9
The N4M0 and N3M0 phases are the result of solid-solid
transformations. There is no true order-disorder
transition temperature for either of them. The N4M0
phase is formed by a peritectoid reaction between gamma
and N3M0: gamma + N3M0 ^=)> N4M0, at 875 C. The N3M0
phase also forms by peritectoid reaction at 910 C; gamma +
NiMo <^=^> N3M0. Above 900 C an alloy of composition N4M0
will be wholly in the gamma disordered FCC region. An
alloy of N3M0 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 AINi,
a congruently melting compound, and N3AI, an ordered LI2
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