Effect of water vapour on morphology of the Si/Ti-rich phase at the interface between oxide layer and aluminide coating

• Published in: Corrosion science 2020-02, Vol.163, p.108240, Article 108240
• Main Authors: Li, Chao, Huang, Taihong, Song, Peng, Yuan, Xiaohu, Feng, Jing, Lü, Kaiyue, Li, Qiaolei, Duan, Wenhao, Lu, Jiansheng
• Format: Article
• Language: English
• Subjects: Aluminides; Aluminium; Aluminum; Dip coatings; Hot dipping; Intermetallic compounds; Intermetallics; Internal oxidation; Morphology; Oxidation; Oxidation resistance; SEM; Silicon; Superalloys; Water vapor; XRD
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2019.108240

[Display omitted] •A continuous Si/Ti-rich phase can prevent O inter diffusion in aluminide coating.•The Si/Ti-rich phase becomes discontinuous in air plus water vapour at 1050 °C.•Si3Ti5 phase is oxidized and decomposed in air plus water vapour at 1050 °C.•Al consumption in aluminide coating is mainly outward diffusion to form Al2O3. Silicon-doped aluminide (Al–Si) coatings were prepared on IN738 superalloy by hot dip. The microstructure and oxidation performance of the Al–Si coatings was investigated at 1050 °C in air and air plus water vapour. Water vapour can significantly reduce the oxidation resistance of Al–Si coatings. The Kirkendall voids were formed under the oxide layer in water vapour environment. The formation of a continuous Si/Ti-rich (SiCr3/Si3Ti5 phases) phase below the oxide layer could possibly slow down the internal oxidation, which increased the coating’s oxidation resistance in air. In addition, the Si/Ti-rich phase was unstable in air plus water vapour atmosphere.