Characterization of the High-Temperature Oxidation Behavior of Inconel 625® Fabricated by Additive Manufacturing and Conventional Methods

The differences between the isothermal oxidation behavior of the Inconel 625 (R) superalloy fabricated by additive manufacturing and wrought conditions are presented. At 900 and 1000 degrees C, the oxidation kinetics of polished specimens exposed to synthetic dry air followed the parabolic rate law. The values of the oxidation rate constant k(p) were similar to values obtained for the same alloy and similar oxidation conditions in different investigations and depended on both, oxidation temperature and alloy condition being k(pW) = 1.2 x 10(-3) mg(2)cm(-4) h(-1) and k(pAM) = 2.9 x 10(-3) mg(2)cm(-4) h(-1) for the alloys in wrought and additive manufacturing conditions, respectively, at 900 degrees C and k(pW) = 16 x 10(-3) mg(2)cm(-4) h(-1) and k(pAM) = 74 x 10(-3) mg(2)cm(-4) h(-1) for the alloys in wrought and additive manufacturing conditions, respectively, at 1000 degrees C. For both alloys, chromia Cr2O3 was the primary oxide found on the surface of the alloy, together with nodules of NiCr2O4 spinel. Metallographic cross sections of the specimens revealed the formation of Al- and Ti-rich intergranular oxides below the metal-oxide interface. The amount of surface and subsurface oxidation of the alloys depended on their microstructures and their porosity.