Ceramic Phase Research Articles

Characterization and solidification of heavy metals in sintered solid-waste ceramics made from zinc-extraction kiln slag.

Zinc-extraction kiln slag is a hazardous solid waste rich in heavy metals. It is a great challenge to utilize it economically and harmlessly. This study aims to convert this zinc-extraction kiln slag (proportion of 50-60%) into solid-waste ceramics, by simultaneously utilizing other solid waste, fly ash, and desulfurization gypsum. By using X-ray diffraction, leaching experiments, and SEM analysis, the paper studied the solid-waste ceramics 'ability to solidify heavy metals. Under optimal conditions, C5 (zinc-extraction kiln slag, desulfurization gypsum, and fly ash with mass percentages of 60:20:20, at a sintering temperature of 1180°C) shows an excellent performance with 43.02MPa bending strength and 0.74% water absorption. The solidification ratios of Cr, Mn, Ni, Cu, and Zn were all exceed 97%. The main phases in the solid-waste ceramics were diopside and hematite. Diopside can efficiently solidify Zn, Mn, and Ni, while Cr and Cu can be solidified in the minor phase of spinel. During the sintering process, the ceramics produced the liquid phase, which promoted crystallization for solid solution of heavy metals and accelerated densification by elimination of pores. The ceramic system with diopside as the main phase not only shows excellent performance but also effectively solidifies heavy metals. Therefore, it is suitable for the resource utilization of metallurgical solid wastes containing heavy metals.

Investigation of Cr2SiC Ceramic MAX Phase Coated Metallic Bipolar Plates in Ex-situ Conditions for Proton Exchange Membrane Fuel Cells

Essential for compact and lightweight proton exchange membrane fuel cell (PEMFC) stacks, metallic bipolar plates (MBPs) suffer from durability and conductivity issues due to surface corrosion and passivation. This study conducts ex-situ characterization of Cr2SiC ceramic MAX phase coatings on stainless steel (SS) 316 L substrates to evaluate their suitability for MBP application. The investigation encompasses coating structure, surface morphology, corrosion resistance, surface wettability, in-plane electrical conductivity, and interfacial contact resistance. X-ray diffraction and X-ray photoelectron spectroscopy confirm the presence of Cr2SiC coatings on SS316L, while energy-dispersive X-ray spectroscopy verifies uniform coverage and elemental weight percentage. Corrosion resistance is evaluated using potentiostatic and potentiodynamic polarization tests, showing excellent resistance with low corrosion current density (Icorr) at both 25 °C (3.29E-03 μA/cm2) and 80 °C (4.32E-02 μA/cm2), meeting US Department of Energy (DOE) technical targets. Potentiodynamic polarization reveals large corrosion potential and small Icorr values at both temperatures, outperforming uncoated samples. Electrochemical impedance spectroscopy post-accelerated corrosion tests show high charge transfer resistance at 25 °C (3.68E+05 Ω cm2) and 80 °C (3.02E+05 Ω cm2), indicating stability in acidic environments. Surface wettability analysis indicates low water affinity with a large contact angle (75°) and low surface free energy (28.92 mJ/m2) for the coated samples as compared to the uncoated samples. Electrical conductivity meets DOE targets with an in-plane conductivity of 4.59E+05 S/m and interfacial contact resistance of 8.04 mΩcm2 after 5-h accelerated corrosion tests at 80 °C. These results suggest that Cr2SiC coated SS316L exhibits excellent corrosion resistance, surface wettability, and electrical characteristics, making them viable for PEMFC applications.

On the dispersion of bulk wave in hygrothermally affected poroelastic gymnastics beams based on refined higher-order shear deformation theory during athlete training

Poroelastic materials have gained prominence due to their beneficial characteristics, prompting the authors to investigate their behavior in wave propagation. Additionally, the balance beam used in gymnastics is a classic example of a beam structure. It is designed to support the weight of the gymnast while providing stability and strength. This paper focuses on analyzing wave dispersion behavior in a hygrothermally excited poroelastic gymnastics beam. It is considered that the beam is made of a composition of Alumina and Aluminum as ceramic and metallic phases, respectively. Initially, the basic characteristics are determined using an improved power-law homogenization scheme. Subsequently, a poroelastic beam is modeled based on a refined higher-order shear deformation theory, and based on it and Hamilton’s principle, the kinetic relations are obtained. The obtained governing equations are then solved through analytical schemes using harmonic functions, and the outcomes are presented. These results are afterward verified through comprehensive comparisons with existing literature. Furthermore, this paper findings shows that the phase velocity and wave frequency of the beam are influenced by gradient parameters, porosity, and environmental factors like temperature and humidity to gain further insights.

