Reaction-formed SiC (RFSC) derived from recycled Si scrap offers a cost-effective route to SiC ceramics, yet improving fracture toughness without deteriorating thermal conductivity remains challenging. Here, an inverse two-step (ITS) hot-press sintering strategy was introduced to separate an alpha-related initial growth state from the final densification stage. With increasing T1 and T2, the phase constitution evolved progressively from 3C-SiC toward hexagonal alpha-SiC polytypes, accompanied by a marked morphology transition from equiaxed to elongated grains. Consequently, the ITS-processed specimens achieved an indentation fracture toughness of up to 6.81 +/- 0.16 MPa m1/2, nearly twice that of the single-step counterparts, with thermal conductivity in the range of 91.5-98.5 W m- 1 center dot K- 1. These results show that process-path design, without external alpha-SiC seeding, offers an effective route to induce microstructural and polytype evolution in RFSC for SiC-based components used in extreme-environment applications.

Aluminum nitride (AlN) is widely used as a heat–dissipation substrate, but its low fracture toughness limits practical reliability. In this study, AlN composites reinforced with tungsten carbide (WC) were fabricated by hot–press sintering at 1800 °C under 50 MPa in a nitrogen atmosphere, and the effects of the WC particle size and the sintering–additive chemistry on the mechanical and thermal properties were investigated. WC was added at a fixed total content of 5 wt% as a bimodal mixture of micrometer–sized and nanometer–sized particles, with the micrometer–to–nanometer ratio varied from 5/0–0/5, and a WC–free composition was prepared as a reference. Two sintering–additive systems were compared: one containing 3 wt% CaF2 alone (ACW) and one containing both 3 wt% CaF2 and 2 wt% Y2O3 (ACYW). Near–full densification was achieved in all compositions. The addition of WC enhanced the indentation fracture toughness relative to the WC–free reference, and the toughness increased as the proportion of micrometer–sized WC increased, reaching 5.78 MPa·m1/2 for ACW and 5.80 MPa·m1/2 for ACYW. In contrast, the thermal conductivity decreased as the fraction of micrometer–sized WC increased, from 136.9 to 111.7 W/(m·K) for ACW and from 148.5 to 120.9 W/(m·K) for ACYW. At a given composition, the ACYW series exhibited higher thermal conductivity than the ACW series, indicating that the combined CaF2–Y2O3 system better preserves heat transport while maintaining densification and mechanical reinforcement. These results show that controlling the WC particle size together with the sintering–additive chemistry provides an effective strategy for tailoring the trade–off between mechanical and thermal performance in AlN composites for heat–dissipation substrates.

Ultrafast high-temperature sintering (UHS) has received significant attention due to its effectiveness in consolidating ceramics in a very rapid manner. However, the application of UHS to non-oxide materials has been limited due to their extremely low sinterability. In this study, the UHS technique was applied to AlN to demonstrate its applicability and examine the resulting microstructure evolution and mechanical properties. High densification was achieved using electric currents of 47 A, 50 A, and 53 A for 240 s, with corresponding specimen temperatures of 1807.5 degrees C, 1872.8 degrees C, and 1935.6 degrees C. Vickers hardness increases up to 240 s but decreases at 300 s due to grain growth and sublimation of secondary phases. Fracture toughness decreases with larger grain sizes showing the inverse relationship between grain size and toughness. This study demonstrates that UHS is applicable to non-oxide ceramics, which offers significant potential for energy savings and rapid processing in non-oxide ceramic manufacturing.

This study presents a catalyst-free methodology for synthesizing silicon nitride (Si3N4) powders through the direct nitridation of Si. The influence of key parameters, including Si particle sizes (1 μm, 5 μm, 20 μm, and 100 μm), nitridation temperatures (1390−1450 ℃), holding times (0−6 h), and gas composition (N2 with or without H2), on the degree of nitridation and α-phase fraction of Si3N4 was investigated. The experimental phase contents and microstructural properties were evaluated using X-ray diffraction and scanning electron microscopy. The α-phase fraction of Si3N4 was quantitively assessed via Rietveld refinement of the XRD data, ensuring precise phase composition analysis. The results demonstrated that the optimal conditions for achieving phase-pure Si3N4 with a predominant α-phase of 95.1

SiC is a crucial structural ceramic, but densification requires very high temperatures, long processing times, and high pressures. This study explores ultrafast high-temperature sintering (UHS) to produce dense reaction-bonded silicon carbide (RBSC) in a few minutes. By adding varying amounts of Si and C with Y2O3 and Al2O3 additives, RBSC with up to 90 % relative density was achieved in 8 min. Microstructural analysis showed grain growth from 4.26 mu m to 15.43 mu m and minimal unreacted Si and C. Although there are some challenges to overcome such as incomplete densification and secondary phase evaporation, this study demonstrates that UHS is a promising technique for efficiently producing dense RBSC.

