In-process spectroscopic detection of chromium loss during Directed Energy Deposition of alloy 718

In this work, a fast optical spectrometer was used to monitor the Directed Energy Deposition (DED) process, during the deposition of Alloy 718 samples with different laser power, thus different energy inputs into the material. Spectroscopic measurements revealed the presence of excited Cr I atoms in the plasma plume. The presence was more apparent for the samples characterized by higher energy input. The Cr depletion from these samples was confirmed by lower Cr content detected by Energy-Dispersive X-ray Spectroscopy (EDS) analysis. The samples were also characterized by higher oxidation and high-temperature corrosion rates in comparison to the samples produced with low energy input. These results prove the applicability of an optical emission spectroscopic system for monitoring DED to identify process conditions leading to compositional changes and variation in the quality of the built material. [Display omitted] •An in-process monitoring system based on a spectrometer allows detecting variation in processing conditions during DED.•Spectroscopic data indicates vaporization and depletion of vital alloying elements from the deposited material.•The system has a high sensitivity, as conditions leading to changes of less than 1 wt% of chromium content were detected.