Pressureless Sintering Research Articles

Preparation and properties of ZrP2O7 matrix composites with high silica fibers reinforcement

AbstractZrP2O7 ceramics exhibit poor mechanical properties after firing, as a major drawback. In this study, ZrP2O7 matrix composites reinforced with high silica fibers were prepared through pressureless sintering by varying the content and length‐to‐diameter ratio of the high silica fibers added to ZrP2O7 powder. After heat treatment at 1200‒1300°C, the room temperature flexural strength of the ZrP2O7 matrix composites with different amounts high silica fibers having different aspect ratios was 14.9‒45.2 MPa, the bulk density was 1.90‒3.03 g·cm−3, the apparent porosity was 2.37%‒39.39%, and the room temperature thermal conductivity was .47‒.95 W/(m·K). With an increase in the heat‐treatment temperature, driven by sintering and fiber crystallization, strength of the interfacial layer between the fibers and the matrix inside the ZrP2O7 matrix composites decreased and then increased. The transfer and blocking effects of the interface enabled effective transfer of the stress of the matrix to the fiber‐reinforced phase and prevented crack extension. The problem of inherent crystallization affecting high silica fibers at high temperatures was relieved by the ZrP2O7 ceramic matrix composites.

Fast pressureless sintering of highly transparent AlON ceramics by reducing Y enrichment with nano-sized granular Y2O3 as additive

Employing nano-sized granular Y2O3 (NGY) as additive, AlON ceramics with transmittance ≥80% across wavelengths at 380–4150 nm were successfully fabricated via pressureless sintering at 1880 °C for 2.5 h, the dwelling duration is much shorter than the ≥7 h reported in literature. The distribution of Y2O3 in starting mixtures, along with phase transformation, microstructure evolution and densification process of the samples during heating were thoroughly studied to reveal the fast densification mechanism. Local enrichment of Y2O3 in the AlON/Y2O3 mixtures was significantly reduced when using NGY instead of micro-sized lamellar Y2O3. The reduction of excessive local Y2O3 concentration resulted in less α-Al2O3 was decomposed from AlON during heating, and further suppressed local aggregation/coarsening at ≤1600 °C. The excellent microstructure obtained at early stage of sintering, together with the improved effective Y2O3 concentration in whole sample led by the decrease in local Y2O3 enrichment accelerate the densification process of AlON.

Ultrafast high-temperature sintering and densification of ZrC-based ceramics

Zirconium carbide (ZrC) ceramics are promising candidates for high-temperature structural components and nuclear reactors. However, their poor sinterability has limited widespread application. This study explored the sintering and densification of ZrC-based ceramics with graphite or B4C additive using ultrafast high-temperature sintering (UHS). A nearly fully dense ZrC ceramic (> 98%) could be obtained by adding 2.5 wt% B4C additive via ultrafast high-temperature sintering at 2300 °C within 3 min. Additionally, the results revealed that adding graphite into ZrC was beneficial to reduce the grain size but detrimental to densification. Compared to ZrC ceramics sintered using conventional pressureless sintering (PLS) at 2400 °C for 60 min, ZrC-based ceramics with 2.5 wt% B4C sintered via UHS at 2400 °C for 30 s exhibited higher relative densities, smaller grain sizes, and greater Vickers hardness due to faster heating rates and shorter sintering processes.

Mechanical and tribological performance of copper matrix self-lubricating composite prepared by resonant acoustic mixing powder

CuNi-WS2 self-lubricating composites with 10 wt% WS2 were fabricated by combining resonant acoustic mixing (RAM) powders and pressureless sintering in an H2 atmosphere. The influence of acceleration, a critical process parameter of RAM, on the microstructures, mechanical and tribological performance of the composites were investigated, then the mechanism of acceleration on the performance of composites was discussed based on the analysis of the morphology and dispersion of WS2. The composite exhibits optimal mechanical and tribological properties at an acceleration of 70 g, with a bending strength of 231 MPa, and the friction coefficient and the wear rate are 0.243 and 9.26 × 10−5 mm3/N·m, respectively. WS2 is primarily dispersed through the composite as small clusters and tiny particles at an acceleration of 70 g. It not only promotes the interfacial reaction of WS2 to generate hard W particles, improving the strength of composites, but also facilitates the formation of compact tribo-film, avoiding massive fractures caused by the fragmentation of large WS2 agglomerations.

