Long-term oxidation behavior of additively manufactured Inconel 625 alloys at 900 °C and 1100 °C

In this study, the long-term oxidation behavior of Inconel 625 alloys fabricated via laser powder bed fusion (LPBF) was investigated. Long-term oxidation tests were carried out at 900 °C and 1100 °C and held at the desired temperature for up to 1080 h in an air atmosphere. The LPBF Inconel 625 alloy initially exhibited relatively poor oxidation resistance during high-temperature oxidation because high residual stress increased the chemical activity of the Cr element in the matrix of the alloy. Its oxidation resistance was found to improve with longer exposure times, reaching up to 1080 h. In the oxidized alloy subjected to an isothermal temperature of 900 °C, a protective Cr 2 O 3 oxide layer and Ni 3 Nb intermetallics formed without spallation. By contrast, at 1100 °C over a duration of 1080 h, nonprotective NiCr 2 O 4 and NiFe 2 O 4 oxides resulted in severe spallation of the alloy. In addition, plastic deformation occurred, which stimulated the formation of intergranular voids due to unbalanced Kirkendall diffusion during oxidation. Furthermore, the oxidized alloy at 1100 °C exhibited a deeper Cr-depleted layer compared to that at 900 °C, primarily due to severe spallation. Severe spallation was unavoidable at higher oxidation temperatures, such as at 1100 °C, demonstrating poor oxidation resistance.