The thermo‐mechanical properties and ferroelastic phase transition of RENbO₄ (RE = Y, La, Nd, Sm, Gd, Dy, Yb) ceramics

Abstract

In this work, RENbO4 (RE = Y, La, Nd, Sm, Gd, Dy, Yb) ceramics with low density, low Young's modulus, low thermal conductivity, and high thermal expansion have been systematically investigated, the excellent thermo‐mechanical properties indicate that RENbO4 ceramics possess the potential as the new generation of thermal barrier coatings (TBCs) materials. X‐ray diffraction and Raman spectroscopy phase structure identification reveal that all dense bulk specimens obtained by high‐temperature solid‐state reaction belonged to the monoclinic (m) phase with C12/c1 space group. The ferroelastic domains are detected in the specimens, revealing the ferroelastic transformation between tetragonal (t) and monoclinic (m) phases of RENbO4 ceramics. The Young's modulus and hardness of the RENbO4 ceramics measured by the NanoBlitz 3D nanoindentation method are discussed in details, and the lower Young's modulus (60‐170 GPa) and higher hardness (the maximum value reaches 11.48 GPa) indicating that higher resistance of RENbO4 ceramics to failure and damage. Lower thermal conductivity (1.42‐2.21 W [m k]−1 at 500°C‐900°C) and lower density (5.330‐7.400 g/cm3) than other typical TBCs materials give RENbO4 ceramics the unique advantage of being new TBCs materials. Meanwhile, the thermal expansion coefficients of RENbO4 ceramics reach 9.8‐11.6 × 10−6 k−1 and are comparable or higher than other typical TBCs materials. According to the first‐order derivative of the thermal expansion rate, the temperature of the ferroelastic transformation of RENbO4 ceramics can be observed.

Effect of Ta5+ doping on the thermal physical properties of defective fluorite Y3NbO7 ceramics

“…As the Ta 5+ content increases, the elastic modulus and hardness slightly increase and then decrease when the Ta 5+ content becomes more than 30%. The elastic modulus of Y 3 (Nb 1‐x Ta x )O 7 is closely related to its crystal lattice energy (Equation ) 48,49 . As the Ta 5+ content increases, the Vickers hardness of the Y 3 (Nb 1‐x Ta x )O 7 ceramics increases and then abruptly decreases when the Ta 5+ content becomes more than 30%.…”

LC/8YSZ TBCs Thermal Cycling Life and Failure Mechanism under Extreme Temperature Gradients

“…The thermal conductivity of YSZ layer decreases, and the inflection point occurs at 800 °C. According to the relationship between the thermal physical property parameters, λ = ραc (7) where λ is thermal conductivity, ρ is density, α is thermal diffusion, and c is specific heat capacity. According to Equation ( 7), the thermal conductivity value of LC/YSZ DCL TBCs should be between the thermal conductivity value of LC and YSZ.…”

“…When the turbine temperature exceeds 1200 • C, APS coatings will sinter quickly, resulting in coating densification and thermodynamic performance degradation [3][4][5]. At present, the sintering of APS coatings mainly focuses on the evolution of thermodynamic parameters of coatings with sintering time [6][7][8][9][10]. Based on experimental observations of microstructure evolution of APS coatings during sintering [11][12][13], Siebert et al found that the formation of an interlaminar sintered neck would increase the Young's modulus of the coating, and no phase change would occur in this process [14][15][16].…”

Thermal conduction mechanism of ferroelastic Zr‐Y‐Yb‐Ta‐Nb‐O high‐entropy oxides with glass‐like thermal conductivity

“…Recently, ferroelastic HEOs based on ABO 4 structure (RETaO 4 15,16 and RENbO 4 17,18 ) with improved fracture toughness (2.05–4.59 MPa m 1/2 ) have attracted significant research attention for TBCs due to their possible ferroelastic toughening derived from a second‐order ferroelastic phase transformation 19–21 . The high‐temperature tetragonal ABO 4 solid solution is closely related to the tetragonal ZrO 2 solid solution with small differences in a lattice structure, which has been systematically studied in the ZrO 2 ‐YO 1.5 ‐TaO 2.5 (ZYTO) ternary system 22–26 .…”