Sintering kinetics and microstructure development of synthetic lunar highlands and mare regolith

Kinetics and microstructure development during pressureless sintering of two Lunar regolith simulants are reported and discussed. Dry-pressed cylindrical specimens of either a Highlands simulant or a Mare simulant were heated at 80 K min−1 to a prescribed sintering temperature and held for ten hours while dimensional changes were tracked in situ by optical dilatometry. The axial and volumetric strains and densification rates were calculated as a function of time and temperature. Possible phase transformations were evaluated by quantitative X-ray powder diffraction. The relative density increased with the logarithm of time at any temperature, and densification rates decreased continuously and sharply with increasing density. Sintered microstructures and compositional characteristics were observed by scanning electron microscopy and X-ray microprobe analysis of polished surfaces. The microstructures of both materials show evidence of heterogeneous densification, with large but isolated high-density domains surrounded by lower-density regions with interconnected porosity. No significant compositional differences were detected between the higher- and lower-density regions, meaning that the heterogeneous local densities are caused by gradients in particle size or packing that induce locally varying thermodynamic driving forces for densification. The apparent activation enthalpy for densification was measured as 445 kJ mol−1 and 440 kJ mol−1 for the Highlands and Mare simulants, respectively, values that were observed to be independent of temperature and sintered density to within the measurement uncertainty.

Microstructure and mechanical properties of high relative density Ti-48Al-1Fe alloy using irregular blend powder

Conventional pressing and sintering methods provide difficulties in achieving high density for PM TiAl alloys. The Ti-48Al-1Fe alloy was prepared via vacuum pressure-less sintering, and the microstructure evolution and mechanical properties during the sintering densification process of the mixed powder system were investigated. The results shows that the density of the mixed powder reached 98.3 ± 0.14% after pressure-less sintering for 3 hours under high vacuum conditions at 1300°C. The microstructure of the as-sintered alloy is a fine duplex structure composed of α2/γ lamellar colonies and the composite structure. The ultimate tensile strength (UTS) of the as-sintered alloy at room temperature is 315 MPa. The density of the as-sintered alloy reach more than 99.9% after non-capsule hot isostatic pressing (HIP). The as-HIPed alloy exhibits an UTS of 332 MPa at room temperature. At high temperatures, it maintains high strength, with an UTS of 408 MPa and yield strength of 386 MPa at 900°C, which is comparable to that of forged TiAl alloy. Furthermore, the elongation of the sample at 900°C is 20.0%. This process offers a novel method for sintering PM TiAl with high density and mechanical properties at a low cost and near-net shape.

Wetting kinetics of TixMo1-xC in molten Fe and its influence on bicontinuous TixMo1-xC/Fe composite mechanics: Experimental, DFT and ML studies

The TixMo1-xC precursor was rendered porous through PUF foam replication using a slurry of TiC and Mo powders. Mo was incorporated to increase the strength of pressureless sintering (PS). The precursor served as a reinforcement for bicontinuous TixMo1-xC/Fe composites through pressureless infiltration. The interaction between Fe and TixMo1-xC was studied through experimental and theoretical analyses, establishing interfacial adhesion as a key determinant of wettability. At 1550 °C, the TiC/Fe interface exhibits non-reactive wetting, with a contact angle of 9.5°. Addition of 10 wt% Mo escalates interfacial adhesion to 3.768 J/m2 and reduces the contact angle to 9.3° at 1400 °C. TixMo1-xC's precursor has a continuous structure, while composites exhibit slight continuity as predicated by convolutional neural networks (CNNs). The morphological classifications of TixMo1-xC/Fe composites were posited. Alteration from TiC to Ti0.95Mo0.05C increases Young's modulus and hardness from 449.74 GPa to 28.58 GPa–520.55 GPa and 32.32 GPa, respectively. Without heat treatment, the tensile strength of composites rises from 125 MPa to 208 MPa. Increased strain energy density increases the prominence of dimples.

