provide an adequate match. They used the B = (111>

pattern to make these measurements. This pattern is a

simple one to analyze because of the threefold symmetry in

the ZOLZ transmitted disc. This pattern could not be used

in the study of the Pratt and Whitney alloys, however,

because of the microstructural scale in these alloys.

When the sample is in a B = (11) orientation, the gamma

prime precipitates usually overlap either the gamma phase

or the gamma phase and another gamma prime precipitate.

The result is either a highly distorted HOLZ pattern or no

pattern at all. If B = (114>, the beam is more closely

parallel to the 100 direction; 19 degrees from the B =

(100> direction. Eades (1977) used this orientation to

study the gamma/gamma prime mismatch in In-100, a Ni-based

superalloy. The B = (114> CBED pattern can be used to

measure both lattice parameter and noncubicity. The

method is outlined in Appendix A.

 The B = <111> pattern has been used recently by

Braski (1982) and by Lin (1984) to measure lattice

parameter change in ordered alloys. In both cases, the

microscope accelerating voltage was continuously variable,

meaning that the HOLZ line positions in these patterns

could be varied. Because the B = 111) pattern in a cubic

material always exhibits either sixfold or threefold

symmetry, it is always possible to find three FOLZ lines

that can be made to pass directly through the center of a

CBED pattern, and hence intersect at a point in the