| Summary: | 碩士 === 國防大學理工學院 === 材料科學碩士班 === 98 === In this study, AISI 1080 carbon steel and SS430 stainless steel are used as the substrates. The rolling or Ni-electroplating technieque is employed as a pretreatment to produce many defects on the surface of the substrate, and then the low temperature (700℃) pack chromium-nickel co-deposition is carried out to improve the corrosion resistance and interfacial contact resistance of the steels. The pack powder mixture composes a codeposition master (chromium-nickel), activator (NH4Cl) and inert filler (Al2O3). The powder mixture is mixed up in accordance with a suitable proportion in order to produce the anti-resistance coatings with rich-chromium and a little amount of nickel. The XRD results show that the coating mainly composes of (Cr, Fe)7C3 and (Cr, Fe)23C6 phases, and little amount of nickel oxides. The co-deposition specimens are conducted with potentiodynamic and potentiostatic test in a 0.5 M H2SO4 solution. The results show that the corrosion potential of SS430 stainless steel treated with chromium-nickel co-deposition can be improved from -0.47 V to 0.05 V, and the corrosion current density can be reduced from 2.6E-3 Acm-2 to 9.86E-8 Acm-2. The corrosion potential of AISI 1080 carbon steel treated with chromium-nickel co-deposition can be improved from -0.5 V to 0.4 V, and the corrosion current density can be reduced from 3.2E-3 Acm-2 to 4.98E-7 Acm-2. Potentiostatic results show that the specimen treated with chromium-nickel co-deposition is more stable than that of simple chromized specimen, which verified that a small amount of nickel in the chromized coating is more stable and can prevent the coating from pitting corrosion in the simulated PEMFC environments.
The Ni-electroplated and chromized specimens exhibit better corrosion resistance than simple chromized specimens as a result of the thicker chromized coating and less amounts of Fe in the coatings, which indicated that the nickel electroplated layer can not only improve the diffusion rate of elements greatly, but alse serve as a barrier layer to enhance the corrosion resistance and interfacial contact resistance of the coating produced in the same processing conditions.
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