Deposition of Silicon Carbide/Titanium Carbide Laminar Ceramics by Electrophoresis and Densification by Spark Plasma Sintering

SiC/TiC laminar ceramic composites were fabricated using electrophoretic deposition (EPD) from acetone-based suspensions. The growth rate of the SiC was almost twice that of the TiC at the same deposition voltage and solids loading. Pressureless sintering and spark plasma sintering (SPS) of the composites were investigated. SiC in the composites without sintering additives could not be densified using pressureless sintering, even at 2000°C. SPS, however, could densify the SiC/TiC composites at 1800°C and 35 MPa. The relative density of the SPS sample was 98.9%.     

Pressureless Sintering of Alumina-Titanium Carbide Composites

The densification of Al₂O₃-TiC composites is detrimentally affected by chemical reactions between Al₂O₃ and TiC. These reactions must be suppressed in order to promote sintering. In this study, the specific reactions occurring in Al₂O₃-TiC composites were modeled, using thermodynamic calculations, and verified by experiments. The reaction between Al₂O₃ and TiC was suppressed by the use of specially prepared embedding powders allowing pressureless sintering to closed porosity. The Al₂O₃-TiC composites were subsequently hot isostatically pressed to > 99% of theoretical density without encapsulation. Typical flexural strength and fracture toughness of Al₂O₃-30 wt% TiC composites were 690 MPa and 4.3 MPa · m^1/2, respectively.     

Sintering Mechanism and Microstructure of TaC/SiC Composites Consolidated by plasma-activated sintering

TaC/SiC composites with 5 wt% SiC addition were densified by plasma-activated sintering (PAS) at 1500–1800 °C for 5 min under 30 MPa. The effects of plasma-activated sintering on microstructures, densification and mechanical properties of the composites were investigated. The results showed that TaC/SiC composites achieved a relative density more than 99% of the theoretical density at 1600 °C. A low eutectic liquid phase generated by the oxide on the particle surface was observed in the composite to realize a relatively low temperature sintering densification. While the TaC particle size decreased insignificantly with increasing sintering temperature, the transformation of morphology of SiC particles changing from equiaxed to elongated grain was activated, accompanying with a slight particle size decreasing of the SiC phase, thus promoting a relatively high flexural strength of 550 MPa under 1800 °C. Besides, some ultra-fine 2 nm Ta₂Si was observed in the glassy pockets, strengthening the amorphous phase and thus increasing the flexural strength.     

Reaction-bond composite synthesis of SiC-TiB2 by spark plasma sintering/field-assisted sintering technology (SPS/FAST)

High-density SiC-TiB₂ composites were fabricated using the displacement reaction spark plasma sintering/field-assisted sintering technology (SPS/FAST) and SiC, B₄C, TiC, and Si powders. The reaction process was performed in a narrow time frame compared hot pressing. The SiC-TiB₂ composites were sintered with precursor SiC at various pressures to determine the effects of processing with SPS/FAST. The composites completed synthesis during SPS/FAST processing, which occurs more quickly than hot pressing. SEM, STEM, and Raman spectroscopy are used to show the conversion and microstructure. The composite of 53.6 wt.% SiC and 46.4 wt.% TiB₂ has 99 % theoretical density, hardness of 26.4 GPa, and fracture toughness of 5.12 MPa m^1/2.     

Fabrication and characterization of sintered TiC-SiC composites

Some TiC-SiC composites with different SiC volume contents (0, 10, 25 and 50%) are prepared by spark plasma sintering (SPS). The relationship between density, grain growth and temperature is studied in order to fabricate dense and nano-sized TiC-SiC composites. A sintering by SPS at 1800 °C during 5 min allowed to form TiC-SiC composites with relative density above 95% and an homogeneous distribution of TiC (grain size from 270 to 900 μm) and nano-sized SiC. With the increasing of SiC volume contents, Vickers hardness and fracture toughness are improved; thermal conductivity at room temperature is increased whereas at high temperature it is reduced. In future studies, those materials will be irradiated to characterize monolithic TiC and TiC-SiC composites behaviour under irradiation.     

Thermodynamic Behavior of Copper-Coated Silicon Carbide Particles during Conventional Heating and Spark Plasma Sintering

75Cu·25SiC (vol%) compacts were prepared using copper-coated SiC particles and spark plasma sintering (SPS). The preliminary thermal performance of the coated particles was determined using simultaneous DSC-TG-MS measurement. Characterization of compacts using XRD and SEM techniques was conducted to investigate the physical and chemical changes during the SPS operation. It was found that CuO decomposed at 850° and 500°C during conventional heating and SPS, respectively. Cu₂O facilitated the densification of Cu/SiC composites. The optimized sintering temperature of Cu/SiC composites using SPS was ∼730°C. The compacts showed improved hardness because of the SiC reinforcement.     

