燃气轮机涡轮叶片定向凝固过程多尺度耦合模拟及枝晶碎臂和雀斑机理研究

Fragmentized dendrites and freckles produced in solidification process are the major reasons that lead to low productivity of gas turbine blades. Researchers have conducted plenty of studies on them by means of simulation and experiments. However, due to the limitations of algorithm and computational scale, macro-micro coupling simulation for blades during directional solidification (DS) process has not really realized, and the simulation for micro dendritic structure of Ni-based superalloy still remains at the level of binary or pseudo-binary for lack of data support. In addition, no systematic research in theory about the formation mechanism of freckles, which cannot satisfy the requirements of engineering. This project will conduct further simulated and experimental research on these problems. Multiple boundary conditions for liquid metal cooling process will be investigated, containing radiation, conduction and convection, and multi-scale mathematical model for blades during DS process will be established coupling with some important physical information of macroscopic, mesoscopic and microscopic. Considering the influence of alloy composition, solute diffusion, fluid flow and wall attachment effect, multi-component dendrite growth model and freckle prediction model will be also established. Based on numerical simulation and in-situ observation experiments, the interaction and internal relation between fragmentized dendrites and freckle defects will be investigated, and the forming mechanism of them will be explored. This will help to find the controlling strategies and methods for defects in Ni-based superalloy turbine blades. Finally, this study may provide valid theory support for practical production in factories.

燃气轮机涡轮叶片在凝固过程中产生的枝晶碎臂和雀斑是导致其合格率低的重要原因，为此研究者们已经开展了大量的数值模拟和实验工作。然而受算法和计算规模的限制，叶片在定向凝固过程中宏微观物理场的模拟尚未实现真正意义的耦合；而且由于缺乏数据支撑，对镍基高温合金微观枝晶组织的模拟还停留在二元或伪二元层面。此外，对雀斑形成机理的研究尚不够系统，不能满足工程要求。本项目将针对这些问题开展进一步的模拟和实验研究，探索包含辐射、传导以及对流的液态金属冷却定向凝固工艺复合边界条件，耦合宏观、介观和微观等物理信息，建立叶片定向凝固过程多尺度数理模型。考虑合金成分、溶质扩散、流体流动以及附壁效应等影响建立镍基高温合金多组元枝晶生长模型和雀斑预测模型。数值模拟结合原位观察实验，探究枝晶碎臂和雀斑之间的交互作用和内在联系，揭示二者的形成机理，提出控制缺陷产生的方法和策略，为工厂实际生产提供理论支持。

燃气轮机常用于工业发电和大型舰船，属于高端工业产品，体现了国家的工业基础、科技水平和国防实力，被誉为现代制造业的“皇冠”。涡轮叶片作为燃气轮机的核心部件，其制造技术被西方发达国家所垄断，我国的研制水平与发达国家尚存在较大差距，严重制约了我国的国防和能源事业的发展。采用传统的试错法研制涡轮叶片，不仅耗费大量人力财力，而且研发周期较长。本项目通过数理建模、计算机编程，开发了具有自主知识版权的模拟仿真软件，用于辅助涡轮叶片的研发，打破了国外的技术垄断，提升了涡轮叶片的制备技术水平，为我国燃气轮机的研制提供了坚实的技术支撑。. 本项目针对燃气轮机涡轮叶片液态金属冷却（LMC）定向凝固过程的工艺控制、枝晶生长和雀斑缺陷开展了数值模拟和实验研究。耦合宏观温度场、介观晶粒组织以及微观枝晶组织等物理信息建立了定向凝固过程的多尺度耦合模型，完善了LMC工艺的传热边界条件。对所建立的模型进行了实验验证，通过试板的浇注实验，采用冷却曲线、晶粒组织和枝晶形貌验证了模型的准确性。基于模拟结果探讨了糊状区演化和晶粒平行度的之间的关系。考虑合金成分、溶质扩散以及各向异性的影响建立了镍基高温合金凝固过程的枝晶生长模型。结合枝晶组织的模拟和原位观察结果研究了枝晶的竞争生长现象，揭示了枝晶碎臂的形成原因。基于G-R判据和瑞利数模型，建立了雀斑缺陷综合判据模型，采用C++编写外挂程序对ProCAST软件进行了二次开发，实现了单晶叶片定向凝固过程雀斑缺陷的模拟预测。结合温度场、流场及Re元素偏析的模拟结果，探究了雀斑的形成机制，提出了控制雀斑缺陷的预防措施，为涡轮叶片的实际生产提供理论支撑。