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以碳化硅(w(SiC)=99%,d50=5μm)、炭黑(w(C)=99.8%,d50=0.38μm)和单质硅(w(Si)=98.6%)为原料,无水乙醇(w(乙醇)=99.6%)、热塑性酚醛树脂(0.074μm、工业级)为结合剂,乌洛脱品为固化剂,以50 MPa的单向压力,分别将采用干混工艺、湿混工艺混合、干燥后的物料压制成型为50 mm×5 mm的生坯,在N2保护下经800℃焙烧、炭化处理,有机物热降解后得到陶瓷素坯。研究了酚醛树脂在不同加入量(其质量分数分别为4%、8%、10%、12%、16%)及混练工艺(干混、湿混)对反应烧结碳化硅素坯强度和烧结体显微结构的影响,并采用SEM和光学显微镜分析了试样的显微结构和断面形貌。结果表明:当酚醛树脂加入量为12%时,采用湿混工艺可以制备出具有良好可浸渗性且抗折强度高达45 MPa的素坯,完全可以满足复杂异型件在烧成以前进行机械加工的要求,烧结体的抗折强度最高可达455 MPa。与干混工艺相比,用湿混工艺制成烧结体的显微结构更加均匀,晶粒更加细小,裂纹扩展更加曲折。 相似文献
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以四甲基氢氧化铵为分散剂,糊精为碳源,通过静电稳定作用,制备了高固相含量、分散良好的碳化硅陶瓷浆料。以水溶性N,N–二甲基丙烯酰胺为单体,N,N’–亚甲基双丙烯酰胺为交联剂,采用实验室开发的偶氮[2–(2–咪唑啉–2–基)]丙烷HCl引发体系,在45~50℃引发单体聚合,制备出水基凝胶注模碳化硅素坯,素坯的相对密度达58%,抗弯强度大于40MPa。进一步通过无压烧结制备相对密度高于98%,硬度达28GPa,强度达530 MPa的SiC陶瓷。对素坯和SiC陶瓷的微结构和力学性能进行了测试和表征。结果表明:采用糊精作为碳源可以提高凝胶注模浆料的分散性,避免凝胶过程中的碳阻聚问题,有利于制备出高性能的碳化硅陶瓷材料。 相似文献
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以碳化硅晶须为增强体、碳化硅--碳为基体制备晶须增强反应烧结碳化硅复合材料,研究了碳化硅晶须、碳含量对复合材料显微结构与性能的影响。结果表明:碳化硅晶须经高温反应烧结后仍保持表面的竹节结构,且晶须增强体与反应烧结碳化硅基体间形成适中的界面结合强度;材料断口处有明显的晶须拔出,当碳黑含量为6%(质量分数)时,随着晶须含量的增加,材料的抗弯强度从200MPa提高到310MPa(晶须含量15%),当碳黑含量为18%时,随着晶须含量的增加,材料断裂韧性从3.3MPa·m1/2提高到4.3MPa·m1/2;碳化硅晶须含量过高时,晶须的"搭桥"效应导致材料中含有较多的游离硅,限制了材料力学性能进一步提高;微氧化处理使材料表面形成致密、均匀的氧化膜,可显著提高反应烧结碳化硅的抗弯强度和断裂韧性。 相似文献
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碳化硅陶瓷的液相烧结及其研究进展 总被引:3,自引:0,他引:3
本文对碳化硅液相烧结添加系统及其烧结机理作了论述。有氧化物参与的碳化硅的液相烧结可以降低碳化硅的烧结温度,促进碳化硅的致密化,提高碳化硅陶瓷的性能。沿晶断裂和穿晶断裂混合断裂机理是液相烧结碳化硅陶瓷强度和韧性提高的原因,表面强化和韧化可以进一步提高碳化硅陶瓷材料的性能。 相似文献
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以SiC粉和莫来石粉为原料,采用凝胶注模成型工艺制备莫来石/碳化硅复合陶瓷,研究了莫来石含量对复合陶瓷显微结构和力学性能的影响,结果表明:随莫来石含量增加,复合陶瓷气孔率先降低后升高,而力学性能呈相反变化趋势。当莫来石含量为20%(体积分数)时,材料气孔率达到最小值9.4%,线收缩率以及弹性模量达到最大值26.5%和148.6 GPa;在莫来石含量为30%时抗弯强度和断裂韧性达到最大值397.7 MPa和4.17MPa.m1/2。适量莫来石的加入明显改善了材料的力学性能,过多则由于莫来石挥发而在材料中产生缺陷,材料性能下降。 相似文献
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以碳化硅(Si C)和炭黑(C)为原料,以石蜡(PW)、高密度聚乙烯(HDPE)、乙烯醋酸乙烯酯(EVA)为有机载体,以硬脂酸(SA)为表面改性剂,研究了反应烧结碳化硅陶瓷注射成型工艺对产品性能的影响。结果表明:在陶瓷粉体含量为80 wt%,有机载体以PW:HDPE:EVA:SA=9:3:3:1的比例,加入量为20 wt%,混炼1 h后,在100 MPa注射压力注射成坯,采用两步法脱脂,于真空烧结炉内1720°C下保温2h烧结,可获得结构致密的碳化硅陶瓷试样,其显气孔率为0.18%,密度为2.96 g/cm~3,抗弯强度达到290 MPa,断裂韧性值达到4.14MPa·m~(1/2),硬度达到21.6 GPa。 相似文献
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以电熔白刚玉、石墨、硅粉和碳纤维为主要原料,通过固定刚玉细粉和硅粉总含量(29%),改变硅粉加入量(0~20%)制得了六组碳纤维增强铝碳耐火材料.采用XRD、SEM及EDS等研究了硅粉加入量对不同温度处理后材料物相组成、显微结构及强度的影响.结果表明:(1)220 ℃热处理后,硅粉含量低于8%时,抗折耐压强度变化不大;硅粉的含量高于8%时,抗折与耐压强度均降低.(2)1400 ℃热处理后,当硅粉含量从0增加到8%时,耐压强度与抗折强度均得到明显改善.而当硅粉量进一步增加时,试样出现裂纹,强度显著下降.(3)综合考虑,硅粉的最佳加入量为8%,此时经220 ℃、1400 ℃热处理后材料具有最好的抗折强度及耐压强度. 相似文献
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Guo-Dong Zhan Mamoru Mitomo Yuichi Ikuhara Taketo Sakuma 《Journal of the American Ceramic Society》2000,83(12):3179-3184
The influence of grain shape and size on superplastic behavior and deformation mechanisms was investigated in annealed β-silicon nitride materials and compared with the results for hot-pressed material. The microstructure of the annealed materials consisted of fine equiaxed β-grains together with some elongated ones. Similar to the deformation behavior in the hot-pressed material, strain hardening did not occur in these annealed materials. Moreover, in contrast to the deformation behavior under tension, grain alignment under compression resulting from the development of a mild texture did not give rise to strain hardening. An annealed