are possible in Ni4Mo. They would be similar in all Dla

structures. They are 1) translational antiphase

boundaries (TAPB), 2) antiparallel twin boundaries (ATB),

and 3) perpendicular twin boundaries (PT).

 A translation APB results when the domains have

parallel axes but the origins are shifted by a lattice

translation vector. Figure 2.10 shows one of four

possible TAPB in Ni4x. The lattice translation vector is

1/5 [130]. The other three vectors are 1/5 [210], 1/10

[135], and 1/10 [3T5].

 The antiparallel twin boundary results when two

contiguous domains have their tetrad axes antiparallel.

The possible twinning planes are of the type 200, 020, and

270, relative to the parent lattice. An APT boundary with

200 twinning plane is shown in Figure 2.11.

 A perpendicular twin results when the c axis of the

ordered domains aligns with two different axes of the FCC

cube. The lattices are not continuous across the

interface, unlike the other two boundaries. This occurs

in Ni4x because c/c' is not an integer (see Section

2.2.1.2). Combinations of all three interfaces are

possible.

2.2.3.2 Ni3x (D022)

 The D022 phase can form twelve variants. The c axis

of the crystal may lie along any one of the FCC cube

axes.