The Ni4Mo and Ni3Mo phases are the result of solid-solid

transformations. There is no true order-disorder

transition temperature for either of them. The Ni4Mo

phase is formed by a peritectoid reaction between gamma

and Ni3Mo: gamma + Ni3Mo <> Ni4Mo, at 875 C. The Ni3Mo

phase also forms by peritectoid reaction at 910 C; gamma +

NiMo 0=) Ni3Mo. Above 900 C an alloy of composition Ni4Mo

will be wholly in the gamma disordered FCC region. An

alloy of Ni3Mo stoichiometry will be a solid solution

above 1135 C.

2.1.1.2 Ni-Al

 Figure 2.2 is the equilibrium diagram for the Ni-Al

system (Hansen, 1958). This diagram has been more

recently confirmed by Taylor and Doyle (1972). Two phases

exist on the Ni rich side of the diagram. They are AlNi,

a congruently melting compound, and Ni3Al, an ordered L12

superlattice phase commonly referred to as gamma prime.

Gamma prime is formed eutectically with gamma (solid

solution Ni and Al) at 1385 C. No solid state reactions

occur in this system at lower temperatures.

2.1.1.3 Ni-W

 The Ni-W binary diagram as modified by Walsh and

Donachie (1973) is shown in Figure 2.3 (Moffatt, 1977).

The modified diagram includes the intermetallics NiW and

NiW2.