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lattice fringes, the latter to N3M0 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 N3M0. The crosshatched region is N4M0. The lattice
fringes in the fault are from {l00} planes of an ordered
phase, either the LI2 {OOl} plane or the DO22 {002}
plane. The fringes are more likely from DO22 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 DO22 phase, as
discussed in Section 5.4.1, would introduce high energy
perpendicular twin boundaries if it were to impinge at the
cube edges.