Precipitation in nickel-rich Ni–Al–Mo ternary alloys in the temperature range from 873 to 1373 K has been investigated by transmission electron microscopy, selected area electron diffraction and hardness measurements. Various stable and metastable phases, γ′, NiMo(δ), Ni2Mo, D022–Ni3Mo and Ni4Mo, and short range order (SRO) are formed during ageing depending on the alloy composition and ageing temperature. Constitutional diagrams showing the fileds in which each precipitate forms are presented. The γ+γ′ two phase region extends to the lower Al region at low temperatures. Ni2Mo, D022–Ni3Mo and SRO form in the alloys of a wide compositional range. Ellipsoidal or polyhedral Ni2Mo, plate-like Mo and cuboidal γ′ are considered to be important in strengthening the Ni–Al–Mo ternary alloys. Precipitation of globular δ phase occurs at high temperatures only in the alloys with high Mo content.
