High-temperature oxidation behavior and mechanism of Inconel 625 super-alloy fabricated by selective laser melting

Abstract

In this work, the high-temperature oxidation behavior and mechanism of Inconel 625 super-alloy manufactured by selective laser melting are systematically analyzed by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), electron back scatter diffraction (EBSD), transmission electron microscopy (TEM), isothermal oxidation tests and X-ray diffraction (XRD). According to the oxidization kinetic curves, the high temperature oxidation resistance capacity of the specimens drops as the laser energy density (LED) decreases from 167 to 76 J/mm3. The oxide structure of the specimen after 100 h oxidation is composed of Cr2O3 oxide layer and Ni-rich oxides and more Ni-rich oxides can be observed as the LED drops. The cross-sectional SEM images present that the oxide scale is consisted of an External Oxide Layer (EOL) and an Internal Oxide Zone (IOZ). The EOL becomes thicker and more severe internal oxidation in IOZ is observed as the LED decreases from 167 to 76 J/mm3. The further analysis reveals that the drop in high temperature oxidation resistance of the specimen is mainly caused by bad surface quality and poor microstructure brought by insufficient input laser energy. The bad surface quality and poor microstructure causes severe spallation in the oxidation process, which makes it difficult to form a protective Cr2O3 oxide layer and leads to further oxidation.