Grain growth kinetics and microstructural evolution in novel cerium-doped zirconia-zirconate composites with hypoeutectic composition

A novel La₂(Zr_1-xCe_x)₂O₇–7.5 mol.% Sc₂O₃-0.5 mol.% Y₂O₃ co-stabilized ZrO₂ (SYSZ) composites with hypoeutectic composition were elaborately designed for potential applications in thermal barrier coatings (TBCs) operating above 1400 °C. This study initially explores the effects of Ce-doping on the phase structure, microstructure, and mechanical properties of the composites, with particular emphasis on high-temperature microstructural stability and grain growth kinetics. Experimental results reveal that these composites exhibit mixed t/c-zirconia and pyrochlore zirconate phases. Compared with La₂Zr₂O₇, the composites exhibit superb Vickers hardness of 11.4 GPa combined with an excellent indentation toughness of 2.8 MPa·m^1/2 could be achieved. La₂(Zr_0.3Ce_0.75)₂O₇-SYSZ exhibits the smallest grain growth, ranging from 0.99 to 2.75 μm after being thermally exposed for 300 h at 1450 °C. The grain growth kinetics with a growth exponent (n) increasing approximately from 2 to 4, indicating a transition in the grain-growth mechanism, which shifts from lattice-diffusion-controlled drag to boundary-diffusion-controlled drag. Our results demonstrate La₂(Zr_1-xCe_x)₂O₇-SYSZ composites are potential candidates for high -temperature TBC applications.