Search

Hot oscillatory pressing (HOP) has been shown to be a more effective technology for sintering various material systems than hot pressing sintering due to the use of oscillatory pressure. However, the effect of oscillatory pressure parameters on the sintering behavior is not clear. In this paper, the effect of pressure amplitude, frequency, and mean pressure of oscillatory pressure on the sintering behavior was studied by using sapphire whisker reinforced zirconia ceramic composite as a model material. The obtained results were discussed by considering grain boundary sliding as a viscoelastic process. The current work would provide scientific guidance for determining optimized HOP parameters. [ABSTRACT FROM AUTHOR]

SiC whisker reinforced ZrB2-SiCw composites were prepared by sol-gel method and spark plasma sintering ( SPS) with designed composition of 10-30 vol% SiCw. The ZrB2-SiCw composite powder was synthesized by sol-gel method using zirconium diboride, tetraethoxysilane ( TEOS), and activated carbon as starting materials, then densified by SPS at 1700°C under a pressure of 40 MPa for 5 minutes. The phase compositions and microstructures of ZrB2-SiCw composites were investigated by X-ray diffraction and scanning electron microscope, respectively. The relative density of ZrB2-SiCw composites increased from 83% to 98.5% with increasing SiCw contents from 10 vol% to 30vol% after sintering at 1700°C without additional sintering additives. Meanwhile, the fracture toughness and flexural strength of as-obtained composites exhibited a similar trend as relative density. ZrB2-30vol% SiCw composite showed the highest fracture toughness of 6.1 MPa·m1/2 and flexural strength of 350 MPa, which were attributed to the formation of SiC whisker. [ABSTRACT FROM AUTHOR]

Abstract: Glass–ceramics were synthesized using ground blast-furnace slag and potash feldspar additives by a conventional ceramic-sintering route. The results show 5wt% potash feldspar can enhance the sintering properties of blast-furnace slag glass and the results glass–ceramics have desirable mechanical properties. The main crystalline phase of the obtained glass–ceramic is gehlenite (2CaO·Al2O3·SiO2). A high microhardness of 5.2GPa and a bending strength higher than 85MPa as well as a water absorption lower than 0.14% were obtained. [Copyright &y& Elsevier]

As a typical ceramic tool, the wear resistance of Al 2 O 3 /SiC w composites is a prominent parameter in engineering applications. Therefore, how to improve its wear resistance has becomes a research emphasis of ceramic tools. In this work, the Al 2 O 3 /SiC w composites with improved wear resistance were prepared by a novel oscillatory pressure-assisted sinter forging (OPSF) process. The composites prepared by OPSF process not only exhibit higher density and significantly improved mechanical properties, but also own lower coefficient of friction than conventional sinter forging and hot oscillatory pressing processes. EBSD results indicated that the OPSF process could improve the texture of (0001) crystal face, low-angle grain boundaries, high-angle grain boundaries with special angles in the Al 2 O 3 matrix and enhance shear deformation at micro-scales, which are multiple contributed to enhanced wear resistance. Therefore, OPSF process is a promising technique to prepare ceramic-based cutting tools with excellent mechanical properties and wear resistance. [ABSTRACT FROM AUTHOR]

In this paper, fully dense Si 3 N 4 /SiC nano-composites were fabricated through polymer-derived ceramics (PDCs) method and spark plasma sintering technique. Polymer-derived SiAlCN ceramic was synthesized by using polysilazane as preceramic precursor, aluminum tri-sec-butoxide as Al source. Then Si 3 N 4 /SiC composites with nanometer sized Si 3 N 4 and SiC phases were formed spontaneously during spark plasma sintering through in-situ phase separation of amorphous SiAlCN ceramics. It's found that with the increasement of Al contents, the densification rate was accelerated significantly and serious degradation of Si 3 N 4 phase was avoided by restricting carbothermal reaction. At the same time, Al contained composites show excellent oxidation/corrosion resistance at 1350 °C and 50% H 2 O - 50% O 2 water vapor environment than that of Al free samples. The Si 3 N 4 /SiC composites derived from Al contained PDCs overcomes the trade-off between abnormal grain growth and serious degradation of Si 3 N 4 phase, which is a very tough problem for traditional PDC route (without Al) to fabricate Si 3 N 4 /SiC composites. For traditional PDC route, (I) if with traditional sintering additives, abnormal grain growth occurs, nano grains cannot be achieved; (II) if without traditional sintering additives, serious degradation of Si 3 N 4 occurs, Si 3 N 4 and SiC composite cannot be formed. Therefore, Al contained polymer-derived ceramics route opens a promising avenue to fabricate Si 3 N 4 /SiC nano-composites with fine grain size, uniform microstructure and excellent oxidation/corrosion resistance. [ABSTRACT FROM AUTHOR]

Highly pure and dense high entropy (Zr 0. 2 Ta 0. 2 Nb 0.2 Hf 0.2 Mo 0.2)B 2 ceramics have been obtained via oscillatory pressure sintering (OPS) at 1800 °C–1900 °C for 1 h under 30 ± 5 MPa. The formation of a single-phase solid solution was confirmed through XRD and TEM. The relative density and hardness of (Zr 0. 2 Ta 0. 2 Nb 0.2 Hf 0.2 Mo 0.2)B 2 sintered at 1900 °C are 96.6% and 24.0 ± 1.0 GPa, respectively. The thermal conductivity of (Zr 0. 2 Ta 0. 2 Nb 0.2 Hf 0.2 Mo 0.2)B 2 is 12.2 W/m·K at 30 °C, which is only 10% of ZrB 2 , which might greatly be related to mass fluctuations and strain filed fluctuations caused by the interaction of solid solution effects. This is the first report of preparation of high entropy ceramics using oscillatory pressure sintering. [ABSTRACT FROM AUTHOR]

