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1.
    
The medium-entropy carbide (W,Ti,V)C0.8 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)C0.8 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)C0.8 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)C0.8 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·m1/2, the flexural strength was 605 ± 4 MPa, and the compressive strength was 1.84 GPa. Most importantly, the addition of TiC0.4 promoted the diffusion among the elements of the medium-entropy carbide (W,Ti,V)C0.8 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)C0.8 ceramics due to the effect of vacancies. This study provides a new idea for the preparation of medium-entropy carbide ceramics.  相似文献   

2.
    
Ceramic fibers have the advantages of low density, high strength, high temperature resistance, and excellent mechanical vibration resistance. In this work, sol-gel and electrospinning were used to prepare ultra-fine rare-earth-zirconate high-entropy ceramic (HEC) fibers with the composition of ((La0.25Nd0.25Sm0.25Gd0.25)0.75Yb0.25)2Zr2O7. The decomposition process and microscopic morphology of the fibers were characterized by thermogravimetry/differential scanning calorimetry, Fourier transform infrared and scanning electron microscope. The results indicated that defective fluorite-structured fibers with a smooth surface were obtained by calcining at 900–1000°C, while fibers with the pyrochlore structure and the diameter within 140 nm were obtained by calcining at temperature higher than 1100°C. The HEC fibers still maintain a continuous microstructure on the surface after calcination. In addition, the porous ceramics prepared from HEC fibers have a comparatively low thermal conductivity (0.22 ± 0.05 W m−1 K−1, 25°C). These promising properties indicate that the HEC fibers could be candidate materials for thermal-insulation application.  相似文献   

3.
以纳米Al2O3和TiN为原料,以SiO2为助烧剂,热压烧结后获得TiN-Al2O3复相陶瓷。TiN-Al2O3复相陶瓷具有较优异的力学性能:三点弯曲强度最高达到565.8MPa,断裂韧性在4～6MPa·m1/2之间。复相陶瓷中立方TiN均匀地分布在Al2O3基体中,TiN颗粒主要分布在Al2O3晶界处。当TiN颗粒的体积含量为5%时,TiN-Al2O3复相陶瓷的电阻率在1012～104Ω·cm范围内,其加载电压可达0.75kV/mm。  相似文献   

4.
    
Grain growth in ceramic-based composites during sintering has always been an unavoidable problem. Based on the theory of fine-grained reinforcement, the concept of rapid densification was coupled with the inhibition of grain growth to fabricate ultrafine-grained WC-based ceramics. Herein, by combining two-step sintering with oscillatory pressure sintering (OPS), a new sintering process—two-step oscillatory pressure sintering (TSOPS), was used for the preparation of ultrafine-grained WC-based ceramics. The comparison of the OPS with the TSOPS validated the feasibility of the strategy in achieving homogeneous and fine-grained microstructures. The optimum mechanical properties of Vickers hardness, fracture toughness, and flexural strength reached up to 29.56 GPa, 7.97 MPa m1/2 and 1591 MPa, respectively. A developed TSOPS process was proposed and proved to dominate the grain size distribution homogenizing, which contributed to the simultaneous enhancement of mechanical properties of the ceramics.  相似文献   

5.
    
(Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high-entropy ceramics (HEC) with a submicron grain size of 400 to 600 nm were fabricated by spark plasma sintering using a two-step sintering process. Both X-ray and neutron diffractions confirmed the formation of single-phase with rock salt structure in the as-fabricated (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C samples. The effect of submicron grain size on the thermal stability and mechanical properties of HEC was investigated. The grain growth kinetics in the fine-grained HEC was small at 1300 and 1600°C, suggesting high thermal stability that was possibly related to the compositional complexity and sluggish diffusion in HEC. Compared to the coarse-grain HEC with a grain size of 16.5 µm, the bending strength and fracture toughness of fine-grained HEC were 25% and 20% higher respectively. The improvement of mechanical properties in fine-grained HEC may be attributed to micromechanistic mechanisms such as crack deflection.  相似文献   

6.
    
