in binary alloys can these differences be accurately and

unambiguously determined. Nevertheless, there are some

generalizations that can be stated regarding the lattice

parameter measurements and the partitioning effects in the

RSR alloys. First, the lattice mismatch as measured by

x-ray diffraction between the gamma and gamma prime phases

is greater in the RSR 209 alloy than in the RSR 197

alloy. In both alloys, the gamma phase lattice parameter

is greater than the gamma prime lattice parameter. The

high Mo content in both alloys is responsible for this

effect. In the Ta containing alloy, RSR 197, the gamma

prime phase has a larger lattice parameter than the gamma

prime phase in RSR 209. One interpretation of these

observations is that the Ta, which substitutes readily for

Al in the gamma prime phase, is the factor that increases

the lattice parameter of the gamma prime in RSR 197. Nash

and West (1979) report that about 8% Ta will increase the

lattice parameter of gamma prime to about 3.59 Angstroms.

The comparable unalloyed Ni3Al lattice parameter is about

3.57 Angstroms. The EDS data supports this Ta

partitioning hypothesis since it was clearly shown that

the Ta partitions predominantly to the gamma prime phase

in RSR 197 under all the aging conditions in which it was

measured. Thus, the local measurement of the gamma prime

lattice parameter using the convergent beam technique can

show the elemental partitioning differences in a