Ultra-high Temperature Ceramic Materials Research Articles

Preparation method and industrialization of Ta-based ultra high temperature ceramic Tujia jar tea baking jar materials

The production materials of traditional Tujia jar tea often face problems such as poor high-temperature performance and poor durability. To improve the temperature resistance and durability of tea baking utensils, this study proposes a new type of TaC ultra-high temperature ceramic. TaC ceramics with excellent performance were prepared through powder metallurgy technology, including high-energy ball milling to ensure uniform mixing, followed by compression molding and high-temperature sintering. The test results demonstrated excellent mechanical properties, with a maximum depth of 948.67 nm and a contact depth of 954.45 nm, proving outstanding compressive and wear resistance. The hardness reached 21.4±0.5 Gpa, and the elastic modulus was 397.2±8.7 Gpa, both of which indicate its stability under high loads. In addition, the fracture toughness was 2.8±0.2 Mpa*m1/2. At a high temperature environment of 1000 °C, the oxidation rate constant of TaC ceramics was only 0.183 mg2 *cm−4 *h, which demonstrates its excellent high-temperature stability. The development of this TaC ceramic not only strengthened the traditional production process of Tujia teapots and tea roasting teapots, thereby improving the product’s service life, but also holds potential for other industrial applications that demand ultra-high temperature stability. These contributions provide new directions for the high-temperature application of ceramic materials and bring tangible economic and technological value to related industries.

Synthesis, crystal structure and properties of YB2C2

ABSTRACT YB2C2 is a novel ultra-high temperature ceramic material with high damage tolerance. In this work, the synthesis mechanism, crystal structure, electronic structure, elastic properties and thermal shock resistance of YB2C2 were systematically investigated through experiments and calculations. It was determined by differential scanning calorimetry with the heating rate of 10°C/min that YB2C2 was formed by the reaction of YB2C and C at about 1202°C, and became the main phase at 1450°C. The space group of YB2C2 was determined to be P4/mbm by X-ray diffraction, transmission electron microscopy, Rietveld refinement and first-principles calculations for the first time. The lattice constants are a = b = 0.5351 nm and c = 0.3561 nm. The atom positions are as follows: Y is located at 2a (0, 0, 0), B is located 4 h (0.133, 0.633, 0.5) and C is located at 4 h (0.662, 0.162, 0.5). The chemical bonding of YB2C2 displayed sharp anisotropy, with strong B-C bond within the B2C2 nets, and weak Y-B/Y-C bond between Y atom layers and B2C2 nets. Additionally, YB2C2 exhibited abnormal thermal shock resistance when the thermal shock temperature exceeded 800°C, with the residual flexural strength at 1300°C being more than 70% of the strength at room temperature.

Heat transfer and behavior of ultra high temperature ceramic materials under exposure to supersonic carbon dioxide plasma with additional laser irradiation

The behavior of the ultra high temperature ceramic material HfB2-SiC-C(graphene) under exposure to a supersonic carbon dioxide plasma, with and without the addition of laser irradiation, has been studied. The material was heated to 1750 °C in an inductively coupled plasma jet without laser irradiation. A temperature jump to 2190 °C was observed when additional ytterbium laser irradiation was applied to the surface. The spectral emissivity of the heated surface at wavelengths of 0.65 and 0.9 μm was studied. It was found that the spectral emissivity decreases as the material oxidizes. The heat flux to the surface of the heated material was measured and compared to the heat flux to a cold copper surface under the same conditions. Analysis of the surface of HfB2-SiC-C(graphene) material after exposure was performed. Differences in microstructure were detected between specimens exposed to carbon dioxide plasma with and without additional laser irradiation.

