article · Materials Science and Engineering A
This research examines how volumetric energy density affects defects, microstructure, and fatigue performance in 316L stainless steel produced via laser beam powder bed fusion. Three energy density levels were tested and evaluated against conventional wrought steel. Higher volumetric energy density increased component density from 91.8 percent to 99.6 percent while reducing the size and complexity of defects, particularly lack-of-fusion voids. Most defects occurred in subsurface areas near the border hatch-fill contour layer. In high cycle fatigue tests, the printed parts underperformed compared to wrought steel because of defect sensitivity. However, under low cycle fatigue conditions, parts made with medium and high energy densities performed closely to wrought material, supported by twinning and martensitic transformation. Reaching high cycle fatigue limits similar to traditional wrought steel requires minimizing defect density.
Components made through metal 3D printing often contain microscopic flaws that cause them to break unexpectedly under repeated mechanical loading. Understanding how printing energy inputs reduce these internal flaws helps engineers produce 3D-printed stainless steel parts that behave more predictably, bringing their structural durability closer to traditionally manufactured metals.
This work provides applied, test-level parameters for manufacturers using laser powder bed fusion to fabricate 316L stainless steel parts subjected to cyclic stresses. By identifying that subsurface defects control high cycle fatigue, the findings inform process optimisation for industrial additive manufacturing users seeking wrought-like performance, though commercial implementation requires further refinement to reliably eliminate critical defect densities.
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Three structures of AISI 316L austenitic stainless steel were additively manufactured using the laser beam powder bed fusion (PBF-LB) process with varying volumetric energy density (VED) levels: low (50.8 J/mm³), medium (79.4 J/mm³), and high (84.3 J/mm³). The impact of VED on defects, microstructure, and fatigue behaviour was investigated and compared to wrought 316L steel. Various novel techniques were used to analyse the grain structure and defects. Fatigue behaviour was assessed through low and high cycle fatigue tests and tensile tests at room temperature. Results showed that increasing VED improved material density (from 91.8 % to 99.6 %) and reduced defect size and complexity. Both lack of fusion (LoF) and pore-type defects were identified, with fewer and less complex LoF defects at higher VED. Defects were primarily located at subsurface regions corresponding to the border hatch-fill contour layer. Printed structures exhibited lower high cycle fatigue (HCF) strength than wrought steel, but this difference diminished in low cycle fatigue (LCF) regimes for medium and high VED structures, where twinning and martensitic transformation enhanced fatigue strength. The defect characteristics significantly influenced HCF strength, and achieving a fatigue limit comparable to wrought steel requires very low defect density even at high VED.
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DOI: 10.1016/j.msea.2025.147868
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