Microstructure and High-Temperature Corrosion Behavior of Wire-Arc Sprayed Ni-Based Coatings

A series of Ni-based cored wires with different boron content were designed to prepare corrosion-resistant coatings by two-roll wire-arc spraying, which was expected to be an alternative method with sufficiently protective ability and reducing maintenance for waste-to-energy (WTE) plants. The as-deposited coatings, which are primarily composed of nanocrystalline, exhibit uniform and dense layered structure with the porosity around 3%. Thermogravimetry technique was selected to investigate the high-temperature corrosion behavior of the coatings in molten salt environment (Na₂SO₄-10 wt. % NaCl) at 800^oC. As a result, all the coatings present extremely lower corrosion rates compared with that of the SA 213-T2 substrate during all the testing duration, due to the formation of composite surface oxide film, including Cr₂O₃, NiO and NiCr₂O₄, which prevents the diffusing or penetrating of the corrosive species. Furthermore, the boron content expresses a significant influence on the corrosion behavior of the designed coatings, leading to the relative best performance of the coating with 16 at. % boron added. In any case, wire-arc sprayed Ni-based coatings could be an effective and economic approach to withstand corrosion and extend the lifetime of the superheater tubes in WTE plants.