Phase evolution and oxidation resistance of Si3N4/HfB2/HfBxCyN1–x–y ceramic nanocomposites prepared from tailored preceramic polymers

Single-source-precursor derived ceramics exhibit advantages for the preparation of Si-based ceramics with controllable phase composition and adjustable functional/mechanical properties, which has significant potential for (ultra)high temperature ceramic materials. Within the present work, a series of hafnium/boron-containing Si3N4-based ceramics (SiHfBCN) are prepared upon pyrolysis/annealing of the corresponding single-source-precursors in N2 atmosphere at different temperatures ranging from 1000 °C to 1700 °C. The high-temperature (micro)structural evolution with respect to the annealing temperatures and boron concentration was studied using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. The results show that the amorphous SiHfBCN ceramics convert upon crystallization into ceramic nanocomposites consisting of a α-Si3N4 matrix with embedded Si, HfB2, and HfBxCyN1–x–y. The formation and stability of HfBxCyN1–x–y solid solution were discussed in detail. Finally, the oxidation resistance of the obtained α-Si3N4/HfB2/HfBxCyN1–x–y ceramic nanocomposites was investigated by thermal gravimetric analysis in air.

Probing the effect of ordered carbon vacancy on the thermophysical properties of VC1-x: A comprehensive first-principles calculations

Vanadium carbides (VC1-x) exhibit stoichiometric flexibility due to the presence of various carbon vacancies, which significantly influence their fundamental physical properties. Despite this, a comprehensive understanding of how carbon vacancies affect the mechanical and thermal properties of vanadium carbides remains elusive. Previous research has primarily focused on stoichiometric VC and has yet to fully explore the impact of carbon vacancies. This study reveals that stoichiometric VC is less stable when compared to ordered substoichiometric VC1-x and employs first-principles calculations to obtain thermodynamic, mechanical, and transport properties of VC1-x. The ordered carbon vacancy leads to an increase in the V–V bond density and volume. Due to the anharmonic effect, the ordered carbon vacancy impairs heat capacity and thermal expansion. The hardness and toughness decrease with increasing carbon vacancy concentrations. The Boltzmann transport equation is used to calculate electrical and thermal transport properties, which shows that growing scattering effects reduce thermal transport capacity. The results provide accurate data support for vanadium carbide research and theoretical support for designing ultra-high temperature ceramic materials.

Reactive laser synthesis of ultra-high-temperature ceramics HfC, ZrC, TiC, HfN, ZrN, and TiN for additive manufacturing

Ultra-high-temperature ceramics (UHTCs) are optimal structural materials for applications that require extreme high temperature resilience (Mp > 3000 °C), resistance to chemically aggressive environments, wear, and mechanical stress. Processing UHTCs with laser-based additive manufacturing (AM) has not been fully realized due to a variety of obstacles. In this work, selective laser reaction sintering techniques (SLRS) were investigated for the production near net-shape UHTC ceramics such as HfC, ZrC, TiC, HfN, ZrN, and TiN. Specifically, group IV transition metal and metal oxide precursor materials (<44 μm) were chemically converted and reaction-bonded into layers of UHTCs using single-step selective laser processing in 100 vol% CH4 or NH3 gas that might be compatible with prevailing powder bed fusion techniques. Conversion of either metals (Hf, Zr and Ti) or metal oxides (HfO2, ZrO2, and TiO2) particles was first investigated to examine reaction mechanisms and volume changes associated with SLRS of single-component precursor systems. SLRS processing of metal or metal oxide alone produced near stoichiometric UHTC phases and yields up to >99.9 wt% total for carbides and nitrides and during the rapid reactive in-situ processing scheme. However, for single-phase feedstocks, gas-solid reactivity induced volumetric changes (correlated with the stochiometry of the rocksalt-type UHTC carbide and nitride products) resulted in residual stresses and cracking in the model-AM product layer. To mitigate conversion-induced stresses of single-phase precursors, composite metal/metal oxide precursors were employed to compensate for the volume changes of either the metal (which expands during conversion) or the metal oxide precursor (which contracts). While conversion of the optimized composite materials produced HfC layers with as little as +0.9% volume change, results indicated interparticle adhesion must be optimized to obtain robust UHTC-AM layers. Computational models of carbon and nitrogen diffusion in host transition metal lattices corroborated experimental results where a progressive particle conversion might inhibit interparticle diffusion unless laser processing parameters are carefully optimized to favor reaction bonding over discrete particle conversion. While this method presents a host of processing considerations, we demonstrate how this reactive approach may be viable for the AM of numerous UHTC materials that are not readily produced using current methods.