Mechanical properties of MoW–HfN surrogate cermet fuel for nuclear thermal propulsion

AbstractThe mechanical performance of MoW‐HfN, a surrogate cermet for MoW‐UN Nuclear Thermal Propulsion (NTP) fuel, was characterized from room temperature to 1600°C. The modulus of elasticity and flexure strength were obtained from four‐point bend tests. Those tests revealed a loss of stiffness with increasing temperature and systematic increase in ultimate strength up to about 1400°C. This was followed by loss of ultimate strength and the onset of plastic deformation, attributed to the increased ductility of the MoW matrix above 1400°C. Chevron notch tests show that failure originates from features with a critical flaw size of ∼30 εm, which is comparable to the mean particle size of the ceramic phase. X‐ray diffraction (XRD) and Williamson–Hall (WH) analysis suggest that residual stress may contribute to the observed strength‐versus‐temperature behavior.

Evaluation of ZrB2/SiC coating for high-temperature alloy under high-energy laser

Although ZrB2/SiC coating has been widely used in high-temperature protection, it remains unclear whether it can be applied in high-energy laser protection. In this study, ZrB2/SiC spherical powder was synthesized, and ZrB2/SiC coatings were deposited on the surfaces of high-temperature alloys via atmospheric plasma spraying. Laser ablation tests were conducted on the ZrB2/SiC coatings. The results indicated that laser parameters, such as irradiation time and laser power density, significantly influenced the phase composition and morphology of the coating. Due to the high temperatures induced by the laser, the ZrB2/SiC coating oxidized rapidly, generating various glass and ceramic phases. As the temperature rose further, the glass phase content increased, encapsulating ceramic particles until vaporization occurred. The ceramic particles experienced partial sintering, which enhanced the coating’s reflectivity. During laser ablation, the vaporization of the glass phase dissipated heat, while the sintering of the ceramic phase increased reflectivity, both of which contributed to improved laser protection performance.

Exploring the mechanical and biological properties of a resin-ceramic composite with biomimetic nacre structure containing zinc used for prosthodontics

Enhancement of the mechanical and biological properties of dental restoration materials is of significant importance. Drawing inspiration from the architecture and mechanical properties of natural nacre, we employed a low-cost accumulative rolling process to develop resin-ceramic composites with suitable hardness and high toughness. Plate-like aluminum oxide powder with diameters of 5–10 μm and nano-zinc oxide (ZnO) with antibacterial properties were mixed as the ceramic phase of the composite. Aluminum oxide ceramic plates were stacked using an accumulative rolling process to achieve a consistent orientation, followed by sintering to obtain porous ceramic scaffolds. The ceramic scaffolds were subsequently immersed in methyl methacrylate resin to complete the fabrication of the biomimetic composites. The mechanical and biological properties of the composites were comprehensively tested. The composites had a suitable hardness (1.09–1.63 GPa), excellent flexural strength (156.7–167.8 MPa), and fracture toughness (KIC = 2.66–3.59 MPa m1/2). Biomimetic composites are expected to mitigate the wear of natural teeth without developing fractures or deformations, while also exhibiting excellent cytocompatibility and antibacterial activity. This study investigated the factors influencing crack propagation in fracture tests and provided insights into enhancing the toughness of dental restorative materials. The biomimetic resin-ceramic composites containing Zn developed in this study have the potential to be used as functional dental restoration materials.

Compatibility of the mechanical properties and thermal conductivity by the formation of a secondary phase in AlN ceramics: application of multifractal analysis for the microstructure evaluation

Aluminum nitride (AlN) ceramics exhibiting different secondary phase morphologies were fabricated using pressureless sintering at varying temperatures ranging from 1700-1850 °C, with a 5 mass% Y2O3 sintering additive. Although the thermal conductivity of the AlN ceramics increased as the sintering temperature increased, the bending strength increased below 1800 °C and decreased above 1800 °C. The morphology of the secondary phase in the AlN ceramics demonstrated granular, reticulate, and linear forms in that order of the low sintering temperature. The value of generalized dimensions Dq obtained by multifractal analysis increased below 1800°C and decreased above 1800°C. Higher values of Dq indicated more complex morphology and higher dispersion, corresponding to the observed morphological changes in secondary phase and the increase or decrease in the value of Dq. The sample sintered at 1800 °C had the highest Dq value and the reticulate secondary phase, with a thermal conductivity of 160 W m-1 K-1 and a maximum bending strength of 324 MPa. These results suggest that the morphology of the secondary phase affects the bending strength of AlN ceramics and that the value of Dq may be an indicator of the microstructure that achieves both thermal conductivity and mechanical properties.

