An investigation into RESZ (RE = Yb, Er, Gd, Sm) materials for CMAS resistance in thermal barrier coatings

The effects of rare earth dopants on the CMAS resistance of zirconia thermal barrier coating materials were systematically investigated using ceramic pellets and CMAS. Yb, Er, Gd and Sm elements were assessed as stabilising agents of zirconia at increasing concentrations for CMAS reactions at 1300 °C across timeframes of 1 to 60-minutes. Two distinct microstructures of the ceramic pellet –CMAS reaction layer were observed then characterised as a dense layer microstructure and a non-dense layer microstructure. The presence of each microstructure was dependent on the RE ionic radius and concentration. The thickness of the reaction layer and overall volume of precipitated reaction products increased with increasing RE ionic radius. Therefore, an optimal RE element would exhibit dense layer forming microstructure with the lowest overall infiltration depth. CMAS loading volume significantly impacted the rate of reaction product precipitation. The volume of apatite precipitate was inversely proportional to the CMAS loading quantity.