无压烧结制备纳米复合碳化硅陶瓷

以水基喷雾造粒而成含5%(质量分数)纳米氮化钛(TiN)颗粒的碳化硅(SiC)造粒粉为原料,采用无压烧结制备纳米复合SiC陶瓷。分析了烧结温度及保温时间对复合陶瓷烧结特性与显微结构的影响规律。结果表明:采取二步烧结可以实现SiC陶瓷在晶粒不明显长大的前提下实现致密化,二步烧结,即先升温到1950℃保温15min后迅速降至1850℃烧结1h,制备的SiC陶瓷具有较高收缩率、较低质量损失以及较高的致密度;纳米TiN颗粒加入后能与基体(SiC,Al2O3)部分发生反应生成TiC和AlN,明显改善SiC陶瓷的烧结性能,获得等轴状、细晶显微结构和优越的力学性能。     

AlN-Re2O3液相烧结碳化硅

采用非氧化物AlN和Re2O3作为复合烧结助剂(Re2O3-La2O3与Y2O3)进行碳化硅液相烧结得到了致密的烧结体.烧结助剂占原料粉体总质量的20%,其中:AIN与(La0.5Y0.5)2O3的摩尔比为2:1,在30MPa压力下,1850℃保温0.5h热压烧结的碳化硅陶瓷,抗弯强度>800MPa,断裂韧性>8MPa·m1/2,明显高于同组分1 950℃无压烧结0.5h的碳化硅陶瓷的抗弯强度(433.7MPa)和断裂韧性(4.8MPam·m1/2.热压烧结的陶瓷晶粒呈单向生长,断裂模式为沿晶断裂.同组分无压烧结碳化硅陶瓷的显微结构可以观察到核壳结构.     

Improved additive manufacturing of silicon carbide parts via pressureless electric field-assisted sintering

High solids loading silicon carbide (SiC)-based aqueous slurries containing only .5 wt. % organic additives were utilized to create specimens of various geometries via an extrusion-based additive manufacturing (AM) technique. Pressureless electric field-assisted sintering was performed to densify each specimen without deformation. The combination of these techniques produced parts with >98% relative density despite containing only 5 wt.% oxide sintering additives. After sintering, specimens contained only the α-SiC and yttrium aluminum perovskite phases. This suggests the evolution of a nonequilibrium yttrium aluminate phase, as well as transformation from β-SiC to α-SiC. The fabrication method presented in this work has advantages over other AM techniques commonly used with SiC, because it does not require significant organic additives nor additional postprocessing steps such as chemical vapor infiltration or polymer impregnation and pyrolysis.     

反应烧结碳化硅陶瓷的制备及烧结机理

用溶胶-凝胶法合成的无机／有机杂化材料结合SiC+C混合粉料制成了反应烧结碳化硅陶瓷素坯,并对由这种素坯制成的碳化硅陶瓷进行了物相鉴定和显微结构观察;借助Si-C相图对反应烧结碳化硅的烧结机理进行了研究,分析表明其主要烧结机理为溶解-再沉淀型。     

碳化硅陶瓷固相烧结的烧结机理及研究进展简

碳化硅陶瓷材料具有高硬度、高强度、抗氧化、耐高温、高热导率、低线胀系数等优良性能,同时具有优良的化学稳定性且能够耐大多数种类的酸碱溶液腐蚀,在石油、化工、建材、航空、机械等诸多领域得到了广泛应用。本文主要阐述了碳化硅陶瓷固相烧结的烧结机理,并对目前国内外关于碳化硅陶瓷固相烧结的研究进展进行了阐述。     

多孔碳化硅陶瓷的原位氧化反应制备及其性能

以SiC为陶瓷骨料,Al2O3作为添加剂,通过原位氧化反应制备了Sic多孔陶瓷,并对其氧化反应特性及性能进行了研究.结果表明:在1 300～1 500℃,随烧结温度的升高,SiC的氧化程度增加,SiC多孔陶瓷的强度逐渐增加,但开口孔隙率有所降低.莫来石相在1 500℃开始生成·当烧结温度升高到1 550℃时,莫来石大量生成,得到了孔结构相互贯通且颈部发育良好的莫来石结合SiC多孔陶瓷;由于在SiC颗粒表面上覆盖了致密的莫来石层,SiC的氧化受到抑制,开口孔隙率因而升高,SiC多孔陶瓷的强度因莫来石的大量生成而增加.由平均粒径为5.0um的SiC,并添加20%(质量分数)Al2O3,经1 550℃烧结2h制备的SiC多孔陶瓷具有良好的性能,其抗弯强度为158.7MPa、开口孔隙率为27.7%.     