Grain coarsening is conventionally considered detrimental to mechanical performance, typically reducing Vickers hardness and indentation fracture toughness in metals, ceramics, and composites. Challenging this paradigm, we demonstrate that controlled grain coarsening, when combined with WC reinforcement, can enhance mechanical toughness of AlN-Y2O3 composites without significantly compromising thermal conductivity. The composites were fabricated via hot-press sintering at 1700 and 1800 degrees C for 2 h under 50 MPa in a nitrogen atmosphere, both achieving near-full densification. The higher temperature promoted substantial grain coarsening, which increased the frequency of crack-WC interactions. These interactions activated fracture energy-dissipating mechanisms such as crack deflection, bridging, branching, and grain pullout. The specimen sintered at 1800 degrees C with 10 wt% WC exhibited the most balanced properties, achieving a fracture toughness of 6.0 MPa center dot m1/2, Vickers hardness of 13.4 GPa, and thermal conductivity of 148.3 W/m center dot K. Finite element simulation based on experimentally informed microstructures reproduced the composition-dependent thermal conductivity trends and supported the validity of the proposed design strategy. These findings demonstrate that grain coarsening, when strategically combined with well-dispersed reinforcement, offers a viable pathway to simultaneously enhance indentation fracture toughness and retain thermal functionality in ceramic composites.

SiC has received significant attention owing to its exceptional properties including superior mechanical properties, high thermal conductivity, and a high melting point, which makes it ideally suited for the aerospace, nuclear, and semiconductor industries. Nevertheless, its strong covalent bonding requires prolonged processing times and high pressure to achieve near-full densification, leading to substantial energy consumption and increased production costs. Herein, we demonstrate the simultaneous synthesis and densification of SiC using Si particles derived from Si scrap through a single-step hot-press sintering. The specimen sintered at 1850 degrees C for 2 h under 30 MPa exhibited an average grain size of 1.86 +/- 0.81 mu m, relative density of 98.90 %, a Vickers hardness of 26.4 GPa, a reduced modulus of 355 GPa, and thermal conductivities ranging from 111.2 W/m & sdot;K at 25 degrees C to 47.6 W/m & sdot;K at 1000 degrees C. Furthermore, an experimental heat transfer model using the finite element method was employed to investigate the impact of microstructural characteristics on the thermal conductivity, showing good agreement between predicted and measured results. This novel recycling of Si scrap for the fabrication of dense SiC through a single-step hot-press sintering is a cost-effective and eco-friendly approach to significantly reduce the production costs of SiC-based ceramics with enhanced thermal conductivity and mechanical performance.

AlN composites reinforced with SiC whiskers and Y2O3 sintering aids were fabricated using the hot-pressing technique to investigate static and dynamic mechanical properties. Microstructure analysis revealed that increasing SiC whisker content yielded grain refinement and decreasing relative density. The Vickers hardness increased from 10.29 to 14.47 GPa, while the fracture toughness improved from 3.03 to 4.39 MPa & sdot;m1/2 with 30 wt% SiC whiskers. A numerical approach for evaluating the dynamic modulus and loss factor is presented utilizing the wave propagation characteristics. The dynamic properties showed decreasing dynamic modulus and increasing loss factor with higher SiC content, attributed to increased porosity and interphase boundaries. Thermal conductivity, however, decreased from 139.53 to 49.95 W/m & sdot;K as SiC whisker content increased, primarily due to enhanced phonon scattering at grain and interphase boundaries. These findings suggest that AlNSiCw composites are promising candidates for heat dissipation ceramic substrates, which offer superior mechanical strength and reliable thermal management.

BiFeO3 is a promising multiferroic material for versatile device applications due to its co-existence of magnetic (i.e., antiferromagnetic) and ferroelectric ordering at room temperature. While its functional properties have been extensively investigated, the exploration of its mechanical behavior was limited mostly to the thin-film form of BiFeO3. In this work, we conducted in situ micropillar compression experiments to investigate the deformation behavior of La-doped BiFeO3 (La-BFO) samples processed by both conventional and flash sintering methods. The conventionally sintered La-BFO exhibited limited deformability at room temperature and 450 degrees C. In contrast, the deformability of the flash-sintered La-BFO specimens was substantially improved by nearly 100% at both testing temperatures. Detailed post-mortem studies suggest that preexisting dislocations and wide anti-phase boundaries introduced during flash sintering can toughen flash-sintered La-BFO by easing dislocation migration and ferroelastic domain switching. This study provides a fresh perspective to design an advanced multifunctional system with improved mechanical properties.