Investigation of the Effect of Supersonic Flow of Dissociated Nitrogen on ZrB2-HfB2-SiC Ceramics Doped with 10 vol.% Carbon Nanotubes.

The method of fabricating dense ultra-high temperature ceramic materials ZrB2−HfB2−SiC−CCNT was developed using a combination of sol-gel synthesis and reaction hot pressing approaches at 1800 °C. It was found that the introduction of multilayer nanotubes (10 vol.%) led to an increase in the consolidation efficiency of ceramics (at temperatures > 1600 °C). The obtained ZrB2−HfB2−SiC and ZrB2−HfB2−SiC−CCNT materials were characterized by a complex of physical and chemical analysis methods. A study of the effects on the modified sample ZrB2−HfB2−SiC−CCNT composition speed flow of partially dissociated nitrogen, using a high-frequency plasmatron, showed that, despite the relatively low temperature established on the surface (≤1585 °C), there was a significant change in the chemical composition and surface microstructure: in the near-surface layer, zirconium−hafnium carbonitride, amorphous boron nitride, and carbon were present. The latter caused changes in crucial characteristics such as the emission coefficient and surface catalyticity.

High-aspect-ratio ZrC whiskers: Synthesis, growth mechanism and electromagnetic wave absorption properties

Stealth materials with high dependability at elevated temperatures and outstanding mechanical properties are urgently needed for practical applications. As one-dimensional ultrahigh temperature ceramic (UHTC) materials, zirconium carbide whiskers (ZrCw) have attracted a great deal of attention due to their desirable mechanical and ablation resistance performance in high-temperature environments. We have successfully synthesized ZrCw using a carbothermal reduction technique without the introduction of metal catalytic in this paper. ZrCw shows a typically prismatic structure with the diameter of 1–2 μm and the aspect ratio of up to 250. The growth of ZrCw is controlled by a solid-liquid-solid (SLS) and vapor-solid (VS) compound mechanism in conjunction with the auxiliary action of mesophase Na3ZrF7. The ZrCw/paraffin hybrids achieve the minimum reflection loss (RL(min)) of −25.77 dB at 13.28 GHz under the thickness of 1.25 mm, and reach an effective absorption bandwidth (EAB) of 3.04 GHz (14.96–18.00 GHz) with a thickness of only 1.0 mm. This work presents a promising approach for large-scale producing high-purity whiskers, and verifies that ZrCw has extensive application prospects in the field of stealth materials.

Preparation of zirconium diboride by reduction of zirconia with calcium hexaboride

ABSTRACT Zirconium diboride (ZrB2) is a typical ultra-high temperature ceramic material (UHTC). In this work, the preparation of ZrB2 by reducing zirconia (ZrO2) with calcium hexaboride (CaB6) was studied in detail. With the assistance of molten salt, the reduction rate was dramatically enhanced. Additionally, the results showed that ZrB2 products with different particle shapes were prepared by changing the type of molten salt (NaCl, KCl, MgCl2, and CaCl2). However, the particle size of products could not be properly refined when nano-ZrO2 was used as the raw material. During the process of reducing ZrO2 by CaB6, B2O3 could be formed, which would cause the loss of B source. To decrease the consumption of CaB6, Ca-assisted reduction was performed, and monophase ZrB2 was obtained. The varied morphologies of ZrB2 particles obtained by Ca-assisted reduction were the result of complex reaction mechanisms.

