Effect of Si on morphology of alumina scales

摘要

Hot dip aluminised coatings with pure Al, AI-3Si and AI-7Si melts had been produced on 9Cr-1Mo steels and subsequently heat treated at 900°C for 5 h under oxidising conditions to generate alumina films over Fe-Al diffused case. The characterisation of these samples by X-ray; cliffraction 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 ?-Al_2O_3 and è-Al_2O_3, while AI-7Si coated samples revealed transformation of metastable è-Al_2O_3 phase to stable á-Al_2O_3 phase. The present paper describes change in morphology of oxide after thermal oxidation from y to è and è to á 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.