共查询到20条相似文献,搜索用时 15 毫秒
1.
Jian-Feng Yang Tatsuki Ohji Koichi Niihara 《Journal of the American Ceramic Society》2000,83(8):2094-2096
The present study investigates the influence of the content of Y2 O3 –Al2 O3 sintering additive on the sintering behavior and microstructure of Si3 N4 ceramics. The Y2 O3 :Al2 O3 ratio was fixed at 5:2, and sintering was conducted at temperatures of 1300°–1900°C. Increased sintering-additive content enhanced densification via particle rearrangement; however, phase transformation and grain growth were unaffected by additive content. After phase transformation was almost complete, a substantial decrease in density was identified, which resulted from the impingement of rodlike β-Si3 N4 grain growth. Phase transformation and grain growth were concluded to occur through a solution–reprecipitation mechanism that was controlled by the interfacial reaction. 相似文献
2.
Novel Two-Step Sintering Process to Obtain a Bimodal Microstructure in Silicon Nitride 总被引:5,自引:0,他引:5
Hai-Doo Kim Byung-Dong Han Dong-Soo Park Byong-Taek Lee Paul F. Becher 《Journal of the American Ceramic Society》2002,85(1):245-252
A two-step sintering process is described in which the first step suppresses densification while allowing the α-to-β phase transformation to proceed, and the second step, at higher temperatures, promotes densification and grain growth. This process allows one to obtain a bimodal microstructure in Si3 N4 without using β-Si3 N4 seed crystals. A carbothermal reduction process was used in the first step to modify the densification and transformation rates of the compacts consisting of Si3 N4 , Y2 O3 , Al2 O3 , and a carbon mixture. The carbothermal reduction process reduces the oxygen:nitrogen ratio of the Y-Si-Al-O-N glass that forms, which leads to the precipitation of crystalline oxynitride phases, in particular, the apatite phase. Precipitation of the apatite phase reduces the amount of liquid phase and retards the densification process up to 1750°C; however, the α-to-β phase transformation is not hindered. This results in the distribution of large β-nuclei in a porous fine-grained β-Si3 N4 matrix. Above 1750°C, liquid formed by the melting of apatite resulted in a rapid increase in densification rates, and the larger β-nuclei also grew rapidly, which promoted the development of a bimodal microstructure. 相似文献
3.
Mark I. Jones Maria-Cecilia Valecillos Kiyoshi Hirao Motohiro Toriyama 《Journal of the American Ceramic Society》2001,84(10):2424-2426
Si3 N4 powders were sintered using a 28 GHz gyrotron source, with Y2 O3 , Al2 O3 , and MgO as sintering aids, in an attempt to investigate the effect of microwave radiation on densification behavior. The microwave-sintered samples were compared with identical samples produced by conventional pressureless sintering. The effect of sintering on the microstructural development and grain growth of the samples was assessed using scanning electron microscopy. Phase transformation behavior was assessed using X-ray diffractometry. In the microwave-sintered samples, densification and α→β transformation occurred at temperatures ∼200°C lower than those of the conventionally sintered samples. More importantly, at comparable stages of densification, the microstructures of the microwave-sintered and conventionally sintered samples were significantly different, with the microwave-sintered samples showing the development of elongated β grains at a much earlier stage of the α→β transformation. It was concluded that the effect of microwave radiation on sintering was not simply a decrease in sintering temperatures, but in possibly a different sintering mechanism, clearly related to localized heating within the grain-boundary phase. 相似文献
4.
Kenji Hatanaka Masashi Katsuyama Hideki Takagi 《Journal of the American Ceramic Society》2003,86(1):135-140
The fatigue tests under push-pull completely reversed loading and pulsating loading were performed for silicon nitride ceramics at elevated temperatures. Then the effects of stress wave form, stress rate, and cyclic understressing on fatigue strength, and cyclic straining behavior, were examined. The cycle-number-based fatigue life is found to be shorter under trapezoidal stress wave loading than under triangular stress wave loading, and to become shorter with increasing hold time under the trapezoidal stress wave loading. Meanwhile, the equivalent time-based life curve, which is estimated from the concept of slow crack growth, almost agrees with the static fatigue life curve in the short and intermediate life regions, showing the small cyclic stress effect and the dominant stress-imposing period effect on cyclic fatigue life. The fatigue strength increased in stepwise stress amplitude increasing test, where stress amplitude is increased stepwise every given number of stress cycles, at 1100° and 1200°C. Occurrence of cyclic strengthening was proved through a gradual decrease in strain amplitude during a pulsating loading test at 1200°C in this material, corresponding to the above cyclic understressing effect on fatigue strength. 相似文献
5.
