Metal Additive Manufacturing Conference 2018

Selective laser melting (SLM) enables the elaboration of metallic alloys and the fabrication of engineering components directly from metallic powder. Such alloys have specific microstructure and therefore their corrosion behaviour is significantly different from that of alloys elaborated by classical methods (wrought structure). Referring to the limited prior work in this field, most of papers show that 316L samples elaborated by SLM exhibited better corrosion resistance than samples with wrought structure. It has also been shown that metastable pit frequency was found to increase with specimen porosity and the repassivation potential was found to decrease with specimen porosity. By contrast, pitting potential values do not change significantly with specimen porosity. The role of other metallurgical parameters (crystallographic orientation…), of the passive film and of the surface preparation has not been considered yet. In this study, the microstructure of 316L stainless steel elaborated by SLM was first investigated by means of FE-SEM/EDS (chemical composition, presence of particles or pores…), EBSD (crystallographic structure, grain orientation spread) and XRD (crystallite size, phase analysis, texture component). The native passive film formed spontaneously in air after surface preparation was also analysed using XPS and AES (composition, structure and thickness). Two surfaces were considered: the first surface (x-y) oriented perpendicular to the build direction and the second surface (x-z) perpendicular to (x-y). The corrosion behaviour of the two surfaces was then determined from potentiodynamic tests in chloride containing media (from 3.5wt.% up to saturation). Results obtained on samples elaborated by SLM were compared to those obtained on wrought structures (316L). The influence of the microstructure (surfaces (x-z) and (x-y)) and of the surface preparation (roughness and cold worked layer generated by mechanical grounding) on pit initiation and propagation was quantified from 3D surface measurements. Obtained results (pitting potential, passive current density, pit morphology…) were discussed considering the samples microstructure and the native passive film properties.