High fracture toughness of 8 YSZ (8 wt% yttria-stabilized zirconia) is linked to its ferroelastic toughening mechanism. In this work, the similar ferroelastic domain is detected in monoclinic Dy1−xTa1−xZr2xO4 ceramics, which derives from the ferroelastic transformation between the high-temperature tetragonal (t) and low-temperature monoclinic (m) phase. The lowest thermal conductivity of Dy1−xTa1−xZr2xO4 ceramics is reduced by 30% compared with 8 YSZ, and the largest thermal expansion coefficients (TECs) is up to 11 × 10−6 K−1 at 1200°C, which is comparable to that of 8 YSZ. Notably, the systematic investigations containing phase, microstructure, thermophysical properties of Dy1−xTa1−xZr2xO4 ceramics will provide guidance for its high-temperature application, especially as thermal barrier coatings.  相似文献   

7.
In this work, a series of polysulfide polymers were synthesized using organic monomer (ethylene dichloride) and sodium-based aqueous monomers via interfacial polymerization. The structural characteristics of aqueous monomers and synthesized polysulfide polymers were identified by Fourier transform infrared (FT-IR), Raman, and ultraviolet–visible-near infrared (UV–VIS-NIR) spectroscopies. The Optimum temperature of polymerization was obtained at 75°C. Benzyltriethylammonium chloride (BTEACl) and tetrabutylammonium bromide (TBAB) were used as phase transfer catalysts (PTC) where BTEACl showed better performance regarding the polymerization yield. Moreover, adding ethanol to polymerization media increased the polymerization yield significantly. The results showed that along with increasing sulfur in the structure of polymers, solubility and flexibility were increased whereas it decreased the hardness, melting point (Tm ) and glass transition temperature (Tg ) of obtained polymers.  相似文献   

8.
    
Control of the durability of commercial biodegradable materials when used as food packaging is relevant to guarantee the safety of food. The service life performance of a commercial material based on poly(lactic acid) was assessed through an aging test which mimics its real use (immersion in water at 40 °C for up to 6.5 months). The ability of different techniques for the evaluation of polymer decomposition was investigated and two types of degradation were shown, a reversible physical aging and a permanent deterioration due to hydrolysis. Physical aging was reflected in differential scanning calorimetry scans by increased glass transition temperature and corresponding enthalpy. A gradual decrease of crystallization temperature and increase of melting temperature and crystallinity were also observed. The progressive loss of mechanical properties reflected the sum of both types of degradation. Hardness, flexural modulus and flexural strength were more sensitive to deterioration than strain. The highest toughness of the material was achieved at two months. The cleavage of polymer chains and release of substances caused increased migration levels, especially marked for long time periods. Water uptake and migration levels followed a concordant pattern and experienced the highest increases. A simple protocol for quality control based on the obtained results is suggested. Copyright © 2012 Society of Chemical Industry  相似文献   

9.
    
Terbium aluminum garnet (Tb3Al5O12, TAG) ceramics have become a promising magneto-optical material owing to the outstanding comprehensive performance, including the magneto-optical, thermal, and mechanical properties. Fine-grained TAG ceramics with high optical quality and mechanical properties have attracted much attention. In this study, TAG ceramics with fine grains and high optical quality are fabricated successfully by a two-step sintering method from co-precipitated nano-powders. After pre-sintered at 1525°C in vacuum and hot isostatic pressed at 1600°C, the in-line transmittance of TAG ceramics reaches 81.8% at 1064 nm, and the average grain size is 7.1 μm. The Verdet constant of TAG ceramics is −179.6 ± 4.8 rad T−1 m−1 at 633 nm and −52.1 ± 1.9 rad T−1 m−1 at 1064 nm, higher than that of commercial Tb3Ga5O12 crystals. The thermal conductivity of TAG ceramics is determined from 25 to 450°C, and the result is 5.12 W m−1 K−1 at 25°C and 3.61 W m−1 K−1 at 450°C. A comparison of mechanical properties between large- and fine-grained TAG ceramics fabricated under different conditions is conducted. The fine-grained TAG ceramics possess a bending strength of 226.3 ± 16.4 MPa, which is 9.7% higher than that of the large-grained ceramics. These results indicate that reducing the grain size on the premise of high optical quality helps improve the comprehensive performance of TAG ceramics.  相似文献   

10.
    
Hexagonal boron nitride (h-BN) with low dielectric loss and high temperature resistance opens up new opportunities for the preparation of polymer-derived SiCN ceramics (PDCs-SiCN ceramics) with excellent mechanical and dielectric properties. BN-containing polymer-derived SiCN composite ceramics (PDCs-SiCN(BN) composite ceramics) with different BN content were prepared via a pyrolysis process of ball-milling-blended Polyvinylsilazane/boron nitride (PVSZ/BN) precursors. BN is stably embedded in the SiCN tissue and tightly bound with it. The appropriate content of BN greatly improves the mechanical properties of PDCs-SiCN ceramics, as BN reduces the number of pores and prevents crack expansion. Additionally, BN is also beneficial in lowering the dielectric loss of PDCs-SiCN ceramics because of the weakened polarization relaxation behavior. PDCs-SiCN (BN) composite ceramics have optimal mechanical and dielectric properties when the BN content is 1 wt%. The flexural strength, flexural modulus and compression strength of PDCs-SiCN(BN) composite ceramics with 1 wt% BN doping content were 189.37 MPa, 46.38 GPa, and 399.02 MPa, respectively. Its average dielectric loss (tanδε) at 12.4-18 GHz is 0.0049.  相似文献   

