Abstract

Directed laser deposition (DLD) has become a popular forming method however it is a process with drastic temperature changes, during which the temperature accumulation effect easily causes deposition defects. Wherein the selection of the process parameters could affect the shape quality and mechanical property of the formed parts. This work investigates the distribution characteristics of the temperature field in the DLD process by finite element (FE) method and derives the temperature-time curves of special nodes which show good agreement with corresponding experimental tests. Moreover, the influence of laser power, scanning speed, and substrate initial temperature on temperature field is also studied. Based on the validation of simulation and analyses of forming defects, Inconel 718 thin-walled part with good shape was prepared by adapting the strategy of changing laser power for different layers. The formed part characterizes the finer microstructure compared with the casting part. The dendrite direction in the molten pool is mainly perpendicular to the bottom of the molten pool, and it grows epitaxially along the direction of heat flow. Besides, the mean tensile strength and elongation of the formed thin-walled part, to a certain extent, show anisotropy in the parallel and vertical direction to depositing, respectively.

摘要

定向激光沉积（DLD）已成为一种流行的成型方法，但它是一个温度变化剧烈的工艺，在此过程中，温度累积效应容易导致沉积缺陷。其中工艺参数的选择会影响成型件的形状质量和力学性能。本工作通过有限元（FE）方法研究了DLD过程中温度场的分布特征，并推导出了与相应实验测试吻合良好的特殊节点的温度-时间曲线。此外，还研究了激光功率、扫描速度和衬底初始温度对温度场的影响。基于模拟验证和成形缺陷分析，采用不同层级改变激光功率的策略，制备出形状良好的Inconel 718薄壁零件。与铸造零件相比，成型零件具有更精细的微观结构。熔池中的枝晶方向主要垂直于熔池底部，沿热流方向外延生长。此外，成型薄壁零件的平均抗拉强度和伸长率在一定程度上分别表现出与沉积平行和垂直方向的各向异性。