Rare earth element distribution and microstructure characteristics of Ti(C,N)-based cermets with added La2O3

The effects of different levels of La2O3 content (0, 0.1, 0.2, and 0.6 wt%) in Ti(C,N)-based cermets prepared via vacuum sintering on their final microstructures as well as on the distribution characteristics of La were explored. Specifically, La2O3 was expected to undergo a reduction reaction during the sintering process when surrounded by components with carbon-donating abilities, which was proven by the formation of carbon-deficient phases, the distribution characteristics of La, and thermodynamic calculations. Metallic La, reduced from La2O3, was preferentially distributed around the Ti(C,N) particles during the heating stage and ultimately diffused into the ceramic phase, including black core–grey rim, white core–grey rim, and black rimless grains. Due to interface purification, adding a moderate amount of La2O3 could decrease the particle size of the black cores and make the core–rim structures more orderly. Along with the increase of La2O3, both the size and volume fraction of the white cores increased. However, adding an excessive amount of La2O3 would result in non-uniform distribution of the core–rim and binder phases. The inward migration of La to the ceramic phase leads to smaller lattice parameters forthe core–rim structure and a larger lattice misfit at the core/rim interfaces.

Phase evolution and steam oxidation behavior of nickel-based composite coatings fabricated by laser cladding

In this study, a variety of synthesized carbides are used as reinforcing phases for Inconel 625 alloy to enhance the performance of surface coatings. The effects of scanning rate and laser power on the microstructure and mechanical properties of coatings were studied, and specific energy was introduced to comprehensively evaluate the mechanisms of their influence. The results show that the percentage of macroscopic defects in the nickel-based composite coatings decreases and the dilution rate increases gradually with increasing specific energy density and the mechanical properties of the composite coating deteriorate gradually. It is worth noting that when the specific energy density is 153.33 J/mm2, the comprehensive performance of the composite coating is the best, which is mainly due to the uniform distribution of the contained (Ti, W)C and Cr carbides. The coating exhibits excellent hardness, corrosion resistance, and high-temperature oxidation resistance. In addition, after determining the optimal process parameter combination, the high-temperature steam oxidation performance of the nickel-based composite coating is analyzed in depth. At 1200°C, the corrosion degree of the composite coating gradually increased with increasing oxidation time. Research shows that the ceramic phase structure of (Ti, W)C and Cr plays a significant inhibitory role in high-temperature environment, effectively decelerating the increase of corrosion rate. Interestingly, before the first 48 h of the oxidation process, the thickness of the oxidation layer on coating surface increases slowly. However, when the oxidation time reaches 96 h, large amounts of WO3 and NiCr2O4 phases are formed, leading to the generation of pores and cracks in the coating. This causes the oxide film to fall off, resulting in a sharp increase in the corrosion layer thickness. The research in this paper is of great significance for optimizing coating materials and preparation processes, as well as improving the long-term high-temperature corrosion resistance of coatings.

Effect of Co content on microstructure and properties of TiCN-TiB2 cermets prepared by spark plasma sintering from a TiCN-B4C-Ti-Co system

Series of TiCN-TiB2 cermets were in situ prepared from the TiCN-B4C-Ti-Co system via spark plasma sintering (SPS). The effects of Co content on the densification, microstructure, mechanical properties, and wear resistance of TiCN-TiB2 cermets were investigated. The results showed that the Co addition had little effect on the phase composition of the sintered cermets, but had significant influences on the densification, microstructure and mechanical properties. Appropriate addition of metal Co could enhance densification and promote the grain growth of ceramic phases, but excessive addition resulted in a decrease in hardness and wear resistance. When the Co content was 10 wt.%, the cermet obtained the optimal comprehensive performance (a hardness of 1757 HV and a fracture toughness of 7.02 MPa•m1/2). Meanwhile, the cermets with 10 wt.% Co addition exhibited optimum wear resistance properties due to a good combination of hardness and toughness and moderate grain size. In addition, the formation process and strengthening mechanism in present system were discussed in detail. Results from this work could provide valuable references for the fabrication of TiB2 reinforced TiCN-based cermets.

