准连续激光镍合金直接沉积调控熔池凝固的机理研究

The control of the solidified microstructure during direct laser deposition still meets certain difficulty for manufacturing of nickel based superalloy. Recently, it is found the quasi-continuous-wave laser can be utilized within direct laser deposition for microstructural refinement, microstructure uniformity and reducing segregation. However, the mechanism of how periotic laser alter the molten pool solidification is not clear, impeding the application of the quasi-continuous-wave laser. This project proposes a study of combined molten pool transport phenomenon and micro solidification process for the direct laser deposition of nickel based superalloy under the quasi-continuous-wave laser parameters. The aim is to clarify how metallurgical properties are coupled with heat/mass transfer of the molten pool and manufacturing parameters. The project is expected to expand current methods for controlling microstructure solidification, and contributes scientifically to the direct laser deposition of functional graded components of nickel based superalloy.

镍基合金激光直接沉积技术在控制凝固组织方面仍存在困难。为此，近年来发展了一种准连续激光工艺，在晶粒大小、组织一致性、溶质偏析等方向体现出调控效果，但动态激光作用下熔池行为与凝固机理尚不明确，制约其工艺的发展应用。本项目提出建立动态激励下宏观瞬态熔池与微观组织生长耦合的数学模型，针对准连续激光下的熔池行为开展理论研究，揭示准连续激光直接沉积制造中熔池凝固条件和微观组织演变的机理。旨在建立准连续激光直接沉积工艺参数-显微组织-力学性能的映射关系，为镍基合金激光直接沉积制造中显微组织及性能的控制提供新途径和方案，为实现更大自由度的功能梯度零部件的整体制造提供科学依据。

准连续激光直接沉积是一种新型的激光增材制造工艺。相比于传统工艺，在增材过程中该工艺采用间断出光和脉冲能量的方式，可以有效改变连续行径的熔池演化，高度定向的热流传导和相对稳定的凝固条件。因此，准连续工艺可以对增材制造金属部件的显微组织、微观偏析、机械性能等重要方面产生调控效果，有望拓展现有增材制造技术方法和应用前景。为了开拓与落实准连续工艺的制造能力，本项目针对镍基合金、奥氏体不锈钢两种常用材料，通过建立物理模型、开展数值仿真和多参数实验探索，研究了准连续激光作用下热物传输与凝固演化的机理问题，建立了工艺参数-显微组织-机械性能的内在关系，开发了“准连续晶粒调控技术”，“高强韧激光直接沉积不锈钢技术”，“增材镍基合金低偏析laves相控制技术”，“镍合金氧化腐蚀控制技术”等激光加工相关技术应用。