = 3.575

Angstroms. The FCC c axis here is parallel to the beam.