ZrB2 SiC Ceramics Research Articles

Effects of adding Si3N4 whiskers to ZrB2–SiC ceramics on microstructure, mechanical properties and oxidation resistance

ZrB2–SiC–Si3N4w ceramics (ZSNw) were prepared via the hot-pressing sintering method. The bending strength and fracture toughness of ZSNw at room temperature reached to 520 ± 24 MPa and 5.2 ± 0.16 MPa m1/2, respectively. The enhancement in mechanical properties is attributed to the grain refinement and attenuation of grain boundary induced by the homogeneous distribution of Si3N4 whiskers. The oxidation resistance of ZSNw were conducted at 1500 °C in an air atmosphere. Remarkably, after 10 h of oxidation, ZSNw remained excellent strength and toughness reaching at 589 ± 26 MPa and 4.8 ± 0.12 MPa m1/2, respectively. This oxidation resistance of ZSNw was mainly attributed to the gain refinement induced by Si3N4 whiskers, which effectively reduced the voids within the ceramic matrix. Therefore, this process promoted the densification and homogenization of the SiO2 protective barriers, accompanied with hindering the inward permeation of oxygen and the outward release of oxides.

Ablation performance and mechanism of fibrous monolithic ZrB2-SiC ceramics prepared by wet-spinning co-extrusion method under plasma flame

The fibrous monolithic structure exhibits extensive graded fracture as well as load redistribution upon fracture due to the unique layered microstructure, providing an effective way to toughen ceramic materials. In this work, fibrous monolithic ZrB2-SiC/SiCw (FZSw) and fibrous monolithic ZrB2-SiC/BN ceramics (FZB) were prepared by wet-spinning and co-extrusion method using SiCw and BN as the interfacial layer. The strengths, toughness, and the work of rupture of FZSw were 117 MPa, 3.9 MPa m1/2, 104 J/m2, while that of FZB were 103 MPa, 2.6 MPa m1/2, 98 J/m2, respectively. FZSw and FZB were subjected to 200 s plasma ablation tests under 12.84 MW/m2 and plasma flame above 3000 °C. The mass and linear ablation rates of FZSw after testing were -0.34 mg/s and -0.2 μm/s, respectively, and remain intact, showing non-ablation characteristics, while FZB underwent delamination and destruction. The introduction of SiCw interface layer improved the thermal conductivity of FZSw and reduced the surface temperature of FZSw. Higher oxidation temperature and higher SiC content of the SiCw interface layer result in a great quantity of SiO2, which effectively isolated oxygen from further erosion.

Кераміка ZrB2 з добавками MoSi2, SiC і B4C: кінетика ущільнення, фазоутворення та опір повзучості

A study was carried out of the processes of compaction, structure formation and mechanical properties of ceramics based on zirconium boride with sintering-activating additives of boron, silicon and chromium carbides, as well as molybdenum silicide, obtained under hot pressing conditions in a CO atmosphere. In ZrB2—18% (vol.) B4C ceramics, the use of the B4C additive reduces the optimal hot pressing temperature to 1940 °C and accelerates the compaction process of the ceramics. The influence of the sample preparation background on high-temperature creep has been established, as a result of which either plastic flow of the material occurs over a wide temperature range, or a high temperature threshold for yield and brittle fracture. In ZrB2—SiC ceramics, during high-temperature plastic deformation both during sintering and in creep tests, a bidisperse structure with a submicrograined component is formed, which is responsible for high creep rates. In ZrB2—B4C ceramics there is no submicrograin component, which provides high creep resistance up to 2000 °C. The phase composition of ZrB2—MoSi2 ceramics changes dramatically during hot pressing; it is represented by a composition of a ZrB2 solid solution with the second phases of SiC and B4C, and in terms of creep resistance it occupies an intermediate position between two other ceramics. Keywords: ultra-high temperature ceramics, zirconium diboride, silicon, boron and chromium carbides, hot pressing in a CO atmosphere, compaction kinetics, structure, creep resistance.

