Precipitation of the Gamma Prime Phase in a Ni-Co-Based Superalloy during Different Stages of Cooling

Abstract

The cooling precipitation of the gamma primary (γ′) phase in a precipitation strengthened Ni-Co-base disk superalloy was investigated by various experimental and analytical methods. The alloy was super-solvus heat treated and then slow cooled to different interrupted temperatures (IT) followed by instant water quenching. It showed that with the IT change, the γ′ phase precipitated in different characteristics, such as morphologies, sizes and distributions. Through using three-dimensional atomic probe (3DAP) technique to study the γ and γ′ compositions and their interface composition profiles, three types of γ′ precipitations, entitled as quenching γ′, primary cooling γ′ and secondary cooling γ′, were identified and their respective precipitation process during cooling was discussed.