The Ni₃Al-Ni₃Cr-Ni₃Mo section of the Ni-Cr-Al-Mo system

Abstract

An investigation is reported of the constitution of the 75 at % nickel section of the Ni-Cr-Al-Mo system in the temperature range 1523 to 1073 K. Alloys in the region 10 to 20 at % Al were annealed at 1523, 1273, and 1073 K, respectively, and subjected to electron microprobe analysis, X-ray diffraction, and microscopical and hardness examination. Constitutional data are presented as partial isothermal sections and as vertical sections. At 1523 K the section consists only of fields containing γ′,γ′+γ and γ, the last mentioned phase being predominant. With decreasing temperature the γ′ and γ′+γ fields increase in extent. Also, the NiMo and Ni₃Mo phases were encountered in the ternary Ni-Al-Mo alloy studied. The quaternary γ+γ′ alloys showed small lattice mismatch values, i.e. up to ∼0.25%. Raft like morphologies of γ′ were found in the quaternary alloys, resulting from directional coarsening. Observations of as-cast structures are also reported.