Preparation, mechanical, and thermal properties of a promising thermal barrier material: Y₄Al₂O₉

In our previous work, anisotropic chemical bonding, low shear deformation resistance, damage tolerance ability, low thermal conductivity, and moderate thermal expansion coefficient of Y₄Al₂O₉ (YAM) were predicted. In this work, phase-pure YAM powders were synthesized by solid-state reaction between Y₂O₃ and Al₂O₃ and bulk YAM ceramics were prepared by hot-pressing method. Lattice parameters and a new set of X-ray powder diffraction data were obtained by Rietveld refinement. The mechanical and thermal properties of dense YAM ceramics were investigated. The measured elastic moduli are close to the theoretical predicted values and the stiffness can be maintained up to 1400 ℃. The flexural strength and fracture toughness are 252.1±7.3 MPa and 3.36±0.20 MPa·m^1/2, respectively. Damage tolerance of YAM was also experimentally proved. The measured average linear thermal expansion coefficient (TEC) of YAM is 7.37×10^-6 K^-1, which is very close to the theoretical predicted value. Using high-temperature X-ray diffraction (XRD) analysis, volumetric TEC is determined (23.37±1.61)×10^-6 K^-1 and the anisotropic TEC are α_a = 7.34×10^-6 K^-1, α_b = 7.54×10^-6 K^-1, and α_c = 7.61×10^-6 K^-1.