3D printing of cordierite glass-ceramics

Compared to traditional ceramic materials, glass-ceramics can also exhibit superior properties and are now widely used in cutting-edge national defense industries technology, aerospace, electronics, construction, and other fields. In this study, it is for the first time reported that novel photopolymerization 3D printable slurries using cordierite glass ceramic powder were prepared. The effects of slurry properties and printing process parameters on the warpage of the printed samples were studied. Cordierite glass-ceramic parts fabricated using photopolymerization 3D printing and heat treatment processes were studied to evaluate the effects of sintering parameters on the properties of the samples. The obtained additively manufactured cordierite glass-ceramics exhibit excellent microstructural and mechanical properties, with a maximum bending strength of 181 MPa, an increase of 95.66 % compared to that of the previously reported 3D printed cordierite ceramics. The underlying mechanisms of the glass and ceramic phase characteristics influence the density and the mechanical properties during and after the courses of sintering were also investigated and unveiled in detail. This study provides a viable method for manufacturing complex-shaped cordierite glass-ceramic components using 3D printing.

Ceramic matrix composites for corrosion-resistant next-generation nuclear reactor systems: A conceptual review of enhancements in durability against molten salt attack

Ceramic matrix composites (CMCs) are emerging as a key material class for enhancing corrosion resistance in next-generation nuclear reactor systems, particularly in high-temperature molten salt environments. These environments, critical for advanced nuclear reactors such as molten salt reactors (MSRs), present severe challenges, including aggressive chemical attacks that degrade traditional structural materials over time. This conceptual review explores the development and application of CMCs to improve the durability and corrosion resistance of nuclear reactors exposed to molten salt attacks. CMCs, which consist of ceramic fibers embedded in a ceramic matrix, offer significant advantages, such as high thermal stability, mechanical strength, and improved corrosion resistance compared to conventional materials. This review examines how CMCs can be tailored to withstand harsh operational conditions, with a focus on the selection of ceramic phases, fiber-matrix interactions, and innovative fabrication techniques that enhance their protective capabilities. Key challenges addressed include the optimization of composite design to resist molten salt corrosion, the effects of temperature on the material properties, and the long-term stability of CMCs under extreme conditions. Advances in surface treatments, coatings, and the development of hybrid CMC systems are also discussed, highlighting their potential to further enhance durability. The review outlines the use of advanced characterization techniques, such as high-temperature corrosion testing and in situ microscopy, to evaluate CMC performance in molten salt environments. Additionally, it identifies knowledge gaps in current research, emphasizing the need for long-term studies on CMC behavior under realistic reactor conditions. This review concludes by proposing future research directions and technological advancements required to integrate CMCs into next-generation nuclear reactor designs, aiming to improve system reliability and operational safety.

Influence of highly dispersed phase of titanium carbide on physical and mechanical properties of alloys AM4.5Kd and AK10M2N

Dispersion-strengthened composite materials belong to the group of promising structural materials characterized by a diverse combination of properties. The work presents examples of the creation and heat treatment of composite materials based on aluminum alloys, strengthened by a dispersed phase of titanium carbide, and characterized by high hardness, elastic modulus and good wettability by the melt. The most accessible, inexpensive and effective way to obtain them is self-propagating high-temperature synthesis (SHS).The work shows the possibility of obtaining new aluminum matrix composite materials based on industrial aluminum alloys AM4.5Kd and AK10M2N by reinforcing them with 10 wt.% highly dispersed titanium carbide or AM4.5Kd–5.95 vol.% TiC and AK10M2N–5.78 vol.% TiC. The reinforcing phase is formed in alloy melts using the technology of SHS from the initial elemental components—titanium powder and carbon black. Using the obtained samples, an assessment was made of the uniformity of the ceramic phase distribution over the volume of the matrix alloys, which amounted to 0.15 and 0.12 for the samples AM4.5Kd–10%TiC and AK10M2N–10%TiC, respectively, which constitutes a high degree of uniformity.An assessment was made of physical properties such as porosity, density, electrical conductivity, as well as the coefficient of thermal linear expansion. Analysis of the data allows us to say that the final composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC have a slightly higher density (↑~4%) than the matrix alloys, due to the presence of a ceramic phase, low porosity values (~1%), lower TCLE (↓~6%) than matrix alloys and low electrical conductivity (~25% IACS). This article also presents data on the values of the mechanical properties of composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC. It has been shown that reinforcement with a ceramic phase contributes to a significant increase in hardness by 15 and 42 HB, as well as higher values of the compressive yield strength by 31 and 17 MPa, respectively, while maintaining a high level of relative deformation. The results obtained allow us to conclude that the developed composite materials can be recommended for products used under conditions of elevated temperatures and significant wear.