Mechanical and plasma ablation properties of double-interface fibrous ZrB2-SiC ceramics for ultra-high-temperature application

Double-interface fibrous ZrB2-SiC ceramics (DZSw) were prepared by wet-spinning and hot-pressing. The introduction of double-interface layers improves the interface bonding and crack tolerance making the bending strength and toughness of DZSw increased to 607 MPa and 6.3 MPa m1/2, respectively. After ablation testing in 9.34 MW/m2 plasma flame, DZSw remained intact, with linear and mass ablation rates of − 0.3 µm s-1 and − 0.11 mg s-1, respectively. However, single-interface fibrous ZrB2-SiC ceramic (SZSw) produced penetrating cracks, so DZSw presented high ablation resistance than SZSw. The introduction of a dense ZrB2-SiC outer interface layer in DZSw interrupts the three-dimensional connected structure of the porous SiCw interface layer in SZSw and consequently reduces the oxygen diffusion rate of the ceramics. Moreover, the high emissivity and thermal conductivity enable DZSw to serve in the high heat flux ablation environment caused by faster flight speed.

A novel strategy for synthesizing porous ZrB2-SiC ceramics via boro/carbothermal reaction process templated pore-forming approach

A novel strategy for synthesizing porous ZrB2-SiC ceramics via boro/carbothermal reaction process templated pore-forming approach

Effect of Zr2Al4C5 Content on the Mechanical Properties and Oxidation Behavior of ZrB2-SiC-Zr2Al4C5 Ceramics.

ZrB2-SiC-Zr2Al4C5 multi-phase ceramics with uniform structure and high density were successfully prepared through the introduction of in situ synthesized Zr2Al4C5 into ZrB2-SiC ceramic via SPS at 1800 °C. A systematic analysis and discussion of the experimental results and proposed mechanisms were carried out to demonstrate the composition-dependent sintering properties, mechanical properties and oxidation behavior. The results showed that the in situ synthesized Zr2Al4C5 could be evenly distributed in the ZrB2-SiC ceramic matrix and inhibited the growth of ZrB2 grains, which played a positive role in the sintering densification of the composite ceramics. With increasing Zr2Al4C5 content, the Vickers hardness and Young's modulus of composite ceramics gradually decreased. The fracture toughness showed a trend that first increased and then decreased, and was increased by about 30% compared with ZrB2-SiC ceramics. The major phases resulting from the oxidation of samples were ZrO2, ZrSiO4, aluminosilicate and SiO2 glass. With increasing Zr2Al4C5 content, the oxidative weight showed a trend that first increased then decreased; the composite ceramic with 30 vol.% Zr2Al4C5 showed the smallest oxidative weight gain. We believe that the presence of Zr2Al4C5 results in the formation of Al2O3 during the oxidation process, subsequently resulting in a lowering of the viscosity of the glassy silica scale, which in turn intensifies the oxidation of the composite ceramics. This would also increase oxygen permeation through the scale, adversely affecting the oxidation resistance of the composites with high Zr2Al4C5 content.

Grain growth inhibition by sluggish diffusion and Zener pinning in high‐entropy diboride ceramics

AbstractThis work reported the grain growth kinetics of high‐entropy diboride (HEB) and HEB‐SiC ceramics containing 10, 20, and 30 vol% SiC during heat treatment at 1800°C. The coarsening of HEB phase occurred in the four kinds of ceramics during heat treatment, especially in HEB ceramics. The kinetic analysis showed that the grain growth of HEB phase in HEB and HEB‐SiC ceramics is controlled by interface‐controlled kinetics and grain‐boundary pinning, respectively. The growth rate constant of HEB grains is lower than ZrB2, which is related to the low grain‐boundary energy and the sluggish diffusion effect in dynamics of high‐entropy materials. The growth rate of matrix phase in HEB‐SiC ceramics is similar to that in ZrB2–SiC ceramics, indicating that the pinning effect of the SiC second‐phase played the dominant role in inhibiting the grain growth of the high‐entropy matrix phase and disguised the sluggish diffusion effect. This study reveals that the grain growth inhibition through sluggish diffusion effect in a high‐entropy ceramic system may be magnified by the possible existence of segregated second‐phase particles located at the grain boundaries.

