stages of ordering. In this study the Ni2Mo existed as a

discreet phase, unlike the Ni2Mo in the Ni4Mo aging study,

which Das and Thomas (1974) presume occurred as the result

of the formation of a non-conservative AFB.

 Van Tendeloo et al. (1975) have summarized their work

on Ni-25% Mo alloys and the works of the others as

follows: at 800 C, the Ni3Mo ordering (decomposition)

follows the sequence FCC SRO D022 Ni4Mo/Ni2Mo HCP

- Ni3Mo orthorhombic. In their work, the D022 phase forms

only when the quench from solid solution is especially

fast. From this observation they presume that the D022

phase precedes the precipitation of both the Ni2Mo and

Ni4Mo phases, and further, that this DO22 precipitation

was not reported by any of the other previous

investigators because the alloys were not quenched fast

enough in the previous studies. Nevertheless, both the

work of Van Tendeloo et al. (1975) and the work of Das et

al. (1973) show that the stabilization of D022 at the

Ni3Mo stoichiometry is especially difficult.

 Ni-lO% Mo. The first work in an off stoichiometric

alloy was that of Spruiell and Stansbury (1965) who

proposed to have found SRO in their x-ray study of

quenched Ni-10% Mo. The diffuse maxima they detected at

(1, 1/2, 0) positions were retained for aging times of up
to 100 hours at a temperature of 450 C, and though these

maxima sharpened with time, no superlattice ever

developed.