TaZr2.75O8 ceramics as a potential thermal barrier coating material for high-temperature applications

A series of TaO2.5-doped ZrO2 (1-x)ZrO2-xTaO(2.5) (x = 0.08, 0.15, 0.2 and 0.28) ceramics were synthesized by solid state reaction at 1600 degrees C for 20 h. XRD results reveal that no tetragonal ZrO2 phase forms in the TaO2.5-ZrO2 system. Instead, a mixture of monoclinic ZrO2 (m-ZrO2 ) and orthorhombic TaZr2.75O8 can be detected for (1-x)ZrO2-xTaO(2.5) ceramic within compositions x <= 0.2. As the doping content increases, the content of m-ZrO2 decreases and the final product in the composition of 0.72ZrO(2)-0.28TaO(2.5) is primarily composed of TaZr2.75O8. Microstructure together with the thermophysical and mechanical properties of TaZr2.75O8 ceramic were investigated for possible applications as thermal barrier coatings (TBC5). The thermal conductivity with a minimum value of 1.65 W/m.K at 800 degrees C for TaZr(2.75)O(8)( )ceramic is similar to 30% lower than that of dense YSZ and the dense ceramic also has a moderate average thermal expansion coefficient (TEC), about 9.14 x 10(-6) K-1 from room temperature (RT) to 1300 degrees C. Besides, TaZr2.75O8 exhibits a high microhardness (11.85 +/- 0.42 GPa) and fracture toughness (3.15 MPa.m(1/2)). These preliminary results indicate that TaZr2.75O8 can be used as an alternative material for the ceramic layer in TBCs system with respect to its superior thermal and mechanical properties. (C) 2019 Elsevier B.V. All rights reserved.