The plastic deformation introduced during the cooling stage (above 1000 °C) of directional solidification is one of the primary reasons for the recrystallization of Ni-based single-crystal (SX) turbine blades in aero-engines during subsequent heat treatment. An as-cast SX superalloy DD33 was compressed at 1200 °C with a Gleeble thermo-mechanical simulator to mimic such deformation. The microstructural evolution, dynamic recovery, and dynamic recrystallization nucleation of the as-cast SX superalloy during hot deformation are investigated. The results show that the highest stored energy occurs in the vicinity of the eutectics, and its energy in the interdendritic regions is higher than that in the dendrite cores/arms. The formation of deformation bands and related transition bands near the eutectics are the primary characteristics of microstructural evolution during hot deformation. The dynamic recovery in the eutectic regions includes the entanglement and annihilation of dislocations at eutectic/matrix interface, within nearby γ matrix or within the eutectic γ′ phase, as well as the formation of dense dislocation networks in these sites. Subsequently, the low-angle grain boundaries in the transition bands migrate, merge, and finally transform into high-angle grain boundaries. In other words, the recrystallized grains nucleate near the eutectics via subgrain growth. In contrast, the dislocations only tangle and annihilate at the γ/γ′ interfaces in other interdendritic regions and the dendrite cores/arms without initiating recrystallization under moderate plastic deformation (εplastic = 11.9 %). This study will be helpful for understanding the local microstructural evolution of SX superalloys during directional solidification, as well as the recovery and recrystallization nucleation during the subsequent annealing.

中文翻译：

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热变形过程中铸态 SX 高温合金的动态恢复和再结晶


在定向凝固的冷却阶段（1000 °C 以上）引入的塑性变形是航空发动机中镍基单晶 （SX） 涡轮叶片在后续热处理过程中再结晶的主要原因之一。使用 Gleeble 热机械模拟器在 1200 °C 下压缩铸态 SX 高温合金 DD33 以模拟这种变形。研究了铸态 SX 高温合金在热变形过程中的微观组织演变、动态恢复和动态再结晶成核。结果表明，共晶附近存储的能量最高，其在枝晶间区域的能量高于枝晶核心/臂中的能量。在共晶附近形成的变形带和相关过渡带是热变形过程中微观结构演变的主要特征。共晶区的动态恢复包括共晶/基体界面处、附近γ基体内或共晶 γ' 相内位错的纠缠和湮灭，以及在这些位点中形成致密的位错网络。随后，过渡带中的小角晶界迁移、合并，最后转变为高角晶界。换句话说，再结晶的晶粒通过亚晶粒生长在共晶附近成核。相比之下，位错仅在其他枝晶间区域的 γ/γ' 界面和枝晶核/臂处缠结和湮灭 （εplastic = 11.9 %） 下不引发再结晶。 本研究将有助于了解 SX 高温合金在定向凝固过程中的局部微观组织演变，以及随后退火过程中的恢复和再结晶成核。