Investigation on solution heat treatment response and γ′ solvus temperature of a Mo-rich second generation Ni based single crystal superalloy

A multi-step solution heat treatment regime of a Mo-rich Ni based single crystal superalloy (Alloy Mo) was designed, and the effect of each solution heat treatment step on microstructure, microsegregation degree and phase transformation characteristic temperatures of Alloy Mo was investigated by experimental analysis and dynamic calculation (via DICTRA). Homogenizations of microstructure and Re element in as-cast Alloy Mo were obtained via first step solution heat treatment (lowest temperature and shortest time) and last step solution heat treatment (highest temperature and longest time), respectively. In addition, appropriate diffusion length for dynamic calculation of homogenization of Re element was determined. Meanwhile, solution heat treatment increased the solidus temperature of as-cast Alloy Mo, while it had less effect on liquidus temperature and γ′ solvus temperature. Moreover, as compared with W-rich single crystal superalloys, effects of solution heat treatment on both solidus temperature and γ′ solvus temperature of Mo-rich single crystal superalloy were lower. Additionally, γ′ solvus temperatures of Mo-rich single crystal superalloys were lower than those of W-rich single crystal superalloys.