lattice fringes, the latter to Ni3Mo lattice fringes. At

the interfaces of these phases there is no discontinuity.

This is completely consistent with the type of stacking

that is possible with 420 phases where the two phases

share a common 420 plane. Only the stacking sequence

changes across the interface.

 Figure 5.13 is an image of the Dla phase in which

there is a small faulted region (Region A), most probably

of Ni3Mo. The crosshatched region is Ni4Mo. The lattice

fringes in the fault are from (l0 planes of an ordered

phase, either the L12 (001) plane or the D022 {0021

plane. The fringes are more likely from D022 since there

are no equivalent fringes in the gamma prime cube, the

areas at the top and bottom of the image.

 Figure 5.14 is a lattice image of the Dla precipitate

on the edge of four gamma prime cubes. This precipitate

covers the edge of all four cubes and grows into the

intergamma prime cuboid region along the cube faces of all

four cubes. This it can do readily without the

introduction of a stacking fault. The D022 phase, as

discussed in Section 5.4.1, would introduce high energy

perpendicular twin boundaries if it were to impinge at the

cube edges.