Role of Elemental Segregation on the Oxidation Behavior of Additively Manufactured Alloy 625

This study presents the microstructure and oxidation behavior at 800°C in the air of Alloy 625 manufactured by conventional manufacturing and laser-assisted additive manufacturing (AM) processes: powder bed fusion and direct energy deposition (DED). The microstructures of the AM samples were cellular-dendritic, with interdendritic segregation of Nb and Mo. The DED samples have higher segregation and coarser cellular-dendritic structures than the LPBF sample. The AM samples had slightly higher oxidation rates than the wrought sample, even though all samples formed a chromia scale. The oxidized samples also formed a discontinuous δ-phase beneath the chromia scale, where the Nb segregation promoted a higher δ-phase fraction. The δ-phase did not affect chromium consumption during oxidation, but an excessive amount of δ-phase became embedded in the chromia, which apparently promoted scale decohesion.