冰刀用高强韧Si3N4陶瓷的制备与性能研究

以α-Si₃N₄粉为原料,MgO-La₂O₃-Lu₂O₃为三元复合烧结助剂,采用气压烧结工艺制备Si₃N₄陶瓷条,研究烧结助剂及添加β-Si₃N₄增强相对Si₃N₄陶瓷微观结构及力学性能的影响。结果表明,三元复合烧结助剂促进了烧结的致密化,提高了材料的力学性能,在最高烧结温度1 750 ℃、复合烧结助剂添加量8%(质量分数)时,得到密度为3.172 8 g/cm³、维氏硬度达到15.85 GPa、断裂韧性和抗弯强度分别为9.69 MPa·m^1/2和1 029 MPa的冰刀用Si₃N₄陶瓷。添加β-Si₃N₄材料的断裂韧性得到提高,最高达到10.33 MPa·m^1/2。Si₃N₄陶瓷本身的高硬度与加入的稀土氧化物使得所制备冰刀的硬度与润滑性能得到提高,表面性能优良。     

The new complex high-entropy metal boron carbonitride: Microstructure and mechanical properties

In this contribution, the ternary BCN anion systems of high-entropy ceramics (HEC) are consolidated by hot-pressing sintering and the impacts of sintering temperature and the content of amorphous BCN addition on microstructural evolution and mechanical performance were evaluated. Results confirmed that high-entropy, oxide, and BN(C) phases were precipitated for (Ta_0.2Nb_0.2Zr_0.2Hf_0.2Ti_0.2)(B, C, N) ceramics after sintering at 1900°C. With the decrease of BCN addition, a new phase of MiB₂ (Mi representing the metal atoms) occurred. The Vickers hardness, bending strength, elastic modulus, and fracture toughness of the optimized bulk HECs were investigated, obtained at 24.5 ± 2.3 GPa, 522.0 ± 2.6 MPa, 478.9 ± 11.1 GPa, and 5.36 ± 0.56 MPa m^1/2, respectively.     

Sintering dense boron carbide without grain growth under high pressure

Traditionally, densification and grain growth are two competing processes in sintering of ceramics. To improve the density, while limiting grain growth at the same time, an ultrahigh pressure (>1 GPa) is employed here and results in plastic deformation as the dominant densification mechanism during the sintering process. In this way, fully dense boron carbide (B₄C) structural ceramics without grain growth is prepared under the pressure of 4.5 GPa at low temperature of 1300°C in 5 minutes, while showing excellent mechanical properties such as Vickers hardness of 38.04 GPa, Young's modulus of 487.7 GPa, and fracture toughness of 3.87 MPa·m^1/2. This study should also facilitate the development of other structural ceramics for practical applications.     

Novel TiC-based composites with enhanced mechanical properties

Novel TiC-based composites were synthesized by reactive hot-pressing at 1800 °C for 1 h with ZrB₂ addition as a sintering aid for the first time. The effects of ZrB₂ contents on the phase composition, microstructure evolution, and mechanical properties were reported. Based on the reaction and solid solution coupling effects between ZrB₂ and TiC, the product ZrC may be partially or completely dissolved into the TiC matrix, and then phase separation within the miscibility gap is observed to form lamellar nanostructured ZrC-rich (Zr, Ti)C. The TiC-10 mol.% ZrB₂ (starting batch composition) exhibits good comprehensive mechanical properties of hardness 27.7 ± 1.3 GPa, flexural strength 659 ± 48 MPa, and fracture toughness of 6.5 ± 0.6 MPa m^1/2, respectively, which reach or exceed most TiC-based composites using ceramics as sintering aids in the previous reports.     

Microstructures and mechanical properties of functionally graded TiCN–TaC ceramics prepared by a novel layer processing strategy

Functionally graded TiCN–TaC ceramics (FGTTCs) were fabricated using a novel layer processing method based on a vacuum hot-press sintering technology. Microstructural investigations revealed a visibly layered structure for the FGTTCs with relatively flat boundaries between the neighboring layers; additionally, the layer thickness was facilely controlled. With an increase in the sintering temperature, the hardness and flexural strength of the surface and middle layers of the FGTTCs initially increased, and then decreased. The fracture toughness of the surface layer did not undergo significant changes after sintering at various temperatures, except at 1500 °C. The FGTTC sintered at 1350 °C contained uniform fine grains and simultaneously exhibited transgranular and intergranular fracture modes. Further, it presented excellent comprehensive mechanical properties, i.e., surface layer hardness = 20.28 ± 0.18 GPa, flexural strength = 1553.76 ± 22 MPa, surface layer fracture toughness = 7.29 ± 0.24 MPa m^1/2. Under the same sintering conditions, our FGTTCs presented superior mechanical properties against homogeneous TiCN–TaC ceramics (HTTCs), achieving a considerably higher flexural strength (1553.76 ± 22 vs 953.35 ± 24 MPa).     

