Experimental Analysis of Emissivity in Inconel 718 for Directed Energy Deposition Temperature Monitoring with Thermal Imaging

Abstract This contribution investigates the emissivity of Inconel 718 in the context of laser-based Directed Energy Deposition (DED), focusing on the impact of surface finish variations resultant from additive manufacturing techniques and the challenges it poses when monitoring the process via thermal imaging. We perform directional spectral measurements from 100 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> C to 900 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> C in high vacuum using a custom-made emissometer and analyze the differences between samples synthesized via casting and laser metal deposition. The data are also treated to obtain total hemispherical emissivity values and to compare them to literature data. Finally, as emissivity is the only input data that can be modified in thermographic cameras to calculate the temperature, we perform a temperature calculation error analysis to clarify the conditions and the emissivity input data under which the infrared cameras should operate in these additive manufacturing processes to make the temperature measurement more reliable.