Sintering of in-Situ Synthesized Sic–TiB2 Composites with Improved Fracture Toughness

TiB₂-particle reinforcement is one of the most successful methods for improving the fracture toughness of SiC ceramics.^1–3 Commercially available TiB₂ powders, however, have a large particle size and/or are highly reactive so that they are not favorable as a starting powder. In the present work, TiB₂ particles are formed by an in situ reaction between TiC and boron. The reaction takes place during sintering between 1000° and 1600°C and is accompanied by a large volume expansion. Under optimum conditions, dense composites (> 98% of theoretical) can be obtained by pressureless sintering using B and C as sintering additives. The in situ reaction method enables, for the first time, a complete densification of SiC-particulate composites by pressureless sintering. The fracture toughness of the composites was approximately 30% higher than that of the monolithic SiC ceramic.     

Sintering of β.q.ss. and gahnite glass-ceramic/silicon carbide composites

The sintering of β.quartz solid solution, β.q._ss., and gahnite glass-ceramic/particulate SiC composites has been studied by two different sintering procedures. In one procedure, the composites were fired above the melting point of the crystalline phase, identified by DTA, at a very high heating rate (800 °C min⁻¹) in air, nitrogen and argon atmospheres, for 1–6 min. It was found that the reduction of ZnO constituent of the glass by SiC particles gives rise to Zn, CO, and SiO gaseous products preventing complete densification of composites. In the other procedure, sintering was done at about crystallization peak temperature of the glass phase, employing a low heating rate (40 °C min⁻¹) in air for 60 min. In this case, the circumferential tensile stress in the glass-ceramic matrix phase, caused by the presence of incompressible SiC particles, retards the densification of the composites. The maximum amount of SiC particles yielding a reasonably dense composite was found to be 9 vol.%.     

Fabrication and Microstructure Characterization of Ti3SiC2 Synthesized from Ti/Si/2TiC Powders Using the Pulse Discharge Sintering (PDS) Technique

Ti/Si/2TiC powders were prepared using a mixture method (M) and a mechanical alloying (MA) method to fabricate Ti₃SiC₂ at 1200°–1400°C using a pulse discharge sintering (PDS) technique. The results showed that the Ti₃SiC₂ samples with <5 wt% TiC could be rapidly synthesized from the M powders; however, the TiC content was always >18 wt% in the MA samples. Further sintering of the M powder showed that the purity of Ti₃SiC₂ could be improved to >97 wt% at 1250°–1300°C, which is ∼200°–300°C lower than that of sintered Ti/Si/C and Ti/SiC/C powders using the hot isostatic pressing (HIPing) technique. The microstructure of Ti₃SiC₂ also could be controlled using three types of powders, i.e., fine, coarse, or duplex-grained, within the sintering temperature range. In comparison with Ti/Si/C and Ti/SiC/C mixture powders, it has been suggested that high-purity Ti₃SiC₂ could be rapidly synthesized by sintering the Ti/Si/TiC powder mixture at relatively lower temperature using the PDS technique.     

Low‐Temperature Sintering of HfC/SiC Nanocomposites Using HfSi2‐C Additives

HfC/SiC nanocomposites were fabricated via the reactive spark plasma sintering (R‐SPS) of a nano‐HfC powder and HfSi₂‐C sintering additives. The densification temperature decreased to 1750°C as the additive content increased. XRD analysis indicated the formation of pure HfC–(19.3–33.8 vol%) SiC within the sintered composites without residual silicide or oxide phases or secondary nonoxide phases. Ultrafine and homogeneously distributed HfC (470 nm) and SiC (300 nm) grains were obtained in the dense composites using nano‐HfC powder through the high‐energy ball‐milling of the raw powders and R‐SPS. Grain growth was further suppressed by the low‐temperature sintering using R‐SPS. No amorphous phase was identified at the grain boundary. The maximum Vickers hardness, Young's modulus, and fracture toughness values of the HfC/SiC nanocomposites were 22 GPa, 292 GPa, and 2.44 MPa·m^1/2, respectively.     

Alumina Sol-Assisted Sintering of SiC—Al2O3 Composites

The composite sol—gel (CSG) technology has been utilized to process SiC—Al₂O₃ ceramic/ceramic particulate reinforced composites with a high content of SiC (up to 50 vol%). Alumina sol, resulting from hydrolysis of aluminum isopropoxide, has been utilized as a dispersant and sintering additive. Microstructures of the composites (investigated using TEM) show the sol-originating phase present at grain boundaries, in particular at triple junctions, irrespective of the type of grain (i.e., SiC or Al₂O₃). It is hypothesized that the alumina film originating from the alumina sol reacts with SiO₂ film on the surface of SiC grains to form mullite or alumina-rich mullite-glass mixed phase. Effectively, SiC particles interconnect through this phase, facilitating formation of a dense body even at very high SiC content. Comparative sinterability studies were performed on similar SiC—Al₂O₃ compositions free of alumina sol. It appears that in these systems the large fraction of directly contacting SiC—SiC grains prevents full densification of the composite. The microhardness of SiC—Al₂O₃ sol—gel composites has been measured as a function of the content of SiC and sintering temperature. The highest microhardness of 22.9 GPa has been obtained for the composition 50 vol% SiC—50 vol% Al₂O₃, sintered at 1850°C.     

