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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]