Microstructure and corrosion performance of 316L stainless steel fabricated by Selective Laser Melting and processed through high-pressure torsion

For the first time, the novel combination of severe plastic deformation (SPD) and Additive Manufacturing (AM) in a single process sequence was explored. 316L stainless steel (316L SS) alloy was firstly fabricated by Selective Laser Melting (SLM) AM process and subsequently processed by high-pressure torsion (HPT) SPD technique under a constant pressure of 6 GPa for different torsional revolutions. All the processed samples were subjected to electrochemical testing in a 3.5 wt % NaCl aqueous solution using open-circuit potential, potentiodynamic polarisation, and electrochemical impedance spectroscopy techniques, and characterised with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microscopic measurement results revealed that the melt pools and cellular structures obtained via SLM become increasingly refined through increased HPT revolutions, accompanied by significant porosity reduction and significant increase in microhardness. TEM observations revealed a homogeneously distributed nano-scale grains after 10 turns. Moreover, the results demonstrated that HPT processing significantly enhances corrosion performance of the 316L SS alloy in NaCl solution, due to the cellular structure refinement, homogeneous microstructure distribution, and the substantial removal of pores and defects. SEM and energy dispersive x-ray spectroscopy (EDX) analysis were also carried out on the corroded samples to determine the influence of cellular structure refinement on the corrosion characteristics of the 316L SS alloy. (C) 2018 Elsevier B.V. All rights reserved.