132 5.1.4.3 Solution Heat Treated, Quenched and Aged at 810 C for up to 1UU 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 DO22 N3M0 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 DO22 has coarsened considerably, as in Figure 5.15b. A B = 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 LI2 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 DO22 and LI2 (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 LI2 superlattice reflection. The other is the DO22