Characterization of the Effects of Internal Pores on Tensile Properties of Additively Manufactured Austenitic Stainless Steel 316L

• Published in: Experimental mechanics 2019-07, Vol.59 (6), p.793-804
• Main Authors: Wilson-Heid, A. E., Novak, T. C., Beese, A. M.
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Austenitic stainless steels; Biomedical Engineering and Bioengineering; Characterization and Evaluation of Materials; Computed tomography; Control; Cross-sections; Destructive testing; Dynamical Systems; Elongation; Engineering; Lasers; Mechanical properties; Morphology; Nondestructive testing; Optical Devices; Optical microscopy; Optics; Photonics; Pore size; Porosity; Powder beds; Radiography; Solid Mechanics; Stainless steel; Steel making; Tensile properties; Ultimate tensile strength; Vibration; X-ray radiography
• ISSN: 0014-4851; 1741-2765
• DOI: 10.1007/s11340-018-00465-0

In this study, the effects of internal pores on the tensile behavior of austenitic stainless steel 316L manufactured with laser powder bed fusion (L-PBF) additive manufacturing (AM) were investigated. Both fully-dense samples and samples with intentional internal pores of varying diameters were fabricated. For each sample with a pore, the internal pore was deliberately fabricated in the center of the cylindrical tensile sample during AM processing. By varying the diameter of the 180 μm-tall initial penny-shaped pores, from 150 to 4800 μm within 6 mm gauge diameter cylindrical samples, the impact of lack-of-fusion, commonly present in AM, as well as the impact of well-defined pores in general, on tensile mechanical properties was studied. To link the pore size and morphology to the mechanical properties, the sizes of the initial pores were evaluated using non-destructive Archimedes measurements, 2D X-ray radiography, 3D X-ray computed tomography, and destructive 2D optical microscopy. Samples with and without the single, penny-shaped pore were subjected to uniaxial tension to evaluate the defect size dependent mechanical properties. The intentional pore began to impact ultimate tensile strength when the pore diameter was 2400 μm, or 16% of the cross-sectional sample area. Elongation to failure was significantly affected when the pore diameter was 1800 μm or 9% of the cross-sectional sample area. This shows that 316L stainless steel manufactured by additive manufacturing is defect-tolerant under uniaxial tension loading.