Elucidating the effect of preheating temperature on melt pool morphology variation in Inconel 718 laser powder bed fusion via simulation and experiment
Elucidating the effect of preheating temperature on melt pool morphology variation in Inconel 718 laser powder bed fusion via simulation and experiment
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DOI：
10.1016/j.addma.2020.101642
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发表时间：
2021-01-01
影响因子：
11
通讯作者：
To, Albert C.
中科院分区：
文献类型：
--
作者：
Chen, Qian;Zhao, Yunhao;To, Albert C.
在L激光粉床熔化添加剂制造中，成形零件的力学性能、显微组织和缺陷与熔池形态密切相关，例如熔池在成形过程中的尺寸和形状。过去的研究主要集中在激光功率和扫描速度等工艺参数如何影响熔池特性。在这项研究中，通过非原位样品表征和计算热流体动力学(CtFD)模拟，研究了导电区、过渡区和小孔区熔池形态随预热温度的变化，以及每个区的潜在机制。在实验中，将不同激光功率和扫描速度组合的单个轨道沉积在Inconel 718裸板上，预热到100-500摄氏度的温度范围。通过对熔体轨迹截面的光学测量，观察到熔池形态随着预热温度的变化而发生显著变化。三个区域的熔池深度随着预热温度的升高而单调增加，如在500℃时，实验熔池深度在导电区、过渡区和小孔区分别增加了49%、34%和33%，但各区域熔池宽度的变化并不都遵循增加的趋势，而取决于熔池区域。导热和过渡区熔池宽度的变化依赖于与温度相关的热性质直接相关的强化导热。通过验证的CtFD模拟发现，在小孔区域，蒸发质量、反冲压力和激光打孔效果随着预热温度的升高而增强，从而产生更深的熔池。模拟还表明，预热温度显著延长了熔体轨迹长度，这是因为增加了流动速度和强大的反冲压力，从而加速了回流。
In laser powder bed fusion (L-PBF) additive manufacturing, the mechanical performance, microstructure and defects of fabricated parts are closely associated with the melt pool morphology, e.g., its dimension and shape through the building process. Past studies have largely focused on how the process parameters such as laser power and scan speed affect melt pool characteristics. In this study, the melt pool morphology variation as a function of preheating temperature in the conduction, transition, and keyhole regimes and the underlying mechanisms in each regime are investigated through ex-situ sample characterization and computation thermal fluid dynamics (CtFD) simulation. Single tracks with different combinations of laser power and scan speed are deposited on an Inconel 718 bare plate preheated to a temperature range of 100-500 degrees C in the experiment. Significant changes are observed in melt pool morphology as a function of preheating temperature from optical measurements of melt track cross sections. The depth of melt pool in the three regimes increases monotonically with preheating temperature, e.g., at 500 degrees C, the experimental melt pool depth is increased by 49% in conduction regime, 34% in transition regime and 33% in keyhole regime, respectively, while the variation of melt pool width in each regime does not all follow an increasing trend but depends on the melt pool regimes. Melt pool width variation in the conduction and transition regimes is found to depend on the enhanced heat conduction directly related to temperature dependent thermal properties. Through validated CtFD simulations, it is found that in the keyhole regime the evaporation mass, recoil pressure, and laser drilling effect is enhanced with higher preheating temperature, which gives rise to a deeper melt pool. The simulations also reveal that preheating temperature significantly elongates the melt track length due to the increased flow rate and strong recoil pressure that accelerates the backward flow.