Infiltration thermodynamics in wrinkle-pores of thermal sprayed coatings

Abstract

Open pores are inevitably formed in thermal sprayed coatings including environmental barrier coatings and thermal barrier coatings as a result of stresses, and supply infiltration channels for corrosives such as CMAS and water vapor in engine environment, causing severe corrosion of substrate. Blocking these pores by melt infiltration is an effective way to prevent corrosion. Infiltration behaviors are normally driven by thermodynamic energy and forces. This work focused on establishing an infiltration thermodynamic theory in complex pores. First, wrinkle pore model was constructed according to real pore morphologies in coatings. Subsequently, thermodynamic states including energy and pressure state were calculated and analyzed. Then, the decisive factors of infiltration depth were obtained. The theoretical calculation results showed that multiple energy barriers and equilibrium states appeared when infiltrating in wrinkle pore. Infiltration ceased once the first equilibrium was reached, leading to a limited terminal depth. Raising the external gas pressure above a threshold can overcome part or all of the barriers and obtain various depths. Elimination of internal pressure helped lower the threshold. Therefore, thermodynamically, infiltration depth can be controlled by adjusting the external and internal gas pressures. This work provides meaningful methodological and theoretical guidance for melt infiltrating in coatings.