Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation
Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation
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DOI：
10.1016/j.addma.2019.100835
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发表时间：
2019-12-01
影响因子：
11
通讯作者：
Hattel, Jesper Henri
中科院分区：
文献类型：
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作者：
Bayat, Mohamad;Thanki, Aditi;Hattel, Jesper Henri
金属添加剂制造虽然具有设计自由度无限、制造时间短等独特功能，但也存在诸多固有缺陷。气孔是严重影响零件性能的缺陷之一。在这方面，使人们能够在这个过程中观察和预测孔隙度是非常重要的。为此，本工作采用数值模拟和实验相结合的方法，分析了Ti6Al4V合金单道L脉冲成形过程中孔洞和孔洞诱导孔洞的形成、演化和消失及其萌生机制。在这方面，开发了基于有限体积法(FVM)的高保真数值模型，并在商业软件Flow-3D中实现。该模型解释了L光子晶体的激光扫描过程中发生的主要物理过程。为了更好地模拟实际激光与材料的相互作用，在菲涅耳吸收函数的基础上，实现了光线跟踪法的多次反射。结果表明，在小孔区域，由于激光在小孔空腔内的大量俘获，加热比浅层熔池区域显著增加。此外，还进行了详细的参数研究，以考察输入功率对吸热系数、换热和熔池解剖的影响。此外，还进行了X射线计算机层析(X-CT)分析，以显示在L-PBF过程中形成的气孔。结果表明，预测的气孔形状、大小和深度与X-CT或光学和三维数字显微图像的结果非常吻合。
Metal additive manufacturing, despite of offering unique capabilities e.g. unlimited design freedom, short manufacturing time, etc., suffers from raft of intrinsic defects. Porosity is of the defects which can badly deteriorate a part's performance. In this respect, enabling one to observe and predict the porosity during this process is of high importance. To this end, in this work a combined numerical and experimental approach has been used to analyze the formation, evolution and disappearance of keyhole and keyhole-induced porosities along with their initiating mechanisms, during single track L-PBF of a Ti6Al4V alloy. In this respect, a high-fidelity numerical model based on the Finite Volume Method (FVM) and accomplished in the commercial software Flow-3D is developed. The model accounts for the major physics taking place during the laser-scanning step of the L-PBF process. To better simulate the actual laser-material interaction, multiple reflection with the ray-tracing method has been implemented along with the Fresnel absorption function. The results show that during the keyhole regime, the heating rises dramatically compared to the shallow-depth melt pool regime due to the large entrapment of laser rays in the keyhole cavities. Also a detailed parametric study is performed to investigate the effect of input power on thermal absorptivity, heat transfer and melt pool anatomy. Furthermore, an X-ray Computed Tomography (X-CT) analysis is carried out to visualize the pores formed during the L-PBF process. It is shown, that the predicted shape, size and depth of the pores are in very good agreement with those found by either X-CT or optical and 3D digital microscopic images.