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

K447A is a nickel-based superalloy extensively employed in critical hot-end components of aerospace engines due to its exceptional high-temperature performance. This study systematically investigates the dynamic mechanical properties of K447A through quasi-static and high strain rate compression tests conducted over a temperature range of 25°C to 1000°C. Detailed analysis is performed on the effects of temperature and strain rate on the plastic flow behavior of this alloy. 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, 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°C, 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. The study also examines the microstructural changes within the material, which are influenced by the coupling of strain rate and temperature. 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 as influenced by the interplay of temperature and strain rate, this study develops a modified Johnson-Cook (J-C) constitutive model. 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.