Development, and characterisation of ultra-high-temperature ceramics composite (UHTC)

ABSTRACT Ultra high-temperature ceramic (UHTC) composite materials are physically and chemically stable at high temperatures (more than 2000°C) and in reactive environments. Generally, the family group of diboride, dicarbide, and dinitride are used as ultra-high temperature ceramic due to their high thermal conductivity and high melting point. The main aim of this paper is the development of zirconium diboride (ZrB2)-based UHTC and characterisation of their density, hardness, porosity, and work considered, three powder constituents B4C (35%), ZrB2 (55%), and Cr (10%) of particle size 30 μm, 15 μm, and 4 μm, respectively, the conventional sintering and spark plasma sintering technique is used for the development of composite. The results revealed that the relative density of conventionally sintered composite at 1600°C and 1700°C are 72% and 80%, respectively, and spark plasma sintered composite at 1900°C is 99.99%. The bulk density and apparent porosity of SPS composite at 1900°C are 4.73 g/cm3 and 4%, respectively. Similarly, bulk density and apparent porosity of conventionally sintered composite, at 1600°C are 2.49 g/cm3 and 30%, respectively, and at 1700°C is 2.89 g/cm3 and 27%, respectively. Furthermore, the hardness of the SPS composite at 1900°C is 2830 HV, while the hardness of conventionally sintered composite at 1700°C and 1800°C were 280 HV and 520 HV, respectively. Additionally, scanning electron microscopy was performed to observe the bonding and porosity in the microstructure of the UHTC.

Binder jet additive manufacturing of ceramic heat exchangers for concentrating solar power applications with thermal energy storage in molten chlorides

Triply periodic minimal surface (TPMS) geometries can only be fabricated by additive manufacturing methods and are of interest for heat exchangers. Ceramic TPMS heat exchangers can operate at higher temperatures and pressures with superior performance and increased operating efficiencies compared to metal heat exchangers. The properties of ultra-high temperature ceramic (UHTC) materials are also favorable for heat exchangers and potentially suited to concentrated solar power (CSP) systems, such as those based on a molten chloride salt thermal energy storage (TES) medium used to heat CO 2 in a closed-loop Brayton power cycle. We intended to demonstrate binder jet additive manufacturing feasibility of a UHTC-TPMS structure by printing and sintering a null candidate. We aimed to achieve parts with a relative density ≥ 92 % of theoretical and to provide a TPMS part demonstration. The target density indicates the transition from intermediate to final stage sintering, a requirement to inhibit gas permeability and for sintering complex near net shapes to full density with sinter-HIP technology. The goal of the TPMS part demonstration was to determine if printing and sintering parameters developed from test coupons apply to the complex geometries that will eventually be used in a heat exchanger design. Our objective was to print cubic TPMS parts with a 9 cm 3 volume and sinter it without distorting and cracking. We were able to sinter ZrB 2 -MoSi 2 composite parts based on the Schwarz-D TPMS and achieve isotropic shrinkage up to 60 % by volume, resulting in densities ranging from 92 % to 96 % of theoretical. • Advanced heat exchanger design based on a triply periodic minimal surface (TPMS). • Ultra-high temperature ceramic (UHTC) materials of construction. • Binder jet additive manufacturing and sintering of ZrB2-MoSi2 Schwarz-D cells. • Utilization of conventional powder feedstocks. • Achieving isotropic shrinkage and densities of 92–98 % of theoretical.

Research on the thermal shock simulation of the super high speed aircraft

Ultra high temperature ceramics (UHTC) with good mechanical properties and thermal physical properties, including high melting point (>30000C), high conductivity, high thermal conductivity, high thermal shock resistance rate, provides a sharp leading edge and smooth surface of a new generation of aerospace vehicle design to the aerospace industry; Due to ultra-high temperature ceramic materials with high strength, oxidation resistance and thermal shock resistance, it can be applied to extreme environments such as hypersonic flight, atmospheric reentry and rocket propulsion system, and have been widely used in key components of aircraft front cone, engine, wing and engine hot end. Based on the application of ultra-high temperature superconducting materials in practical application, the solid modeling of ultra-high temperature superconducting front-end components of ultra-high speed aircraft wing is carried out by using ABAQUS software, the ultra-high temperature thermal field of loaded aircraft flying at ultra-high speed is simulated, the stress-strain field at the flange is obtained, and the thermal mechanical coupling analysis is carried out.