Pressureless sintered lithium disilicate glass-ceramics: Influence of particle size and crystallization state

The pressureless sintering process is essential to densify near net shaped parts with good shape fidelity. In this work, the impact of the particle size distribution and crystallization state on the processing and properties of final sintered multicomponent lithium disilicate (SiO2-Li2O-K2O-P2O5-Al2O3-ZnO) was evaluated. Higher densification was achieved by pressureless sintering at lower temperatures for samples prepared with fine glass-based powders (825 °C; ≈96%) rather than coarse crystallized powders (975 °C; 92.9%). However, samples based on fine powders presented a microstructure characterized by low aspect ratio crystals, while those based on coarse powders presented needle-like crystals with high aspect ratio. Best mechanical properties were found in samples prepared with coarse glass powders (relative density≈ 95.1%; Vickers Hardness≈ 5.2 GPa; indentation fracture toughness≈ 2 MPam0.5; flexural strength≈ 317 MPa) sintered at 875 °C-1 h. These results can provide valuable orientations for the post-processing of lithium disilicate glass-ceramics prepared by additive manufacturing techniques.

Potential plasma facing materials: A case study on CeB6 particulate reinforced W–1Ni matrix composites produced via different sintering techniques

Tungsten (W) is the most promising material for future plasma-facing materials. Its alloys or composites reinforced with various compounds have been studied to improve the irradiation resistance of W. This study aimed to investigate the effect of boron-containing reinforcement in the W matrix against He+ ion irradiation. Cerium hexaboride (CeB6) particulates, which have high neutron shielding properties, were incorporated into the W matrix pre-alloyed by 1 wt% Ni (W1Ni). CeB6 powders were home-made and prepared from CeO2/Mg/B2O3 powder blends via mechanochemical synthesis and purification steps. 1, 5, and 10 wt% CeB6 powders were added to pre-alloyed W1Ni by mechanical alloying, and then they were consolidated by using pressureless sintering (PS, 1400 °C, 1 h) and spark plasma sintering (SPS, 1410 °C, 1 min) techniques. CeB6 particle-reinforced W1Ni composites contained different amounts of reinforcements were prepared by two different sintering methods and were compared with respect to their compositional, microstructural, and microhardness properties and wear and irradiation behaviors. Based on the results, increasing the CeB6 reinforcement amount in the composite triggered the formation of the W2B phase, especially in the W1Ni–10CeB6 composite after both sintering methods. The mechanical and irradiation properties were enhanced more by increasing the CeB6 amount in the case of using the SPS method. When compared to other sintered samples, the SPS'ed W1Ni–10CeB6 composite has the lowest specific wear rate of ∼4 × 10−7 mm3/Nm and the maximum hardness value of ∼21 GPa. According to surface deformation, the W1Ni–5CeB6 composite exhibited comparatively higher resistance to He+ ion irradiation.

Development and Characterizations of Fine Pitch Flip-Chip Interconnection Using Silver Sintering

Flip-chip interconnects made of silver are promising candidates to overcome the intrinsic limits of solderbased interconnects and match the demand for increased current densities of high-performance microprocessors. Dipbased interconnects have been demonstrated to be a promising approach to form electrical interconnects by sintering paste between copper pillars and pads. However, the quality of the process is limited by residual porosity and poor performances of the sintered joint formed between the pillar and the pad during sintering if a pressure > 50 MPa is not applied in order to decrease the final porosity. In this study, development has been focused on varying key dipping process parameters allowing a pressureless sintering process. Dip-transfer process was optimized on test vehicle and has shown electrical continuity over 700 interconnections with diameter down to 50 μm. We demonstrate high reliability of the process with microstructural observations, tomography X and thermal cycle up to 200 cycles without breakdown.

Preparation and Tribological Behaviors of Antigorite and Wollastonite Mineral Dual-Phase-Reinforced Polytetrafluoroethylene Matrix Composites

Research on polymer matrix composites with excellent tribological properties has received increasing attention in recent years. In this study, antigorite and wollastonite mineral dual-phase-reinforced polytetrafluoroethylene (PTFE) matrix composites were prepared by filling PTFE with mineral powders using ball-milling, cold-pressing, and pressureless sintering methods. The phase structure, microstructure, chemical composition, Shore hardness, and tribological behavior of the composites rubbed against steel balls under dry friction conditions were investigated. The results show that the composites have a dense structure and uniform distribution of mineral phases, with a Shore hardness of 62–68.8, an increase of 18.7–23.7% compared to pure PTFE. Compared with the addition of mono antigorite or wollastonite, the composites prepared by simultaneously filling the two minerals exhibited excellent tribological properties. The average friction coefficient and wear volume of the (10Atg + 20Wl)/PTFE composites were reduced by 44.2% and 71.4%, respectively, compared to those of pure PTFE. A dense and continuous tribofilm composed mainly of SiO2, MgSiO3, Mg2SiO4, MgO, CaO, CaMg(SiO3)2, and CaF2 was formed on the worn surfaces of both the dual-phase-reinforced PTFE matrix composites and counterpart steel balls during the friction process. The reduction in friction and wear is attributed to the reinforcement effect of the minerals on the PTFE matrix as well as the complex physical and chemical reactions at the friction interface stimulated by the synergistic effects between the two minerals. The addition of wollastonite reduced the phase transition temperature of antigorite, promoting more tribochemical reaction products with good abrasion resistance and friction-reducing properties, which contributed to the excellent tribological behavior of the composites.

