High-Temperature Corrosion Characterization of Ni-Al Laser Cladding: The Effect of Al Content and Fe

To further enhance the high-temperature corrosion resistance of boiler tubes for improved power generation efficiency of biomass and waste-to-energy plants, Ni-Al cladding layers with Al contents of 2, 4, 6 and 8 wt.% were prepared by laser cladding technique. The corrosion characteristics of Ni-Al cladding layers in two salts (NaCl-KCl and NaCl-KCl-K₂SO₄, at 650 °C) were investigated. The critical Al content of Ni-Al cladding layers with better corrosion resistance was determined, and the effect of Fe dilution from the substrate on the corrosion products was studied. In NaCl-KCl, the corrosion rates of all cladding layers were high at the initial stage. As the corrosion proceeded, a continuous and dense Al₂O₃ scale was gradually formed on the Ni-8Al surface, while the other three cladding layers failed to be generated. Therefore, Ni-8Al exhibited the best corrosion resistance. However, in NaCl-KCl- K₂SO₄, Al₂O₃ was continuously dissolved due to the “basic fluxing” mechanism and Ni-8Al underwent significantly severe corrosion. Fe oxides were detected in the corrosion products of all cladding layers. Since Fe ions diffuse more easily through the Al₂O₃ scale, Fe oxides were in the outermost layer and were prone to spalling, which affected the corrosion resistance.