Microstructural and mechanical characterization of thin-walled tube manufactured with selective laser melting for stent application

This paper focuses on microstructural and mechanical characterisation of metallic thin-walled tube produced with additive manufacturing (AM), as a promising alternative technique for the manufacturing of tubes as a feedstock for stents micromachining. Tubes, with a wall thickness of 500 μm, were made of 316L stainless steel using selective laser melting (SLM). Its surface roughness, constituting phases, underlying microstructures and chemical composition were analysed. The dependence of hardness and elastic modulus on the crystallographic orientation were investigated using electron backscatter diffraction and nanoindentation. Spherical nanoindentation was performed to extract the indentation stress-strain curve from the loaddisplacement data. The obtained results were compared with those for a commercial 316L stainless steel stent. Both tube and commercial stent samples were fully austenitic, and the as-fabricated surface finish for the tube was much rougher than the stent. Microstructural characterisation revealed that the tube had a columnar and coarse grain microstructure, compared to equiaxed grains in the commercial stent. Berkovich nanoindentation suggested an effect for the grain orientation on the hardness and Young’s modulus. The stress-strain curves and the indentation yield strength for the tube and stent were similar. The work is an important step towards AM of patient-specific stents.