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The quantitative analysis of the effect of the porosity, the volume of fraction of reinforcing phase and the thermal spraying methods, on corrosion properties of composite coatings in marine environment

Starosta R.

Journal of KONES

2016

Vol. 23, No. 1

321--327

In the paper an assessment of the impact of the thermal spray methods, porosity and the volume fraction of reinforcing phase (aluminium oxide) on the corrosion properties (corrosion current density and corrosion potential) of Ni-5%Al alloy coatings and Ni-5%Al-Al2O3 composite coatings reinforced by particle dispersion was presented. The volume fraction of reinforcing phase in the coatings was 15, 30 and 45%. These materials would potentially be used in the shipbuilding industry as regenerative coatings for repair of marine pump shafts. The samples (substrates) were made of carbon C45 (0.45%C) steel. For thermal spray of coatings, two oxy-acetylene (Casto-Dyn DS 8000 and Roto-Tec 80) torches and one plasma gun (PN120) were deployed. The two distances 100 mm and 150 mm from the nozzle onto the substrate were used. In addition, the two substrate temperatures 150°C or 250°C were applied. Corrosion properties of the coatings were tested in a replacement seawater (3.5% NaCl) by polarization curves method. It has been found that among the independent variables considered: a method of thermal spraying, fraction of reinforcing phase and porosity, the last mentioned has the greatest influence on the corrosion properties of thermally sprayed coatings on the matrix of Ni-5% Al. The value of the corrosion potential of coatings depended on the used thermal spray method. It has been found that the more modern method of producing coatings of the higher velocity of the coating material in a sprayed stream has a significant positive effect on the porosity of the coatings. The presence of the reinforcing phase (Al2O3) in composite coatings contributes to a reduction of value of the corrosion current density and increase of the corrosion potential value.