同步送粉激光熔覆沉积过程粉末颗粒与移动熔池的微观作用机制

Synchronous powder feeding laser clad deposition is an advanced digital laser multi-layer additive manufacturing technology of the metallic parts, which can realize the direct manufacturing of the metallic components and the high-performance repair of the damaged parts. In this study, the scientific problem “interaction between the powders and the moving molten pool” was studied in the micro level, and the micro effect of the powder particles contacting the moving molten pool was discussed. Firstly, a interaction model the powder particle and the liquid-vapor interface of the molten pool was established based on the high speed photography experiment and the molten pool temperature and geometry measurement, and the effect of the liquid-vapor interface of the molten pool on the initial moving state of the powder particles was disclosed. Secondly, a mathematical model coupling the melting and moving process of the powder particles in the molten pool was developed based on the temperature field analysis and the effect of the powder particles on the flow field of the molten pool, and the moving and melting mechanism of the powder particle in the high temperature molten pool was disclosed. Finally, the capture and rebound mechanism of the solid-liquid interface on the powder particle was investigated based on the interfacial energy analysis and the mechanical analysis of collision, and the physical metallurgical processes in the moving molten pool was proved. The research will provide the theoretical support for the metallurgy quality control and the surface accuracy control.

同步送粉激光熔覆沉积是一项先进的金属零件的数字化增材制造技术，能够实现复杂结构致密金属零件的直接制造以及受损零件的高性能修复。本项目提出从微观层面针对激光熔覆沉积中的科学基础问题“粉末-移动熔池”交互作用展开研究，探讨粉末颗粒接触移动激光熔池后的微观作用过程。首先结合粉末输送过程的高速摄影实验及熔池温度、几何形状检测，建立粉末颗粒与熔池气液界面交互作用模型，揭示熔池气液界面对粉末颗粒初始运动状态的影响；基于熔池温场以及粉末颗粒对熔池液相流场的作用分析，建立粉末颗粒在熔池内熔化-运动耦合的数学模型，揭示粉末颗粒在高温熔池内的变质量运动-熔化行为；在此基础上，结合粉末颗粒与移动熔池固液界面的界面能变化及碰撞力学分析，揭示移动熔池对粉末颗粒的裹入、反弹作用机制，探明粉末颗粒在快速移动熔池内的物理冶金过程。项目的研究成果将为激光熔覆沉积的冶金质量控制以及表面精度控制提供新的思路和理论支持。

激光熔覆沉积技术是材料加工领域研究的热点，在航空航天、医学植入体、船舶、机械、能源、动力等领域展现出极为广阔的应用前景。粉末与移动激光熔池的微观作用机制对沉积层形成具有至关重要的影响，是该技术发展过程中亟待解决的关键科学问题之一。本项目针对粉末颗粒与移动熔池气液界面、固液界面微观交互作用过程展开研究，探讨了粉末颗粒在熔池内的运动熔化过程。首先对粉末颗粒与熔池气液界面作用过程进行解析，采用Fluent流体力学软件建立粉末颗粒与熔池气液界面交互作用的有限元模型，结合粉末颗粒与气液界面交互过程的微距高速摄影验证，揭示了粉末颗粒与熔池气液界面交互作用特性及规律，获得了粉末颗粒在进入熔池过程中，不同时刻熔池对粉末颗粒运动状态的影响以及粉末颗粒对熔池液体运动状态的影响。结合粉末颗粒与移动熔池固液界面的界面能变化及碰撞力学分析建立了粉末颗粒与熔池固液界面作用过程的解析模型，计算研究了熔池区域温度、粉末颗粒直径对粉末熔化时间的影响；建立了粉末颗粒与熔池固液界面的交互作用模型，计算了粉末颗粒与熔池固液界面交互作用下的裹入-反弹临界条件，揭示了固液界面对粉末颗粒的裹入，反弹作用机制。基于以上研究，探讨了粉末材料性质、粉末初始运动状态、送粉工艺条件等对沉积层表观质量、冶金质量的影响。在此基础上，探讨了不完全熔化粉末颗粒对合金凝固组织的影响，提出了一种包覆制备复合粉末的方法，实现了激光熔覆沉积钛合金的晶粒细化。项目研究成果具有显著的科学意义以及应用前景，为解决激光熔覆沉积中晶粒细化，进而提高合金综合力学性能奠定重要科学基础。