Strontium titanate (SrTiO3) 3 ) is a versatile material with various applications but understanding its mechanical properties, especially in polycrystalline form prepared via field-assisted sintering methods, is limited. This study investigates the high-temperature mechanical properties of flash-sintered SrTiO3 3 through in-situ micro- compression tests comparing the behaviors near the positive and negative electrodes. Due to a significant irregularity in densification, the negative electrode exhibited superior fracture strength and strain across all temperatures when compared to its positive counterpart. Micropillars near the positive electrode contained multiple pre-existing pores that became crack initiation sites, and thus inducing catastrophic failure. Micropillars near the negative electrode exhibited prominent intergranular cracks accompanied by high-density dislocations in the vicinity of the fracture surfaces. This study elucidates the effect of flash sintering-induced defects on the mechanical properties of polycrystalline SrTiO3 3 at various temperatures.

Aluminum nitride (AlN) has gained significant attention as a promising ceramic substrate for electronic devices due to their extremely high thermal conductivity and superior electrical resistivity. However, their application is often limited by poor mechanical properties. Here, we employed pressure-assisted two-step sintering to prepare AlN-Y2O3 ceramics, aiming to enhance mechanical performance through grain refinement. Pressure-assisted high-temperature heating at 1680 degrees C followed by microstructural freezing at lower temperatures led to a significant reduction in grain size from 2.21 mu m to 1.08 mu m, resulting in improved flexural strength, Vickers hardness, and fracture toughness. Particularly, T2 of 1650 degrees C has produced a well-balanced performance of mechanical and thermal properties exhibiting a flexural strength of 417 MPa and a thermal conductivity of 144 W/m center dot K. These findings provide valuable insights into the development of advanced AlN-Y2O3 ceramics for electronic device applications, while maintaining the composition free from additional reinforcement additives.

This study demonstrates the fabrication of dense AlN-based ceramics through the flash sintering technique for the first time. Flash sintering was performed at a furnace temperature of 1500 degrees C with 10 wt% Y2O3 as a sintering aid in a nitrogen atmosphere. The effects of the current density and holding time on the microstructure evolution and mechanical properties were investigated. The results show that the relative density, grain size, and Vickers hardness of specimens increase with increasing current density and holding time. The specimen showed the highest relative density of 98.6 % and a Vickers hardness of 12.68 GPa when a current density of 100 mA/mm2 and a holding time of 60 min were used. Additionally, the grain sizes at the positive side of the electrodes were found to be larger than those at the negative side. These findings suggest that dense AlN-based ceramics can be fabricated in a rapid and efficient way through the flash sintering technique.

Ceramic materials with high strength and chemical inertness are widely used as engineering materials. However, the brittle nature limits their applications as fracture occurs before the onset of plastic yielding. There has been limited success despite extensive efforts to enhance the deformability of ceramics. Here we report a method for enhancing the room temperature plastic deformability of ceramics by artificially introducing abundant defects into the materials via preloading at elevated temperatures. After the preloading treatment, single crystal (SC) TiO 2 exhibited a substantial increase in deformability, achieving 10% strain at room temperature. SC α-Al 2 O 3 also showed plastic deformability, 6 to 7.5% strain, by using the preloading strategy. These preinjected defects enabled the plastic deformation process of the ceramics at room temperature. These findings suggest a great potential for defect engineering in achieving plasticity in ceramics at room temperature.

Ceramic materials with high strength and chemical inertness are widely used as engineering materials. However, the brittle nature limits their applications as fracture occurs before the onset of plastic yielding. There has been limited success despite extensive efforts to enhance the deformability of ceramics. Here we report a method for enhancing the room temperature plastic deformability of ceramics by artificially introducing abundant defects into the materials via preloading at elevated temperatures. After the preloading treatment, single crystal (SC) TiO(2 )exhibited a substantial increase in deformability, achieving 10% strain at room temperature. SC alpha-Al2O3 also showed plastic deformability, 6 to 7.5% strain, by using the preloading strategy. These preinjected defects enabled the plastic deformation process of the ceramics at room temperature. These findings suggest a great potential for defect engineering in achieving plasticity in ceramics at room temperature.

Alumina (alpha-Al2O3) is one of the most versatile engineering ceramics, and its mechanical properties have been extensively studied. However, the micromechanical properties of Al2O3 with a fine microstructure are less well understood. Here, we present one of the first investigations that probe the micromechanical properties of fine-grained polycrystalline Al2O3 fabricated via spark plasma sintering, employing in situ microcompression tests inside a scanning electron microscope. This study explores the influence of temperature variations on the deformation mechanisms, particularly the involvement of microcracks and dislocation activities throughout the deformation process. As temperature rises, substantial deformability occurs in the inherently brittle Al2O3 at intermediate temperature, where the improved plastic deformability mainly arose from prominent dislocation activities accompanied by grain boundary sliding. This study sheds light on understanding the relationship between defect evolution and mechanical behavior in Al2O3 with fine grain sizes.