material with small elongated grains had a flow-stress dependency of n = 1, whereas other annealed materials with large elongated grains exhibited a flow-stress dependency of n = 1.6. In terms of texture development and the effect of grain shape on the creep rate when diffusion was the rate-controlling mechanism, a single curve with a stress exponent of ∼1 and a grain-size exponent of 3 were obtained for all materials. This suggests that the deformation mechanism in these annealed materials was the same as that of fine equiaxed β-silicon nitride. 相似文献
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Beate Balzer Michael Hagemeister Peter Kocher Ludwig J. Gauckler 《Journal of the American Ceramic Society》2004,87(10):1932-1938
ZnO-based varistor ceramics were sintered under various conditions to optimize their mechanical strength. For highest strength, the optimum sintering temperature was 1070°C or below. At higher maximum temperature, the strength decreased because of grain coarsening and the increasingly inhomogeneous distribution of secondary phases thereby induced. Fracture typically started from holes associated with hollow or poorly compacted sprayed granules. All series contained the same type of critical flaws, but, depending on the sintering temperature, the fracture toughness changed, which led to different strengths. At sintering temperatures above 1050°C, the density started to decrease slightly because of swelling attributed to the pressure of gas entrapped in closed pores. 相似文献
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采用CO2养护加速碳化镁渣砂浆,制备了低碳胶凝材料。研究了水灰比和碳化龄期对碳化镁渣砂浆的力学性能及微观结构的影响。结果表明:在CO2浓度为99.9%、压力为0.1 MPa、温度为23℃的碳化养护条件下,水灰比为0.4的镁渣砂浆碳化14 d后,抗压强度是其碳化前强度值的9.9倍,延长碳化时间有利于强度的提高。水灰比对碳化砂浆强度影响显著,低水灰比试件碳化后强度提高更多。通过微观分析发现,碳化养护提高镁渣砂浆强度的原因是,碳化后生成大量的CaCO3,使试件更加致密,孔隙率降低。 相似文献
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Mineo Mizuno 《Journal of the American Ceramic Society》1991,74(12):3017-3022
The microstructure of mullite ceramics hot-pressed and sintered at different temperatures was studied using transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) with EDS, and electron probe microanalysis (EPMA). The specimens, consisting of stoichiometric mullite grains without glassy phase, are obtained by hot-pressing stoichiometric mullite powder at 1575°C for 1 h. Silica-rich glassy phases are observed using TEM at three-grain junctions of mullite grains in specimens heated at and above 1600°C. However, high-resolution transmission electron micrographs show no glassy phase at two-grain boundaries in all specimens. SEM with EDS analyses show that the average value of Al2 O3 contents of mullite grains increases slightly with increasing temperature. These results are consistent with a published Al2 O3 –SiO2 phase diagram. The flexural strength of mullite specimens at room temperature depends on their microstructure, such as the grain size and grain size distribution of mullite grains. The strength is high at room temperature and up to 1200°C, and it decreases at and above 1350°C, irrespective of the presence of the glassy phase. 相似文献
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Michael K. Cinibulk Gareth Thomas Sylvia M. Johnson 《Journal of the American Ceramic Society》1990,73(6):1606-1612
