Partitioning behavior and lattice misfit of γ/γ′ phases in Ni-based superalloys with different Mo additions

A low-density single crystal (LDS) alloy with the composition of high Mo content was designed. The extra 1.5 wt% Mo was added in the Alloy A with the composition of Ni–6.5Al–8.0Mo–2.4Cr–6.2Ta–4.9Co–1.5Re–(0.01–0.05)Y (wt%) to study the influence of Mo on the lattice parameter and partitioning behavior. Scanning electron microscope (SEM) with energy-dispersive spectrometer (EDS), transmission electron microscopy (TEM) and high-temperature X-ray diffraction (HT-XRD) were used to observe the microstructure, analyze the elemental content and measure the lattice parameter of the alloys. The natural lattice misfit was calculated by lattice constants which were measured by HT-XRD at the temperature from 25 to 1150 °C, and the results showed that the lattice misfit would be more and more negative with temperature increasing. It was found that 1.5 wt% addition of Mo will increase the absolute value of the lattice misfit of γ/γ′ phases and the volume fraction of γ′, and at the same time, influence the elemental distribution in γ and γ′ phases, especially Re and Cr. Re has a higher partitioning ratio (k) after the addition of Mo.