采用有限元方法(FEM),考虑了粉末-实体状态的转变以及相变潜热等因素,建立了不同扫描速度下的单层多道温度场仿真模型,并结合实验分析缺陷的产生、微观组织以及力学性能的各向异性。实验结果表明:随着激光扫描速度的增加,液相的润湿性降低,内部孔隙率增大,且熔池的深度和宽度逐渐减小,不易形成良好的冶金结合。熔池内包含大量的胞状晶和树枝状枝晶,高温度梯度易诱导产生胞状晶,而低温度梯度易诱导产生树枝状枝晶。仿真结果也表明,由于不同方向上温度梯度的差异性,横截面与纵截面的平均晶粒尺寸、晶粒取向、应变分布以及晶界取向差分布呈现一定差异。另外,水平放置的试样具有较高的屈服强度,但延性明显低于沿着构建方向且具有细长柱状晶粒的垂直放置试样。

Herein, the finite element method (FEM) is used to simulate a single-layer and multi-track temperature field considering the powder-to-solid transition and latent heats of melting at different scanning speeds. The generation of defects, anisotropy of microstructure, and mechanical properties are experimentally analyzed. Results show that increasing the laser scanning speed tends to reduce the wettability of the liquid phase and increase porosity. Moreover, the depth and width of molten pool gradually decrease, which hinders the formation of good metallurgical bonding. Numerous cellular and dendrites are formed in the molten pool, and the high temperature gradient tends to induce planar or cellular dendrites, while the low temperature gradient tends to induce dendritic dendrites. The simulation also demonstrates that the average grain size, grain orientation, strain distribution, and the distribution of the boundary-misorientation angle on the cross-section and longitudinal section show some differences owing to differences in the temperature gradient along different directions. Furthermore, the transverse samples display a higher yield strength, but the ductility is significantly lower than that of vertical samples containing elongated columnar grains along the building direction.