Hydrothermal Degradation Behavior of Y‐TZP Ceramics Sintered by Nonconventional Microwave Technology

Different factors such as the characteristics of starting powders, their processing, the sintering technique and the final sintering temperature were assessed with the goal to improve the low‐temperature degradation (LTD) resistance of 3Y‐TZP materials without compromising on the mechanical properties. The degradation of hydrothermally treated specimens was studied by AFM, nanoindentation technique, micro‐Raman spectroscopy, and electron microscopy. 3Y‐TZP previously prepared in laboratory by colloidal processing, and sintered by microwave method at low temperature (1200°C) led to excellent mechanical and LTD resistance, as compared to dental restorations based on Y‐TZP commercial material. In the former, the presence of m‐phase was almost nonexistent even after 200 h of exposure to LTD conditions and the initial mechanical properties were maintained, giving 16 and 250 GPa mean values for hardness and Young's modulus, respectively. The influence of the fast‐technology by microwave heating is presented with a nonconventional sintering method to fabricate 3Y‐TZP ceramics for dental application with very high resistance against LTD and optimized mechanical properties.     

In situ synthesis,mechanical properties,and microstructure of reactively hot pressed WB4 ceramic with Ni as a sintering additive

In this study, tungsten tetraboride (WB₄) ceramics were synthesized in situ from powder mixtures of W and amorphous B with Ni as a sintering aid by reactive hot pressing method. The as-synthesized ceramics exhibited porosity as low as 0.375% and ultra-high Vickers hardness (H_v), as much as 49.808?±?1.683?GPa (for the low load of 0.49?N). It was seen that the addition of Ni greatly improved the sinterability of WB₄ ceramic. Besides, the flexural strength and fracture toughness of WB₄ ceramic were measured for the first time to be 332.857?±?36.763?MPa and 4.136?±?0.259?MPa?m^1/2, respectively, suggesting that the ceramic has good mechanical properties. The effects of sintering temperature and holding time on the densification, Vickers hardness, and mechanical properties of WB₄ ceramics were also investigated systematically as part of our study. The results indicated that increasing the sintering temperature can obviously improve the densification and mechanical properties of the ceramics. The bulk density and Vickers hardness of WB₄ ceramic sintered at 1650?°C for 60?min under 30?MPa revealed the highest values of 6.366?g?cm^?3 and 27.948?±?0.686?GPa (for the high load of 9.8?N), respectively. The flexural strength increased to the highest value of 332.857?±?36.763?MPa for sintering temperature up to 1550?°C, but decreased slightly as the sintering temperature further increased to 1650?°C. On the other hand, the fracture toughness increased gradually with increasing temperature. It was also found that Vickers hardness showed a similar trend as the densification of the samples with increasing temperature and holding time. Besides, no obvious improvements in the densification, mechanical properties, and Vickers hardness of the samples with sintering time were observed in this study. The microstructure and fracture behaviours of the as-synthesized WB₄ ceramic were also revealed, and the toughening mechanism has been discussed.     

High hardness (TiZr)C ceramic with dislocation networks

Raising the configurational entropy in a solid solution ceramic is regarded as a promising strategy to improve the mechanical properties of ceramics, especially when five or more elements are mixed to form so-called high-entropy ceramics. However, in this study, we report that the binary (TiZr)C solid solution ceramics can demonstrate high hardness comparable or even superior to high-entropy ceramics. Followed by a carbothermal reduction synthesis of carbide powders, the bulk ceramics were synthesized by hot pressing. Via increasing the hot pressing temperature to 2200°C, a full solid solution of equimolar (TiZr)C was obtained in contrast to phase separation at lower sintering temperatures, for example, 2000 and 2100°C. The dislocation networks are observed in the single-phase (TiZr)C ceramic and should be the product of competition between enthalpy and entropy in a binary full solid solution. These defects finally contribute to the high nano-hardness of 41.9 ± 1.4 GPa (H) and the Vickers hardness of 22.0 ± 0.6 GPa (H_V at 49 N).     

