<p>The high-temperature damage behavior and deformation mechanisms of Inconel 617 nickel-based superalloy were systematically investigated through isothermal uniaxial tensile tests across a range of temperatures and strain rates. The experimental results demonstrate a strong dependence of mechanical properties on deformation conditions: fracture strain exhibits a positive correlation with increasing strain rate and decreasing temperature, resulting in enhanced plasticity. Microstructural analysis reveals a temperature- and strain-rate-dependent fracture mode transition. The fracture morphology evolves from characteristic ductile dimples at lower temperatures and higher strain rates to a predominantly rock-sugar-like morphology at elevated temperatures and reduced strain rates, indicating a gradual transition from ductile to brittle fracture behavior. Furthermore, the degree of dynamic recrystallization in the fracture-proximal region increases significantly with rising temperature and decreasing strain rate. This recrystallization process leads to reduced dislocation density, material softening, and consequent decrease in peak stress. The strength disparity among the work-hardened matrix, recrystallized regions, and M₂₃C₆ carbides promotes preferential microvoids nucleation at recrystallized grain boundaries and carbide interfaces. These microstructural observations provide a mechanistic explanation for the deterioration of material plasticity with increasing recrystallization degree under low strain-rate conditions.</p>