Study On Technical And Mechanism Of Ni-based Composite Coatings By Direct And Pulse Current Electrodeposition

Electrodeposition is one of the most useful and effective methods to produce functional coatings. Comparing to plasma thermal spray or physical vapor deposition methods, electrodeposition is a simple, low-temperature and low-cost technique to fabricate matrix composite coatings and nanostructured materials. Electroplating is not be restricted by the size and shape of the substrate materials, and it usually can be completed once for all without further complicated subsequent treatment, and thus frequently become popular in processing of metal protection, nanomaterials and catalytic materials.Electrodeposition Ni-Cr alloy coatings have attractive properties such as good corrosion resistance performance, good wear resistance and high microhardness. As a result, the technical and performance of electrodeposition Ni-Cr alloy coatings are the focus of this study, the TiO2 particles were used to enhance the performance of electrodeposition Ni-Cr alloy coatings. Comparing to Ni-Cr alloy coatings, the Ni-Cr-TiO2 composite coatings have better corrosion resistance performance and higher microhardness. The main results are as follows:(1) The Ni-Cr alloy coatings were successfully prepared on mild steel surface by direct current and pulse current deposition technique, respectively. The electrolyte used for the electrodeposition contained CrCl3·6H2O 75g/L, NiSO4·6H2O 50g/L, NiCl2· 6H2O 45g/L, H3BO350g/L, Sodium citrate 135g/L, Surfactant 0.2g/L. The Ni-Cr-TiO2 composite coatings were also successfully prepared by direct current and pulse current deposition technique.(2) The microstructure and performance of the coatings were greatly affected by electrodeposition method. The average grain diameter of the PC Ni-Cr alloy coatings is much smaller than that of the DC Ni-Cr alloy coatings. The Ni-Cr alloy coatings trend to get fine compact structure by doping TiO2 particles.(3) The DC and PC alloy coatings were obtained at different current densities (15-35 A dm"2). The microhardness tests were carried out on the prepared Ni-Cr alloy coatings, when the current density is 25 A dm-2, microhardness values of the DC and PC alloy coatings are higher. The maximal microhardness value of the alloy coatings prepared by PC deposition was measured to 825 Hv, while that of the alloy coatings prepared by DC deposition was 715 Hv. The maximal microhardness value of DC improvement than that of oven-dried paper. While the non-polar solvent such as water, ethanol soaking Ni-Cr-TiO2 composite coatings was 1210Hv, and PC Ni-Cr-TiO2 composite coatings is 1400Hv. It is apparent that the TiO2 particles play an important role in improving the microhardness of the Ni-Cr alloy coatings.(4) The weight loss of the test samples after the corrosion tests were used to evaluates their corrosion rates. The corrosion rates of the DC and PC Ni-Cr alloy coatings are 0.295 g m-2 h-1 and 0.198 g m-2 h-1, respectively. The corrosion rates of mild carbon steel is 1.05 g m-2 h-1. The corrosion rates of the DC and PC Ni-Cr-TiO2 composite coatings are 0.295 g m-2 h-1 and 0.198 g m-2 h-1, respectively. The coatings prepared by electrodeposition method can efficiently protect the substrates against corrosion. The electrodeposition method and the TiO2 particles play an important role in improving the microstructure and performance of the Ni-Cr alloy coatings.