Microstructure evolution process of porous silicon carbide ceramics prepared through coat-mix method

Porous silicon carbide ceramics were prepared through the coat-mix method and molding, carbonization and sintering process with silicon powders and phenolic resin as raw materials. The crystalline phase, microstructure, and porosity of samples treated at different stages were characterized. Results showed that the fabricated porous silicon carbide ceramics consist of pure β-SiC phase with a homogeneous structure and porosity of above 60%. Each of the processing stages, including coat-mix, molding, carbonization, and sintering, has certain contribution to the porosity of the final porous silicon carbide ceramics, in which the mole ratio of resin carbon to silicon and the molding temperature are the main factors to affect the porosity. A porosity evolution process of porous silicon carbide ceramics during fabrication process was also proposed.     

Silicon infiltrated silicon carbide from extruded thermoplastic wood polymer composites

Silicon-infiltrated silicon carbide (SiSiC) is an important technical ceramic material for several demanding applications such as heat exchangers, nozzles or mechanical seals. However, shaping and machining tools are quickly worn down, due to the application of hard abrasive silicon carbide (SiC) particles as part of the conventional starting compounds for monolithic SiSiC ceramics. Within this work, an alternative route fabricating SiSiC without primary SiC particles and with low residual carbon contents derived from thermoplastic wood polymer composites (WPC) is described. By varying the proportions of the raw materials, the phase compositions of the SiC ceramic could be modified. A reduction in the average wood particle size from 120 to 60 µm led to a homogenous SiSiC with high SiC content. SiSiC with flexural strengths up to 230 MPa and a Weibull modulus of 16 were developed. The residual carbon content could be reduced below 1 wt%.     

喷雾造粒对固相烧结SiC陶瓷的影响

采用离心式喷雾造粒技术对SiC浆料进行造粒,研究了喷雾造粒对SiC粉体的流动特性、成型行为、烧结性能、力学性能及显微结构的影响机制。研究结果表明:喷雾造粒后,碳化硅粉体流动性得到较大改善,素坯密度增加,微观结构致密;固相烧结后,碳化硅陶瓷的烧结性能提高,陶瓷显微结构得到改善。     

Crack tolerant silicon carbide ceramics prepared by liquid-phase assisted oscillatory pressure sintering

Silicon carbide ceramics were prepared by liquid-phase assisted oscillatory pressure sintering (OPS) with graphene and in-situ synthesized SiC whisker as the reinforcements. The effects of sintering temperature on the densification, morphology and mechanical performances of the SiC_p-SiC_w-graphene ceramics were investigated. In the temperature range from 1700 to 1800 °C, the densification rate of SiC_p-SiC_w-graphene ceramics was accelerated, ascribing to the reduction in viscosity of the glassy phase. At 1800 °C, the flexural strength and fracture toughness of the OPS ceramics corresponded to 697 MPa and 5.8 MPa m^1/2, respectively, which were higher than that of the hot-pressed ceramics under the same temperature conditions. Multiphase toughening mechanisms, such as whisker bridging and pullout, graphene bridging and delamination, were considered as the primary mechanisms. This work demonstrates an effective strategy to prepare silicon carbide ceramics at low sintering temperature.     

