Corrosion of rare-earth disilicate environmental barrier coatings in gas turbine environments—Part 2: Microstructure model

A model for the volatization of ytterbium disilicate (YbDS) by water vapor is developed. The new model is based on the Deal & Grove theory of the thermal oxidation of silicon [1], generalized here to account for the multistep, second-order chemical reactions for silica depletion, multi-component mixture effects, and the unsteady porous microstructural evolution of the corroded inner zone. With the new model, the fundamental kinetic rate and standard porous media parameters are determined using the atmospheric steam jet impingement experiment of Ridley & Opila [2] and compared to results from the original Deal & Grove model. Fixing the input parameters in each respective model, a validation study (blind prediction) is presented for the high Reynolds number (1 × 105) and high pressure (14.7 atm) burner rig experiment of Wan et al. [3]. [1] B. E. Deal and A. S. Grove (1965). General relationship for the thermal oxidation of silicon, J. Appl. Phys., 36(12), pp. 3770 - 3778. [2] M. Ridley and E. Opila (2021). Thermochemical stability and microstructural evolution of Yb2Si2O7 in high-velocity high-temperature water vapor, J. Euro. Ceram. Soc., 41, pp. 3141 - 3149. [3] J. Wan, P. J. Meschter, and B. Bertram (2023). Modeling microvoiding kinetics of rare-earth disilicates in flowing atmospheres containing water vapor, J. Am. Ceram. Soc, DOI:10.1111/jace.19261.