Precipitation And Growth Behavior Of Gamma ' Phase In Ni3al-Based Superalloy Under Thermal Exposure

Precipitation and growth behavior of gamma ' (Ni3Al) phase are crucial to evaluate the service stability of superalloys. In this work, precipitation and growth mechanisms of gamma ' phase in different areas of a newly designed Ni3Al-based superalloy were investigated under short-term thermal exposure conditions. Results showed that twinning gamma ' phase and foliated gamma ' phase precipitated in eutectic area and interface area, respectively. gamma ' phase went through from sphere to precursor plate and plate twinning eventually in eutectic area, which was related to preferred orientation of gamma ' phase and local segregation of Al element. Dislocation and sidestep interface between matrix and the precipitation were the main reasons for the formation of twinning gamma ' phase. Meanwhile, the morphology of gamma ' phases in interface area went through a process from sphere to rod-like, and foliated gamma ' phases formed eventually which grew toward eutectic areas with thermal exposure time increasing. Vacancies, distortions caused by different thermal expansion coefficients, lattice mismatch between dual-phase area and eutectic area contributed to the formation and growth of spherical phase. Moreover, reduction in interface energy promoted the transformation of spherical phase to rod-like and foliated gamma ' phases. In addition, concentration gradient of Al element and adequate holding time were responsible for the directional growth of foliated gamma ' phase.