Hot dip aluminised coatings with pure Al, Al-3Si and Al-7Si melts had been produced on 9Cr-1Mo steels and subsequently heat treated at 900uC for 5 h under oxidising conditions to generate alumina films over Fe-Al diffused case. The characterisation of these samples by X-ray diffraction and SEM-EDX techniques indicated reduction in the post-heat treated aluminide case depth with increasing Si concentration. Further, it was observed that after oxidation heat treatment, pure Al coated samples indicated c-Al 2 O 3 and h-Al 2 O 3 , while Al-7Si coated samples revealed transformation of metastable h-Al 2 O 3 phase to stable a-Al 2 O 3 phase. The present paper describes change in morphology of oxide after thermal oxidation from c to h and h to a as a function of the Si content of Al melt in hot dip aluminised 9Cr-1Mo steels. The effect of Si on the diffused aluminide case depth is also discussed.

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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 M 23 C 6 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.