Metal Additive Manufacturing Conference 2019

The market and research for additive manufactured (AM) materials are currently in fast development. However, there are few studies on the influence of the different AM processes on corrosion properties of the final materials. Moreover, due to the heating history during manufacturing process AM metals have a more complex microstructure compared to conventionally manufactured metals. Since the microstructure has a major influence on the corrosion behaviour there is a need for using advanced characterisation techniques that allow a correlation between microstructure features and corrosion properties. In this work the materials investigated were a nickel-based alloy, Inconel 718, and an austenitic stainless steel, 316L. The manufacturing methods were two powder-bed fusion techniques and a direct energy deposition technique. The corrosion properties of the printed materials were evaluated by standard electrochemical testing, including pitting potential, repassivation behaviour and critical pitting temperature. In addition to the standard corrosion tests the Atomic Force Microscopy (AFM) based techniques, Scanning Kelvin Probe Force microscopy (SKPFM) and In-situ AFM, were used to study the electrochemical response and corrosion susceptibility at microstructural level. Areas on the specimen with a positive or negative work function were mapped with SKPFM and correlated to anodic and cathodic zones of the microstructure. In the in-situ AFM the specimens were immersed in a corrosive electrolyte and the topography variations due to corrosion were investigated. A correlative investigation was performed between the AFM results and the microstructure and composition using Electron backscatter diffraction (EBSD). This work showed that the investigated AM processes lead to different corrosion properties of the studied materials compared to the reference alloys. With the AFM based techniques specific microstructures in the alloys were correlated to corrosion initiation. The combined tests provided new insights into the corrosion properties of AM manufactured metals, however, further work is necessary to develop general standards.