Study On Characterization Of Ni-SiC Nano-composite Coatings By High Frequency Pulse Currents

With the excellent function of the nano-composite coatings in strength, light,electricity,heat and magnetism,the technique of nano-composite electroplating has a good development foreground.The technique of nano-composite pulse electroplating as a newly arisen realm,has advantages of both pulse electroplating and nano-composite electroplating.By restraining concentration grades of discharge ions(that is,electrodeposited ions),Within the liquid layer on the surface of the cathode,pulse plating has attenuated real thickness of diffused layer.Then it also reduced the concentration polarization during the cathode process,increase the limiting diffusion current density of cathode and gain the higher value of cathode polarization within the range of working current density.Since the value of cathode polarization increase,it will need a smaller work of nucleation,then the probability of nucleation and the number of crystal nucleus increased,the electrodeposited coating produced in these conditions will have a compact surface,a low porosity and refined crystals which caused small angle boundaries and in the end resulted in augmentation of materials performance such as hardness,wear resistance,oxidation resistance,corrosion resistance and etc.This text makes a lot of research in the disperse of SiC,electroplating parameter and the hardness,wear resistance,oxidation resistance,corrosion resistance of Ni-SiC nano-composite coatings.By choosing the appropriate dispersant,based on the orthogonal tests,the best dosage of the dispersant have been made sure.The effect of some factors(such as current density,PH value,temperature and addition agent) on Ni-SiC nano-composite coatings were studied.The optimal technological conditions have been made sure for plating Ni-SiC coatings.Ni-SiC nano-composite coating was prepared on copper plate by high pulse electroplating.The characterization of Ni-SiC nano-composite coatings were studied by wear test,oxidation test and micro-hardness.The corrosion resistance of Ni-SiC nano-composite coatings deposited by high frequency pulse current has been studied in 10wt.%NaOH,15wt.%H2SO4 and 3.5wt.%NaCl solution.The morphology of the nano-composite coatings in 10wt.%NaOH,15wt.%H2SO4 and 3.5wt.%NaCl solution before and after were analyzed by scanning electron microscope(SEM).The effect of pulse frequency and the SiC concentration in the electrolyte on the corrosion resistance of Ni-SiC nano-composite coatings were studied.The results show that a Ni-SiC nano-composite coating was prepared on copper plate by high pulse electroplating,with a stable bath into which a mixed dispersant of PEG and CTAB was added,pulse average current density was about 3 A/dm~2,pH was 6, bath temperature was 45℃,when pulse frequency and the SiC concentration in the electrolyte get higher,the best micro-hardness,wear resistance,oxidation resistance and corrosion resistance can be obtained.The wear resistance,oxidation resistance and corrosion resistance of Ni-SiC nano-composite coating is much better than Ni coatings. The behavior of high frequency pulse coatings is also much better than of DC coatings.