准连续激光动态调控梯度组织的机理研究与同质异性功能构件定制

Homogeneous and functionally-graded component realizes its property grads by spatial arrangement of different microstructure and grain morphology with the same material, and it has important application prospects in many fields, such as aerospace, defense, military and biological medicine. At present, it is difficult to realize the locally spatial customization of microstructure and property of the functionally-graded component using traditional processing methods. This project, breakthrough the limitation of traditional continuous-wave laser processing methods, proposes a quasi-continuous-wave laser processing method to dynamically excite the molten pool for tailoring the microstructure and property of the component. The macro- and micro-scopic coupling mathematical model is established to study dynamic fluctuation laws of molten pool and their influence mechanisms on solidification microstructure. The processing windows are optimized during quasi-continuous-wave laser additive manufacturing. The critical transformation process parameters are determined. The mapping relationship between target microstructures and process parameters is obtained. The homogeneous and functionally-graded component can be directly manufactured using the customized processing route. This project will enrich the non-equilibrium rapid solidification theory and provides theoretical and experimental basis for direct laser manufacturing of homogeneous and functionally-graded components. Simultaneously, it also will improve the design freedom of heterogeneous and functionally-graded components to realize the design and manufacturing of functionally-graded component with more freedom.

同质异性功能梯度构件通过同种材料不同组织形态的空间布局实现其梯度性能，在航空航天、国防军工及生物医疗等领域具有重要应用前景。目前，采用传统加工方法难以实现此类功能梯度构件组织及性能的定制化制造。本项目突破传统连续激光增材制造思路，提出采用准连续激光对熔池进行主动激励以实现凝固组织及性能的局部精确调控。本项目拟通过建立准连续激光动态激励下宏-微观耦合数学模型，结合实验观测与表征手段，揭示熔池动态波动规律及其对凝固组织的影响机理；通过优化准连续激光增材制造工艺参数，探寻动态激励下凝固组织转变临界参量，获得目标组织性能与工艺参数的映射关系；通过定制化的工艺路线实现同质异性功能梯度构件的直接激光制造。本项目将丰富与发展非平衡快速凝固理论，为实现同质异性功能梯度构件的直接激光制造提供重要理论及实验依据。同时，也将增加异种材料梯度功能构件的设计维度，实现更大自由的功能梯度构件设计与制造。

增材制造由于典型外延生长特性，制造样品呈现典型的柱状组织，造成产品存在各向异性、易开裂、力学性能差、残余应力高和服役性能差等问题。本项目针对上述问题，创新地提出了准连续时域调控的增材制造模式，建立了宏观三维瞬态热-质传递模型和微观薄界面相场模型的宏-微耦合模型，实现了熔池形貌、温度分布、热历史、熔质流动演变规律的模拟，提取了凝固界面推进速度、温度梯度和冷却速率等凝固参数，揭示了准连续模式中界面周期推进过程形核与生长对外延生长的抑制作用，建立了傅立叶数划分组织形貌的临界条件。优化了准连续激光增材制造工艺窗口，实现了织构、晶粒、枝晶、二次相等形貌的协同调控，并实现了晶粒形貌、偏析、位错密度的协同调控，提升了打印产品力学、残余应力、抗氧化等性能的提升。通过结合连续工艺和准连续工艺，实现了镍基IN718等轴、柱状和近单晶同质异性样品的定制化生产，满足了定制组织功能打印的需求。项目建立了准连续增材工艺、热处理工艺和路径工艺的工艺数据库，建立了准连续工艺下力学性能、残余应力、硬度、抗氧化等性能数据库，为实现准连续工艺-组织-性能的调控提供了大量数据基础。