Fundamental investigation of the degradation laws of aluminide coatings during high-temperature oxidation

During high-temperature oxidation, the aluminide coating degrades by two mechanisms, one is the oxidation of the outer surface, and the other is A1 diffusion into the substrate. The relevant laws are investigated for coatings on Co-base superalloys oxidised in air at high temperatures. The driving force mainly comes from the oxidation reaction for the outer degradation layer, and the chemical potential for the inner degradation layer. By an approximation approach, it can be concluded that the life of the outward-diffusion coating is roughly directly proportional to the second power of the main-phase thickness of the coating.