Precipitates in Nickel-rich Ni–Al–Mo Ternary Alloys

抄録

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.