High temperature air oxidation behavior of Hastelloy X processed by Electron Beam Melting (EBM) and Selective Laser Melting (SLM)

•The initial microstructure of the AM alloys was strongly dependent on the build procedure, parameters, composition and heat treatment (EBM versus SLM).•Faster oxidation kinetics were observed for the alloys with high Mn and Si contents. The alloys with high Mn and Si contents formed an outer oxide scale consisting of MnCr2O4 on top of a Cr2O3 layer with underlying SiO2 precipitates.•In the presence of a MnCr2O4 layer, a finer Cr2O3 grain microstructure and larger Mn depletions were observed in the underlying alloy.•The Cr depletion induced the dissolution of Mo-rich carbides underneath the oxide layers.•The significant spallation of the EBM1 alloy was associated with presence of a continuous SiO2 layer along with carbide dissolution/oxidation at grains boundaries and the large elongated grain alloy microstructure. The microstructure and oxidation behavior of Laser Beam Melted, Electron Beam Melted and wrought Hastelloy X were studied at 950 °C in dry air, 50 h cycles, up to 1000 h. The variability of processing parameters and powder compositions strongly impacted the oxidation and spallation behavior. The alloys with high Mn and Si were associated with higher oxidation rates, finer Cr2O3 grain microstructure and increased spallation was observed for the alloys with large elongated grain microstructures (aspect ratio of 10 ± 3).