Effect of Si on morphology of alumina scales

Abstract

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.

Compatibility study of plasma grown alumina coating with Pb–17Li under static conditions

“…Subsequently, the cleaned samples were then fluxed in aqueous K 2 ZrF 6 solution and dried. Based on the process optimized in previous work [10], the fluxed samples were subjected to hot dip aluminizing (HDA) in Al-7%Si bath at 720°C for 30 s immersion time and slowly withdrawn. After aluminizing, the cleaned samples were subjected to normalizing heat treatment at 980°C for 20 min in muffle furnace and air cooled.…”

“…Hot dip aluminizing of P91 steels in Al-7%Si melt resulted in $25 lm Al-Si coating with a 6-8 lm Al 8 Fe 2 Si (s 5 ) intermetallic layer at the coating-substrate interface [10]. Subsequently on normalizing and tempering treatment at 980°C for 20 min and 750°C for 1 h respectively, this metallic layer transforms into an alumina layer on the top followed by a diffused Fe-Al case.…”

“…An Al diffusion zone (FeAl) between the alumina coating and substrate is thus desired as a self-healing coating [5,9]. Hot dip aluminizing process followed by heat treatment under oxidizing environment leads to generation of a-Al 2 O 3 + FeAl coatings on 9Cr steel substrates [10,11].…”

Al2O3 reinforced Fe–Al composite coatings prepared by double glow discharge technique

“…10 According to the representative GAXRD pattern in Fig. 2a, the Fe-Al composite coatings were successfully obtained, mainly consisting of FeAl and FeAl 3 phases.…”

Microstructural evolution and oxidation behavior of hot-dip 55 wt.% Al–Zn–Si coated steels

“…One of the methods was the application of inorganic coatings [5][6][7][8] such as Alxwt.%Si (x = 0~31.9) coatings [9][10][11][12], Zinc silicate coatings [13] and zinc coatings [14,15].…”