Measurements of stresses in -(Y,Yb)₂Si₂O₇ environmental barrier coating layers using Raman spectroscopy

Residual stress measurements in environmental barrier coatings (EBCs) can help in understanding coating durability and potential damage mechanisms. We demonstrate the capability of Raman spectroscopy to measure average residual stresses in two different beta-RE2Si2O7 (RE = rare earth or Y3+, denoted as REDS) EBCs with a nominal (Yb,Y)(2)Si2O7 composition, focusing on macroscopic residual stresses acting at macroscopic length scales. Uniaxial compression measurements of dense beta-(Yb,Y)(2)Si2O7 ceramics are used for calibration curves for applied stress versus Raman peak shift. We use these calibration curves to evaluate the macroscopic thermoelastic residual stress in the (Yb,Y)(2)Si2O7 layers from coefficient of thermal expansion (CTE) mismatch of two different (Yb,Y)(2)Si2O7-based EBCs on SiC-based substrates. Microscopic stress contributions to Raman peak shifts are subtracted using reference free-standing coatings and analytic estimates for inclusion stresses when (Yb,Y)(2)Si2O7 coatings have a high, variable volume fraction of (Yb,Y)(2)SiO5. The macroscopic thermal residual stress in these (Yb,Y)(2)Si2O7 EBCs is compressive, as expected from the smaller CTE of beta-REDS versus SiC. These thermal residual stresses can vary between different YbYDS EBC coatings by more than a factor of three with a measured layer residual stress of approximately -180 MPa (compressive) for a high modulus, low CTE coating, and our measured values generally agree with calculated estimates.