Effect of Gd content on mechanical properties and erosion durability of sub-stoichiometric Gd₂Zr₂O₇

Advanced thermal barrier coating materials are necessary to improve the efficiency of next-generation gas turbine engines. As such, different TBC chemistries must be developed with enhanced temperature stability above that of 7YSZ (~ 1200 °C) while maintaining thermal and mechanical reliability. The present study investigates the effect of rare earth content on the mechanical properties of ZrO₂ TBCs. Various cubic compositions in the ZrO₂-GdO_1.5 system were investigated in the form of monolithic pellets and coatings with stoichiometric GZO serving as reference. The fracture toughness and erosion durability were evaluated, and it was found that fracture toughness decreased with increasing rare-earth content, 15.66 mol% GdO_1.5 yielding 1.25 MPa m^1/2, compared to 1.04 MPa m^1/2 for GZO (50 mol% GdO_1.5). It was observed that the erosion performance of the coatings was much more sensitive to the changes in mechanical properties than the bulk specimens and showed a 125% increase through the fluorite region to GZO whereas the dense pellets only exhibited a 33% increase in erosion behavior. These results indicate that cubic ZrO₂ phase with reduced rare-earth content show promise as TBC materials with improved durability over GZO as well as temperature stability in this region of the phase diagram.