A rapid, cost-effective and eco-friendly approach for fabricating SiC using Si particles derived from Si scrap is highly recommended from both economic and environmental standpoints. Herein, we demonstrate the fabrication of β-SiC effectively in argon atmosphere at 1500°C by utilizing combustion synthesis followed by flash sintering in a single-step experiment for the first time. Synthesis of β-SiC was relied on exothermic reaction between Si and C elements present in the powder compact whereas densification was accomplished eventually through flash sintering. In addition, the effects of different flash sintering conditions on the properties of β-SiC are examined with and without Y2O3 sintering additive. A high relative density of 85% was realized when a current density of 60mA/mm2 was applied for 60min with Y2O3 addition. This novel one-step fabrication approach has the potential to reduce production cost of β-SiC significantly and has both commercial and environmental advantages.

Flash sintering involves very rapid densification of ceramic powder compacts during a thermal runaway induced by an applied voltage and current. The mechanisms of fast densification are still not well-understood. The present study investigates the impact of high heating rates during flash sintering on densification, dislocation density and plasticity of SrTiO3. After flash sintering, a high dislocation density of almost 1014 m- 2 was observed by TEM. Uniaxial compression at 1150 degrees C revealed very high deformation rates. It is argued that for SrTiO3, dislocations are generated and migrate during flash sintering. This becomes possible by the very high heating rates, which conserve high driving forces for sintering up to high temperatures. High driving forces of several 10 MPa are preserved up to high temperatures. Thus, the sintering stress can be above the flow stress of SrTiO3 (5 MPa), and the nucleation of dislocations occurs, paving the path for plastic flow.

Alumina (alpha-Al2O3), one of the most widely used structural ceramics for industrial applications, requires high temperature and long sintering time to achieve a fully dense structure through conventional pressureless consolidation and sintering methods. Recently, several attempts have been made to reduce sintering time and temperature of Al2O3 through the application of electric field with limited success. In this study, alternating current (AC) and direct current (DC) flash sintering techniques were employed to obtain high-density Al2O3 within 10 min. The density of flash-sintered (FS) specimens was greater than the specimens prepared by the pressureless sintering technique (hereinafter designated as conventional sintering) at the same temperature for 10 h. Furthermore, AC technique can reduce the electric field necessary for flash sintering substantially comparing to the DC flash sintering. The microindentation measurements reveal that the AC-FS Al2O3 provides the highest fracture toughness and a high hardness among all sintered specimens. The improved mechanical properties of AC-FS Al2O3 are attributed to defects, such as dislocations as well as stacking faults observed in the FS specimens. This study provides a fresh perspective on the low-energy manufacturing of structural ceramics with improved properties.

This work reports a cost-effective and environmentally friendly method for preparing high-quality and highlycrystalline silicon nitride (Si3N4) powders from silicon (Si) scrap through direct nitridation. With Si scrap from semiconductor manufacturing processes being a critical and imperative global issue in recent times, an efficient methodology is essentially required to recycle it. For this purpose, ball milling parameters for Si scrap were optimized using different solvents to obtain homogeneous and fine-micron sized silicon powders for efficient nitridation. Ethanol was found to be the most effective in producing the required conditions of Si powders. Direct nitridation was performed at 1450 degrees C in an atmosphere of nitrogen and hydrogen gas flow to prepare Si3N4 powders. Various characterization techniques were used to analyze particle sizes, phase compositions, and morphologies of raw Si scrap, ball-milled Si powders, and Si3N4 powders. Results indicated that the nitridation reaction resulted in 90.1% conversion of Si into Si3N4 and the alpha-Si3N4 phase accounted for 85% of the total Si3N4 produced. This study provides a fundamental perspective from both industrial and environmental standpoints on the recycle of Si waste and production of cost-effective and high-quality Si3N4 powders. This novel approach of using Si scrap as a silicon source for Si3N4 powder preparation has the potential to significantly reduce the large volumes of Si waste generated from semiconductor industries.

This review article highlights the potential of flash sintering as a novel densification technology for advanced ceramics. Conventional ceramic sintering methods involve heating a powder compact at high temperatures for several hours to trigger the solid-state diffusion of atoms. In contrast, flash sintering takes advantage of electric field and current to drastically lower processing time and temperature, providing a promising solution to reduce the economic, energetic, and environmental costs associated with traditional ceramic sintering methods. The effects of electric field and current during flash sintering result in unique non-equilibrium microstructures that enhance the mechanical properties of advanced ceramics through defect-mediated inelastic deformation mechanisms. This article provides an overview of the flash sintering mechanisms, the unique microstructural features observed in flash-sintered ceramics, and their impacts on mechanical properties.