Microstructural characterization of three different size of gamma prime precipitates in Rene 65

Cast and wrought Ni-based superalloy Rene 65 was developed for turbine engine components applications. In the as-extruded condition the alloy presents trimodal distribution of gamma prime (γ′) precipitates. A detailed microstructural and chemical characterization of the precipitates is presented at a near atomic-scale before and after a softening sub-solvus heat treatment. Scanning and Transmission Electron Microscopy (SEM and TEM) as well as Atom Probe Tomography (APT) were employed to identify the differences in compositions. In the as received condition differences in Cr, Ti and Al content were found between the three precipitate sizes. After a softening sub-solvus heat treatment, the interface between secondary and grown tertiary γ′ with the matrix had become chemically homogenized. Lattice mismatch of secondary and tertiary γ′ were empirically calculated based on the APT compositions. •As-extruded Rene 65 samples were characterised by SEM/TEM and A PT before and after a softening heat treatment.•In the as extruded condition,γ’(I) and γ'(ΙΙ) have higher Ti than Al, whereas γ’(ΙΙΙ) has higher Al. This increases the mismatch of γ’(ΙΙ) with the matrix and its lattice parameter.•Smaller tertiary precipitates were richer in γ forming elements indicating a lower formation temperature.•After heat treatment, Ti increased in γ′(ΙΙ) and a homogenous precipitate-matrix interface is developed.