Effect of volume energy density (VED) on the porosity and mechanical properties of Inconel 718 alloy manufactured by laser pwder bed fusion

Abstract

The work investigates the effect of volumetric energy density (VED) on the formation of porosity and mechanical properties of the heat-resistant nickel alloy Inconel 718 manufactured by the LPBF method. The relevance of the study is due to the fact that in most modern works, the relative density (porosity) of the material is considered as the main criterion for the quality of additively manufactured products, while the effect of VED variation under the condition of achieving the same level of relative density remains insufficiently studied. The test specimens were manufactured at two VED values - 48.7 and 57.6 J/mm³ - ensuring the same high relative density at the level of 99.8%. Metallographic analysis of polished sections with a quantitative assessment of porosity, as well as tensile tests, was carried out. It was established that at the same relative density, the nature of the type and size of pores differs significantly depending on the VED value. At a higher VED value, an increased number of small pores with a size of 2-3 μm is observed, while at a lower VED value, their total number is smaller, but there are single pores of larger size (up to 17-20 μm). It is shown that the change in VED has practically no effect on the temporary resistance. At the same time, a significant effect of VED on plastic characteristics was found: samples manufactured at a VED of 57.6 J/mm³ are characterized by increased values of relative elongation and narrowing compared to samples obtained at a VED of 48.7 J/mm³. The obtained results confirm that assessing the quality of LPBF products only by the relative density indicator is insufficient. Variation in VED can cause different defect morphology and different levels of plastic properties even with the same relative density of the material. This indicates the need for a comprehensive approach to optimizing LPBF modes, taking into account not only density, but also stability and reproducibility of mechanical characteristics.