Fabrication and characterization of medium-entropy carbide ceramics in low temperature sintering

The medium-entropy carbide (W,Ti,V)C_0.8 ceramics were prepared by sparking plasma sintering at temperatures between 1400 and 1700°C. The effects of sintering temperature on the microstructure and mechanical properties of the medium-entropy carbide (W,Ti,V)C_0.8 ceramics were investigated. X-ray diffraction, scanning electron microscope, and energy dispersive spectrometer were used to confirm the formation of single-phase face-centered cubic (FCC) solid solution of the medium-entropy carbide (W,Ti,V)C_0.8 ceramics prepared at a sintering temperature of 1600°C. It was found that the mechanical properties of the material were improved by solid solution strengthening during the formation of single-phase FCC solid solution, and the best overall performance of the medium-entropy carbide (W,Ti,V)C_0.8 ceramics was achieved at 1600°C, when the hardness value was 22.3 ± 1.8 GPa, the fracture toughness was 5.7 ± 0.8 MPa·m^1/2, the flexural strength was 605 ± 4 MPa, and the compressive strength was 1.84 GPa. Most importantly, the addition of TiC_0.4 promoted the diffusion among the elements of the medium-entropy carbide (W,Ti,V)C_0.8 ceramics, which contributed to the formation of single-phase FCC solid solution and significantly reduced the sintering temperature of the medium-entropy carbide (W,Ti,V)C_0.8 ceramics due to the effect of vacancies. This study provides a new idea for the preparation of medium-entropy carbide ceramics.     

Review: Effect on physical,mechanical, and wear performance of ZrB2-based composites processed with or without additives

Because of unique combination of properties, ultra high temperature ceramics (UHTCs) are considered the most suitable material for applications in extreme environments as in hypersonic flights, atmospheric reentry, and rocket propulsion system. Processing of UHTCs especially ZrB₂-based ceramic composites with additives offer advantages in terms of simple processing methodology and excellent properties. Processing route highly controls the ceramic properties. Present review share out systematically and explain the processing strategies of ZrB₂-based ceramic composites––conventional, hot press or spark plasma sintering and their effect on microstructure features, physical, and mechanical properties and tribological performance. Present review suggests that it is possible to process full dense ZrB₂–SiC ceramic composite with ultrafine or nano size particles via fast sintering technique like spark plasma sintering and gives better mechanical and wear resistant properties.     

Fabrication of ZrB2-SiC ceramic composites by optimized gel-casting method

The ZrB₂-SiC ceramics with homogenous microstructures were successfully fabricated by the optimized gel-casting method and pressureless sintering. The effects of the processing parameters, including the monomer content, cross-linker/monomer ratios, initiator addition, catalyst concentration and polymerization temperature, on the final gel properties were systematically investigated. The rheological behavior and stability of ZrB₂-SiC suspensions were evaluated, and the microstructures and mechanical properties of sintered ceramics were also analyzed. The homogenous gel networks containing low monomer content (4 wt%) and without catalysts had been successfully obtained, which could be mainly attributed to the homogeneous distribution of crosslinking points and temperature-induced gelation. The crack-free and complex-shaped ZrB₂-SiC ceramic composites were achieved by the optimized gel-casting, which could reach the highest relative density of 97.2% and the flexural strength of 402 ± 57 MPa, respectively. This study provides an optimized gel-casting process for fabricating ZrB₂-SiC ceramics with excellent properties by low colloidal additives and without catalysts.     

Low-temperature reactive spark plasma sintering of dense SiC-Ti3SiC2 ceramics

SiC-based ceramics are of great interest for various advanced applications. However, its fabrication requires high-temperature treatment at ～2000 – 2100 °С. In this study, we developed an approach based on low-temperature reactive spark plasma sintering to produce dense SiC-based ceramics with superior mechanical properties. It was found that an SPS temperature of 1600 °C and introduction of 10 – 15 wt% of mechanically activated non-oxide Ti–Si–C additive is required to manufacture ceramics with a theoretical density of higher than 90%. Nonetheless, employing 5 – 15 wt% of the additive mixture and an SPS temperature of 1700 °C, the maximum density of ～ 98% was achieved. The controlled formation and decomposition of the in-situ Ti₃SiC₂ MAX phase enables the fabrication of the engineering ceramics with enhanced compressive strength (550 MPa), elastic modulus (485 GPa), and microhardness (32 GPa), which are comparable to the best-reported SiC ceramics. The study has a significant potential for practical application in the production of advanced SiC-based ceramics for various purposes and could be used for further understanding and development of the high-temperature sintering methods.     

