Hot corrosion performance of a NiCr coated Ni-based alloy

The hot corrosion performance of high velocity oxy-fuel sprayed Ni–20Cr wire coating on a Ni-based superalloy is evaluated for 1000 h at 900 °C under cyclic conditions in a coal-fired boiler. The performance of bare and Ni–20Cr coated Superni 75 is assessed via thermogravimetric data, metal thickness loss corresponding to the corrosion scale formation, scale thickness loss and the depth of internal corrosion attack. The better hot corrosion resistance of the coated alloy is mainly attributed to the formation of a thick band of chromium oxide just above the scale–substrate interface and chromium oxide stringers along the splat boundaries, as well as to the nickel oxide and the dense and uniform fine grain structure of the as sprayed coating.