11.
Thermal protection materials with high optical reflectivity, low thermal conductivity, and good high-temperature stability are required for the development of laser technologies and the protection of the critical equipment components. Herein, we synthesize a novel thermal protective material, La0.9Sr0.1Ti1−xNbxO3+δ (LSTN; x = 0.1, 0.125, 0.15), with different Nb5+-ion contents using solid-state sintering. Phase structure analysis demonstrates that LSTN (x = 0.1, 0.125, 0.15) presents a single-phase monoclinic structure with a uniform element distribution. In particular, the LSTN0.125 ceramic exhibits ultrahigh optical reflectivity (96%, 2300 nm) and excellent thermophysical properties, such as a high thermal expansion coefficient (10.3 × 10−6 K−1, 1000°C), an ultralow thermal conductivity (0.408 W (m K)−1, 300°C), and excellent high-temperature stability. Aberration-corrected scanning transmission electron microscopy reveals that the disordered substitution of Nb5+ ions induces numerous lattice distortions and mass fluctuations, which decrease the thermal conductivity, and makes difference in the relative refractive indices of atomic layers causing the high reflectivity of the material. These remarkable properties render the LSTN0.125 ceramic as an ideal alternative for near-infrared thermal protection applications.  相似文献   

12.
    
Bending strength of commercially relevant lead-free piezoceramics – 0.935Na0.5Bi0.5TiO3-0.065BaTiO3 (NBT-6.5BT) with and without acceptor Zn-doping and 0.92(K0.5Na0.5)NbO3-0.02(Bi0.5Li0.5)TiO3-xBaZrO3; x = 0.06, 0.07 (KNN-BZ100x) have been quantified using 4-point bending tests and contrasted to that of commercial lead zirconate titanate (PZT, PIC151). The compressive and tensile strength probed using additional strain gauges under 4-point bending indicate negligible non-linear deformation, in stark contrast to that of commercial PIC151. The bending strength of KNN-BZ100x is about 100 MPa, comparable to PIC151, while that of NBT-6.5BT-based materials is about twice that of PIC151 at ∼160 MPa. These results are rationalized based on the intrinsic characteristics of the lead-free piezoceramics in terms of fracture toughness, coercive stress, and Young's modulus. Weibull statistics indicate a higher fracture probability for KNN-based materials, with NBT-6.5BT-based materials featuring Weibull modulus twice that of KNN-based materials.  相似文献   

13.
研究了碳化硼粉末除氧处理对样品致密度和力学性能的影响。采用XRD、SEM测试手段对样品的物相组成和显微结构进行分析。结果表明,经过除氧处理后,碳化硼粉末中氧化硼含量由3.25wt%降至0.84wt%。当硼的加入量为11.6wt%时,样品的硬度、断裂韧性、抗弯强度和弹性模量分别可达到34.2GPa、3.91 MPa.m1/2、576.5MPa和420.3GPa,分别比未经除氧处理制得的B4C陶瓷力学性能提高3.95%、10.76%、5.82%和3.70%。  相似文献   

14.
3Y-TZP材料的液相烧结   总被引：1，自引：1，他引：0       下载免费PDF全文
通过在3Y-TZP(Tetragonal Zirconia Polycrystals stabilized with 3mol% Y2O3)中加入适当含量的硅酸盐玻璃添加剂,使其烧结温度明显降低,并且制备出具有细晶粒、高强度的四方相氧化锆增韧陶瓷材料.本文分析了添加剂对3Y-TZP材料烧结特性及显微结构的影响.发现液相烧结的3Y-TZP具有良好的抗弯强度,但韧性有待于提高.  相似文献   

15.
通过添加烧结助剂,采用常压烧结工艺制备出不同气孔率(19%～54%)的氮化硅陶瓷.采用Archimedes法、三点弯曲法和Vickers硬度测试法测量了材料的密度、气孔率、抗弯强度及硬度.用X射线衍射及扫描电镜检测了相组成和显微结构.用谐振腔法测试了氮化硅陶瓷在10.2 GHz的介电特性.结果表明:材料具有优良的介电性能.随着烧结助剂的减少,样品中气孔率增加,力学性能有所下降,介电常数和介电损耗降低.添加Lu2O3所制备的氮化硅陶瓷的力学性能和介电性能优于添加Eu2O3或Y2O3制备的氮化硅陶瓷.当气孔率高于50%时,多孔氮化硅陶瓷(添加入5%的Y2O3或Lu2O3,或Eu2O3,质量分数)的抗弯强度可达170 MPa,介电常数为3.0～3.2,介电损耗为0.000 6～0.002.  相似文献   

