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

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 degrees 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.