Interlamellar boundary characterization in Ni-based alloy thermally sprayed coating

The use of thermal spraying process for corrosion protection requires a high level of knowledge concerning the material modifications during coating deposition. The effect of the high velocity oxygen fuel process on inconel 718 thermally sprayed coating microstructure was studied by XRD, transmission electron microscopy and STEM analyses. Thermally sprayed coating exhibits an interlamellar oxidation related to the in-flight and cooling particles. The in-flight oxidation is characterised by a globular oxide which results from convective motion in the liquid phase of the molten particles before impact on the substrate. The oxide was identified as CrNbO4. The cooling step on the substrate induces a duplex oxide with an outer layer composed of columnar spinel oxide (Ni, Fe)Cr2O4 and an inner oxide corresponding to a nanocrystalline CrNbO4 oxide, which is related to the rapid cooling of the flattened particles.