For nickel-based superalloys with medium volume-fraction γʹ phase (20 %–40 %), dual or multi-stage aging treatments are usually conducted to generate a microstructure containing the multimodal distribution of γʹ for a balance of strength and plasticity. In the present study, the microstructure and high-temperature properties of a novel cast nickel-based superalloy K4800 were investigated after being subjected to three heat treatments (HT) procedures, namely HT1: 1180 °C/4 h + 1090 °C/2 h + 800 °C/16 h, HT2: 1180 °C/4 h + 1060 °C/2 h + 800 °C/16 h and HT3: 1180 °C/4 h + 800 °C/16 h. It was found that the sub-solvus aging treatments at 1090 and 1060 °C precipitated sub-micron-sized (∼300 nm) primary γʹ phase which enhanced the ductility during 800 °C tensile (the total elongation of T1, T2, and T3 samples were 6.75 %, 7.3 %, and 3.25 %, respectively) without evidently impairing the strength. After careful microstructure observation and deformation mechanism analysis, the enhancement of elongation was rationalized that the precipitation of the sub-micron-sized primary γʹ phase decreased the volume-fraction and size of the nanometer-sized γʹ phase which was precipitated at 800 °C, and simultaneously, promoted the dislocation movement by suppressing the non-planar slip. However, an excessive amount of the sub-micron-sized primary γʹ phase led to a faster ripening process of the nanometer-sized γʹ during creep, which decreased the creep life at 800 °C/430 MPa (T1: 125 h, T2: 199 h, and T3: 198 h). Based on this, we monitored the number density of nanometer-sized γʹ phase coexisting with different amounts of large γʹ during creep. An area fraction less than 7 % of the sub-micron-sized γʹ phase was considered to have little detrimental effect on the creep life of K4800 alloy, which corresponded to a sub-solvus temperature range about 1080–1090 °C.

对于中等体积分数γʹ相（20%~40%）的镍基高温合金，通常进行两级或多级时效处理，以产生含有γʹ多峰分布的显微组织，以实现强度和塑性的平衡。在本研究中，研究了新型铸造镍基高温合金 K4800 经过三种热处理（HT）程序（即 HT1：1180 °C/4 h + 1090 °C/2）后的显微组织和高温性能。 h + 800 °C/16 h，HT2：1180 °C/4 h + 1060 °C/2 h + 800 °C/16 h 和 HT3：1180 °C/4 h + 800 °C/16 h。研究发现，1090 和 1060 °C 的亚固溶线时效处理会析出亚微米尺寸（~300 nm）的初生 γʹ 相，从而增强了 800 °C 拉伸期间的延展性（T1、T2 和 T3 的总伸长率）。样品的含量分别为 6.75%、7.3% 和 3.25%），但强度没有明显降低。经过仔细的微观组织观察和变形机制分析，伸长率的提高合理化为亚微米级初生γ′相的析出降低了800℃时析出的纳米级γ′相的体积分数和尺寸，同时，通过抑制非平面滑移来促进位错运动。然而，过量的亚微米级初生γʹ相导致蠕变过程中纳米级γʹ的成熟过程加快，从而降低了800 ℃/430 MPa下的蠕变寿命（T1：125 h，T2： 199 小时，T3：198 小时）。在此基础上，我们监测了蠕变过程中与不同数量的大γ′共存的纳米级γ′相的数密度。 亚微米尺寸γ′相的面积分数小于7%被认为对K4800合金的蠕变寿命几乎没有不利影响，其对应于约1080-1090°C的亚固溶线温度范围。