The precipitation behavior of η phase with lamellar morphology in a newly designed K439B nickel-based superalloy

The microstructure of nickel-based superalloys significantly influences their mechanical properties and performance. The precipitation behavior of η phase during heat treatment of a newly designed K439B superalloy was studied. The results demonstrate that the precipitation temperature of η phase in this alloy varies from 1040 to 1070 °C. A detailed analysis of the microstructure indicates that the η phase exhibits a ~10nm lamellar structure, unlike the needle-like form reported in previous research. The γ' phase is distributed on both sides of the η phase, and the Ti content in the η phase is higher than that in the γ' phase, although the content of Al and Ti in the η and γ' phases are higher than that in the matrix γ phase. Moreover, the γ′ phase demonstrates an orientation relationship of {111}γ||{0001}η and [110]γ/γ′||[11—20]η with the η phase. This study can be used as reference for heat treatment process design and optimization.