Theoretical prediction on mechanical and thermal properties of a promising thermal barrier material: Y4Al2O9

Abstract

Abstract:The mechanical and thermal properties of Y 4 Al 2 O 9 were predicted using a combination of first-principles and chemical bond theory (CBT) calculations. Density functional theory (DFT) computations were performed for the structural, mechanical, and thermal properties, and the results were confirmed by chemical bond theory. Based on the calculated equilibrium crystal structure, heterogeneous bonding nature has been revealed, i.e., Al-O bonds are stronger than Y-O bonds. Low second-order elastic constants c 44 , c 55 , and c 66 demonstrate the low shear deformation resistance. Low G/B ratio suggests that Y 4 Al 2 O 9 is a damage tolerant ceramic. Y 4 Al 2 O 9 shows anisotropy in elastic behavior based on the discussion of direction dependence of Young's modulus. The hardness is predicted to be 10.2 GPa from calculated elastic moduli. The thermal expansion coefficient (TEC) calculated by chemical bond theory is 7.51×10 6 K 1. In addition, the minimum thermal conductivity of Y 4 Al 2 O 9 is estimated to be 1.13 W·m 1 ·K 1, and the thermal conductivity decreases with temperature as 1305.6/T.

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

“…The consistency between the theoretical calculated and the experimental measured elastic properties demonstrates the high reliability of our density functional theory (DFT) calculations [2]. In our previous work [2], YAM was predicted to be a damage tolerant ceramic based on the low Pugh's ratio G/B = 0.576.…”

“…The consistency between the theoretical calculated and the experimental measured elastic properties demonstrates the high reliability of our density functional theory (DFT) calculations [2]. In our previous work [2], YAM was predicted to be a damage tolerant ceramic based on the low Pugh's ratio G/B = 0.576. Using the experimentally measured shear modulus and bulk modulus, the Pugh's ratio is calculated to be G/B = 0.530, which is also close to the theoretical value, confirming the damage tolerance of YAM.…”

“…3(b). The formation of nanolayered layers on the fracture surfaces is mainly due to anisotropic bonding and the presence of weakly bonded atomic planes [2]. We have shown through DFT calculations that the anisotropic elastic moduli are E x = 208 GPa, E y = 179 GPa, and E z = 176 GPa.…”

“…The high-and low-directions correspond to the high-and low-fracture-energy directions. Thus, shear-induced sliding along the low Young's modulus directions like (0 11) / [0 11] or (011)/[011] forms nanolayered cleavage steps on the fracture surfaces [2]. From the crystal structure shown in our previous work [2] and the crystallite shape of YAM simulated based on the Donnay-Haker theory [21][22][23], {0 11}, {011}, and {100} planes are of morphological importance in crystal morphology of YAM.…”

“…Previous theoretical [1][2][3] and experimental [4,5] investigations have demonstrated that Y 4 Al 2 O 9 (YAM) has a unique combination of high melting point (2020 ℃), low density (4.44 g/cm 3 ), low high-temperature thermal conductivity (the minimum thermal conductivity is 1.13 W·m 1 ·K 1 ), relative low Young's modulus (191 GPa), and moderate thermal expansion coefficient (7.51 × 10 6 K 1 ) and damage tolerant ability, which endure it as a prospective material for thermal and/or environmental barrier coating applications. However, besides Young's modulus and thermal conductivity, other mechanical and thermal properties have not been experimentally explored.…”