In this work, a comprehensive framework consisting of coaxial gas-powder flow and melt-flow dynamics models is developed for the laser-assisted directed energy deposition process. Firstly, by using the coupled Eulerian-Lagrangian models, the dynamics of the carrier-shielding gases, the particle-stream trajectory, and the in-flight temperature rise of the powder-particles are predicted. This is done by solving the momentum transfer equations, the k-ε turbulence equations, the discrete phase equation and the energy equation. Thereafter, using the particle-stream characteristics above the melt-pool free-surface, an interface-tracking melt thermo-hydrodynamics model is developed in an open-source environment to track the incident powder-particles in the melt-pool. Using the developed framework, the spatial and temporal variation of the melt-pool morphology due to the powder-particle impingement is analyzed. The computational results of particles-melt interaction show an erratic flow pattern with an oscillatory behavior of the melt-pool free-surface. The incident powder-particle creates a crater on the free-surface of the melt-pool and generates a radially outward strong ripple-wave. The velocity field of the melt-pool shows a highly non-linear behavior which is extremely sensitive to the particle impact. It was found that the thermo-capillary stresses dominate only at the instances when there is no particle insertion and the flow is stabilized. Using the solidification parameters obtained from the melt-pool dynamics model, the influence of the fluctuating thermo-fluidic field on the resultant columnar dendritic microstructure is studied. The comparison of the numerically predicted deposition dimensions and the dendritic arm spacings shows a good correlation with the corresponding experimentally measured values from the in-house controlled experiments.

在这项工作中，为激光辅助定向能量沉积过程开发了一个由同轴气体粉末流动和熔体流动动力学模型组成的综合框架。首先，通过使用耦合的欧拉-拉格朗日模型，预测了载流子保护气体的动力学，粒子流的轨迹以及粉末粒子的飞行中温度升高。这是通过求解动量传递方程k-ε来完成的湍流方程，离散相位方程和能量方程。此后，利用熔池自由表面上方的颗粒流特性，在开源环境中建立了界面跟踪熔体热流体动力学模型，以跟踪熔池中入射的粉末颗粒。使用开发的框架，分析了熔池形态由于粉末粒子撞击而引起的时空变化。颗粒-熔体相互作用的计算结果显示出不稳定的流动模式，并且熔池自由表面具有振荡行为。入射的粉末颗粒在熔池的自由表面上形成一个火山口，并产生一个径向向外的强波纹波。熔池的速度场显示出高度非线性的行为，对颗粒的冲击极为敏感。已经发现，仅在没有颗粒插入并且流动稳定的情况下，热毛细应力才占主导地位。使用从熔池动力学模型获得的凝固参数，研究了波动的热流场对所得柱状树枝状显微组织的影响。数值预测的沉积尺寸和树枝状臂间距的比较显示出与来自内部对照实验的相应实验测量值的良好相关性。使用从熔池动力学模型获得的凝固参数，研究了波动的热流场对所得柱状树枝状显微组织的影响。数值预测的沉积尺寸和树枝状臂间距的比较显示出与来自内部对照实验的相应实验测量值的良好相关性。使用从熔池动力学模型获得的凝固参数，研究了波动的热流场对所得柱状树枝状显微组织的影响。数值预测的沉积尺寸和树枝状臂间距的比较显示出与来自内部对照实验的相应实验测量值的良好相关性。