Conventionally, the main goal of process optimization in selective laser melting is to achieve the highest relative density. However, for Inconel 718, this study has demonstrated that the highest relative density does not correspond to the best mechanical properties. Moreover, similar relative densities can result in significant differences in mechanical properties. This phenomenon arises from the presence of cracks in the microstructures. The research was carried out to study the problem systematically using combinations of 2 layer thicknesses (40 and 50 μm) and 2 laser energy densities (3.17 and 3.47 J/mm²). Microcracks were observed near the melt pool boundaries and within the heat-affected zones of the newly deposited layer, occurring along the grain boundaries and interdendritic regions. Evidence was obtained to show that the cracking was associated with remelting of Laves phase; therefore, it was identified as liquation cracking. It is interesting to observe that layer thickness has a much greater influence on crack formation than laser energy density, owing to the significant change in the melt pool shape and grain boundary morphology when the layer thickness was changed. The influence of laser energy density was only observed at the larger layer thickness as the severity of cracking was amplified when laser energy density was increased due to microstructural coarsening. Thus, this presents a unique problem in additive manufacturing (AM) regarding liquation cracking in Inconel 718 as one of the key differences from conventional manufacturing is the successive heating and reheating of multiple layers of material in AM.

传统上，选择性激光熔化工艺优化的主要目标是实现最高的相对密度。然而，对于 Inconel 718，这项研究表明最高的相对密度并不对应于最佳的机械性能。此外，相似的相对密度会导致机械性能的显着差异。这种现象源于微观结构中裂纹的存在。该研究旨在系统地使用 2 层厚度（40 和 50 微米）和 2 种激光能量密度（3.17 和 3.47 J/mm ²）。在熔池边界附近和新沉积层的热影响区内观察到微裂纹，沿晶界和枝晶间区域发生。获得的证据表明开裂与 Laves 相的重熔有关；因此，它被确定为液化开裂。有趣的是，由于当层厚度改变时熔池形状和晶界形态发生显着变化，层厚度对裂纹形成的影响比激光能量密度大得多。激光能量密度的影响仅在较大的层厚度下观察到，因为当激光能量密度由于显微组织粗化而增加时，裂纹的严重程度被放大。因此，