Effect of some technological parameters on structure formation in materials based on reaction-sintered silicon carbide

Results of petrographic, x-ray, chemical, and spectral investigations of the structure and composition of materials based on SiC fabricated by reaction sintering of preforms pressed from grainy silicon carbide and its mixtures with petroleum coke in molten and volatilized silicon are presented. It is shown that the structure and composition of reaction-sintered silicon carbide materials can be controlled by changing the proportion of silicon carbide and petroleum coke in the pressed preform, the coarseness of carbide and carbon particles, the density of the pressings, and the temperature of reaction sintering. It is established experimentally that secondary silicon carbide formed as a result of the reaction between petroleum coke and silicon binds the grains of the initial carbide into a dense silicon carbide skeleton, whereas the retained pores are filled with free silicon. A single-phase material consisting entirely of silicon carbide can hardly be obtained by the method of reaction sintering. In practice, this method gives double-phase (SiC-Si) and triple-phase (SiC-Si-C) materials with a maximum content of the principal phase (SiC) equal to 94–96% (mass fractions).Translated from Ogneupory i Tekhnicheskaya Keramika, No. 8, pp. 2–8, August, 1996.     

烧结助剂对低温制备碳化硅多孔陶瓷性能的影响

分别采用十二烷基苯磺酸钠、氢氧化钠以及NaA分子筛残渣为烧结助剂,碳粉为造孔剂,干压法成型,在1150℃空气气氛下烧结制备碳化硅多孔陶瓷支撑体。考察了助剂添加量对微结构、平均孔径、孔隙率以及抗热震性等方面的影响;分析了添加助剂的低温烧成机理。研究结果表明：三种添加剂均有助于提高支撑体的气体渗透性、抗弯强度和耐热震性;添加NaA分子筛残渣助烧结剂获得的碳化硅多孔陶瓷各项性能最佳,气体渗透率为1300 m³/(m²·h·kPa),强度可达27 MPa,且抗热震性能良好。     

Properties of liquid phase pressureless sintered silicon carbide obtained without sintering bed

High density pressureless sintered silicon carbide bodies with yttria and alumina as sintering aids were obtained without sintering bed (LPSSC-NB). Sintering behavior of this material was studied between 1850 °C and 1950 °C and it was compared to the liquid phase sintered SiC material obtained using sintering bed (LPSSC-B). Sintered density was 97% of the theoretical density (T.D.) at 1875 °C. Mechanical properties like fracture toughness, hardness, flexural strength were determined and compared to other SiC-based materials. In this manner we were able to demonstrate that silicon carbide could successfully be sintered by means of liquid phase mechanism also without sintering bed. This fact opens liquid phase sintered silicon carbide to a wide range of industrial application.     

High entropy carbide ceramics from different starting materials

Three typical ceramic processing were respectively used to synthesize (Ti_0.2Zr_0.2Nb_0.2Ta_0.2W_0.2)C high-entropy carbide (HEC) ceramics by spark plasma sintering. Although single-phase composition characterized by X-ray diffraction were obtained by the three processes, the microstructures and elemental distributions are different. The reasons for the formation of these features are preliminarily discussed. The results demonstrate that the particle sizes of the starting metallic powders was a key factor for obtaining a homogeneous distribution of each elements in the HEC. Carbide process with relatively finer starting carbide powders compared to the above metallic starting powders resulted in an HEC with homogeneous distribution of elements, but the obtained ceramics showed the lowest relative density. For oxide process, it is considered that the obviously higher reaction temperature between ZrO₂ and graphite resulted in a two-phase structure of an HEC and a zirconium-rich phase, but the obtained HEC showed the highest relative density.     

Effect of carbon nanoparticle reinforcement on mechanical and thermal properties of silicon carbide ceramics

This research presents an analysis of the influence of graphene reinforcement on the thermal and mechanical properties of silicon carbide ceramics, at 2.5% (wt%) graphene content. The SiC composites, containing various carbon nanofillers (graphene oxide and graphene nanoparticles), were sintered by the classical two stage spark plasma sintering method. Two current modes were used, the continuous mode and the pulsed current mode. The results from photothermal radiometry and investigations of the mechanical properties showed that graphene additives significantly improve the thermal properties and toughness of material, sintered from a SiC powder. An 45% growth in the toughness was observed, which increased from 1.21 to 1.75?MPa/m^1/2. The thermal diffusivity value also increased from 0.60 to 0.71?cm²/s and giving an improvement in thermal properties of 18%. The friction coefficient reached 7% giving an increase in value from 0.62 to 0.66. Microscopic investigations supported the photothermal radiometry (PTR) results. Whilst, thermal imaging revealed homogeneity of the local thermal properties of the products fabricated from the starting SiC powder.     

