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aged for one hour there appears to be DO22 and possibly
(1, 1/2, 0) short range order. After aging at the highest
temperature for 100 hours, only SRO spots are present
after the quench. These SRO spots are also imageable.
Since the as-quenched microstructure contained D022>
the presence of DO22 in the material aged for one hour at
870 C might mean that the DO22 that had precipitated
during the quench was not fully in solution after one hour
at 870 C. The solvus for DO22 has been reported at about
800 C for an A1 containing ternary (Martin, 1982). It is
stable to at least 810 C in the RSR 197 alloy. In the
ternary alloy aged for one hour at 870 C and water
quenched, no reflections corresponding to SRO or DO22
phase were seen. Thus, the presence of SRO and DO22
phases in RSR 197 alloy air quenched from the aging
temperature is probably the result of precipitation from
solution during the air quench. The fact that in one
case, the one hour aging case, both SRO and DO22 form and
in the other, only SRO, implies that the gamma phase could
be depleting in Mo during high temperature aging which
would show that the Mo in the as-quenched and lower
temperature aged samples is supersaturated in the gamma
phase with respect to the equilibrium concentration. This
would be expected since no equilibrium Mo rich phases are
present in the alloys aged at lower temperature.