Microstructure evolution behavior of Ni3Al (γ′) phase in eutectic γ-γ′ of Ni3Al-based alloy

Based on its excellent high-temperature performances, polycrystalline Ni3Al-based alloys have attracted more and more attention. In this work, different thermal cycle aging treatments (TCAT) were applied to investigate microstructure evolution behavior of Ni3Al (gamma') phase in eutectic gamma-gamma' area of JG4246A alloy. SEM equipped with energy dispersive X-ray spectrometer (EDS) and high-resolution transmission electron microscopy (HRTEM) were used for microstructure observation and mechanism analysis. The results showed that plate-like Ni3Al (gamma') phase and twinning Ni3Al (gamma') formed in eutectic gamma-gamma' area due to its initial state of the alloy and thermal cyclic aging treatment conditions. Meanwhile, blocky Ni3Al (gamma') phase precipitated along eutectic gamma-gamma' area and dual phase (gamma + gamma') area ((gamma-gamma')/(gamma-gamma')) interfaces. Vacancies and dislocations generated during short-term TCAT were responsible for the formation of plate-like Ni3Al (gamma') phases in eutectic gamma-gamma' area of as-cast alloy. While, for the solution-treated alloy, dislocations and internal stress generated during long-term TCAT led to the formation of twinning Ni3Al (gamma') in eutectic gamma-gamma' area and blocky Ni3Al (y') phase along (gamma-gamma')/(gamma + gamma) interface.