High-entropy ferroelastic(10RE_(0.1))TaO_(4) ceramics with oxygen vacancies and improved thermophysical properties

The primary purpose of this work is to optimize the thermophysical properties of rare-earth tan-talate ceramics using the high-entropy effect.Here,the high-entropy rare-earth tantalate ceramic(Y_(0.1)Nd_(0.1)Sm_(0.1)Gd_(0.1)Dy_(0.1)Ho_(0.1)Er_(0.1)Tm_(0.1)Yb_(0.1)Lu_(0.1))TaO_(4)((10RE_(0.1))TaO_(4))is synthesized successfully.The lat-tice distortion and oxygen vacancy concentration are characterized firstly in the rare-earth tantalates.Notably,compared with single rare-earth tantalates,the thermal conductivity of(10RE_(0.1))TaO_(4) is reduced by 16%-45%at 100℃ and 22%-45%at 800℃,and it also presents lower phonon thermal conductivity in the entire temperature range from 100 to 1200℃.The phonon thermal conductivity(1.0-2.2 W m^(-1) K^(-1),100-1200℃)of(10RE_(0.1))TaO_(4) is lower than that of the currently reported high-entropy four-,five-and six-component rare-earth tantalates.This is the result of scattering by the ferroelastic domain,lattice distortion associated with size and mass disorder,and point defects,which target low-,mid-and high-frequency phonons.Furthermore,(10RE_(0.1))TaO_(4),as an improved candidate for thermal barrier coatings materials(TBCs),has a higher thermal expansion coefficient(10.5×10^(-6)K^(-1) at 1400℃),lower Young’s modulus(123 GPa)and better high-temperature phase stability than that of single rare-earth tantalates.

Bending fracture behavior of freestanding (Gd0.9Yb0.1)2Zr2O7 coatings by using digital image correlation and FEM simulation with 3D geometrical reconstruction

It is important to investigate the mechanical performances of (Gd0.9Yb0.1)2Zr2O7 (GYbZ) materials deposited on irregular substrates for improving new thermal barrier coatings. Three-point bending fracture characteristics of freestanding GYbZ coating prepared by supersonic plasma sprayed(SPS) technique were investigated with the help of digital image correlation technique. The cracking time, crack propagation path, and mechanical properties of GYbZ coating were obtained. Meanwhile, the X-ray computed tomography technique was introduced to scan the microstructure of freestanding GYbZ coatings, which are used to establish three-dimensional(3D) finite element model by using the Avizo software. The brittle cracking criterion was applied to describe the bending fracture process of GYbZ coatings. The critical cracking strain was estimated as 0.36%±0.03% by repeatedly comparing the difference between the experimental and simulated curves. The results would be extended to predict the dangerous region and failure mechanisms of GYbZ coatings deposited on irregular substrate during finite element simulations.

Low thermal conductivity and anisotropic thermal expansion of ferroelastic(Gd_(1−x)Y_(x))TaO_(4) ceramics

In this paper,(Gd_(1−x)Y_(x))TaO_(4) ceramics have been fabricated by solid-phase synthesis reaction.Each sample was found to crystallize in a monoclinic phase by X-ray diffraction(XRD).The properties of(Gd_(1−x)Y_(x))TaO_(4) were optimized by adjusting the ratio of Gd/Y.(Gd_(1−x)Y_(x))TaO_(4) had a low high-temperature thermal conductivity(1.37–2.05 W·m^(−1)·K^(−1)),which was regulated by lattice imperfections.The phase transition temperature of the(Gd_(1−x)Y_(x))TaO_(4) ceramics was higher than 1500℃.Moreover,the linear thermal expansion coefficients(TECs)were 10.5×10^(−6) K^(−1)(1200℃),which was not inferior to yttria-stabilized zirconia(YSZ)(11×10^(−6) K^(−1),1200℃).(Gd_(1−x)Y_(x))TaO_(4) had anisotropic thermal expansion.Therefore,controlling preferred orientation could minimize the TEC mismatch when(Gd_(1−x)Y_(x))TaO_(4) coatings were deposited on different substrates as thermal barrier coatings(TBCs).Based on their excellent properties,it is believed that the(Gd_(1−x)Y_(x))TaO_(4) ceramics will become the next generation of high-temperature thermal protective coatings.