Structure, thermal and mechanical properties of mid-entropy thermal barrier ceramic (Y_0.3Gd_0.3Yb_0.4)₄Hf_{3O12 prepared by ultrafast high-temperature sintering}

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)(4)Hf3O12(YGYbH) ceramic material was designed based on r(RE)(3+)/r(Hf)(4+) 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 degrees 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 degrees C for 30 h, its grain size only grows from the initial 1.19 mu m-1.61 mu m, which is conducive to stabilizing the mechanical properties of YGYbH at higher service temperature. YGYbH has a low thermal conductivity of 0.89 W/(mk) at 1100 degrees C, which is much lower than that of 6%-8%Y2O3 partially stabilized ZrO2(YSZ) (similar to 2.5 W/(mk)), while having a high coefficient of thermal expansion (CTE), from 8.8 x 10(-6)/K at room temperature to 11.0 x 10(-6)/K at 1500 degrees 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 m(1/2)) 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.