Direct laser sintering of reaction bonded silicon carbide with low residual silicon content

Additive manufacturing (AM) techniques are promising manufacturing methods for the production of complex parts in small series. In this work, laser sintering (LS) was used to fabricate reaction bonded silicon carbide (RBSC) parts. First, silicon carbide (SiC) and silicon (Si) powders were mixed in order to obtain a homogeneous powder. This powder mixture was subsequently laser sintered, where the Si melts and re-solidifies to bind the primary SiC particles. Afterwards, these SiSiC preforms were impregnated with a phenolic resin. This phenolic resin was pyrolysed yielding porous carbon, which was transformed into secondary reaction formed SiC when the preforms were infiltrated with molten silicon in the final step. This resulted in fully dense RBSC parts with up to 84?vol% SiC. The optimized SiSiC combined a Vickers hardness of 2045?HV, an electrical conductivity of 5.3?×?10³?S/m, a Young's modulus of 285?GPa and a 4-point bending strength of 162?MPa.     

Densification of SiC by colloidal processing and SPS without sintering additives

Abstract

Silicon carbide is one of the most important ceramics used as structural and functional materials in a wide variety of applications. Many studies have reported the densification of SiC using oxide and nonoxide additives such as the Al₂O₃, B₄C and Al–B–C system. However, it is difficult to densify SiC at temperatures below 2000°C without sintering additives even if spark plasma sintering (SPS) is used. The authors attempted to densify SiC using colloidal processing and SPS without sintering additives. A commercially available SiC powder with the average particle size of 0·55 μm was used as the starting material. The densities of the green body prepared by slip casting and the sintered body by SPS were 65·5 and 98·7% respectively.     

Pressureless sintering of multilayer graphene reinforced silicon carbide ceramics for mechanical seals

ABSTRACT

The silicon carbide (SiC) ceramics containing multilayer graphene derived from graphite exfoliation were successfully prepared by pressureless sintering, and the effect of graphene content on the sintering behaviours, microstructure, mechanical, tribological, electrical and thermal properties was investigated in detail. The bulk density, bending strength and hardness of the composite ceramics gradually decrease with the increase of graphene content, but the friction, conductance and thermal conductance properties are improved obviously. When the graphene content reaches 5?wt-%, the dry friction coefficient of 0.22, electrical conductivity of 2724.14 S?1?m?1 and thermal conductivity of 8.5?W?(m?1?K?1) can be obtained, indicating good comprehensive mechanical, tribological, electrical and thermal properties. This multilayer graphene reinforced silicon carbide ceramic is a promising seal material instead of SiC seal materials containing graphite to be applied in next-generation mechanical seals.     

Influence of silicon carbide particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide ceramics

The influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide (ZrB₂–SiC) ceramics was investigated. ZrB₂-based ceramics containing 30 vol.% SiC particles were prepared from four different α-SiC precursor powders with average particle sizes ranging from 0.45 to 10 μm. Examination of the dense ceramics showed that smaller starting SiC particle sizes led to improved densification, finer grain sizes, and higher strength. For example, ceramics prepared from SiC with the particle size of 10 μm had a strength of 389 MPa, but the strength increased to 909 MPa for ceramics prepared from SiC with a starting particle size of 0.45 μm. Analysis indicates that SiC particle size controls the strength of ZrB₂–SiC.     

Pressureless sintering of dual-phase,high-entropy boride–carbide ceramics

Dual-phase, high-entropy boride–carbide ceramics were densified by pressureless sintering. Relative densities up to approximately 96% were obtained for ceramics containing about 30 vol% high-entropy boride and 70 vol% high-entropy carbide. Isostatic pressing at 200 MPa resulted in higher relative densities of both the green bodies and final ceramics compared to uniaxial pressing. The highest relative density of 96.3% was achieved for a ceramic that was isostatically pressed at 200 MPa and sintered at 2300°C for 2 h. Grain sizes of the resulting ceramics were approximately 2 µm. This is the first report of pressureless sintering of dual-phase, high-entropy boride–carbide ceramics.