Abstract: This study developed K-doped SiO₂ coatings on TiAl alloys to enhance oxidation resistance by controlling phase structures. The results indicate that K can promote the densification of the SiO₂ coating and reduce the oxidation mass gain of the pure SiO₂ coating by 89.1 %. Increasing K content can reduce the precipitation of cristobalite and suppress crack formation, therefore decreasing direct contact between oxygen and substrate. On the other hand, although the amorphous phase with K improves densification, it compromises stability due to lower diffusion barrier (5.743 eV) and stronger oxygen adsorption energy (-0.698 eV) compared to cristobalite SiO₂ (6.057 and -0.249 eV). Thus, under the premise of no cracks, keeping a certain amount of cristobalite is beneficial to strengthening the structure of the oxide scale.

Key words: High temperature oxidation, Densification capability, SiO₂ coating, Cristobalite, Potassium modification