Exceptional strength-toughness-hardness integrated B4C ceramics with synergistic reinforcement of nano-BN and in-situ ceramic phases

Boron carbide (B4C) ceramics with enhanced mechanical properties were fabricated by incorporating nano boron nitride (nano-BN), obtained through high-energy ball milling (HEBM) using ZrO2 balls as the medium, and utilizing the spark plasma sintering (SPS) technique. During the densification process of B4C/nano-BN composite powders, an in-situ reaction between the B4C matrix and ZrO2 resulted in the formation of ZrB2 ceramic phases at 1200–1300 °C. Additionally, the rapid sintering densification temperature of composites is reduced to 1500–1700 °C, approximately 80 °C lower than that required for pure B4C ceramics. Notably, while maintaining a high relative density (99.5 %), the Vickers hardness, flexural strength, and fracture toughness of B4C ceramics reinforced with synergistic effects of nano-BN and ZrB2 fabricated at 1750 °C are significantly improved to reach values of 36.8 ± 0.15 GPa, 701 ± 12 MPa, and 5.01 ± 0.13 MPa m1/2 respectively; representing an increase of 3.5 GPa (10.5 %), 225 MPa (47.3 %), and 1.72 MPa m1/2 (52.3 %) compared to pure B4C ceramics alone. The multiple reinforcement mechanisms including pinning effects provided by nano-BN and in-situ formed ZrB2 ceramic phases, B4C/ZrB2 grain boundary pressure and intracrystalline pressure within B4C, interlayer dislocations of nano-BN and turbulent layer of B4C/BN boundaries contribute to energy dissipation during fracture processes, such as crack deflection, bridging, propagation hindrance and branching effect; ultimately resulting in exceptional strength-toughness-hardness integrated B4C-based ceramics.

Fabrication and High Dielectric Properties of Sandwich-Structured Ba0.6Sr0.4TiO3/Polyvinylidene Fluoride Layered Composites with Multiscale Parallel Interfaces.

Ba0.6Sr0.4TiO3/polyvinylidene fluoride (BST/PVDF) dielectric functional composites have been widely used in flexible wearable devices, capacitors, and energy storage devices. In addition to the ceramic phase type, polymer matrix type, composition, and interfacial connectivity of BST/PVDF composite materials, their morphology also significantly influences their electrical characteristics. Therefore, herein, sandwich-structured BST/PVDF layered composites were designed and prepared via tape-casting processing using different types of BST fillers [i.e., formless zero-dimensional (0D)-BST, rod-like one-dimensional (1D)-BST, and plate-like two-dimensional (2D)-BST]. The microstructures and electrical characteristics of sandwich-structured BST/PVDF composites were studied in relation to the BST morphology. The effects of the internal mechanisms of different interfacial models on the breakdown strength of BST/PVDF composites were discussed. According to our findings, unlike the 0D-BST and 1D-BST powders, 2D-BST powders form multiscale parallel interfaces in sandwich-structured composites due to their unique lamella-like morphology, which enhances the breakdown strength of sandwich-structured composites. Sandwich-structured BST/PVDF composites containing 2D-BST powders exhibit good electrical characteristics with an energy storage density of 19.71 J/cm3, an energy storage efficiency of 85.3%, a dielectric constant of 30.4 (1 kHz), a dielectric loss of 0.036 (1 kHz), and a dielectric tunability of 93.2%. This study provides a method for preparing functional composites with high dielectric tunability and high energy storage characteristics.

Developing High-Performance Ceramics from Multicomponent Grain Boundary Entropy Design.

Grain boundary (GB) glassy phase often results in poor ceramic performances. Here, a Multicomponent Grain Boundary Entropy (MGBE) descriptor extracted from high-throughput first-principle calculations is proposed to capture the nature of high-entropy GB phases in ceramics. In a Si3N4 ceramic model system, MGBE is found to have a direct correlation with GB phase crystallinity, element segregation, and formation of pores. The predicted highest MGBE sintering additive combination (MgO-Y2O3-Er2O3-Yb2O3) leads to high-performance ceramics of homogenous microstructure and pure GB (YErYb)2Si3O3N4 phase without observable glassy film. Conversely, low MGBE additives result in a substantial amount of GB glassy phase, element segregation, and pore clusters. The MGBE descriptor can make a rapid screening of multicomponent sintering additives, offering a novel approach for rational designing of ceramics with targeted microstructure and performances.

