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 Ni3Mo. 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 D022 phase in binary Ni-25%

 alloys. In aged ternary alloys containing 2 at.% and less

 Ta, no D022 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 D022 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 D022 are presumed therefore to

 be V, Fe, and Co, even though Ni3V as D022 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 Ni3Mo 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