Ansari Dezfoli Amir Reza, Lo Yu-Lung, Raza M Mohsin
Department of Mechanical Engineering, National Cheng Kung University, No.1, Daxue Rd., East Dist., Tainan City 701, Taiwan.
Materials (Basel). 2021 Sep 10;14(18):5202. doi: 10.3390/ma14185202.
The mechanical properties of selective laser melting (SLM) components are fundamentally dependent on their microstructure. Accordingly, the present study proposes an integrated simulation framework consisting of a three-dimensional (3D) finite element model and a cellular automaton model for predicting the epitaxial grain growth mode in the single-track SLM processing of IN718. The laser beam scattering effect, melt surface evolution, powder volume shrinkage, bulk heterogeneous nucleation, epitaxial growth, and initial microstructure of the substrate are considered. The simulation results show that during single-track SLM processing, coarse epitaxial grains are formed at the melt-substrate interface, while fine grains grow at the melt-powder interface with a density determined by the intensity of the heat input. During the solidification stage, the epitaxial grains and bulk nucleated grains grow toward the top surface of the melt pool along the temperature gradient vectors. The rate of the epitaxial grain growth varies as a function of the orientation and size of the partially melted grains at the melt-substrate boundary, the melt pool size, and the temperature gradient. This is observed that by increasing heat input from 250 J/m to 500 J/m, the average grain size increases by ~20%. In addition, the average grain size reduces by 17% when the initial substrate grain size decreases by 50%. In general, the results show that the microstructure of the processed IN718 alloy can be controlled by adjusting the heat input, preheating conditions, and initial substrate grain size.
选择性激光熔化（SLM）部件的力学性能从根本上取决于其微观结构。因此，本研究提出了一个由三维（3D）有限元模型和元胞自动机模型组成的集成模拟框架，用于预测IN718单道SLM加工中的外延晶粒生长模式。考虑了激光束散射效应、熔体表面演变、粉末体积收缩、整体异质形核、外延生长以及基板的初始微观结构。模拟结果表明，在单道SLM加工过程中，粗大的外延晶粒在熔体 - 基板界面处形成，而细小晶粒在熔体 - 粉末界面处生长，其密度由热输入强度决定。在凝固阶段，外延晶粒和整体形核晶粒沿着温度梯度向量向熔池顶面生长。外延晶粒生长速率随熔体 - 基板边界处部分熔化晶粒的取向和尺寸、熔池尺寸以及温度梯度而变化。观察到，通过将热输入从250 J/m增加到500 J/m，平均晶粒尺寸增加了约20%。此外，当初始基板晶粒尺寸减小50%时，平均晶粒尺寸减小17%。总体而言，结果表明，通过调整热输入、预热条件和初始基板晶粒尺寸，可以控制加工后的IN718合金的微观结构。