Microstructure and phase evolution behavior of SiZrBC ceramic precursors synthesized via sol–gel method

ZrB2–SiC ceramics were successfully prepared via sol–gel method using phenyltrichlorosilane, borane dimethyl sulfide, and zirconium tetrachloride in stoichiometric amounts as the raw materials. The macromolecular network structure formed after the sol–gel process was investigated via Fourier transform infrared (FT–IR) spectroscopy. The phase evolution of the ZrB2–SiC ceramics were analyzed by FT–IR spectroscopy, X–ray diffraction, and transmission electron microscopy, whereas morphological and elemental analyses were performed using scanning electron microscopy. In particular, the change in phase composition was monitored after the pyrolysis from 1400 to 1500 ​°C, and the heat treatment of BZ6 precursor at 1500 ​°C enabled one to produce the ZrB2–SiC ceramic with a homogeneous crystal phase distribution. Therefore, the controllable microstructure adjustment of the ceramic phase composition could be achieved and a new way was paved for the structural and functional applications of ultra–high–temperature ceramics (UHTCs) series.

Oxidation Behaviors of ZrB2–SiC Ceramics with Different Porosity

ZrB2–SiC ceramics have great application potential in thermal protection system of hypersonic aircraft, due to their excellent oxidation resistance and mechanical properties. Porosity is one of the main factors which will obviously affect the oxidation behaviors of ZrB2–SiC ceramics. Herein, ZrB2–SiC ceramics with three different porosity are sintered by spark plasma sintering at different temperatures. Then, a series of oxidation tests of the ceramics with different porosity are carried out at different temperatures and with different time. Morphologies and microstructures of the oxidation surface and cross section, as well as the oxide layer thickness and weight change are discussed in detail. Results show that the porosity of ZrB2–SiC ceramics has great influence on the oxidation behaviors of ceramics. The oxide layer thickness and weight change gradually increase with the increase of oxidation temperature and oxidation time for ZrB2–SiC ceramics with different porosity. As the porosity of ZrB2–SiC ceramics decreases, the oxide layer thickness and weight change generally decrease, which shows that the ceramics with lower porosity have stronger oxidation resistance. This work provides a relative systematic analysis of the effects of porosity on the oxidation behaviors of ZrB2–SiC ceramics.

3D nearest neighbor index model combined with Nano-CT to analyze SiC particles in ZrB2–SiC ceramics

ZrB2–SiC nanocomposite ceramics are desirable for applications in the aeronautics and astronautics fileds. Analyzing SiC nanoparticles is important for developing ZrB2–SiC ceramics, but due to the limitations of existing methods and the performance of experimental equipment, few methods provide comprehensive three dimensional (3D) characterization and information mining. Therefore, we propose a 3D nearest neighbor index (NNI) model combined with large field of view (LFOV) X-ray nanoscale computed tomography (nano-CT). First, we drew conclusions about 3D NNI by simulating particles with different distribution patterns. We next designed an X-ray LFOV nano-CT experiment, then nondestructively reconstructed and visualized 3D tomographic images of ZrB2–SiC. Finally, we used the 3D NNI model and relevant conclusions to analyze the extracted nanoparticles in samples. The results showed that the 3D NNI model combined with LFOV nano-CT could be used to nondestructively, qualitatively and quantitatively characterize the distribution of SiC nanoparticles in an arbitrary 3D morphological region, and obtain multi-scale information about agglomerates.

Microstructural and nanoindentation study of TaN incorporated ZrB2 and ZrB2–SiC ceramics

This study assessed the sinterability and microstructure of ZrB2-SiC-TaN and ZrB2-TaN ceramics. Spark plasma sintering at 2000 °C and 30 MPa for 5 min produced both ceramics. The relative density of ZrB2 ceramic containing TaN was 95.3%; the addition of SiC increased this value to 98.1%. SiC’s contribution to the elimination of ZrB2 surface oxides was the primary factor in the advancement of densification. The in situ formation of hexagonal boron nitride at the interface of TaN and ZrB2 was confirmed by high-resolution transmission electron microscopy, field emission-electron probe microanalyzer, X-ray diffractometry, and field emission scanning electron microscopy. Moreover, the in situ graphite might be produced as a byproduct of the SiC-SiO2 process, hence boosting the reduction of oxide compounds in the ternary system. The SiC compound had the highest hardness (29 ± 3 GPa), while the ZrB2/TaN interface exhibited the greatest values of elastic modulus (473 ± 26 GPa) and stiffness (0.76 ± 0.13 mN/nm).