Stability, mechanical, and thermodynamic behaviors of (TiZrHfTaM)C (M = Nb, Mo, W, V, Cr) high-entropy carbide ceramics

Multicomponent high entropy carbide ceramics (HECCs) have drawn increasing attention because of their potential applications as ultra-high temperature and super-hard materials. In this work, the stability, mixing behavior, mechanical, and temperature-dependent properties of rock-salt (TiZrHfTaM)C (M = Nb, Mo, W, V, or Cr) HECCs were first systematically investigated by density functional theory (DFT) and Debye-Grüneisen model methods. The five HECCs are thermodynamically stable owing to the negative formation enthalpies and cohesive energies. They could form the single-phase high entropy solid solution ceramics, owing to the evaluation of atom size and lattice differences, as well as mixing enthalpy criteria. Except for the system containing Cr, the others have already been confirmed by experimental findings. Among these, (TiZrHfTaNb)C most readily forms homogeneous solid solution phase, and is the most stable, brittlest, and hardest HECC material. Significantly, (TiZrHfTaV)C behaves slightly better than (TiZrHfTaNb)C with increasing temperature, owing to the comparable bulk modulus and Debye temperature, smaller volumetric expansion, and lower anharmonic effects. This work provides the instructive information for predicting and designing the high-performance ultra-high temperature ceramic materials applicable in extreme environments.

Processing of ZrB2- and HfB2-Based Ultra-High Temperature Ceramic Materials: A Review

Abstract ZrB2 and HfB2 are leading materials in the category of ultra-high temperature ceramics (UHTCs). UHTCs are a group of ceramic materials that can withstand ultra-high temperature (&amp;gt;2,000°C) in oxidizing conditions. Such a high temperature will be encountered by future hypersonic reentry vehicles. Future reentry vehicles will have sharp edges to improve aerodynamic performance. The sharp leading edges will cause higher surface temperature than that of the actual blunt-edged vehicles. The sharp edges have less surface area to dissipate heat and thus the temperature gets increased. To withstand the intense heat generated when these vehicles reenter the earth’s upper atmosphere, UHTC materials are needed. UHTC materials are composed of borides of early transition metals. From the larger list of borides, ZrB2 and HfB2 have received the most attention as potential candidates for leading edge materials because their oxidation resistance is superior to that of other borides because of the stability of the ZrO2 and HfO2 scales that form on these materials at elevated temperatures in oxidizing environments. Processing of these materials is very difficult because these materials are very refractory in nature. Powder synthesis usually involves high-temperature solid state reactions. Dense bodies are generally produced by hot pressing and spark plasma sintering. For coating preparation, plasma spray, chemical vapor deposition, and physical vapor deposition is used. All these processing methods for ZrB2 and HfB2 are difficult because of the involvement of very high temperatures. In this review, the present state of the knowledge on processes employed for powder synthesis, fabrication of dense bodies, and coating processes is discussed. The advantages, limitations, and challenges in the different processing methods are addressed.

