(Invited) Passivity and Pitting Corrosion Behavior of Additive Manufactured 17-4PH Stainless Steel

Abstract

Conventionaly manufactured, i.e. wrought, 17-4PH martensitic stainless steel (MSS) is widely used in a large variety of applications, going from biomedical ustensils to large turbine blades. Recently, it appeared as a good candidate for additive manufacturing processes, e.g. laser beam melting (LBM), which is certainly the most common and developed process at this time. The specific microstructures generated by LBM have been well discussed in the literature for many types of materials. Nevertheless, these peculiarities can also affect the durability of the LBM-manufactured parts and specifically their corrosion behavior.The main goal of this work was to propose a detailed study of the pitting corrosion behavior of a 17-4PH MSS manufactured by LBM. In this framework, LBM parts were built from 17-4PH MSS powder, using optimized machine parameters. Samples of a commercial counterpart (CM –MSS) machined from a wrought cylindrical bar were studied as references. The pitting corrosion behavior of both MSSs was studied in chloride-containing solutions by combining linear potentiokinetic polarization associated with the determination of pitting potentials, and a statistical analysis of the current transients observed during potentiostatic experiments for metastable pitting. Significant differences were observed between the LBM and CM MSSs. They were explained considering the passive film composition, structure and morphology evaluated by combining transmission electron microscopy (TEM), scanning TEM (STEM) using the high-angle annular dark field (HAADF) mode, and Energy dispersive X-ray Spectroscopy (EDS) analyses. Results were related to the specific microstructure of the LBM samples as compared to that of the CM MSS, both microstructures being characterized by TEM, STEM and EDS.