Structure, thermal and mechanical properties of mid-entropy thermal barrier ceramic (Y0.3Gd0.3Yb0.4)4Hf3O12 prepared by ultrafast high-temperature sintering

Abstract

Thermal barrier coatings (TBCs) have an important role to play in the development of aero engines. In this paper, mid-entropy rare-earth hafnate (Y0.3Gd0.3Yb0.4)4Hf3O12(YGYbH) ceramic material was designed based on rRE3+/rHf4+ and was successfully fabricated in only 7 min using an ultrafast high-temperature sintering (UHS) process. The YGYbH ceramic bulk exhibits a single homogeneous fluorite structure and excellent high temperature phase stability, which can remain phase constant for 80 h at 1500 °C due to its unique cation radius ratio and high-entropy effect. YGYbH possesses sluggish grain growth characteristics and great anti-sintering properties, and when annealing at 1500 °C for 30 h, its grain size only grows from the initial 1.19 μm–1.61 μm, which is conducive to stabilizing the mechanical properties of YGYbH at higher service temperature. YGYbH has a low thermal conductivity of 0.89 W/(m·k) at 1100 °C, which is much lower than that of 6%–8%Y2O3 partially stabilized ZrO2(YSZ) (∼2.5 W/(m·k)), while having a high coefficient of thermal expansion (CTE), from 8.8 × 10−6/K at room temperature to 11.0 × 10−6/K at 1500 °C which is nearly to that of the YSZ. Furthermore, YGYbH has a high hardness (11.94 GPa) and a low elastic modulus (147.4 GPa), but a slightly lower fracture toughness (1.26 MPa m½) than that of 8YSZ, exhibiting great overall mechanical properties. Based on the results of this work, YGYbH with excellent overall performance exhibits great potential as the next-generation TBC material.