Enhancing Semiconductor Package Reliability through Mechanical Property Optimization of Pressureless Sintering Die Attach Adhesives

There is growing demand for high-power devices, wide bandgap SiC and GaN semiconductor materials in semiconductor market, and a drive to integrate die attach materials that can replace lead-containing solders. However, epoxy-based and solder materials face challenges to meet high thermal conductivity and survive elevated working temperatures. Pressure-assisted silver sintering has overcome these challenges, but downsides of pressure-assisted silver sintering are that it requires special equipment and for some applications, packages are unable to withstand the pressure required to facilitate sintering. Pressureless sintering materials could be processed using the same equipment as traditional die attach adhesives. It develops strong metal bonds to substrates, providing high thermal conductivity and withstanding high temperatures. However, compared to pressure-assisted sintering, pressureless materials may have difficulties to form a dense bondline structure if the formulation design is not optimized. Moreover, once the sintered structure is built during cure, further bondline reduction may induce additional stress. Therefore, it is critical that the pressureless sintering material’s mechanical properties are formulated to effectively manage stress and pass all reliability testing – especially for automotive packages. This paper will present the findings from a study that evaluated the impact of various formulation components – such as silver packing and resin chemistry – on the mechanical properties and interfacial bonding of pressureless sintering die attach adhesives. The effect on in-package reliability performance was also investigated to better understand material properties that can pass reliability testing while maintaining high thermal and electrical conductivity adhesive requirements.

3D printing of potassium sodium niobate by binder jetting: Printing parameters optimisation and correlation to final porosity

Binder Jetting (BJT) is a non-fusion-based Additive Manufacturing (AM) technique. It consists of the selective deposition of a liquid binder to join powder particles, thereby enabling the creation of near-net-shaped parts.In this study, the main printing parameters correlated to the binder distribution and infiltration (binder saturation, binder set time, drying time, and target bed temperature) were optimised to improve the precision of green parts printed with potassium sodium niobate (KNN) powder. The optimisation procedure was conducted using the Taguchi statistical method. An L9 orthogonal array with four factors of control at three levels each was employed. The analysis showed that the drying time had the greatest influence on the precision of green parts, followed by binder saturation and target bed temperature. Binder set time did not seem to affect the results.Dimensional analysis, microstructural and piezoelectric characterisation of parts densified by pressureless sintering were conducted. The highest average relative density exceeded 80% for the specimens printed with the lower binder saturation. Piezoelectric properties exhibit more complex behaviour. The prolonged infiltration of larger binder volumes is correlated to higher g33, thus FOMh and FOM33, and lower values for ε33T. On the other hand, d33 does not display a specific dependence on density or printing parameters.The results of this study indicate that BJT can be used to fabricate high-precision KNN components with good piezoelectric properties. The optimisation of printing parameters is essential to achieve the desired results.

Self-densification behaviors and oxidation resistance properties of a slurry-derived ZrB2-SiC coating with kyanite additive

The great advantages of component designability, operation convenience, and cost reduction make the slurry-sintering method promising for preparing oxidation resistant coatings. However, the porous structure caused by the volatilization of liquid in the slurry and shrinkage of particles in the pressureless sintering limits its practical and wide application. Herein, a dense ZrB2-SiC coating with improved oxidation resistance was fabricated via a slurry-sintering method on C/SiC composites by introducing kyanite into the slurry. The self-densification of the coating is achieved due to the volume expansion of 26.1 % related to the irreversible thermal transformation from kyanite to mullite during sintering. The resultant dense coating with a thickness of 150 μm shows the good interfacial bonding strength of 19.2 MPa and the low weight changes of 1.7 %, −0.6 %, and −1.7 % at 800 °C, 1000 °C, and 1200 °C for 40-h oxidation, respectively.