Gas pressure sintering kinetics of silicon nitride powder coated with 10 wt% (9:1) Al2 O3 and TiO2 have been studied at 1850°C with a pressure schedule of 0.3 MPa in the first stage and 1 MPa in the second stage. The rates have been analyzed with a liquid-phase sintering model. Diffusion-controlled intermediate-stage kinetics have been observed. The role of second-step pressurization with nitrogen and argon has been determined by monitoring the kinetics. Pressurization at an earlier stage (∼90% relative density) reduces the densification rate but produces a denser material at the final stage. Although final density is greater, a porous surface layer forms on samples sintered with argon pressurization at the second stage. No such porous layer is formed in the case of pressurization with nitrogen. The mechanism of the intermediate-stage kinetics has been discussed with respect to the nature of the product analyzed by XRD after sintering. 相似文献
6.
Joanna R. Groza Justin D. Curtis Martin Krämer 《Journal of the American Ceramic Society》2000,83(5):1281-1283
Nanosized TiN powder was densified via field-assisted sintering at temperatures of 1150°–1350°C and a pressure of 66 MPa under vacuum. A maximum relative density of ∼97% and a maximum mean grain size of 150–200 nm were obtained. Densification and microstructural evolution have been discussed, in terms of superplasticity and electric-field effects. 相似文献
7.
Naoki Kondo Masahiro Asayama Yoshikazu Suzuki Tatsuki Ohji 《Journal of the American Ceramic Society》2003,86(8):1430-1432
A sinter-forging technique was successfully applied to fabricate a silicon nitride with a lutetia (Lu2 O3 ) additive. The sinter-forged specimen had a strongly anisotropic microstructure where rodlike silicon nitride grains preferentially aligned perpendicular to the forging direction. The specimen exhibited superior strength of ∼700 MPa at 1500°C. This strength was highest when compared with previous silicon nitrides at temperatures >1400°C. Such superior high-temperature strength was attributed to grain alignment as well as to the refractory grain-boundary glassy phase and the existence of glass-free grain boundaries. 相似文献
8.
Densification and Sintering Kinetics in Sintered Silicon Nitride 总被引:1,自引:0,他引:1
The sintering sequence of Y2 O3 -Al2 O3 -doped Si3 N4 was investigated with respect to the relationship between densification, α→β transformation, and microstructural development. Quenching studies were performed to reveal these interactions during a complete sintering cycle. Isothermal studies were conducted to examine the sintering kinetics and compared to Kingery's liquid-phase sintering model. The bulk density increased to ≥90% of theoretical density with only minor transformation taking place. Major transformation occurred in a late sintering stage and was accompanied by the development of elongated grains. The kinetic order of the densification process, taking into account an appropriate correction, was larger than any of the rate exponents predicted by the Kingery model, indicating that other single or mixed mechanisms were active. 相似文献
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Juliana Marchi José Carlos Bressiani Ana Helena de A. Bressiani 《Journal of the American Ceramic Society》2003,86(7):1208-1210
Silicon carbide is a promising structural ceramic used as abrasives and applied in metallurgical components, due to its low density, high hardness, and excellent mechanical properties. The composition and content of the additive can control liquid-phase sintering of SiC. Compositions based on the SiO2 –Al2 O3 –RE2 O3 system (RE = rare earth) have been largely used to promote silicon carbide densification, but most studies are not systematically presented. The aim of this work is to study the effect of several oxide additives in the SiO2 –Al2 O3 –Y2 O3 system on the densification of silicon carbide using experimental design. This technique seems to be effective in optimizing the values of maximum density with minimum weight loss. 相似文献
13.
Effect of Silicon Substitution on the Sintering and Microstructure of Hydroxyapatite 总被引:3,自引:0,他引:3
Iain R. Gibson Serena M. Best William Bonfield 《Journal of the American Ceramic Society》2002,85(11):2771-2777
The substitution of between 0 and 1.6 wt% silicon (Si-HA) in hydroxyapatite (HA) inhibited densification at low temperatures (1000°–1150°C), with these effects being more significant as the level of silicon substitution was increased. For higher sintering temperatures (1200°–1300°C), the sintered densities of HA and Si-HA compositions were comparable. Examination of the ceramic microstructures by scanning electron microscopy (SEM) showed that silicon substitution also inhibited grain growth at higher sintering temperatures (1200°–1300°C). The negative effect of silicon substitution on the sintering of HA at low temperatures (1000°–1150°C) was reflected in the hardness values of the ceramics. However, for higher sintering temperatures, e.g., 1300°C, where sintered densities were comparable, the hardness values of Si-HA compositions were equal to or greater than that of HA, reflecting the smaller grain sizes observed for the former. 相似文献
14.
