Investigation of Microstructure, Mechanical, and Wear Behavior of Lanthanum Zirconate, Yttrium Zirconate, and Lanthanum Yttrium Zirconate

Rare-earth zirconates have received attention in recent years due to satisfying the required properties of TBCs application. In this study, three compounds of lanthanum zirconate (LZ), yttrium zirconate (YZ), and lanthanum-yttrium zirconate (LYZ) with a molar ratio of La³⁺/Y³⁺ = 1 were prepared through co-precipitation and spark plasma sintering. In LYZ sample, a part of yttria is dissolved in LZ phase and its excess is precipitated as defect fluorite phase. In addition, after the Spark Plasma Sintering (SPS) process, the crystallinity of all three samples increased, and no phase change occurred. Despite using the same parameters in the SPS process, the porosity percentages of LZ, YZ, and LYZ samples was 18.5, 14.8, and 12.7, respectively. Based on the microhardness results, the hardness values of the LZ and YZ samples were close to each other (6.7 ± 0.7 and 7.1 ± 0.5 GPa, respectively), but the LYZ sample showed a higher hardness (8.3 ± 0.4 GPa) due to its better sinterability and solid solution strengthening mechanism. The wear rates of LZ, YZ, and LYZ were 0.05, 0.2, and 2 × 10⁻³mm³/N m, respectively. The higher fracture toughness of the LZ sample has prevented further crack propagation during the wear test. Delamination and adhesive were the main wear mechanisms in all samples.