| Nano-composite coating has been given more and more attention because of the excellent performance. In this article, Ni-Al2O3 nano-composite coating has been prepared by high frequency pulse electrical source. The role of pulse frequencies and content of nano-particles in the initial deposition behavior was a key in the research. At the same time, high temperature oxidation-resistance and corrosion-resistance of the coatings were studied systemically.In the preparation process, nano-particles not only could be dispersed well in the bath, but also distributed uniformly in the coatings and made surface of coatings smooth by choosing fit dispersant. According to test micro-hardness, the best experimental factors could be determined.In order to study the texture and microstructure, SEM was used to observe the surface morphology of coatings. The results showed that texture of the composite coatings could be more refined and particles distributed more uniformly in the coatings as pulse frequency increased. Because nucleation rate of crystal nucleus increased and propagation rate of crystal nucleus was slow as pulse frequency raised and concentration polarization reduced. When nano-Al2O3 participated in deposition action, there were many point and extension defects in matrix of Ni, which made crystal faces grow differently and a lot of irrecoverable steps were formed in surfaces of coatings. X-ray was used to analyze how pulse frequencies affect the crystallization process and crystallization behavior in the electro-deposition. We found that crystalline lattices increased as pulse frequency raised, which induced that lattice distortion changed from minus to positive. Crystalline lattice distortion prompted that grains were more refined. At the same time, the preferred orientation of crystal faces changed when pulse on-time shortened. New atomics tended to diffuse to face of (111) from face of (200), because atomic packing density of the former was higher. This action made the atomics deposit in face of (111), the surface energy of which is lower. Then face of (111) was the twin interface and crystal particles formed twins. The result was validated by TEM.The weight-increase was studied in the process of heat treatment. The result was that weight gain of deposition prepared by high pulse frequency was less than the one by lower pulse frequency. It showed that the high temperature oxidation resistance of coatings was better when pulse frequency increased. Optical microscope was used to observe the surface of coatings after heat treatment. The result was that the coatings' high temperature resistance was good when temperature was low. The grains grew notably as the coating was burned for 12 hours at 1000℃, which showed that the high temperature resistance of coatings reduced.According to investigate corrosion resistance of coatings, we found that pulse frequencies and corresponding nano-particles took effect differently in corrosion resistance of coatings as the solution changed. Anodic polarization curves of coatings in solution of 3.5% NaCl indicated that the corrosion rate of high frequency (120kHz) pulse coating was slowest in active region and the coating (120kHz) was best in corrosion-resistance. We also studied the corrosion resistance of coatings in 15% H2SO4 solution and 10% NaOH solution. The result indicated that the middle frequency (60kHz) pulse coating was damaged badly in solution of H2SO4. All the coatings were not etched in solution of NaOH, owing to excellent corrosion-resistance.
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