Editorial: Special Issue on Materials for Extreme Environments, Part 1

Abstract Limits on materials behavior are among the greatest technical obstacles to improving the safety and reliability of engineering systems. When subjected to extreme environments, materials can behave in unexpected and unpredictable ways. The need to develop materials that can perform well in severe operating environments is a major challenge for materials scientists, and it requires a fundamental understanding of material response under extreme conditions of heat flux, stresses, strain rates, and corrosive environments. Chemical and physical processes must be probed, understood, and controlled at different length scales, over varying time periods for successful development of materials for engineering applications. Further, understanding and exploiting extreme environments is critical for meeting the demanding applications in diverse areas of engineering research for creating new materials, that not only survive but also function under the challenging conditions. It has been a real pleasure to be guest editors for the Materials Performance and Characterization two-part special issue on Materials for Extreme Environments. The call for papers attracted a large number of abstracts from leading scientists and engineers for these special issues. After scrutiny and their acceptance, a total of 48 full-length manuscripts have been submitted for consideration. The first part of this two-part special issue covers 16 papers that were submitted and subjected to the peer review process, performed by experts from the respective fields. Importantly, the issue consists of three review articles, authored by eminent researchers that are of significant addition to this volume. The first article, by Prof. Osamu Umezawa, is an authoritative review on the mechanical properties of high strength alloys at cryogenic temperatures. In his illustrious career, he has immensely contributed to the cryogenic testing procedures and to the understanding of fatigue and fracture of several structural materials operating at cryogenic temperatures. The second article is a review of steels for cryogenic applications from the materials researchers of the Indian Space Research Organization. This article presents an exhaustive study of different classes of steels used for cryogenic applications including recent advances in materials such as high entropy alloys and those processed through additive manufacturing for applications down to 4K. The third article is a review on processing of ZrB2 and HfB2 based ultra-high temperature ceramic materials from the research group of Homi Bhabha National Institute, India. This article discussed the challenges involved in the fabrication of dense di-borides for leading edge applications in hypersonic vehicles. This is followed by 13 manuscripts describing the latest advances in materials for extreme environments. A very interesting article by Perepezko et al. on Mo-Silicide alloys for high temperature structural applications brings out the latest developments in these classes of materials. Advanced materials and manufacturing technologies for gas turbines, creep, creep-fatigue, high strain rate behavior of different types of materials, fibers for high temperature applications, coatings for functional applications, C/SiC fasteners for high temperature applications, fire resistant steels, welding, and tribological properties of superalloys are presented in subsequent manuscripts. These articles describe the latest advances in the materials for extreme environments. We sincerely thank both the authors and reviewers for their hard work and dedication. We wholeheartedly thank the ASTM staff dealing with the issues related to the process of publishing an outstanding journal. We sincerely hope that you enjoy these papers and look forward to the second part of this special issue that is currently under processing.

Performance Comparison of Microchannel Heat Sink Using Boron-Based Ceramic Materials

Microchannel heat sink plays a vital role in removing a considerable amount of heat flux from a small surface area from different electronic devices. In recent times, the rapid development of electronic devices requires the improvement of these heat sinks to a greater extent. In this aspect, the selection of appropriate substrate materials of the heat sinks is of vital importance. In this paper, three boron-based ultra-high temperature ceramic materials (ZrB2, TiB2, and HfB2) are compared as a substrate material for the microchannel heat sink using a numerical approach. The fluid flow and heat transfer are analyzed using the finite volume method. The results showed that the maximum temperature of the heat source didn’t exceed 355K at 3.6MWm-2 for any material. The results also indicated HfB2 and TiB2 to be more useful as a substrate material than ZrB2. By applying 3.6 MWm-2 heat flux at the source, the maximum obtained surface heat transfer coefficient was 175.2 KWm-2K-1 in a heat sink having substrate material HfB2.

Compact fiber-coupled UV-NIR hyperspectral imaging sensor for characterizing ultra-high temperature ceramic materials.

