Stress-dependent creep behavior and deformation mechanisms in a Ni₃Al single-crystal alloy under 1200℃ ultra-high temperature

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Abstract
A novel Ni₃Al-based single-crystal superalloy was subjected to creep testing at 1200°C under applied stresses ranging from 60 to 100 MPa. The stress-related deformation mechanism was elucidated through creep performance testing and examination of microstructure evolution. The results reveal pronounced stress sensitivity, with creep life decreasing from 360.5 h to 22.6 h as the stress increased from 60 to 100 MPa. Meanwhile, the creep strain during the primary creep stage rises from 0.59% to 1.68%. In contrast, during the steady-state creep stage, a decrease in applied stress from 100 MPa to 60 MPa leads to a significant reduction in the minimum creep rate, which drops from 2.77×10⁻⁷ s⁻¹ to 5.02×10⁻⁹ s⁻¹. This behavior is closely associated with the evolution of the interfacial dislocation network at γ/γ′ interfaces, whose spacing plays a critical role in controlling the steady-state creep rate. Throughout the tertiary creep stage, the degree of topological inversion is markedly enhanced with increasing applied stress. At the same time, a concomitant decline is observed in the number density of γ′ subgrains adjacent to the fracture surface. Under an applied stress of 60 MPa, the predominant creep mechanism is confirmed to be dislocation climb. At 100 MPa, the mechanism transitions to dislocation shearing of the γ′ precipitates. In summary, this study reveals the microstructural evolution and dominant deformation mechanisms under varying stress conditions at 1200℃, providing foundational data for the material selection of turbine blades in advanced aeroengines.

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