Martin (1982) has studied the nucleation of the D022

phase. (Mishra (1979), Chevalier and Stobbs (1979), and

Nesbit and Laughlin (1978) studied nucleation in NiMo

binaries using electron microscopy, but were only able to

study the nucleation of Ni4Mo Dla and Ni2Mo Pt2Mo. The

D022 is not stable in the binary alloy.) In Martin's

Ni4Mo Al containing ternary (this ternary does not contain

gamma prime), the DO22 and Pt2Mo were shown to form more

or less simultaneously when aged at 600 C. The Dla formed

sluggishly and was present after 2000 hours. The D022 and

Pt2Mo were still present after this long aging time.

Pt2Mo was the predominant phase, very similar to alloy RSR
209.

 In the RSR 197 alloy, the D022 phase nucleates during

the slow quench from solution heat treatment temperature.

The streaks that appear to emanate from the D022

reflections towards the Dla reciprocal lattice positions

shown in Figure 5.3a could be better described as

emanating from Ni4Mo nodes. This would imply that the

Ni4Mo Dla has formed as very thin platelets, possibly as

faults in the Ni3Mo crystal structure. This could be

determined by lattice imaging. Figure 5.3c shows both the

D022 phase and the bright faults that would correspond to
the Ni4Mo.

 In the RSR 197 alloy quenched and aged at 870 C, two

(1, 1/2, 0) microstructures have formed. In the sample