The electric conductivity of zirconia in the steady stage of flash sintering is measured under various current densities. We find that the steady stage conductivity ( σ s ) is higher than the normal conductivity ( σ n ) measured at non-flashing conditions, even Joule heat is considered. The higher conductivity is ascribed to the increase in charge carrier concentration. The difference between σ s and σ n is then used to estimate the oxygen vacancy concentration. It is found that the concentration increases with increasing current density at beginning and then decreases with further increasing current density. A speculative explanation is proposed to account for this phenomenon. [ABSTRACT FROM AUTHOR]

Abstract Dense Boron-doped diamond (BDD) composites were fabricated by high pressure and high-temperature sintering (HPHT) at 5 GPa and 1450 °C for 300 s in presence of Al, B and C as sintering additives. Phase compositions, microstructures, and electrochemical performances of sintered specimens were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemistry. Results suggested that Al 3 BC 3 and Al 4 C were formed by in-situ reaction between sintering additives and diamond, which can promote densification of BDD. In addition, BDD composites containing 10 wt% sintering additives exhibited the highest electrical resistivity (4.40 × 10−4 Ω m) and hole concentration (4.55 × 1025/m3). The working potential windows of BDD composite electrodes in 0.1 M H 2 SO 4 , 0.1 M Na 2 SO 4 and 0.1 M NaOH electrolytes were estimated to 1.9 V, 2.9 V and 2.3 V, respectively. Electron transfer coefficients of composite electrodes approached 0.5, confirming good reversibility. Finally, methylene blue was completely degraded by BDD composite electrodes within 120 min using NaCl as supporting electrolyte. [ABSTRACT FROM AUTHOR]

ZrSi 2 and SiC are good candidates to improve both sinterability and mechanical properties of ZrB 2 ceramics, which were synthesized simultaneously by an in-situ reaction of ZrC and Si additives during the sintering processing in this work. The ZrB 2 ceramic composites with different amount of ZrSi 2 and SiC were fabricated by reactive spark plasma sintering (RSPS) method. X-ray diffraction, scanning microscopy and Archimedes's method are used to characterize the phase, microstructure and density of the composites. Meanwhile, fracture toughness and flexural strength of the obtained composites were investigated too. It's found that a fully dense composite can be achieved at 1500 °C by SPS. Both fracture toughness and flexural strength of ZrB 2 ceramics increased with increasing the concentration of ZrSi 2 and SiC additives and reached a maximum of 7.33 ± 0.24 MPa·m 1/2 and 471 ± 15 MPa, respectively, with the ZrSi 2 + SiC content of 30 wt%. [ABSTRACT FROM AUTHOR]

Abstract: Al3BC3 was fabricated by in-situ reaction of Al, B4C and activated carbon additives, which improved both sinterability and mechanical properties of the ZrB2 ceramics. The densification of ZrB2 was nearly completed at 1700°C using spark plasma sintering (SPS). Both fracture toughness and flexural strength of ZrB2 ceramics increased with the content of sintering additives, which respectively reached a maximum of 6.17MPam1/2 and 529MPa at 15wt% ABC content. [Copyright &y& Elsevier]

Abstract: Laminated SiC/ZrB2 ceramic was fabricated by roll-compaction and spark plasma sintering at 1600°C. A maximum fracture toughness of 12.3±0.3MPam1/2 was measured for the sintered SiC/ZrB2 laminated ceramic. This significant improvement in fracture toughness can be attributed to the crack deflection along the interfacial layer and the presence of residual stresses in the sample. The effect of interlayer composition on the residual stresses was discussed in detail. It is observed that the residual thermal stress could be reduced by addition of ZrB2 particles to the SiC interlayer. The bending strength can be increased to 388±44MPa with the addition of 20vol% ZrB2 to the SiC interlayer. [Copyright &y& Elsevier]

ZrB 2 –SiC ceramics have become popular candidates as ultra-high temperature structural materials in recent years; however, their poor sinterability and poor thermal shock resistance has limited their application. In this paper, high density ZrB 2 –SiC–Al 3 BC 3 ultra-high temperature ceramics were successfully fabricated via the Spark Plasma Sintering(SPS) process using Al, B 4 C, and carbon powders as sintering additives. The thermal shock resistance of the sintered ZrB 2 –SiC–Al 3 BC 3 ceramics was estimated via the water quenching method and the flexural strength of the quenched specimens were determined. The critical thermal shock temperature of the sintered ZrB 2 –SiC–Al 3 BC 3 ceramics increased with rising sintering temperature. The fracture toughness and flexural strength of the sample sintered at 1800 °C were improved to 748.27 ± 77.35 MPa and 6.15 ± 0.01 MPa m1/2, respectively. This sample showed excellent thermal shock resistance behavior, with a critical thermal shock temperature of 592 °C. The improvement of the thermal shock resistance was attributed to its higher fracture toughness and the distribution of rod-like grains. • Rod-like ZrB 2 grains can be observed in the composite sintered at 1800 °C. • The composite gained at 1800 °C showed excellent mechanical properties. • The composite gained at 1800 °C showed well thermal shock resistance behavior. [ABSTRACT FROM AUTHOR]