Application of a Novel Process Called Vacuum-Encapsulated Slurry Method to Form a Silicide-Aluminide Protective Coating on Ti6Al4V Alloy

In the present work, a novel process called vacuum-encapsulated slurry method is used to form the silicon-modified aluminide coating on Ti-6Al-4V alloy. In this research, the microstructure and high temperature oxidation resistance of such a coating have been investigated. The obtained coating had a triple layer structure. The inner layer was TiAl₂, the middle layer contained very thin Ti₅Si₃ lamellae within the TiAl₃ matrix, and was ultimately the outermost layer of Ti(Al,Si)₃ into which the Ti₇Al₅Si₁₂ particles were distributed. The evaluation of isothermal oxidation at 700 °C for 400 h revealed that the formation of silicon-modified aluminide coating is able to improve the high temperature oxidation resistance of the uncoated Ti-6Al-4V alloy. It should be noted that the remarkable improvement in the high temperature oxidation resistance of the sample coated with the silicon-modified aluminide coating produced by the vacuum-encapsulated slurry method is due to the fact that the protective Al₂O₃+ SiO₂ mixed oxide scale along with the continuous, compact and uniform layers of Ti(Al,Si)₃ and Ti₅Si₃ act as a barrier against oxygen diffusion toward the Ti-6Al-4V substrate surface during the high temperature oxidation.