Design of a new yttrium silicate Environmental Barrier Coating (EBC) based on the relationship between microstructure, transport properties and protection efficiency

Yttrium mono- and di-silicates are excellent candidate materials for Environmental Barrier Coatings (EBC), to protect Ceramic-Matrix Composites (CMC). A large distribution of microstructures can be generated by varying the duration of sintering, the particle size distribution of the precursor and/or the deposition method. In the present work, investigations of the corrosion resistance of yttrium silicate coatings with various microstructures in the high temperature range, under different oxidizing environments are reported. An original experimental methodology has allowed quantifying the influence of the microstructure (especially grain size and grain boundary surface area) on properties such as ionic conductivity, resistance to oxygen diffusion, volatilization rate and surface recession, and showing that they directly affect their protection efficiency against oxidation. Based on these results, guidelines for the design of an optimized yttrium silicate EBC featuring microstructural and compositional variations are proposed.