Surface, microstructure, and tensile deformation characterization of LPBF SS316L microstruts micromachined with femtosecond laser

• Published in: Materials & design Vol. 210; p. 110045
• Main Authors: Ghosh, Abhi, Biswas, Sanchari, Turner, Tiffany, Kietzig, Anne-Marie, Brochu, Mathieu
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-11-2021; Elsevier
• Subjects: Femtosecond laser; Laser powder bed fusion; Micromachining; Microstruts; Stainless steel 316L; Surface roughness; Tensile deformation; Laser powder bed fusion; Tensile deformation; Micromachining; Microstruts; Femtosecond laser; Surface roughness; Stainless steel 316L
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2021.110045

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•For the first time, femtosecond laser micromachining has been utilized to eliminate the as-built surface roughness of LPBF fabricated microstruts, including its surface-associated microstructures.•The femtosecond laser micromachining causes no significant microstructural damage at the surface and sub-surface of the microstruts.•Micromachined microstrut tensile specimens experience a considerable enhancement in uniform tensile elongation in comparison to their as-built state.•Micromachining-associated surface features affect the non-uniform tensile elongation; ablation-induced surface asperities evolve into notches and initiate the final failure.
Considerable surface roughness, dimensional deviation, and non-uniform microstructure are a few of the characteristics found on thin or micro-scale features fabricated via laser powder bed fusion (LPBF) that yield inferior and/or inconsistent mechanical properties. Femtosecond laser micromachining can aid in fabricating micro-scale parts with ultra-high dimensional precision. In this work, the surface and tensile behavior of microstruts of 500μm nominal diameter micromachined with Gaussian laser pulses of <100fs duration are characterized. Roughness parameters such as Ra=0.9±0.2μm and Rz=3.4±1.3μm are achieved on the micromachined faces. Surface-associated grains are successfully ablated with negligible microstructural damage to the microstruts. As a result, the average uniform strain under quasi-static tensile loading is measured as 0.54±0.02 compared to 0.42±0.01 for the as-built microstruts. Uniform and non-uniform deformation strain portions are separated analytically and characterized primarily via in-situ imaging. Progressive degradation of the surface and dimensional variance is observed on the micromachined test specimens. Post necking initiation, ablation-associated asperities on the micromachined surfaces evolve into notches, leading to tensile failure.