Self-Lubricating Effect of WC/Y–TZP–Al2O3 Hybrid Ceramic–Matrix Composites with Dispersed Hadfield Steel Particles during High-Speed Sliding against an HSS Disk

WC/Y–TZP–Al2O3 hybrid ceramic–matrix composites (CMCs) with dispersed Hadfield steel particles were sintered and then tested at sliding speeds in the range of 7–37 m/s and contact pressure 5 MPa. Fast and low-temperature sinter-forging allowed obtaining micron-sized WC grains, submicron-sized alumina-reinforced yttria partially stabilized polycrystalline tetragonal zirconia (Y–TZP–Al2O3), and evenly distributed Hadfield steel grains. Such a microstructure provided new hybrid characteristics combining high hardness with high fracture toughness and tribological adaptation. The CMCs demonstrated low friction and high wear resistance that were better than those demonstrated by other composite materials such as, for example, MAX-phase composites, zirconia-base ceramics, ZrB2-SiC ceramics, and metal matrix WC–(Fe–Mn–C) composites. These good tribological characteristics were obtained due to the in situ mechanochemical formation of iron tungstates FeWO4 and Fe2WO6 on the worn surfaces of composite samples. These mixed oxides were included in multilayer subsurface structures that provided the self-lubricating and self-healing effects in high-speed sliding because of their easy shear and quasi-viscous behavior.

Strain rate effect on the mechanical properties of ZrB2-SiC ceramics characterized by nanoindentation

ZrB2-SiC ceramics are one of the most promising materials for high temperature applications, and their mechanical properties are key indicators that determine whether they can long-time serve safely. In this work, the mechanical properties of ZrB2-SiC ceramics are determined by nanoindentation under six different strain rates. The relative density of ZrB2-SiC ceramics prepared by spark plasma sintering reaches 99.1%. The effects of strain rate on the elastic modulus, hardness, creep and pop-in behaviors are discussed in detail. Results show that the effect of strain rate on the elastic modulus can be ignored. The hardness increases with the increase of strain rate, and the increase gradually slows down. The relationship between the natural logarithms of hardness and strain rate can be accurately described as a linear function. The creep strain rate under indentation declines rapidly in the initial holding stage, and then gradually transitions into a constant in the steady-state creep stage under different strain rates. The pop-in load and displacement also showed obvious strain rate-dependence, based on which the shear strength of ZrB2 gains was estimated and compared with the theoretical value.

Simulation of microscopic interface damage of ZrB2 based ceramics based on cohesive zone model

The interfacial energy release rate of ZrB2-based ceramics was obtained by combining the equivalent relationship between the stress intensity factor criterion in the local range of crack tip and the energy balance criterion. Cohesive zone model (CZM) is introduced to simulate the intergranular failure behavior. The damage parameters required by the CZM are calculated by Mori-Tanaka theory. Based on the microstructure of ZrB2-SiC ceramics, the representative volume element (RVE) is established and subjected to displacement load. Finally, the stress nephogram and damage evolution process of RVE are obtained and the process of stress change of matrix, particles, damage interface and undamaged interface of RVE with the load applied gradually are outputted.

Mechanical and ablation properties of laminated ZrB2-SiC ceramics with Si3N4 whisker interface

Laminated ZrB2-SiC/Si3N4w ceramics were prepared by using Si3N4 whiskers as interface layer. Toughness of the laminated ceramics was remarkable improved, because of the deflection and bifurcation of crack. Moreover, the laminated ZrB2-SiC/Si3N4w ceramics showed better ablation resistance than monolithic ZrB2-SiC ceramics, which was tested at 3000 °C for 100 s. Higher thermal conductivity of laminated ceramics than that of monolithic ceramics in both the in-plane direction and through-plane direction, leads to faster heat transfer in laminated ceramics during the ablation process.

Controllable preparation of porous ZrB2–SiC ceramics via using KCl space holders

In this work, a novel and facile technique based on using KCl as space holders, along with partial sintering (at 1900 °C for 30 min), was explored to prepare porous ZrB2–SiC ceramics with controllable pore structure, tunable compressive strength and thermal conductivity. The as-prepared porous ZrB2–SiC samples possess high porosity of 45–67%, low average pore size of 3–7 μm, high compressive strength of 32–106 MPa, and low room temperature thermal conductivity of 13–34 W m−1 K−1. The porosity, pore structure, compressive strength and thermal conductivity of porous ZrB2–SiC ceramics can be tuned simply by changing KCl content and its particle size. The effect of porosity and pore structure on the thermal conductivity of as-prepared porous ZrB2–SiC ceramics was examined and found to be consistent with the classical model for porous materials. The poring mechanism of porous ZrB2–SiC samples via adding pore-forming agent combined with partial sintering was also preliminary illustrated.

