140
It is possible to form an image using a (1, 1/2, 0)
reflection, as shown in Figure 5.19b. Figure 5.19a is a B
= <^100^> microdiffraction pattern showing only gamma prime
and short range order (1, 1/2, 0) reflections. As after
one hour aging, an interfacial dislocation network is
present, as shown in Figure 5.18b.
5.1.4.5 Aging Summary -- RSR 197
At 760 C, all three NixMo metastable phases form and
coarsen with time. The N3M0 DO22 and N4M0 Dla phases
predominate. After one hundred hours, the matrix has
become highly ordered, the DO22 and Dla phase essentially
filling the intercuboidal regions. These two phases are
crystallographically related. Aging at 810 C produces
only DO22 precipitate. This precipitate coarsens and
eventually fills the intercuboidal regions. At 870 C, no
metastable phase forms during aging. An interfacial
dislocation network forms, apparently very rapidly since
it is present after only one hour at temperature.
The equilibrium NiMo phase may be present at all
aging temperatures. At the two lower aging temperatures,
it is usually found decorating the grain boundaries,
usually in regions contiguous to the cellular
intergranular gamma prime. At the highest aging
temperature, the NiMo forms throughout the grains.