Microstructural studies of electrospark deposited aluminide coatings on 9Cr steels

Electrospark deposition (ESD) technique has been used to apply an iron aluminide coating on 9Cr reduced activation steel, which is a structural material for test blanket modules of fusion reactors. Phase identification and microstructural analysis of the aluminide coating along with the interface region were performed with the support of X-ray diffraction technique, optical microscopy, scanning electron microscopy and nanoindentation hardness measurements. Microstructural examination indicated prominent changes in the near interface microstructure of the steels processed by the ESD process. The substrate side of the coating/substrate interface consisted of a soft zone that is possibly of quasi-amorphous nature and of an M23C6 type carbide segregation rich area below this interface. The coating, however, showed extensive crack defects that need to be removed for reliably assessing its suitability as a barrier layer for blanket applications