Corrosion of Ni-Al and Ni-Al-Al_2O_3 Flame Sprayed Coatings of 'CastoDyn 8000' System in 0.01 M H_2SO_4 and 3.5 NaCl Solutions

摘要

In the paper researches results of corrosion properties of Ni-Al alloy and Ni-Al-Al_2O_3 composite coatings were presented. Coatings were obtained by flame spraying of "Casto-Dyn 8000" torch. During coatings flame spraying of torch was used a small distance from the substrate. Instead of commonly used spray distance 150 mm, 100 mm was used. The studies in 0.01 M H_2SO_4 and 3.5% NaCl (artificial seawater) environments were realized. Evaluated coatings are more corrosion resistant in the 3.5% NaCl environment than in the 0.01 M H_2SO_4. Corrosion current density for alloy coatings in artificial seawater was 20 μA/cm~2 and 223 μA/cm~2 in an acidic environment. The value of corrosion potential in an environment of 3.5% NaCl is about 200 mV lower than in 0.01 M H_2SO_4. Composite coatings Ni-Al-Al_2O_3 were characterized by a lower corrosion current densities and increased resistance than Ni-Al coatings in acidic environment. The presence of alumina in the coating matrix caused increased corrosion current density in sea water environment.