Comparison of the Oxidation Behavior at High Temperature of INCONEL 625 Forged and Produced by Additive Manufacturing

The microstructure and oxidation resistance at 900 and 1000 degrees C of additively manufactured (AM) by directed energy deposition (DED) and conventionally manufactured (CM) Inconel 625 alloys were studied. The microstructure of the AM samples was cellular, with Nb and Mo segregations located in the dendritic and interdendritic regions. At 900 degrees C, the oxidation rate was similar for both materials, but was clearly higher for the AM material at 1000 degrees C, being related to the segregation and porosity present in the microstructure of the AM samples. Decrease in porosity by DED changing parameters allowed better oxidation resistance, but still considerably inferior than CM samples at 1000 degrees C. After oxidation, a layer of Cr2O3 was identified under all conditions, providing high resistance to oxidation. Internal oxidation of alumina was also observed in the CM and AM samples. The delta phase Ni3(Nb, Mo) was observed for the CM and AM alloys at the grain boundaries (900 degrees C) and at the metal/oxide interface for both temperatures as a result of chromium depletion. Finally, the oxide layer formed was compact and dense, and some voids were formed in the subsurface region of the samples produced by AM.