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5.1.4.3 Solution Heat Treated, Quenched and Aged at
 810 C for up to 100 Hours


 The aging behavior of this alloy at this temperature

is considerably less complex than that previously

described for the 760 C aging practice. The only NixMo

phase that forms during aging is the D022 Ni3Mo phase.

After one hour at 810 C, the DO22 phase is well

established, as shown in Figure 5.15a, a 1/4 (420), B =

[001] dark field image. After ten hours, the D022 has

coarsened considerably, as in Figure 5.15b. A B = <100>

diffraction pattern showing only DO22 is shown in Figure

5.15c. Though the dark field image should be sufficient

to establish the presence of this NixMo phase, the

diffraction pattern is shown to serve as an example of one

method used to differentiate among the L12 superlattice

reflections, overlapping DO22 superlattice reflections,

and diffuse (1, 1/2, 0) SRO reflections, all three of

which, as previously discussed in Section 2.3.3, are

difficult to differentiate from the diffraction pattern.

 The D022 and L12 (100) and (010) reflections which

would normally occupy the same reciprocal lattice

positions are split into two discreet and distinct

reflections that are easily differentiable when the g

vector is large. One of the two reflections is the L12

superlattice reflection. The other is the D022