反应烧结碳化硼/碳化硅凝胶注模成形工艺的研究

以碳化硼颗粒为增强相,采用凝胶注模成形工艺制备反应烧结B_4C/SiC复合材料。通过对低粘度、高固相含量碳化硼、炭黑和碳化硅浆料的制备技术以及凝胶注模成形工艺参数的研究,制备出了结构均匀、致密度高的反应烧结碳化硼/碳化硅复合陶瓷。并分析了碳化硼、炭黑和碳化硅料浆制备过程中不同碳化硅颗粒级配、碳化硼含量和碳化硼颗粒大小、球磨时间、料浆pH值、固相含量对料浆粘度的影响。     

中国卫生陶瓷行业的发展与努力方向

经过30多年的迅猛发展,中国卫生陶瓷产量已多年位居世界第一,成为名符其实的世界卫生陶瓷生产大国。笔者介绍了中国卫生陶瓷行业由最初引进国外先进技术和设备到消化吸收,科技创新,逐步形成完整的工业体系的发展历程;指出了中国卫生陶瓷目前尚存在的不足;提出了中国卫生陶瓷行业会今后努力的方向。     

Sintering effect on microstructural evolution and mechanical properties of spark plasma sintered Ti matrix composites reinforced by reduced graphene oxides

Ti matrix composites reinforced with 0.6?wt% reduced graphene oxide (rGO) sheets were fabricated using spark plasma sintering (SPS) technology at different sintering temperatures from 800?°C to 1100?°C. Effects of SPS sintering temperature on microstructural evolution and mechanical properties of rGO/Ti composites were studied. Results showed that with an increase in the sintering temperature, the relative density and densification of the composites were improved. The Ti grains were apparently refined owing to the presence of rGO. The optimum sintering temperature was found to be 1000?°C with a duration of 5?min under a pressure of 45?MPa in vacuum, and the structure of rGO was retained. At the same time, the reaction between Ti matrix and rGO at such high sintering temperatures resulted in uniform distribution of micro/nano TiC particle inside the rGO/Ti composites. The sintered rGO/Ti composites exhibited the best mechanical properties at the sintering temperature of 1000?°C, obtaining the values of micro-hardness, ultimate tensile strength, 0.2% yield strength of 224 HV, 535?MPa and 446?MPa, respectively. These are much higher than the composites sintered at the temperature of 900?°C. The fracture mode of the composites was found to change from a predominate trans-granular mode at low sintering temperatures to a ductile fracture mode with quasi-cleavage at higher temperatures, which is consistent with the theoretical calculations.     

Spark plasma sintering of TiC–SiCw ceramics

Silicon carbide whiskers (SiC_w) in TiC had impressive impacts on the properties and made it possible for special applications which generally would not be conceivable with TiC alone. In the present work, SiC_w reinforced TiC based composites were prepared by spark plasma sintering (SPS) technique, at the temperature of 1900 °C under the pressure of 40 MPa for sintering time of 7 min. To test out the effects of different amount of SiC whisker (0, 10, 20 and 30 vol%) on the characteristics of TiC, the sintered samples were investigated about sinterability and physical-mechanical properties. Microstructure observations and density measurements confirmed that the composites were dense with uniformly distributed reinforcement, and the specimen doped with higher than 10 vol% SiC_w could attain higher relative density (>100%) than pure TiC and TiC–10 vol% SiC_w. Also, the highest values for hardness (29.04 GPa) and thermal conductivity (39.2 W/mK) were achieved in specimen containing 30 vol% SiC_w, whereas the optimum bending strength (644 MPa) was recorded in material containing 20 vol% SiC_w. It seems that one of the reasons which contributes to this trend of properties variation is the generation of near-stoichiometric TiC_x phase and new Ti₃SiC₂ compound.     

Influence of Cu2O on Interface Behavior of Copper/SiCp Composite Prepared by Spark Plasma Sintering

Copper/SiC_p composites were prepared by spark plasma sintering. X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy techniques were used to characterize the sintered samples. Cu₂O was found to facilitate the physical wetting at the interface through the formation of an amorphous intergranular phase. The reaction between SiC and copper was detected in the samples containing little Cu₂O. It led to the degradation of SiC reinforcements and the decrease in hardness of copper/SiC_p composites.     

