共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Mani Gopal Mark Sixta Lutgard De Jonghe Gareth Thomas 《Journal of the American Ceramic Society》2001,84(4):708-712
High-strength joining of Si3 N4 ceramics has been achieved by developing a process that effectively eliminates the seam, and may allow for fabrication of large or complex silicon nitride bodies. This approach to joining is based on the concept that when sintering aids are effective in bonding individual grains, they could be equally effective in joining bulk pieces of Si3 N4 . Optimization of the process led to Si3 N4 /Si3 N4 joints with room-temperature bend strengths as high as 950 MPa, corresponding to more than 90% of the bulk strength of the Si3 N4 . At elevated temperatures of 1000° and 1200°C joint strengths of 666 and 330 MPa, respectively, were obtained, which are the highest values reported to date for these temperatures. These bend strengths are also more that 90% of the strength of bulk Si3 N4 measured at these temperatures. 相似文献
3.
Koji Okuda Hiroshi Takai Tokumitsu Nishi Hiroaki Yanagida 《Journal of the American Ceramic Society》1993,76(6):1459-1465
The electrical joining of sintered Si3 N4 ceramics by Joule heating was studied. A mixture of CaF2 /kaolinite (70/30 wt%) with excellent electroheating characteristics and reactivity with Si3 N4 ceramics was selected as a joining agent. The optimum conditions for electrical joining were determined using this joining agent. Analysis of the joint obtained under optimum conditions revealed that joining was accomplished by the formation of reaction zones and a joining layer through the mutual diffusion of the components in the joining agent and the sintering aids in the Si3 N4 . The joint layer was composed of a glassy substance consisting of Ca─Al─Si─Y─O─(F)─(N) and contained a few particles of β─Si3 N4 . Four-point bend tests indicated that joined bodies could be obtained which maintained a strength of about 300 MPa up to 800°C. Finally, a comparative study was made with a joint obtained using furnace heating. These results indicated that the joints obtained using electrical joining were superior to those produced in the furnace. 相似文献
4.
Liquid-Phase Bonding of Silicon Nitride Ceramics 总被引:1,自引:0,他引:1
Mg-Si-O-N glasses were used to bond dense Si3 N4 ceramic pieces by a liquid-phase diffusion bonding mechanism. In this case, it was difficult to achieve defect-free bonding because, at low nitrogen content in the glass, a large mismatch in thermal expansion coefficient produced cracks perpendicular to the bonding glass layer. With an increase in nitrogen content, the glass layer became frothy and contained "bubbles." However, when a small amount of elemental silicon was added to the glass, volatile reaction was suppressed and intimate bonding was achieved without thermal cracks. 相似文献
5.
Silicon nitride (Si3 N4 ) ceramics, prepared with Y2 O3 and Al2 O3 sintering additives, have been densified in air at temperatures of up to 1750°C using a conventional MoSi2 element furnace. At the highest sintering temperatures, densities in excess of 98% of theoretical have been achieved for materials prepared with a combined sintering addition of 12 wt% Y2 O3 and 3 wt% Al2 O3 . Densification is accompanied by a small weight gain (typically <1–2 wt%), because of limited passive oxidation of the sample. Complete α- to β-Si3 N4 transformation can be achieved at temperatures above 1650°C, although a low volume fraction of Si2 N2 O is also observed to form below 1750°C. Partial crystallization of the residual grain-boundary glassy phase was also apparent, with β-Y2 Si2 O7 being noted in the majority of samples. The microstructures of the sintered materials exhibited typical β-Si3 N4 elongated grain morphologies, indicating potential for low-cost processing of in situ toughened Si3 N4 -based ceramics. 相似文献
6.
Silicon nitride ceramics show an accelerated oxidation rate under load in air. This phenomenon was observed for porous and dense ceramics with and without additives in a wide temperature range (700°–1450°C) and can be interpreted as stress corrosion in oxygen-containing environments. Stresses cause an alteration of the amount and composition of oxidation products, formation of pits and cracks on stressed parts of specimens, and changes of the surface coloration and oxide scale morphology. Both tensile and compressive stresses can affect the oxidation process. An exponential dependence of mass gain on stress was found. On the other hand, oxidation of silicon nitride-based ceramics can affect the material response to mechanical stresses as, for example, deformation, cavitation and cracking. Stress-assisted chemical reaction at lower temperatures and stress-affected diffusion at higher temperatures seem to be the main reasons for the susceptibility of Si3 N4 ceramics to stress corrosion. The effect of stress corrosion on mechanical properties is discussed. 相似文献
7.
Junichi Tatami Tomofumi Katashima Katsutoshi Komeya Takeshi Meguro Toru Wakihara 《Journal of the American Ceramic Society》2005,88(10):2889-2893
Carbon nanotube (CNT)-dispersed Si3 N4 ceramics with electrical conductivity were developed based on the lower temperature densification technique, in which the key point is the addition of both TiO2 and AlN as well as Y2 O3 and Al2 O3 as sintering aids. This new ceramic with a small amount of CNTs exhibits very high electrical conductivity in addition to high strength and toughness. Since Si3 N4 ceramics with Y2 O3 –Al2 O3 –TiO2 –AlN were originally used as a wear material, electrically conductive Si3 N4 ceramics are expected to be applied for high-performance static-electricity-free bearings for aerospace and other high-performance components. 相似文献
8.