Microstructure and mechanical properties of in-situ grown mullite toughened 3Y-TZP zirconia ceramics fabricated by gelcasting

In-situ grown mullite toughened zirconia ceramics (mullite-zirconia ceramics) with excellent mechanical properties for potential applications in dental materials were fabricated by gelcasting combined with pressureless sintering. The effect of sintering temperature on the microstructure and mechanical properties of mullite-zirconia ceramics was investigated. The results indicated that the columnar mullite produced by reaction was evenly distributed in the zirconia matrix and the content and size of that increased with the increase of sintering temperature. Mullite-zirconia ceramics sintered at 1500 °C had the optimum content and size of the columnar mullite phase, generating the excellent mechanical properties (the bend strength of 890.4 MPa, the fracture toughness of 10.2 MPa.m^1/2, the Vickers hardness of 13.2 GPa and the highest densification). On the other hand, zirconia particles were evenly distributed inside the columnar mullite, which improved the mechanical properties of columnar mullite because of pinning effect. All of this clearly confirmed that zirconia grains strengthened columnar mullite, and thus the columnar mullite was more effective in enhancing the zirconia-based ceramics. Simultaneously, the residual alumina after reaction was distributed evenly in the form of particle, which improved the mechanical properties of the sample because of pinning effect. Overall, the synergistic effect of zirconia phase transformation toughening with mullite and alumina secondary toughening improved the mechanical properties of zirconia ceramics.     

Sintering behavior and mechanical properties of spark plasma sintering SiO2-MgO ceramics

SiO₂-MgO ceramics containing different weight fractions (0, 0.5, 1, 2, and 4 wt%) of SiO₂ powder were prepared by mixing nano MgO powder, and the powder mixtures were densified by spark plasma sintering (SPS). The effect of SiO₂ addition and SPS method on the sintering behavior, microstructure and mechanical properties were investigated. Results were compared to specimens obtained by conventional hot pressing (HP) under a similar sintering schedule. The highest relative density, flexural strength and hardness of 2 wt% SiO₂-MgO ceramics reached 99.98%, 253.99 ± 7.47 MPa and 7.56 ± 0.21 GPa when sintered at 1400 °C by SPS, respectively. The observed improvement in the sintering behavior and mechanical properties are mainly attributed to grain boundary "strengthening" and intragranular "weakening" of the MgO matrix. Furthermore, the spark plasma sintering temperature could be decreased by more than 100 °C as compared with the HP method, SPS favouring enhanced grain boundary sliding, plastic deformation and diffusion in the sintering process.     

无压烧结氮化硅陶瓷的物理性能研究

以α-Si₃N₄粉末为原料,Y₂O₃和MgAl₂O₄体系为烧结助剂,采用无压烧结方式,研究了烧结温度、保温时间、烧结助剂含量以及各组分配比对氮化硅致密化及力学性能的影响。结果表明:以Y₂O₃和MgAl₂O₄为烧结助剂体系,氮化硅陶瓷在烧结温度为1 600 ℃,保温时间为4 h,烧结助剂含量为12.5%(质量分数),Y₂O₃和MgAl₂O₄质量比为1∶1时,综合性能最好;氮化硅陶瓷显气孔率为0.21%,相对密度为98.10%,抗弯强度为598 MPa,维氏硬度为15.55 GPa。     

Properties of MgO transparent ceramics prepared at low temperature using high sintering activity MgO powders

Transparent MgO ceramics are successful fabricated via spark plasma sintering at lower temperature using the high sintering activity powders synthesized by precipitated method. The samples were detected by XRD, SEM, TEM, BET, UV-Vis-NIR, microhardness, and so on. The results show that all ceramics prepared at 700°C-900°C are visually transparent and the sample sintered at 860°C for 5 min exhibits the superior transmittance of 60% (800 nm). It is also found that the mechanical and thermal properties of MgO ceramics are all increasing firstly and then decreasing with the increase in the sintering temperature. And the maximum value of hardness, fracture toughness, MSP strength, and Young's modulus of MgO ceramics is 8.25 GPa, 2.01 MPa·m^1/2, 206 MPa, and 286 GPa, respectively. Moreover, the thermal conductivity of MgO ceramics sintered at 860°C can reach 48.4 W/mK at room temperature.     