16.
利用常规烧结方法制备出了多种A位离子掺杂的钛酸铋纳[(Bi1/2Na1/2)TiO3,BNT]无铅压电陶瓷.对BNT基陶瓷的电学性能和力学性能进行了研究.在(1-x)(Bi1/2Na1/2)0.900Ba0.088Sr0.012TiO3-x(Bi1/2K1/2)TiO3(x=0-0.14)陶瓷体系中,当x=0.10时,可获得最大压电常数(168pC/N).在1 kHz,这种陶瓷的介电常数、介电损耗和平面机电耦合系数分别为1 221,0.0361和0.2281.Curie温度随x的增加先增加,当x=0.12时,达到最高值(300℃),随后,当x值进一步增加,Curie温度降低.该种无铅压电陶瓷的Vickers硬度和断裂韧性分别为5.0GPa和2.0MP·m1/2,均高于Pb(Zr,Ti)O3陶瓷.  相似文献   

17.
    
Yttrium tantalate ceramics with ferroelasticity are potential candidates for thermal barrier coating (TBC) ceramics. During the phase transition process, there are three main phases with monoclinic (I2/a), monoclinic-prime (P2/a), and tetragonal structures (I41/a), and a comprehensive understanding of their thermophysical properties is required. In this study, the thermal and mechanical properties of polymorphous yttrium tantalate (YTaO4) ceramics are systematically investigated under finite temperature by performing first-principles calculations combined with quasi-harmonic approximation. The first-principle study results show that the volume change from M' to T phase is 12.85 Å3 to 12.95 Å3 per atom, whereas the T to M is 12.95 Å3 to 12.84 Å3 per atom, and the change is less than 1%, showing that this process produces almost no volume change. However, the thermal expansion coefficients (TECs) and Young's modulus vary greatly, the TECs value of M YTaO4 is about 11.13 × 10−6 K−1, which is smaller than T YTaO4 as the value 12.01 × 10−6 K−1, and the Young's modulus values of M, M', and T phases are 140.34, 156.68, and 123.29 GPa, respectively. Lastly, the calculated O–Ta bond is stronger than the O–O and O–Y bonds according to the mean bond population and average bond length, resulting in a higher modulus. This work will not only expand the internal mechanism of the thermophysical properties of YTaO4, but also provides support for the design and application of TBC systems.  相似文献   

18.
    
Aluminum nitride (AlN) ceramics and oxygen-free Cu were brazed with multilayer filler consisted of Ag-Cu-Ti +Ni foam. The microstructure and forming principle of AlN/Cu joints were studied and the influence of Ni foam on the joints was focused. The result shows that the composition of AlN/Cu joint was AlN/TiN/Ni3Ti+Cu(s,s)+CuTi+Ni foam+Ag(s,s)/Cu. The joint strength was only 66.7 ± 3.7MPa with pure Ag-Cu-Ti solder and the fracture occurred inside AlN ceramics due to the residual stress. The foam nickel reacted with Ag-Cu-Ti filler metal to form Ni3Ti during brazing process. Ni foam still retained the basic skeleton structure during brazing, and the mechanical capacity of AlN/Cu joint was enhanced significantly. The maximum shear strength of the brazed joint can reach 89.6 ± 4.5 MPa with .1 mm Ni foam, and the fracture position changed to the brazing filler. The result shows that nickel foam can reduce the residual thermal stress, and the mechanical properties of AlN/Cu joints were improved.  相似文献   

19.
    
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 (Ta0.2Nb0.2Zr0.2Hf0.2Ti0.2)(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 m1/2, respectively.  相似文献   

20.
    
Dense (Hf, Zr, Ti, Ta, Nb)C high-entropy ceramics were produced by hot pressing (HP) of carbide powders synthesized by carbothermal reduction (CTR). The relative density increased from 95% to 99.3% as the HP temperature increased from 1750°C to 1900°C. Nominally phase pure ceramics with the rock salt structure had grain sizes ranging from 0.6 µm to 1.2 µm. The mixed carbide powders were synthesized by high-energy ball milling (HEBM) followed by CTR at 1600°C, which resulted in an average particle size of ~100 nm and an oxygen content of 0.8 wt%. Low sintering temperature, high relative densities, and fine grain sizes were achieved through the use of synthesized powders. These are the first reported results for low-temperature densification and fine microstructure of high-entropy carbide ceramics.  相似文献   

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