Multi-scale ceramic TiC solves the strength-plasticity equilibrium problem of high entropy alloy

High entropy alloys (HEAs) with single FCC structure exhibits unique structure and properties. However, lack of strength hinds the engineering application ability seriously. Therefore, it is urgent to propose effective methods and theories to enhance the strength while maintaining favorable plasticity. Introducing reinforced phases is one crucial research approach for improving the mechanical properties of HEAs. However, the resulting reduction in ductility has been neglected. In this work, we propose a novel multi-scale TiC coupling reinforced alloy which preserves the high plasticity while increasing the strength. The results demonstrate that TiC (μm) hinders the dislocations movement and improves strength through the second phase strengthening mechanism. Apart from acting as barriers to dislocation motion, the TiC (nm) also provides more dislocation sources in the distortion area at the junction with the matrix, which increasing the number of movable dislocations and enhancing the plastic strain capacity. Compared with the Al0.4 alloy, the tensile yield strength of the Al0.4-TiC (μm + nm) alloy is increased by 145 %, the ultimate tensile strength is up to 574 MPa, while maintaining a high plastic strain by 30.1 %. The addition of multi-scale ceramic phase TiC provides a novel approach to obtain high strength and high plasticity HEAs.

An Investigation of Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating.

Recent progress has seen multiple Ta2O5 polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta2O5 particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an 18O2 atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta2O5 phase or a similar, but not identical, crystalline β-Ta2O5 phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic "H-Ta2O5" phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta2O5. Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta2O5. We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air.

Effect of boron on phase, nanostructure, and thermal stability of polycarbosilane-derived SiC ceramics

The current study explores the formation, evolution, and thermal stability of polymer-derived SiBC at high temperatures. It focuses on the phase evolution of SiBC ceramics derived from the doping of boron in an allyl-containing polycarbosilane preceramic polymer after 1200 °C–1600 °C pyrolysis. Different SiBC ceramic monoliths have been obtained. Boron is incorporated into the carbon phase at lower pyrolysis temperatures but into both the carbon phase and the SiC lattice structure at high pyrolysis temperatures. B–C bonds form in SiBC and hinder the growth of graphitic carbon and SiC. Boron improves the densification and thermal stability of the SiBC ceramics. This work provides an improved understanding of boron effects in polymer-derived SiC nanostructures at high temperatures.

Micromechanical properties of reaction-bonded silicon carbide using atomic force microscopy and nanoindentation

Reaction-bonded silicon carbide (RB-SiC) ceramics have been produced using advanced technology for the production of space mirrors. Changing the volume content of SiC (from 78 to 93 %) in the ceramic's composition allows for improved the mechanical properties, which is achieved by a combination of the SiC and Si phases properties. In this work, a thorough study of the structure and micromechanical properties of individual SiC and Si phases for RB-SiC ceramics (with a SiC content of 78–93 vol%) was carried out at the micro- and nanolevel using atomic force microscopy and nanoindentation. The studies have shown the crack resistance limit each phase (an important factor for RB-SiC space mirrors) under mechanical loads, after which microcracks appear (sources of further degradation and destruction). The surface morphology, deformation area and crack propagation in each phase after exposure to mechanical load during indentation were studied using atomic force microscopy. Nanomechanical mapping of elastic modulus and microhardness on the surface, analysis of boundaries between phases (SiC and Si), assessment of mutual influence of phases and determination of micromechanical properties were carried out using the nanoindentation method. The fracture toughness KIC was determined using an improved indentation method with visualization of the deformation areas using atomic force microscopy. The highest values of microhardness H, elastic modulus E and fracture toughness KIC on the SiC and Si phases were obtained on a ceramic sample with 93 vol % SiC: for the SiC phase – E=486 GPa, H=35.6 GPa, KIC=5.03 MPa m1/2, for the Si phase – E=205 GPa, H=12.2 GPa, KIC=2.73 MPa m1/2. This study demonstrated the efficiency and possibility of using the atomic force microscopy and nanoindentation to determine the micromechanical properties of ceramics at the micro- and nanolevel.