Al2O3/TiC Based Metal Cutting Tools by Microwave Sintering Followed by Hot Isostatic Pressing

The feasibility of producing Al₂O₃/TiC metal cutting tools by fast microwave sintering followed by hot isostatic pressing was examined. Microwave heating profiles able to ensure near-full densification of Al₂O₃/TiC ceramic components were determined. Simple-shape specimens could be sintered to a bulk density of 97% theoretical density (TD) while in the case of tool-shaped ones maximal densification levels attained were somewhat lower, i.e., ∼95% TD. Temperature uniformization—within the heating chamber—by using a particulate SiC susceptor noticeably reduced tool cracking propensity. Densification levels in the range acceptable for commercial tool manufacturing (≥98% TD) were achieved by hot isostatic pressing of the microwave-sintered parts. The isostatically pressed parts exhibited a Vickers hardness H _v≅ 2000 kg/mm² and a fracture toughness K _IC∼ 4.3 MPa·m^1/2.     

微波烧结SiC-Cu/Al复合材料的工艺及机理

用微波烧结工艺成功制备了铜包裹碳化硅颗粒增强铝基(SiC-Cu/Al)复合材料,利用扫描电镜和X射线衍射分析仪对烧结样品进行表征,并讨论了烧结过程及机理.研究表明:采用多晶莫来石纤维棉、硅碳棒和氧化铝坩锅组合设计的保温结构能很好地促进烧结.烧结温度为720℃时,SiC-Cu/Al复合材料的密度取得最大值为2.53g/cm3.SiC-Cu/Al复合材料的硬度随烧结温度的升高的变化成马鞍状.烧结温度对样品显微结构的影响较大,随着烧结温度的升高,相分布的均匀性降低,在较高的烧结温度下会出现SiC颗粒的偏聚.涡流损耗和界面极化损耗是促进微波烧结的主要动力.     

Enhancing toughness and strength of SiC ceramics with reduced graphene oxide by HP sintering

In this paper, the silicon carbide-reduced graphene oxide (SiC/rGO) composites with different content of rGO are investigated. The hot pressing (HP) at 2100?°C for 60?min under a uniaxial pressure of 40?M?Pa resulted in a near fully-dense SiC/rGO composite. In addition, the influence of graphene reinforcement on the sintering process, microstructure, and mechanical properties (fracture toughness, bending strength, and Vickers hardness) of SiC/rGO composites is discussed. The fracture toughness of SiC/rGO composites (7.9MPam^1/2) was strongly enhanced by incorporating rGO into the SiC matrix, which was 97% higher than the solid-state sintering SiC ceramics (SSiC) by HP. Meanwhile, the bending strength of the composites reached 625?M?Pa, which was 17.3% higher than the reference materials (SSiC). The microstructure of the composites revealed that SiC grains were isolated by rGO platelets, which lead to the toughening of the composite through rGO pull out/debonding and crack bridging mechanisms.     

Effect of co-addition of SiC and WC on the densification behaviour and microstructural evolution of TiC-based composites

In the present study, the effect of simultaneous incorporation of SiC and WC additives on the densification behaviour and microstructural development of TiC-based composites is studied. Four different TiC-SiC-WC (TSW) composites with varying SiC and WC content were synthesized by ultrasonic wet milling followed by spark plasma sintering (SPS) at 1750 °C for 5 min under 40 MPa external pressure. The average particle size of the ultrasonic wet-milled mixture underwent an appreciable refinement from 2.48 μm (un-milled powder) to between 0.9 and 1.25 μm. The sintered compacts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermodynamic assessment. All TSW sintered specimens exhibited a relative density of greater than 98% with TiC +10 wt% SiC +15 wt% WC reaching the highest value of 99.2%. The XRD analysis and microstructural evaluation confirmed the in-situ formation of Ti₃SiC₂ compound for specimens TiC +15 wt% SiC +10 wt% WC and TiC +20 wt% SiC +5 wt% WC as suggested by the thermodynamic evaluation. Besides, except for specimen TiC +20 wt% SiC +5 wt% WC, some of the SiC grains with unclean grain boundaries were found to be dissolved partially within the (Ti, W) C solid solution, thereby indicating the formation of (Ti, W, Si) C solid solutions as confirmed by the SEM/EDS analysis. The optimum hardness and indentation fracture toughness of 22.43 GPa and 6.54 MPa m^½ were obtained for the samples TS10W15 and TS15W10, respectively. Crack deflection, branching, and bridging induced by the untwine SiC grains, partly un-dissolved WC particles, and (Ti, W) C solid solution phase are among the main toughening mechanisms responsible for improving the fracture toughness of the co-reinforced specimens besides the break of intertwining SiC grains.