Densifying silicon nitride with a YSiAlON glass additive produced 99% dense materials by pressureless sintering. Subsequent heat-treating led to nearly complete crystallization of the amorphous intergranular phase. Transmission electron microscopy revealed that for heat treatments at 1350°C, only β-Y2 Si2 O7 was crystallized at the grain boundaries. At a higher temperature of 1450°C, primarily YSiO2 N and Y4 Si2 O7 N2 in addition to small amounts of Y2 SiO5 were present. Al existed only in high concentrations in residual amorphous phases, and in solid solution with Si3 N4 and some crystalline grain-boundary phases. In four-point flexure tests materials retained up to 73% of their strengths, with strengths of up to 426 MPa, at 1300°C. High-strength retention was due to nearly complete crystallization of the intergranular phase, as well as to the high refractoriness of residual amorphous phases. 相似文献
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The relationship of joint strength of solvent welded joints of polycarbonate to their microstructure is investigated. We used three solvents - butanone, acetone, and cyclohexanone - to test the effect of solubility parameters, and a mixture of cyclohexanone with ethanol to test the effect of a cosolvent; the effect of variation of welding temperature-on both the joint strength and the microstructure is also investigated. Three fracture modes in shear, tensile and tear tests are analyzed. Polycarbonate treated with butanone has maximum joint strength. Cyclohexanone at 78 vol% in ethanol produces the maximum joint strength of polycarbonate. The joint strength of polycarbonate joints welded with cyclohexanone increases with the temperature at which the weld is made. Comparing microstructure with joint strength, tongues, equiaxed dimples and elongated dimples are responsible for the maximum shear, tensile and tear strength, respectively. 相似文献
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研究了ZrB2-SiC复合材料的凝胶注模成型技术。着重讨论了分散剂、pH值、固相体积含量、有机单体等对ZrB2-SiC复合材料料浆的影响;分析了凝胶注模成型后,排胶前复合材料素坯断面的显微结构以及相对应的烧结体的显微结构。结果表明:当分散剂用量为8.74‰(质量分数),pH为10.8,有机单体含量为3.1%时,可制得固相体积含量为40%,粘度为610mPa.s的ZrB2-SiC复合浆料,此时烧结体的断面主要以穿晶断裂为主;凝胶注模成型的坯体内部的有机聚合物网络因高温而完全分解,使素坯的气孔分布较均匀,利于烧结体致密度的提高。 相似文献
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You Zhou Kiyoshi Hirao Motohiro Toriyama Yukihiko Yamauchi Shuzo Kanzaki 《Journal of the American Ceramic Society》2001,84(7):1642-1644
Based on the processing strategy of improving the mechanical properties of liquid-phase-sintered materials by modifying the secondary phase chemistry, four rare-earth oxides (RE2 O3 , RE = La, Nd, Y, and Yb), in combination with alumina, were used as sintering aids for a submicrometer-size β-SiC powder. Doped with 5 vol% RE2 O3 + Al2 O3 additives, all specimens were hot-pressed to near full-densities at 1800°C, and they exhibited similar microstructures and grain size distributions. The SiC grains in all specimens revealed a core-rim structure after being plasma-etched, indicating that they were densified via the same solution-reprecipitation mechanism. It was found that a decrease in the cationic radius of the rare-earth oxides was accompanied by an increase in Young's modulus, hardness, and flexural strength of the SiC ceramics, whereas the fracture toughness was improved by incorporating rare-earth oxides of larger cationic radius. The changes in the mechanical properties were attributed to the difference in the chemistry of the intergranular phases in the four ceramics. 相似文献