presence of the ternary phase Ni6TaAl, and also NigTa.

The former phase is hexagonal and is not isostructural

with any Ni-Mo-Al phase. According to their 1000 C

section, Ta can substitute for Al up to 8.0 at.% in gamma

prime (Ni3Al). It is soluble to approximately 10.0 at.%

at 1250 C.


2.1.2.3 Ni-Al-W


 This diagram has been recently determined by Nash et

al. (1983). A 1250 C isotherm from their work is shown in

Figure 2.6. No ternary phase is shown in the isotherm,

nor is a ternary phase reported at temperatures as low as

1000 C. The diagram is qualitatively very similar to the

Ni-Mo-Al ternary diagram shown in Figure 2.5b.


 2.2 Binary Phases

2.2.1 Ni-Mo

 In addition to the equilibrium phases mentioned in

the previous section, there are intermediate metastable

phases that can precipitate from Ni rich solutions of

Ni-Mo binaries. The practical limit of Mo solubility in

Ni is about 27 atomic percent. Molybdenum in excess of

this amount cannot be put into solution. If a Ni-Mo

binary of 27.0 at.% or less Mo is quenched from a

temperature high enough for the alloy to have been a