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In polycrystalline nickel-base superalloys, the presence of secondary phase precipitation at grain boundaries significantly influences mechanical properties. Numerous studies have revealed that the Ni 3 (Al/Ti) 0.5 Nb 0.5 phase precipitated at grain boundaries can optimize stress rupture and reduce notch sensitivity, However, there was limited consideration given to the presence of the secondary phase within the grains. Herein, the atomic structure of η- Ni 3 (Al/Ti) 0.5 Nb 0.5 phase in grain was investigated using atomic scale STEM-HAADF, and the η/γ interface and interfacial dislocation during tensile and creep process were also discussed. The results indicated that the η/γ interface exhibited different characteristic features in different stages, and interfacial dislocation interaction occurred during the tensile process, resulting in the formation of a parallel array of dislocations in a nano space. However, dislocations within the η phase and stacking faults (SFs) surrounding the interface are evident for the creep process. STEM-HAADF images also revealed that η/γ interfacial dislocation interaction coordinated the deformation of two phases and provided the driving force of misfit lattice, which positively influenced the mechanical properties of 718Plus. The crystal structure of the η phase was reconstructed using VESTA software, and its ordered structure was found to be consistent with the corresponding HAADF images for B = [2 1 ¯ 1 ¯ 0] zone axils. This present work provides valuable insights into the atomic-scale coordinated deformation of secondary phases and matrix. • The atomic structure of η- Ni 3 (Al/Ti) 0.5 Nb 0.5 phase in grain was investigated. • The η/γ interface and interfacial dislocation were also discussed. • The η/γ interfacial dislocation interaction provided the driving force of misfit lattice. [ABSTRACT FROM AUTHOR]