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Tuesday, December 4, 2007 - 4:30 PM
Characterization and Corrosion Properties of Thermally Sprayed Al-CoCe Alloys
An Al-Co-Ce alloy coating has been developed to protect an AA 2024-T351 substrate against localized corrosion. The Al-Co-Ce coating can function as a corrosion barrier, a sacrificial anode and a reservoir to supply soluble inhibitor ions to protect defects site exposing AA 2024-T351 to an aqueous environment. Initial studies have been conducted on spun-melt amorphous ribbons and the three functions described can be achieved. However, it is unclear whether these corrosion mitigating functions can be similarly met when a spray applied coating is applied to AA 2024-T351. Al88Co10Ce2 (at %) coatings were deposited onto AA 2024-T351 substrates using a Pulsed Thermal Spray (PTS) process. The feedstock powders and processed coatings were characterized using X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy. Preliminary corrosion experiments were conducted to determine barrier and sacrificial anode properties on PTS coated AA 2024-T351 surfaces. The pitting potentials of PTS surfaces exceeded the pitting potential of AA 2024-T351, indicating favorable corrosion barrier properties with respect to chloride induced pitting. However, the pitting potentials of the PTS surfaces were not as high as seen for as-spun or heat treated ribbons. Cracks, porosity, and intermetallics may be preventing the PTS coatings from reaching their optimum performance. Characterization of the Al-Co-Ce feedstock powders and coatings indicates the coatings were amorphous with small amounts of Al rich nanocrystals, or nanocrystalline, with intermetallics present. Various diagnostic tests have been undertaken to understand the basis for the reduced corrosion resistance of the spray deposit. The open circuit potentials of PTS surfaces were below those of AA 2024-T351, suggesting favorable sacrificial anode properties. Inhibitor release capability associated Ce3+ was verified by low pH, low chloride concentration experiments on AA 2024-T351 wires with and without the presence of Al-Co-Ce ribbons and spray deposits. The AA 2024-T351 wires received the best resistance to pit initiation when galvanically coupled to Al-Co-Ce ribbons. Even when the Al-Co-Ce ribbons were electrically decoupled from the AA 2024-T351 wires, but still present in the cell, the AA 2024-T351 still received corrosion protection by the chemical inhibition mechanism.
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See more of The 2007 Tri-Service Corrosion Conference (December 3-7, 2007)
See more of The 2007 Tri-Service Corrosion Conference (December 3-7, 2007)