Potentiodynamic Evaluation of Selected Corrosion Resistant Thermally Sprayed Coatings in Comparison with Nitrided Stainless Steal

摘要

The corrosion behavior of coatings was evaluated by polarization performed using an electrochemical cell. The 5% solution of H_2(SO)_4 was used as electrolyte. Potentiostat (Gamry 600) with possible range for creating curves from 0,7 to 1,2 V was used. The scanning speed was set at 2 mV/s. To activate the surface before polarization, the samples were cathodically cleaned for 60 seconds at 50 mV. To evaluate the passivation properties using this method, it is also important to monitor the change in curve direction in passivation area of the graph. Different curve shape in passivation area indicates the creation of various passivation films on the coating surface. Positive change in curve direction indicates the creation of three-dimensional passive film protecting the coating. Negative change signifies the creation of one-dimensional layer which only slows further corrosion attack. The resulting surfaces after the test were evaluated by scanning electron microscopy (SEM). Based on the test results using 5% solution of H_2(SO)_4 as electrolyte, some cermet coatings shows higher resistance. Hastelloy C-276 reached the highest resistance out of alloy based coatings.