High-temperature dynamic mechanical properties and intrinsic relationships of K447A alloy

K447A, a nickel-based superalloy, is widely used in critical hot-end components of aerospace engines due to its excellent high-temperature performance. Through quasi-static and high strain rate compression experiments within the temperature range of 25 ℃ to 1000 ℃, the dynamic mechanical properties of K447A superalloy were systematically investigated. The effects of temperature and strain rate on its plastic flow behavior and material microstructure were analyzed. By examining the stress-strain curves under quasi-static conditions and utilizing electron backscatter diffraction (EBSD), the microstructural characteristics of specimens deformed at various strain rates and temperatures were analyzed. The results reveal that during the plastic deformation of K447A, strain hardening, temperature softening, and strain rate strengthening phenomena coexist. As the strain rate increases from quasi-static levels to 5000 s⁻¹, the temperature sensitivity index (s) gradually decreases, indicating a diminishing temperature softening effect at higher strain rates. Notably, at an elevated strain rate of 800 ℃, an anomalous stress peak appears in the flow stress-strain curve of the K447A alloy, suggesting complex interactions between temperature and strain rate during deformation. Furthermore, the strain rate sensitivity coefficient (p) increases with temperature, highlighting a more pronounced strain rate strengthening effect at elevated temperatures. Microstructural changes within the material, which are influenced by the coupling of strain rate and temperature, are also examined. An increase in strain rate leads to grain refinement, while higher temperatures result in a decrease in the proportion of low-angle grain boundaries, facilitating dynamic recrystallization within the material. To accurately describe the flow stress influenced by the interplay of temperature and strain rate, a modified Johnson-Cook constitutive model was developed. This revised model demonstrates improved predictive capability compared to the original formulation, effectively capturing the plastic flow behavior of K447A across a broad range of temperatures and strain rates. The predictive error is significantly reduced from 26.36% to 9.05%, underscoring the model’s enhanced accuracy and reliability in simulating the mechanical performance of K447A alloy under varying operational conditions.