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2.2.5.2 Ternary Alloys
Yamamoto et al. (1970) studied the effects on the
precipitation behavior of the NixMo of small ternary
additions of Ta to stoichiometric N3M0. They found that
the DO22 phase was formed in the alloy containing 5 at.%
Ta. Van Tendeloo et al. (1975) and Das et al. (1973) were
not able to stabilize the DO22 phase in binary Ni-25%
alloys. In aged ternary alloys containing 2 at.% and less
Ta, no DO22 phase was detected. The diffuse scattering at
the (1, 1/2, 0) positions in electron diffraction patterns
was characteristically present, but no DO22 superlattice
spots developed during aging. They speculate that other
elements might stabilize DO22 phase, for example, Ti and
Nb. These are similar to Ta in that the atomic radius of
each is larger than the atomic radius of the Mo. Elements
which might not stabilize DO22 are presumed therefore to
be V, Fe, and Co, even though N3V as DO22 is the stable
precipitate in the Ni-V system (Section 2.2.1.2). These
atoms are of smaller atomic radius than Mo. No evidence
is offered to support these speculations.
Martin (1982) has recently studied the effects of
additions of Al, Ta, and W to N3M0 stoichiometric alloys
on the nucleation and growth of NixMo metastable phases.
His explanations for the precipitation of phases in these
alloys follow closely those of deFontaine (1975), deRidder
et al. (1976), Chevalier and Stobbs (1979), and