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Abstract: Coating of aluminide on a TiAl-based alloy (49.1at.% Al) was carried out by thermal spraying pure aluminum and subsequent diffusion treatment at 1100°C. The growth of a Ti–Al intermetallic layer in the coating layers during diffusion treatment for 120–1800s as well as the oxidation resistance of the aluminized TiAl-based alloy was investigated. The outermost surface layer was comprised of Al-rich intermetallic TiAl3 and contained pores. In contrast, an Al concentration gradient layer consisting of Ti2Al5, TiAl2, and Al-rich TiAl containing 55at.% Al was formed between the outermost layer and the substrate. The thickness of the outermost layer decreased with increasing diffusion time, while the thickness of the intermediate layer grew to approximately 30μm. In addition, the coating/substrate interface changed from a wavy to a linear form with the growth of the intermediate layer. The aluminized coating, at all diffusion times, showed good oxidation resistance in cyclic oxidation tests at 900°C in air. [Copyright &y& Elsevier]

Abstract: Foil aluminizing of steel, wherein Al diffuses to the base steel material by diffusion treatment after hot pressing of the aluminum foil at a lower temperature than the melting point, was performed in this study. Alloy layers formed by diffusion at temperatures ranging from 700 to 1000 °C were investigated, and their features were compared with those of hot-dip aluminized steel. In hot-dip aluminizing, an intermediate Fe2Al5 layer was formed between the aluminum layer and the base steel during aluminum coating before the diffusion treatment. In contrast, the coating layer of the foil-aluminized steel specimen after diffusion bonding of the aluminum foil consisted only of the Al layer. An Fe2Al5 layer, an FeAl layer and an Al diffused layer were formed in both the aluminized specimens subsequent to the diffusion treatment. The numbers of voids formed in the Fe2Al5 layer and at the FeAl/Al diffused layer interface of the foil-aluminized specimens are smaller than those for hot-dip aluminizing. Moreover, the FeAl and Al diffused layers are formed with a greater thickness in the foil-aluminized steel under identical diffusion conditions. The Al concentration in hot-dip aluminized steel decreased in stages from the surface to the base steel, whereas, in the foil-aluminized steel, it decreased gradually. The Fe2Al5/base steel interface in the foil-aluminized steel was thus indistinct, and cross-sectional hardness also decreased gradually. [Copyright &y& Elsevier]