9.
The fracture behavior of multilayer Si3 N4 /BN ceramics in bending has been studied. The materials were prepared by a process of tape casting, coating, laminating, and hot pressing. The Si3 N4 layers were separated by thin, weak BN interlayers. Crack patterns in bending bars were examined with a scanning electron microscope. The weak layers deflected cracks in bending and thus prevented catastrophic failure. In one well-aligned multilayer ceramic A, a main crack propagated through the specimen although along a zigzag path. A second multilayer ceramic B was made to simulate a wood grain structure. Its failure was dominated by shear cracking along the weak BN layers. Besides crack deflection, interlock bridging between toothlike layers in the wake of the main crack appeared also to contribute to toughening. 相似文献
10.
刘大成 《陶瓷研究与职业教育》2000,(4)
分析了二氧化锆的性质及氧空位对二氧化锆相变的影响 ,讨论了二氧化锆韧化氮化硅陶瓷的影响因素 ,提出了二氧化锆韧化氮化硅陶瓷时避免氮化锆生成、促进复相氮化硅陶瓷烧结的途径。 相似文献
11.
12.
13.
Peelamedu D. Ramesh Rainer Oberacker Michael J. Hoffmann 《Journal of the American Ceramic Society》1999,82(6):1608-1610
This paper describes a method for the preparation of silicon nitride (Si3 N4 ) seeds that have an average aspect ratio of ∼4. The seeds are prepared via heat treatment of a powder mixture that contains alpha-phase-rich Si3 N4 and 0.5 wt% Y2 O3 at a temperature of 1800°C and a nitrogen pressure of 35 kPa. A Y-Si-O-N liquid forms during heat treatment; this liquid acts as a flux for seed precipitation. During cooling, the Y-Si-O-N liquid transforms to a thin intergranular grain-boundary phase and causes strong agglomeration of the seeds. The seeds can be isolated by dissolving the grain-boundary phase in hot phosphoric acid, followed by an ultrasonic treatment (for 30 min). The method can be used to produce large quantities of seeds. 相似文献
14.
15.
16.
17.
Priya Mukundhan Jianqing Wu Henry H. Du 《Journal of the American Ceramic Society》1999,82(8):2260-2262
The oxidation behavior of NBD 200 Si3 N4 containing 1 wt% MgO sintering aid was investigated in oxygen at 900°-1300°C. The oxide growth followed a parabolic rate law with an apparent activation energy of 260 kJ/mol. The oxide layers were enriched with sodium and magnesium because of outward diffusion of intergranular Na+ and Mg2+ cations in the ceramics. The 2-4 orders of magnitude higher oxidation rate for NBD 200 Si3 N4 than for other Si3 N4 ceramics with a similar amount of MgO could be attributed to the presence of sodium. The oxidation process was most likely rate limited by grain-boundary diffusion of Mg2+ . 相似文献
18.
19.
Elevated-Temperature Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics 总被引:1,自引:0,他引:1
A unique, all-ceramic material capable of nonbrittle fracture via crack deflection and delamination has been mechanically characterized from 25° through 1400°C. This material, fibrous monoliths, was comprised of unidirectionally aligned 250 μm diameter silicon nitride cells surrounded by 10 to 20 μm thick boron nitride cell boundaries. The average flexure strengths of fibrous monoliths were 510 and 290 MPa for specimens tested at room temperature and 1300°C, respectively. Crack deflection in the BN cell boundaries was observed at all temperatures. Characteristic flexural responses were observed at temperatures between 25° and 1400°C. Changes in the flexural response at different temperatures were attributed to changes in the physical properties of either the silicon nitride cells or boron nitride cell boundary. 相似文献
20.
Desiderio Kovar M. D. Thouless § John W. Halloran 《Journal of the American Ceramic Society》1998,81(4):1004-1112
Crack deflection and the subsequent growth of delamination cracks can be a potent source of energy dissipation during the fracture of layered ceramics. In this study, multilayered ceramics that consist of silicon nitride (Si3 N4 ) layers separated by boron nitride/silicon nitride (BN/Si3 N4 ) interphases have been manufactured and tested. Flexural tests reveal that the crack path is dependent on the composition of the interphase between the Si3 N4 layers. Experimental measurements of interfacial fracture resistance and frictional sliding resistance show that both quantities increase as the Si3 N4 content in the interphase increases. However, contrary to existing theories, high energy-absorption capacity has not been realized in materials that exhibit crack deflection but also have moderately high interfacial fracture resistance. Significant energy absorption has been measured only in materials with very low interfacial fracture resistance values. A method of predicting the critical value of the interfacial fracture resistance necessary to ensure a high energy-absorption capacity is presented. 相似文献