Fabrication and characterisation of high-performance joints made of ZrB2-SiC ultra-high temperature ceramics

Joining is crucial for ultra-high temperature ceramics (UHTCs) to be used in demanding environments due to the difficulty in manufacturing large and complex ceramic components. In this study, ZrB2-SiC composite UHTCs parts were joined via Ni foil as filler, and the mechanical properties and oxidation behaviour of the fabricated ZrB2-SiC/Ni/ZrB2-SiC (ZS/Ni/ZS) joint were investigated. Firstly, dense ZrB2-SiC composites were prepared from nano-sized powders by spark plasma sintering (SPS). The ZrB2-SiC parts were then joined using SPS. Furthermore, the elastic modulus, hardness, shear strength and high temperature oxidation behaviour of the ZS/Ni/ZS joint were examined to evaluate its properties and performance. The experimental results showed that the ZrB2-SiC parts were effectively joined via Ni foil using SPS and the resultant microstructures were free from any marked defects or residual metallic layers in the joint. Although the elastic modulus and hardness in the joining zone were lower than those in the base ZrB2-SiC ceramics, the shear strength of the joint reached ∼161 MPa, demonstrating satisfactory mechanical properties. Oxidation tests revealed that the ZS/Ni/ZS joint possesses good oxidation resistance for a wide range of elevated temperatures (800–1600 oC), paving the way for its employment in extreme environments.

Thermally stimulated self-healing capabilities of ZrB2-SiC ceramics

The ultrahigh temperature ceramic-matrix composites (UHTCMCs) are the core class of innovative materials. One of the key-features that such a new class of materials should exhibit is self-repair of damage without any external intervention. In the present work, a set of ZrB2-SiC ceramics (SiC from 5 to 15 vol.%) was produced by hot-pressing: besides SiC, also 5 vol.% Y2O3 was added in the starting mixture to search for an improved self-healing capability (SH). Dedicated set-ups to thermally stimulate samples in severely oxidizing atmosphere up to 2278 K were designed and realized. To assess the SH capabilities, the retained flexural strengths were measured at room temperature using samples damaged by indentations and then heat treated from 1773 K to 2278 K. The strength recovery rates were measured and correlated to the SH efficiency.

Subsurface multilayer evolution of ZrB2–SiC ceramics in high-speed sliding and adhesion transfer conditions

High-speed continuous sliding experiments on ZrB2-20 vol% SiC ultra-high temperature ceramics have been carried out to elucidate specifics and details of tribooxidation under conditions of subsurface deformation and friction generated heating. Subsurface multilayer structure layer phase composition was obtained to testify on the intense mass transfer processes. Generation of thick boron-depleted and mechanically mixed layer (MML) composed of silicate glass, iron, high-temperature zirconia phases as well as silicon carbide insulated the underlying ZrB2 grains and served to generation of two transition layers composed of borosilicate glass, zirconia and iron oxyborides. This and sealing the voids and cracks by borosilicate glass had its effect on oxidation of silicon carbide grains, which might have caused intense formation of spherical particles even far below the worn surface. Mass transfer of iron and oxygen into ceramic composite grains has been discovered along with evaporation of boron anhydride from the MML.

Effect of Mo2C addition on the mechanical properties and oxidation resistance of ZrB2-SiC ceramics

Simple hot pressing and vacuum pre-treatment at 1600 °C followed by hot pressing were used for obtaining dense composites of ZrB2–15 vol% SiC– 5 vol% Mo2C. The room temperature strength was around 820 MPa for the hot-pressed material and 650 MPa for the material obtained by use of thermally treated powders. At 1800 °C, the strength converged to 154 and 182 MPa, respectively, as was mostly driven by SiC grain sliding. Oxidation in static air at 1600 °C for 2 h showed the formation of a 3-layered scale for both materials but with different thickness. The outermost layer was a borosilicate glass; the intermediate layer consisted of a phase based on zirconium oxide, silicon oxide, molybdenum boride and oxide; and the last layer was a silicon-depleted boride matrix. The two-step processing route resulted in a material with higher oxidation resistance, due to coarser grain size and higher amount of (Mo,Zr)B phase, which remained stable as solid compound in the sub-scales.