A compact fiber-coupled hyperspectral imaging sensor (HSIS) operating within the range of ultraviolet to near-infrared (UV-NIR) wavelengths is designed and developed for the remote recording of two-dimensional (2D) spectrally resolved thermal radiation and chemiluminescent emission from ultra-high-temperature ceramics (UHTCs). Using simulations, the entire system is optimized to improve the collection efficiency and minimize aberrations. The design, construction, and characterization of the HSIS sensor are discussed in detail. We present the 2D spectrally resolved measurements of the simultaneous thermal radiation and BO2∗ chemiluminescent emission from a commonly used UHTC (HfB2-SiC) material under high-heat-flux conditions. Our results show that BO2∗ chemiluminescence corresponds directly to material ablation and can be used to track the formation of the protective heat-resistant glass/oxide layer. Furthermore, the temperature measurements demonstrate the heat distribution properties of the sample and indicate the locations at which BO2∗ chemiluminescence is possible. These results highlight the application prospects of the compact fiber-coupled HSIS for high-temperature material characterization in practical arc-jet facilities with limited optical access.

Behavior of Ultra-High Temperature Ceramic Material HfB2–SiC–Y3Al5O12 under the Influence of Supersonic Dissociated Air Flow

Ultra-high-temperature ceramic (UHTC) materials with a density of 94.5 ± 1.3% have been manufactured by hot pressing a (HfB2–30 vol % SiC)–5 vol % Y3Al5O12 composite powder, which has been prepared sol–gel method, at a moderate temperature of 1850°C (holding time, 30 min; pressure, 30 MPa). The oxidation resistance of this ceramic has been studied at elevated temperatures under the effect of a supersonic dissociated air flow (on a high-frequency induction plasmatron). The maximum surface temperature has been ~2550°C. An analysis of the kinetics of temperature changes depending on the heat load indicate that, when five percent of Y3Al5O12 by volume of HfB2–30 vol % SiC is introduced into the ceramics, the thermal conductivity of the material decreases. This is not critical from the point of view of the stability of the obtained sample to single temperature drops of ~700–1400°C in a few seconds with sharp heating and cooling of the sample. A decrease of ~35–40% in weight loss of the (HfB2–30 vol % SiC)–5 vol % Y3Al5O12) sample has been noted as the result of exposure as compared with unmodified analogs. Due to the presence of Y3Al5O12 in the initial ceramics, there is also a certain amount of the stabilized phase of cubic HfO2 in the oxidized layer in addition to the monoclinic.

Microstructure and strengthening mechanism of grain boundary strengthened W-ZrB2 alloy

Using the unique properties of ultra-high temperature ceramic material, a new kind W-ZrB2 alloy was prepared. Compared with pure tungsten (PW), the mechanical properties of W-ZrB2 alloy were obviously improved. In particular, the sintered alloy showed complete transgranular fracture morphology, and the originally weak grain boundaries of tungsten were greatly strengthened. From macroscopic fracture to microscopic crystal structure, the strengthening mechanism of ZrB2 in tungsten matrix was studied by means of transmission electron microscope and energy spectrum analysis. The decomposition of ZrB2 and the structure of its decomposition products had been confirmed. The formation of the second phases of various crystal structures and the distribution of B element on the grain boundaries were the key factors to strengthening mechanism.

Pushing the limits of atomistic simulations towards ultra-high temperature: A machine-learning force field for ZrB2

Determining thermal and physical quantities across a broad temperature domain, especially up to the ultra-high temperature region, is a formidable theoretical and experimental challenge. At the same time it is essential for understanding the performance of ultra-high temperature ceramic (UHTC) materials. Here we present the development of a machine-learning force field for ZrB2, one of the primary members of the UHTC family with a complex bonding structure. The force field exhibits chemistry accuracy for both energies and forces and can reproduce structural, elastic and phonon properties, including thermal expansion and thermal transport. A thorough comparison with available empirical potentials shows that our force field outperforms the competitors with the merits of high accuracy and great versatility. Most importantly, its effectiveness is extended from room temperature to the ultra-high temperature region (up to ∼ 2500 K), where measurements are very difficult, costly and some time impossible. Our work demonstrates that machine-learning force fields (MLFF) can be used for simulations of materials in a harsh environment, where no experimental tools are available, but crucial for a number of engineering applications, such as in aerospace, aviation and nuclear.