Comparative analysis of insulating properties of plasma and thermally grown alumina films on electrospark aluminide coated 9Cr steels

• Iron aluminide coatings were deposited on 9Cr steels by electrospark technique.
• Thin alumina films were produced at 750 °C by thermal and plasma oxidation methods.
• Plasma oxidation resulted in thinner alumina films and larger Al diffusion depths.
• Plasma grown alumina showed improved electrical insulation properties.

Iron aluminides with a protective alumina layer are considered candidate coating for test blanket modules of fusion reactor. In order to study the properties of plasma grown alumina in comparison with thermally grown alumina, oxidation studies on electro spark deposited (ESD) FeAl coating have been conducted. Glow discharge plasma oxidation has been adopted as plasma oxidation technique. Reduced activation 9Cr steel samples were coated with a coating of iron aluminide (FeAl) layer containing 45 at% Al. The ESD coated 9Cr steels were oxidized in air and plasma environments at 750 °C for 48 h. Resultant surfaces were studied using X-ray diffraction, electron probe microanalysis, SEM and electrochemical impedance spectroscopy (EIS) techniques. Although the presence of Al2O3 was found on both thermally oxidized and plasma oxidized samples, the EIS studies clearly revealed improved dielectric properties of plasma grown Al2O3. The plasma grown oxide thin films seems a promising approach to apply alumina coatings with improved dielectric properties onto fusion reactor materials.