Abstract
Spheroidal graphite cast iron was treated by a duplex surface treatment process, which was combined plasma nitriding and oxidation. The surface and cross-sectional microstructures and corrosion characteristics were analyzed. Potentiodynamic polarization curves were obtained at room temperature from samples immersed in 3% NaCl solution. In the case of oxidation after nitriding, an oxide layer (double layers of Fe 2O 3 and Fe 3O 4) was found to be formed on top of the compound layer (γ′-Fe 4N). The value for the average roughness ( R a) of the plasma nitrided sample was higher than that of the plasma oxidation-treated sample. The untreated sample showed typical graphitic corrosion, and the plasma treatment was found to increase the corrosion resistance.
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