Production of new type Ni-Cr/hBN functional composite coatings by electrodeposition method and investigation of mechanical and corrosion properties

In this thesis, AISI 1040 steel substrate was coated with electrodeposition method in for different ways. Firstly, Ni-Cr alloy coating was applied on the substrate. By referring to three different levels for pH, temperature, current density and stirring speed parameters, the samples were produced in according to the L9 orthogonal sequence suggested by the Taguchi experimental design method and then compared to each other by their corrosion rate. Also, by utilizing ANOVA, the percentages of the parameters affecting the results were determined. Secondly, different amounts of saccharin (0, 0.5, 1, 2 g/l) were added into the coating bath to remove the cracks that are characteristic of Ni-Cr alloy coatings. Thus coating samples were produced, characterized and their mechanical and corrosion behavior were examined. Thirdly, in order to improve the wear and mechanical properties of Ni-Cr coatings, the hBN addition was considered. Coatings were produced by adding different amounts (0, 5, 10, 20, 30 g / l) of hBN to bath concentrations. Finally, Ni-Cr/hBN coatings were produced functionally by using three different baths in order to improve the adhesion between the coating and the substrate. The electrochemical behavior of the coatings produced using the cyclic voltammetry technique. The investigation of crystal structures were conducted with X-ray diffraction and the surface morphologies and content analysis were conducted with scanning electron microscopy and energy dispersive X-ray analysis. The microhardness, nano hardness and surface roughness measurements were also concluded. Moreover, the wear resistance of the coatings was examined. Also, the corrosion performances of the coatings obtained were investigated in 3.5% NaCl solution by utilizing open circuit potential, tafel extrapolation and electrochemical impedance spectroscopy methods. Results proved that the cracked structures of Ni-Cr coatings were removed by adding saccharine to the plating bath and improvements in both mechanical and corrosion behavior were achieved with hBN addition. As a final note, the adhesion strength of the coatings were determined to be increased with the functional coating.