Figure 2.9a, with lattice constants a' = 2.588 Angstroms,

b' = 7.674 Angstroms, and c' = 3.618 Angstroms. It is

again best described in relation to the FCC lattice. Here

the stacking sequence is 420 planes of Mo separated by two

420 planes of Ni. This stacking is shown in Figure 2.9b.

The Pt2Mo phase is stable in the Ni-V system (Tanner,

1972).

2.2.1.4 NiMo

 The equilibrium delta NiMo phase is orthorhombic with

 lattice constants a = 9.107 Angstroms, b = 9.107

 Angstroms, and c = 8.852 Angstroms (Shoemaker and

 Shoemaker, 1963; Shoemaker et al., 1960). This phase has

 deleterious effects on the mechanical behavior of Ni-Mo-Al

 superalloys (its crystal structure is very similar to

 structures for the embrittling sigma phases) and the

 conditions under which it will form in ternary and higher

 order alloys should be more extensively studied now that

 its deleterious effect on mechanical properties is better

 understood.

 2.2.2 Ni-W

 According to the published phase diagram shown in

 Figure 2.3, a NiW alloy of Ni4W stoichiometry cannot be

 put into solid solution. However, a NiW alloy of 20 at.%

 W or less quenched from above the peritectoid reaction

 temperature and subsequently aged below this temperature