感应加热辅助激光熔覆修复的定向凝固镍基高温合金的组织结构调控研究

Thanks to the low heat input and the epitaxial growth of cladding layers relative to the substrate, laser cladding technique has great potential for the application of repairing the damaged directionally solidified Ni-based superalloys. However, high density of microdefects (mainly dislocations) and high level of residual stresses/strains accumulate in cladding layers and heat affect zone (HAZ) of substrate due to the rapid solidification process, leading to the microstructural inhomogeneity and poor thermal stability. Therefore, in this project, induction heating technique is propose to tune the temperature field distribution near the melt pool, thus to unravel the optimization mechanism of the microstructures in laser cladded directionally solidified Ni-based superalloy DZ125L. After collecting the temperature field distribution by means of an infrared temperature measurement system, thermal analysis model of induction-laser hybrid heating source will be established to study the temperature distribution evolution of melt pool under different induction heating parameters. By investigating the effect of temperature distribution evolution on the phase constituents and growth behavior of dendrites, the solidification conditions for fabrication of epitaxial cladding layers will be obtained. The spatial distribution of microdefects measured by multi-scale characterization techniques will be linked to the behavior of γ' phase transition, elucidating the reduction mechanism of microdefect density and residual stresses/strains. The outputs of this project will provide a valuable reference for the application of repairing the directionally solidified / single crystal Ni-based superalloy by induction assisted laser cladding technique.

激光熔覆技术以其热输入小、熔覆层与基材外延性好等优势，可用于定向凝固镍基高温合金叶片的修复，但快速凝固过程导致熔覆层和热影响区存在高密度位错等微观缺陷和残余应力/应变，对组织结构均匀性和热稳定性不利。本项目拟采用感应加热技术，通过改变熔池温度场分布，优化熔覆修复的定向凝固高温合金DZ125L的组织结构，并揭示其内在调控机制。利用红外测温系统采集熔池温度场数据，构建感应-激光耦合热源的热分析数学模型，揭示不同感应加热条件下的熔池温度场的演化规律；探索熔池温度场演化对γ'析出相等凝固产物形成和枝晶生长行为的影响规律，获得制备外延熔覆层的凝固条件；借助微观缺陷的跨尺度表征技术，阐明微观缺陷不均匀分布规律与γ'相变行为的内在联系，揭示感应加热对熔覆合金微观缺陷及残余应力/应变分布的调控机制。项目研究成果可为感应加热辅助激光熔覆技术在定向凝固/单晶高温合金修复领域的推广应用提供理论依据。

激光熔覆技术因其热输入小、热源集中、熔覆层与基材外延性好等优势，在定向凝固/单晶高温合金的外延修复方面具有巨大应用前景，但激光熔覆过程产生的热应力导致熔覆层存在大量微观缺陷和残余应力/应变，易引发开裂和组织不稳定性。本项目采用感应加热辅助激光熔覆技术对定向凝固高温合金增材修复中的一些基本问题展开研究。首先利用多尺度表征技术对激光熔覆高温合金的组织结构进行了系统表征，然后结合有限元模拟和同步辐射微束衍射等实验手段研究了感应加热对激光熔覆过程的温度场和组织性能演化的影响规律，发现感应加热可以有效降低熔覆修复过程的温度梯度和残余应力/应变水平，但热裂纹依旧无法抑制。鉴于此，本项目又拓展研究了电子束增材制造难焊接高温合金，成功制备了无裂纹定向晶组织，揭示了电子束增材制造高温合金定向性保持与裂纹抑制的协同机制和工艺策略。研究成果为增材制造技术在高温合金部件修复和再制造领域的推广提供了实验和理论依据。