Improving oxidation resistance of wire arc additive manufactured Inconel 625 Ni-based superalloy by pack aluminizing

The aluminide coating layer was formed on wire arc additive manufactured (WAAM) Inconel 625 (IN625) Ni-based superalloy by a pack-aluminizing process at 700 degrees C for 3 h. The aluminide coatings were evaluated utilizing X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and nanoindentation techniques. In addition, the oxidation performances of the aluminide coatings were compared with as-built WAAM IN625 samples based on their exposure in the open-air environment for 5, 25, and 50 h at 1000 degrees C. The aluminizing process provided a dense aluminide coating with a thickness of 35 mu m, continuous throughout the surface. The coating layer consists of mainly NiAl, Ni2Al3, Cr2Al, and MoAl5 phases and exhibited a nano-hardness of 12.85 +/- 0.43 GPa. Moreover, the applied heat treatment also improved the surface hardness and elasticity modules of WAAM Inconel 625. The stability of aluminide phases (NiAl, Ni2Al3) at temperatures exceeding 1000 degrees C and the formation of stable Al2O3 oxide islands on the surface provided 6.63 times, 2.70 times, and 2.65 times better oxidation resistance in the aluminized samples than the as-built WAAM IN625 in the 5 h, 25 h and 50 h oxidation periods at 1000 degrees C, respectively. In contrast, the increase in the oxidation time changed the oxidation mechanism of as-built WAAM IN625 from Cr2O3 to Cr2O3 and spinel phases such as NiCr2O4, NiMoO4, and NiO. On the other hand, the increase in the oxidation time in aluminized samples caused Kirkendall voids formation and their degradation. Therefore, it was concluded that the mechanical properties could be improved, and the oxidation resistance of these alloys could be improved with the aluminizing heat treatment.(c) 2023 CIRP.