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1 Journal of KONES

1 2010

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Corrosion of Ni-5 percent Al AND Ni-5 percent Al-Al2O3 flame sprayed coatings of "CastoDyn 8000" torch in 0.01 M H2SO4 and 3.5 percent NaCl solutions

Starosta R., Czoska P.

Journal of KONES

2010

Vol. 17, No. 4

471-476

One of methods of regenerating parts of machines is flame thermal spraying, which can be used by ship engine room crew. This method does not require great skill of the operator and is not associated with expensive workstation equipment. Flame sprayed coatings are characterized bv porosity and the presence of oxide inclusions. The presence of pores affects negatively on the corrosion properties of coatings. There is a corrosive environment which may be passed thmugh the pores of the coating to the substrate. This phenomenon is especially dangerous in case of applying cathodic coatings (copper, copper alloys and nickel alloys). The substrate corrosion may then proceed below coating. In the paper researches results of corrosion properties of Ni-Al alloy and Ni-Al-Al2O3 composite coatings were presented. Coatings were obtained by flame spraying of "Casto-Dyn 8000" torch. The studies in 0.01 M H2SO4 and 3.5 NaCl (artificial sea water) environments were realized. Measurements were made following methods: polarization and impedance spectroscopy. Rated coatings are more resistant to the 3.5% NaCl environment than the 0.01 M H2SO4. Corrosion current density for alloy coatings in artificial seawater was 7 miA/cm2 and 232 miA/cm2 environment acidic. Impedance spectroscopy studies showed that the alloy coatings are characterized by more than four times greater resistance in sodium chloride solution than in sulphuric acid solution. Curves flattened in the Nyquist plots may indicate that the appearance of products of corrosion coatings in the pores of the samples during exposure to sea water substitute. The value of corrosion potential in an environment of 3.5% NaCl is about 200 mV lower than 0.01 MH2SO4. Composite coatings Ni-Al-Al2O3 were characterized by a lower corrosion current densities and increased resistance than Ni-Al coatings. This is connected with the operation of non-conducting barrier electrim particles of alumina.