Power Cycling Reliability with Temperature Deviation of Pressureless Silver Sintered Joint for Silicon Carbide Power Module

SiC devices can enhance power conversion in electric vehicles. However, traditional soldering techniques are limited by their low melting temperatures. Therefore, we used pressureless Ag sintering to assemble a 1200 V/200 A SiC metal-oxide-semiconductor field-effect transistor power module and compared the long-term reliability, electrical properties, and driving performance of the module with those of a similar module assembled using the solder Sn-3.0Ag-0.5Cu (SAC305). To assess sinter joint reliability, we performed power cycling tests over two temperature ranges, 50–150°C and 50–175°C, for 15,000 cycles. Subsequently, we compared the breakdown voltage (BVDSS) and drain-source on-resistance (RDS(ON)) of the SiC power modules and performed cross-sectional analyses of the device bonding interfaces. No difference in BVDSS was found between the Ag-sintered and SAC305-soldered joints. However, the RDS(ON) exhibited minimal variation for the Ag-sintered module but significantly varied for the SAC305-soldered module, suggesting that the former better maintained its characteristics. Furthermore, the electrical characteristics of the SAC305-soldered module underwent more significant alterations with increasing temperature change during power cycling, indicating that cracks propagated throughout the SAC305 soldered joint over time. Therefore, Ag sintering was quantitatively validated as the superior die attachment technology compared to soldering for long-term reliability.

Novel design of Mo-Si-B + La2O3 powder with multi-shell structure for ideal microstructure and enhanced mechanical property

In this study, the multi-shell structured Mo-Si-B powder with La2O3 particles (MSB + L powder) was designed to obtain the ideal microstructure of sintered body, and the effects of the La2O3 addition on the microstructural and mechanical characteristics were investigated. Mo-Si-B powder (MSB powder) was prepared via mechano-chemical powder metallurgy methods, and MSB + L multi-shell powder was fabricated via chemical methods such as mixing and calcination processes. Using this powder, MSB + L alloys were prepared under cold isostatic pressing followed by pressureless sintering. Our unique powder's architecture allows us to fabricate the ideal microstructure of MSB + L alloys which consist of isolated intermetallic compound phases and uniformly dispersed La2O3 particles in continuous α-Mo matrix. This ideal microstructure contributes to the enhancement of fracture toughness of MSB + L alloys by changing fracture behavior, compared to MSB alloys without La2O3 particles. For example, intergranular fracture mode in MSB alloys changed to intragranular fracture mode in MSB + L alloys. In addition, the fracture toughness was enhanced around 26% in MSB with 0.3 wt% La2O3 particle at room temperature (17.0 MPa·m1/2) while MSB alloys have around 13.50 MPa·m1/2. The addition of La2O3 particles in MSB alloys highly affect the fracture behavior at room temperature through the grain refinement and oxide particle strengthening.

Fabrication of highly transparent AlON ceramics by inhibiting decomposition of AlON

In consolidation of AlON, the extensive decomposition of AlON into α-Al2O3 and AlN during sintering is one of the major reasons that significantly retard its densification process. To accelerate densification of AlON, an ultra-low concentration of La2O3 (0.03 wt%) and Y2O3 (0.02-0.04 wt%) was co-doped as sintering additives to inhibit decomposition of AlON during sintering for fast fabrication of highly transparent AlON ceramics. The phase transformation, microstructure evolution and densification process of the samples undoped and doped additive during heating were studied to investigate the densification mechanism. The results reveal that, compared to the samples undoped additive and single-doped with La2O3, the α-Al2O3 content of the samples co-doped with La2O3 and Y2O3 is significantly deduced at ≤1600 °C, which indicates that the decomposition of AlON is effectively inhibited by co-doping La2O3 and Y2O3. The reduction of α-Al2O3 along with the deceleration effect of La3+ on mass transfer, contributes to more small particles being conserved at high temperatures. Base on this, at later stage of sintering, benefiting from the enhanced mobility of grain boundary by Y3+, AlON ceramics with high relative density (99.79 %) and excellent transparency were obtained via pressureless sintering at 1880 °C for 2.5 h by co-doping 0.03 wt% La2O3 and 0.04 wt% Y2O3. The maximum transmittance of the fabricated AlON ceramics is up to 81.6 % at 3600 nm, and a transmittance of 76.0 % was measured at 400 nm. The ultra-low doping amount of La2O3 and Y2O3 and the high relative density should be the main reasons that lead to the outstanding transparency of the obtained AlON. Additionally, the fabricated AlON ceramics also exhibit a high Vickers hardness of 18.89 ± 0.18 GPa.