Role of Carbon in the Sintering of Boron-Doped Silicon Carbide 总被引:3,自引:0,他引:3
William J. Clegg 《Journal of the American Ceramic Society》2000,83(5):1039-1043
The effect of carbon on the sintering of boron-doped SiC was studied. The free carbon present in the green compact was found to react with the SiO2 covering the surfaces of the SiC particles; however, even if no carbon was added, the surface SiO2 reacted with the SiC itself at a slightly higher temperature. This latter reaction was associated with the onset of substantial pore growth in the shrinking green body, which, as the pores continued to grow at higher temperatures, prevented complete densification. Therefore, the reaction of the SiC with the SiO2 may have led to the fracture of interparticle contacts, resulting in the onset of coarsening. Thus, the role of the carbon was to prevent reaction between the SiC and the surface SiO2 , by removing the SiO2 at a temperature below that at which this reaction could occur. 相似文献
15.
Fabrication of Dense Nanostructured Silicon Carbide Ceramics through Two-Step Sintering 总被引:3,自引:1,他引:3
Young-Il Lee Young-Wook Kim Mamoru Mitomo Doh-Yeon Kim 《Journal of the American Ceramic Society》2003,86(10):1803-1805
SiC powder compacts were prepared with Al2 O3 , Y2 O3 , and CaO powders. By two-step sintering, fully dense nanostructured SiC ceramics with a grain sizes of ∼40 nm were obtained. The grain size–density trajectories are compared with those of conventional sintering processes. 相似文献
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Isao Tanaka Giuseppe Pezzotti Taira Okamoto Yoshinari Miyamoto Mitue Koizumi 《Journal of the American Ceramic Society》1989,72(9):1656-1660
Fully densified silicon nitride without additives was fabricated by means of hot isostatic pressing. The sintering process of highly pure powder was investigated with special interest in the evolution of α–β phase transformation, densification, and microstructure development. It was observed that the transformation occurred without a liquid phase below 1730°C, which corresponds to the melting point of SiO2 . Above 1730°C, the densification and β-grain elongation accelerated concurrently because of the appearance of liquid SiO2 . However, full densification was attained at 1950°C together with marked grain growth. Flexural strength, microhardness, fracture toughness, and Young's modulus of sintered bodies were measured as a function of temperature. In the sintered body started from highly pure powder, excellent MOR behavior was found up to 1400°C. Impurity content of a few hundred ppm was found to be sufficient to make densification easy and to degrade high-temperature strength. 相似文献
18.
以α-Si3N4粉末为原料,Y2O3和MgAl2O4体系为烧结助剂,采用无压烧结方式,研究了烧结温度、保温时间、烧结助剂含量以及各组分配比对氮化硅致密化及力学性能的影响。结果表明:以Y2O3和MgAl2O4为烧结助剂体系,氮化硅陶瓷在烧结温度为1 600 ℃,保温时间为4 h,烧结助剂含量为12.5%(质量分数),Y2O3和MgAl2O4质量比为1∶1时,综合性能最好;氮化硅陶瓷显气孔率为0.21%,相对密度为98.10%,抗弯强度为598 MPa,维氏硬度为15.55 GPa。 相似文献
19.
Julin Wan Matthew J. Gasch Amiya K. Mukherjee 《Journal of the American Ceramic Society》2003,86(3):526-528
Starting with Si-C-N(-O) amorphous powders, and using the electric field assisted sintering (EFAS) technique, silicon nitride/silicon carbide nanocomposites were fabricated with yttria as an additive. It was found that the material could be sintered in a relatively short time (10 min at 1600°C) to satisfactory densities (2.96–3.09 g/cm3 ) using 1–8 wt% yttria. With decreasing yttria content, the ratio of SiC to Si3 N4 increased, whereas the grain size decreased from ∼150 nm to as small as 38 nm. This offers an attractive way to make nano-nanocomposites of silicon nitride and silicon carbide. 相似文献
20.
D. Doni Jayaseelan N. Kondo M. E. Brito T. Ohji 《Journal of the American Ceramic Society》2002,85(1):267-269
High-strength porous alumina has been fabricated with a microstructure control using the pulse electric current sintering (PECS) technique. During sintering the discharge, which is assumed to take place in the voids between the particles, is thought to promote the bridging of particles by neck growth in the initial stages of sintering, leaving high porosity. The effect of dopants (MgO, 200 ppm; TiO2 , 1000 ppm) and of secondary inclusions (3 vol% 3Y-TZP) on the constrained densification and the improvement in the mechanical behavior of porous alumina ceramics has been reported. The porosity of the fabricated porous alumina was controllable between 30% and 50% depending on the sintering temperature. The flexural strength of alumina having 30% and 42% porosity showed impressive values of 250 and 177 MPa, respectively. The dominance of the preferential neck growth of grains over densification significantly improved the mechanical properties of porous alumina, besides leaving high porosity. 相似文献