Corrosion Behavior Of High-frequency Pulse-deposited Nano-crystalline Ni Coating

In recent years, nanocrystalline materials with grain size of less than 100nm have received considerable attentions, and become a popular research field in material science. Specially, application and industrialization of nanocrystalline materials have been given more and more attentions. Among numerous synthesis methods for nanocrystalline materials, electrodeposition is considered to be one of the most dominant methods, not only for obtaining pure metals, binary alloys, ternary alloys and composites of nano-structures, but also easily transferring this technology from the research laboratory into industrialization.At present, there is a little research on high-frequency pulse-electrodeposition, in this thesis, the level of pulse-electrodeposition could reach to 140 kHz. The point of this thesis is on deposits' corrosion behavior.Prepared Ni deposits using high-frequency pulse power-supply. The surface morphology and configuration were investigated by X-ray diffraction technique(XRD), scanning electronic microscope(SEM). The results show that, compared to DCdeposits, high-frequency pulse deposits have much more clear and level surface. Calculated the average grain size of Ni deposits, using Scherrer formula. Ther result shows that, the deposits which is prepared under the condition of pulse-frequency 140 kHz, has the smallest grain size, about 45nm. Also it's the most level deposit.The corrosion behavior of high-frequency pulse electrodeposits were deeply researched. Corrosion media included: 3.5% NaCl, 10% NaOH, 15% H₂SO₄. Testing methords were immersing corrosion test and Anodic polarization curse test. The corrosion behavior of Ni deposits could be judged according to the lost weight in these solutions, and the E_corr,i_corr of different Ni deposits.The result shows that, among all these pulse-deposits, the lost weight value is becoming smaller as the pulse-frequency raises, which means the corrosion resistance is getting much better as the pulse-frequency raises.The Anidic polarization was dealed with by extrapolation, each deposit's E_corr and i_corr value could be obtained. The value becomes bigger as the pulse-frequency raises, the biggest value means the best corrosion resistance propersity, the high-frequency pulse deposits have good anti-corrosion propersity.The influence of pulse-electrodeposition parameters on deposit's corrosion behavior was studied. The parameters include: J_m,r,f,pH. Using orthogonal experiment of 4 factors and 5 levels, 25 deposits could be prepared. The corrosion behavior was investigated by immersing corrosion test and Anodic polarization curse test. According to the E_corr and i_corr values, the trend curse of parameters on corrosion property could be gained.The result shows that, as J_m raises, the corrosion propersity raises first and then falls down. The optimum corrosion propersity of deposits in NaOH and H₂SO₄ solutions could be gained when J_m is about 3.5 A·cm², and the optimum corrosion propersity in NaCl solution could be gained when Jm is about 6 A·cm².As r raises, the corrosion propersity falls, so the smallest r value is needed. The pH level of solution is important too, pH=3.3 is preferred for a better corrosion propersity.