Impact of feedstock recycling on the corrosion resistance of inconel 625 processed by L-DED

The corrosion resistance of Inconel 625 processed by L-DED additive manufacturing using virgin and reused powders was investigated to optimize the cost-effectiveness of the process. Samples were manufactured under a controlled argon atmosphere. Feedstock and samples were characterized by optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, and rheology analysis. Corrosion resistance was investigated by cyclic polarization and electrochemical impedance spectroscopy in NaCl 3.5% media. Rheology accused a slight decrease in powder flowability with reuse, but no further appreciable powder degradation was observed. Samples developed a dendritic microstructure with Mo- and Nb-rich Laves phase in the interdendritic region. Samples processed with reused powder were found to have a high content of oxides, which accounted for a slightly inferior impedance and reduced the charge transfer resistance by nearly 50%. Specimens had an overall similar cyclic polarization, with the specimen processed with virgin powder having a slightly superior performance, with a 60mV more noble E_corr and higher R_p, but similar I_corr. Samples presented uniform and pitting corrosion mechanisms, with pits being preferentially located in the Mo-depleted dendritic regions. In summary, the reuse of Inconel 625 powder processed under argon-controlled conditions was not considered to be significantly detrimental to the alloy corrosion resistance. (author)