摘要:
K447A是一种广泛用于航空发动机关键热端部件的镍基高温合金，本文通过在25℃-1000℃温度范围内进行准静态和高应变率压缩实验，系统研究了K447A高温合金的动态力学性能，并分析了温度和应变率对其塑性流动行为的影响。研究结果表明：K447A合金的塑性变形过程中同时存在应变硬化、热软化和应变率强化现象。随着应变率从准静态增加到5000/s，温度敏感指数s逐渐减小，而在800℃时，K447A合金在高应变率范围出现反常应力峰。随着温度的升高，应变率敏感因子p逐渐增大；材料内部的微观组织结构受应变率和温度耦合影响，应变率增加会导致晶粒细化，而温度升高会导致材料内部低角晶界占比减少从而出现动态再结晶现象。基于流动应力受温度和应变率耦合影响的考虑，本文建立了修正的Johnson-Cook(J-C)本构模型，与修正前相比，预测误差从26.36%降低到9.05%。
Abstract:
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.
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