Review on ultra-high temperature boride ceramics

High-entropy ceramics with five or more cations have recently attracted significant attention due to their superior properties for various structural and functional applications. Although the multi-component ceramics have been of interest for several decades, the concept of high-entropy ceramics was defined in 2004 by producing the first high-entropy nitride films. Following the introduction of the entropy stabilization concept, significant efforts were started to increase the entropy, minimize the Gibbs free energy and achieve stable single-phase high-entropy ceramics. High-entropy oxides, nitrides, carbides, borides and hydrides are currently the most popular high-entropy ceramics due to their potential for various applications, while the study of other ceramics, such as silicides, sulfides, fluorides, phosphides, phosphates, oxynitrides, carbonitrides and borocarbonitrides, is also growing fast. In this paper, the progress regarding high-entropy ceramics is reviewed from both experimental and theoretical points of view. Different aspects including the history, principles, compositions, crystal structure, theoretical/empirical design (via density functional theory, molecular dynamics simulation, machine learning, CALPHAD and descriptors), production methods and properties are thoroughly reviewed. The paper specifically attempts to answer how these materials with remarkable structures and properties can be used in future applications.

High-entropy ceramics: Review of principles, production and applications

Influence of SiAlON addition on the microstructure development of hot-pressed ZrB2–SiC composites

Role of graphite nano-flakes on the characteristics of ZrB2-based composites reinforced with SiC whiskers

As a superhard material with properties similar to diamond including chemical inertness, cubic boron nitride (cBN) is an excellent candidate as a pressure calibration standard for high-temperature high-pressure research using its pressure-volume-temperature (P-V-T) equation of state. However, the elastic properties of cBN at ambient conditions reported in the literature vary by up to 8%, which can likely be attributed in part to variability in the cBN composition and defect structure and measurement uncertainties. We have measured the single-crystal elastic moduli of high-purity cBN with high precision by Brillouin scattering measurements, making an effort to minimize experimental uncertainties. We obtain values of C11 = 798.4 ± 1.7 GPa, C44 = 469.0 ± 1.0 GPa, and C12 = 172.4 ± 1.1 GPa, from which the isotropic aggregate bulk modulus Ks = 381.1 ± 1.3 GPa and shear modulus G = 398.8 ± 1.2 GPa (the Hill average) were calculated. Our results improve the precision and reduce the uncertainties in the elastic m...

Elasticity of cubic boron nitride under ambient condition

Oscillatory pressure sintering of high entropy (Zr0.2Ta0.2Nb0.2Hf0.2Mo0.2)B2 ceramic

ZrSi 2 and SiC are good candidates to improve both sinterability and mechanical properties of ZrB 2 ceramics, which were synthesized simultaneously by an in-situ reaction of ZrC and Si additives during the sintering processing in this work. The ZrB 2 ceramic composites with different amount of ZrSi 2 and SiC were fabricated by reactive spark plasma sintering (RSPS) method. X-ray diffraction, scanning microscopy and Archimedes's method are used to characterize the phase, microstructure and density of the composites. Meanwhile, fracture toughness and flexural strength of the obtained composites were investigated too. It's found that a fully dense composite can be achieved at 1500 °C by SPS. Both fracture toughness and flexural strength of ZrB 2 ceramics increased with increasing the concentration of ZrSi 2 and SiC additives and reached a maximum of 7.33 ± 0.24 MPa·m 1/2 and 471 ± 15 MPa, respectively, with the ZrSi 2  + SiC content of 30 wt%.

Xiaotong Zhao

Papers

Oscillatory pressure sintering of high entropy (Zr0.2Ta0.2Nb0.2Hf0.2Mo0.2)B2 ceramic

ZrB2-ZrSi2-SiC composites prepared by reactive spark plasma sintering

The Influence of Additive and Temperature on Thermal Shock Resistance of ZrB2 Based Composites Fabricated by Spark Plasma Sintering

Synthesis of rod-like ZrB2 crystals by boro/carbothermal reduction

Processing and properties of polycrystalline cubic boron nitride reinforced by SiC whiskers