Characterization of glass composite material by pressureless sintering of soil and its application to uranium contaminated soil as a waste form

Abstract When operating and dismantling a nuclear facility that handles uranium, the surrounding soil may be contaminated, emphasizing the need for appropriate treatment and disposal methods for soil waste. This study assessed high-temperature sintering technology for uranium contaminated soil waste to overcome limitations in existing decontamination methods and the volume increase associated with current solidification technology. The sintering process was found to effectively vitrify and re-mineralize complex chemical components in the soil. Sintered bodies were produced under varying conditions, adjusting molding pressure, heating temperature, and time. Optimized conditions resulted in sintered bodies with a volume reduction rate exceeding 30 % and a compressive strength surpassing 10 MPa, indicating a significant impact on the phase conversion and re-mineralization of silt and clay minerals. The soil sintering mechanism was identified through comprehensive microscopic observations and mineral phase change analysis. Leaching evaluations of sintered bodies, made from simulated uranium-contaminated soil, demonstrated their applicability to contaminated soil wastes. Additionally, it was confirmed that the sintering temperature of the soil could be lowered by incorporating a small amount of B2O3, suggesting a means to enhance the economic feasibility of the treatment process. The findings of this study highlight the applicability of pressureless sintering technology, based on glass composite materials, capable of simultaneously reducing and stabilizing uranium-contaminated soil waste.

Tooling in Spark Plasma Sintering Technology: Design, Optimization, and Application

Spark plasma sintering as the prominent field‐assisted sintering technique (FAST/SPS) is a novel technology for the rapid, pressure‐assisted consolidation of powder materials. The main feature of FAST/SPS is the direct Joule heating of the applied tooling. Tooling is a challenging part of the FAST/SPS setup, which must withstand high pressure at elevated temperatures and ensure a uniform temperature distribution in the sintered part. This review looks at the standard FAST/SPS tooling, the specific tooling for sintering complex‐shaped parts, and for pressureless sintering. A particular focus lies on graphite, the commonly used tooling material, and on alternative materials such as steel, alloys, ceramics, and composites. The review also considers the add‐on tooling elements, such as spacers, foils, and thermal insulation. Furthermore, the article discusses the basics of FAST/SPS modeling, and the computer‐based optimization of FAST/SPS tooling, the procedure used, and the modeling accuracy. The review briefly describes the tooling and equipment for manufacturing upsized parts and large‐scale production. In addition, the article considers the tooling for FAST/SPS sintering under high pressure (up to 1 GPa) and ultra‐high pressure (over 1 GPa). The article concludes with an analysis of the challenges and prospectives for the smart design of FAST/SPS tooling.

Pressureless densification and properties of high-entropy boride ceramics with B4C additions

High entropy boride ceramics have great potential as structural materials serving in extreme environments. However, their applications are limited by the difficulty of sintering. In the present study, dense (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 ceramics with B4C additions were prepared through pressureless sintering at as low as 1900 °C. Calculations based on the CALPHAD approach predict that (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 starts to melt at about 3315 °C whilst B4C additions reduce the temperature and broaden the temperature region where solid and liquid coexist. Results showed that the introduction of B4C could trigger the densification of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 at a lower temperature and promote their densification significantly. The relative density of samples with 5 wt% of B4C additions sintered at 1900 and 2000 °C was 97.7 % and 99.7 %, respectively. While the sintering temperature was further increased to 2100 °C, the liquid phase was reactively formed, leading to the rapid grain coarsening in samples with B4C additions. Strengthened by well-dispersed B4C grains, the sample with 5 wt% B4C sintered at 2000 °C exhibited excellent mechanical properties with the Vickers hardness, flexural strength, and fracture toughness of 21.07 ± 2.09 GPa, 547 ± 45 MPa, and 5.24 ± 0.14 MPa m1/2, which are comparable or even higher than counterparts sintered under pressure.