Dense and strong ZrO2 ceramics fully densified in <15 min

ABSTRACT

Crack-free zirconia ceramics were consolidated via sintering by intense thermal radiation (SITR) approach at 1600–1700°C for 3–5?min. The resulted ceramic bulks can achieve a relative density up to 99.6% with a grain size of 300–1200?nm. Their bending strength, Vickers hardness and indentation toughness values are up to 1244?±?139?MPa, 13.3?±?0.3?GPa and 5.5?±?0.1?MPa?m^1/2, respectively. Quantitative Raman and XRD analysis show the presence of minor m phase on the natural surface (<7%), fracture surface (<10%) and indentation areas (<15%). It reveals that the SITR method is efficient for rapidly manufacturing zirconia ceramics with desired density, fine grained microstructure and good mechanical properties that are strongly demanded in dental applications.     

Mechanical properties and pre-oxidation behavior of spark plasma sintered B4C ceramics using (Ti3SiC2+CeO2/La2O3) as sintering aid

B₄C ceramic with the addition of 5 wt % (Ti₃SiC₂+ CeO₂/La₂O₃) as sintering aids was fabricated by spark plasma sintering at a relatively low temperature of 1650 °C for 5 min at 80 MPa. The phase composition, microstructures, and comprehensive mechanical properties of the ceramics were studied in detail. The existence of reinforced second phase particles, the refinement of the matrix grains, the formation of residual stress along the grain boundaries and the appearance of the mixed fracture mode had a synergetic strengthening effect on the mechanical properties. The flexural strength, fracture toughness and Vickers hardness of B₄C ceramics reached 565.2 ± 21.8/551.0 ± 25.2 MPa, 6.28 ± 0.01/6.41 ± 0.12 MPa·m^0.5, and 28.51 ± 0.86/27.23 ± 1.08 GPa, respectively. In addition, to reduce the crack sensitivity of the ceramic, the ceramics were pre-oxidized at 800 °C for different durations. The flexural strength was increased by approximately 13.4% after the ceramic was oxidized at 800 °C for 45 min due to the crack-healing effect induced by the oxide glass B₂O₃ on the ceramic surface.     

On the fabrication and mechanical properties of Si3N4 ceramics with low content sintering additives

Si₃N₄ ceramics were prepared by hot pressing (HP) and spark plasma sintering (SPS) methods using low content (5 mol%) Al₂O₃–RE₂O₃(RE = Y, Yb, and La)–SiO₂/TiN as sintering additives/secondary additives. The effects of sintering additives and sintering methods on the composition, microstructures, and mechanical properties (hardness and fracture toughness) were investigated. The results show that fully density Si₃N₄ ceramics could be fabricated by rational tailoring of sintering additives and sintering method, and TiN secondary additive could promote the density during HP and SPS. Besides, SN-AYS-SPS possesses the most competitive mechanical properties among all the as-prepared ceramics with the Vickers hardness as 17.31 ± .43 GPa and fracture toughness as 11.07 ± .48 MPa m^1/2.     

Cold sintering process for ZrO2‐based ceramics: significantly enhanced densification evolution in yttria‐doped ZrO2

We recently developed a novel technique of cold sintering process (CSP) to obtain dense ceramics at extraordinarily low temperatures. In this communication, we demonstrate the feasibility of applying CSP to zirconia‐based ceramics. As exemplified by 3Y‐TZP ceramics, a significantly enhanced densification evolution is observed. Water is simply utilized as a sintering aid to assist the ceramic densification under an applied external pressure. The low‐temperature advantage of CSP outstands in contrast to the densification curves compiled from other sintering techniques. A gradual monoclinic‐to‐tetragonal phase transformation is revealed in correspondence to the densification development, as well as contributes to the mechanical hardness evolution. A Vickers Hardness reaches ~10.5 GPa after annealing the cold‐sintered ceramics at 1100°C, which is comparable to those values reported in the previous studies at higher sintering temperatures. Such a sintering methodology is of significant importance as it provides a roadmap for cost‐effective processing of zirconia‐based ceramics and composites that enable broad practical applications.