Si3N4及其复合材料强韧化研究进展

简述了氮化硅陶瓷的结构、性能和制备工艺，并分别通过自增韧补强、纤维／晶须强韧化、层状结构强韧化、相变强韧化以及颗粒弥散强韧化等方法对氮化硅陶瓷的强韧化研究进行了分类叙述。     

Seamless Joining of Silicon Nitride Ceramics

High-strength joining of Si₃N₄ 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 Si₃N₄. Optimization of the process led to Si₃N₄/Si₃N₄ joints with room-temperature bend strengths as high as 950 MPa, corresponding to more than 90% of the bulk strength of the Si₃N₄. 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 Si₃N₄ measured at these temperatures.     

Electrical Joining of Silicon Nitride Ceramics

The electrical joining of sintered Si₃N₄ ceramics by Joule heating was studied. A mixture of CaF₂/kaolinite (70/30 wt%) with excellent electroheating characteristics and reactivity with Si₃N₄ 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 Si₃N₄. 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─Si₃N₄. 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.     

Liquid-Phase Bonding of Silicon Nitride Ceramics

Mg-Si-O-N glasses were used to bond dense Si₃N₄ 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.     

Sintering Silicon Nitride Ceramics in Air

Silicon nitride (Si₃N₄) ceramics, prepared with Y₂O₃ and Al₂O₃ 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% Y₂O₃ and 3 wt% Al₂O₃. Densification is accompanied by a small weight gain (typically <1–2 wt%), because of limited passive oxidation of the sample. Complete α- to β-Si₃N₄ transformation can be achieved at temperatures above 1650°C, although a low volume fraction of Si₂N₂O is also observed to form below 1750°C. Partial crystallization of the residual grain-boundary glassy phase was also apparent, with β-Y₂Si₂O₇ being noted in the majority of samples. The microstructures of the sintered materials exhibited typical β-Si₃N₄ elongated grain morphologies, indicating potential for low-cost processing of in situ toughened Si₃N₄-based ceramics.     

Stress-Enhanced Oxidation of Silicon Nitride Ceramics

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 Si₃N₄ ceramics to stress corrosion. The effect of stress corrosion on mechanical properties is discussed.     

Electrically Conductive CNT-Dispersed Silicon Nitride Ceramics

Carbon nanotube (CNT)-dispersed Si₃N₄ 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 Y₂O₃ and Al₂O₃ 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 Si₃N₄ ceramics with Y₂O₃–Al₂O₃–TiO₂–AlN were originally used as a wear material, electrically conductive Si₃N₄ ceramics are expected to be applied for high-performance static-electricity-free bearings for aerospace and other high-performance components.     

Si3N4陶瓷烧结中烧结助剂的研究进展

研究了多种烧结助剂对氮化硅烧结性能和烧结过程的影响.研究表明,多组分助剂比单一组分助剂对氮化硅的助烧效果好,其中稀土氧化物和MgO-Al2O3-SiO2体系比较受重视.     

Fracture Behavior of Multilayer Silicon Nitride/Boron Nitride Ceramics

The fracture behavior of multilayer Si₃N₄/BN ceramics in bending has been studied. The materials were prepared by a process of tape casting, coating, laminating, and hot pressing. The Si₃N₄ 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.     

氧化锆复合氮化硅陶瓷

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。     

氮化硅陶瓷在现代制造业中的应用

本文论述了氮化硅结构陶瓷材料的性能,着重介绍了此种材料在国内外制造业中的应用现状,也讨论了氮化硅陶瓷的缺陷及研究方向。     

多孔氮化硅陶瓷的研究进展

综述了多孔氮化硅陶瓷材料的国内外研究现状和进展,介绍了多孔氮化硅陶瓷的主要制备方法,分析了微观组织对多孔氮化硅陶瓷力学性能的影响,并与其他多孔陶瓷进行了性能比较,最后展望了多孔氮化硅陶瓷的发展前景.     

Preparation of β-Silicon Nitride Seeds for Self-Reinforced Silicon Nitride Ceramics

This paper describes a method for the preparation of silicon nitride (Si₃N₄) 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 Si₃N₄ and 0.5 wt% Y₂O₃ 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.     

新奇的生物材料制碳化物陶瓷工艺

概述了木材等生物材料制碳化硅及其复合材料的工艺。列举了碳化硅晶须，木质碳化硅，碳化硅反射镜，波纹蜂窝及叠层碳化硅陶瓷的制备实例。     

氮化硅陶瓷的制备及进展

本文着重介绍了氮化硅陶瓷的制备工艺，提高氮化硅陶瓷高温性能的方法以及改善共断裂韧性的途径，并展望了氮化硅陶瓷的研究前景。     

氮化硅常压烧结研究进展

本文着重论述了氮化硅陶瓷常压烧结过程中助烧剂的选择、烧结机理和高温性能的改善方面的研究进展。     

Oxidation Behavior of NBD 200 Silicon Nitride Ceramics

The oxidation behavior of NBD 200 Si₃N₄ 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 Si₃N₄ than for other Si₃N₄ 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⁺.     

氮化硅陶瓷的制备及进展

本文郑重介绍了氮化硅陶瓷的制备工艺、提高氮化硅陶瓷高温性能的方法以及改善其断裂韧性的途径,并展望了氮化硅陶瓷的研究前景。     

Elevated-Temperature Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics

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.     

Crack Deflection and Propagation in Layered Silicon Nitride/Boron Nitride Ceramics

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 (Si₃N₄) layers separated by boron nitride/silicon nitride (BN/Si₃N₄) interphases have been manufactured and tested. Flexural tests reveal that the crack path is dependent on the composition of the interphase between the Si₃N₄ layers. Experimental measurements of interfacial fracture resistance and frictional sliding resistance show that both quantities increase as the Si₃N₄ 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.