Corrosion Behavior of Low-Temperature Nickel and Iron Aluminized Martensitic Stainless Steel Substrates with Different Surface Roughness in Acidic Medium

The initial surface roughness and its variations during service affect the function of components with aerodynamic surfaces, such as compressor blades. In the current investigation specimens of martensitic stainless steel 1.4938 were prepared to produce different surface roughness values, and then aluminized via a pack cementation process at 470 degrees C to obtain Fe-aluminide coating. Furthermore, some of the specimens were electroplated by a thin layer of nickel before aluminizing to produce Ni-aluminide coating. The corrosion behavior of the substrate and coatings were studied using electrochemical impedance spectroscopy and potentiodynamic polarization in 0.5M H2SO4 solution as the electrolyte. The results showed that the surface roughness can significantly affect the corrosion rates. Lower roughness followed by lower corrosion rates of the substrate and aluminide-coated specimens. Aluminizing treatment reduced the corrosion current density but increased the passive current density. Electrochemical impedance spectroscopy results supported the polarization results and provided an insight into the corrosion mechanisms of the specimens by equivalent circuit models.