Tough Alumina/Polymer Layered Composites with High Ceramic Content

Ceramic composites found in nature, such as bone, nacre, and sponge spicule, often provide an effective resolution to a well‐known conflict between materials' strength and toughness. This arises, on the one hand, from their high ceramic content that ensures high strength of the material. On the other hand, various pathways are provided for stress dissipation, and thus toughness, due to their intricate hierarchical architectures. Such pathways include crack bridging, crack deflection, and delamination in the case of layered structures. On the basis of these inspiring ideas, we attempted here to create simultaneously strong and tough laminated alumina composite with high ceramic content. Composites were prepared from high‐grade commercial alumina with spin‐coated interlayers of ductile polymers (PMMA and PVA). The specimens' ultimate properties (strength, fracture toughness, and work of fracture) were measured by a four‐point bending method. In some cases, fracture toughness of the composites was increased by up to an order of magnitude, reminiscent of the natural layered composites. It is proposed that this increase may be attributed to an interlocking mechanism, often encountered in biological composites. The significance of sample architecture and the role of the interfacial and bulk properties of the interlayer material are discussed.     

压电陶瓷颗粒增韧陶瓷基复合材料研究进展

本文综述了压电陶瓷颗粒增韧陶瓷基复合材料的研究进展,重点讨论了增韧机理、极化及不同工艺对增韧效果的影响.分析认为,研究一种低成本、烧结性能较好且能够与基体稳定共存的压电材料,以及能够获得最佳性能的合适的制备工艺是目前的研究趋势,具有广阔的发展前景.     

Damage-Resistant SiC–AlN Layered Composites with Surface Compressive Stresses

Three-layer samples in the SiC-AlN system with outer layers richer in SiC, as well as monolithic samples of uniform composition, were fabricated by hot-pressing. The strain gage technique, previously described, was used to estimate residual compressive stress in the outer layers developed because of the difference in coefficients of thermal expansion between inner and outer layers. Bar-shaped samples were indented using a Vickers indenter under loads as high as 20 kg (196 N) on outer layers and were fractured in three-point bending. Three-layer samples with outer layers under compression exhibited increased resistance to the contact-induced damage in comparison to the monoclinic samples.     

纤维增强陶瓷基复合材料界面及增韧机制的进展

陶瓷基复合材料以其优异的耐高温、热稳定性好、耐磨损等性能,在高技术领域和航空航天领域有重要应用。界面在纤维和陶瓷基体之间起着决定性的作用,复合材料的界面相是纤维与基体连接的纽带,也是应力及其它信息传递的桥梁。本文分别从不同复合方式、复合材料的界面研究及纤维增强基体的增韧机制和界面的力学性能等方面进行了综述。     

Rolling-Contact Fatigue and Wear of CVD-SiC with Residual Surface Compression

The rolling-contact fatigue life and wear of CVD-SiC coatings with surface compression were studied using a three- ball-on-rod rolling-contact fatigue (RCF) tester. Two levels of surface compression in the coatings, approximately 190 μm thick, were introduced by using substrates of a liquid-phase sintered SiC and a SiC-30 vol% TiC to obtain desired thermal-expansion mismatches with the CVD-SiC. Residual surface compressions of 250 and 680 MPa were measured in the CVD-SiC coatings on SiC and SiC-30 vol% TiC substrates, respectively, by a strain-gage technique. In the RCF test, the fatigue life of the CVD-SiC coating with the moderate surface compression was limited by severe wear by a brittle fracture mechanism at a Hertzian contact stress of 5.5 GPa. The CVD-SiC coating on the SiC-30 vol% TiC composite, on the other hand, did not show measurable wear. A majority of the tests (11 out of 16) were suspended at 100 h or stopped due to failure of the steel balls. Five tests stopped due to spalling of the CVD-SiC coating at weak interfaces 10 to 15 μm below the contact surface. Examination of the microstructure of the CVD-SiC coating in cross sections revealed that the weak interfaces that led to the spalling were related to discontinuous growth of the CVD-SiC in the form of nodules or growth regions. Elimination of these defective structures is likely to enhance the tribological performance of surface-toughened CVD-SiC.     

偶联剂处理陶瓷颗粒增强聚丙烯复合材料的性能

用熔融共混法制备了陶瓷颗粒增强聚丙烯复合材料,测试了复合材料的力学性能,探讨了研究了表面处理对PP复合材料性能的影响。结果表明:偶联剂处理陶瓷颗粒表面后,复合材料的拉伸强度和冲击强度均比未处理的有所提高。拉伸断面的扫描电镜照片分析表明,未活化处理陶瓷颗粒与PP的界面粘结较差,界面发现许多空隙;而偶联剂KH-550活化处理后,陶瓷颗粒能与PP界面粘结良好,在拉伸过程中多数陶瓷颗粒被基体牢固粘附而难以脱出。     

Toughening of a Cordierite Glass–Ceramic by Compressive Surface Layers

An indentation fracture mechanics analysis is developed to characterize the toughening effects of a compressive surface layer in brittle materials. The analysis is used to describe the enhanced toughness of cordierite glass–ceramic laminate composites, in which thermal-expansion mismatch effects induced uniform stress in the exterior layers of the symmetric exterior:interior:exterior structures. Interpretation of indentation crack length and inert strength tests via the analysis shows that cracks can be viewed as experiencing discrete regions of decreasing stabilization on propagation from small cracks and complete containment within the compressive layer to large cracks and partial extension into the compensating tensile interior. The observations are described using a stress-intensity factor for circular cracks in linear stress fields that includes different base and surface values for extended cracks. Deconvolution of inert strength data for the model cordierite system studied suggested an increase in toughness from 1.4 MPa·m^1/2 for the base material to a peak of about 5 MPa·m^1/2 for a 1:18:1 composite structure, with attendant increases in strength and flaw tolerance.     

Modeling of Chemical Vapor Infiltration for Ceramic Composites Reinforced with Layered, Woven Fabrics

A homogeneous model is developed for the chemical vapor infiltration by one-dimensional diffusion into a system of layered plies consisting of woven tows containing bundles of filaments. The model predictions of the amount of deposition and the porosity of the sample as a function of time are compared with the predictions of a recent nonhomogeneous model with aligned holes formed by the weave. The nonhomogeneous model allows for diffusion through the aligned holes, into the spaces between plies, and into the gaps around filaments; i.e., three diffusion equations apply. Relative to the nonhomogeneous results, the homogeneous model underestimates the amount of deposition, since the absence of holes and spaces allows earlier occlusion of gaps around filaments and restricts the vapor infiltration.     

三元层状Ti2AlC陶瓷强化TiAl基复合材料的研究

三元层状Ti2AlC陶瓷作为H相的典型代表,兼具陶瓷和金属的优点,在TiAl基中引入部分Ti2AlC,制备的TiAl/Ti2AlC复合材料,兼具两者的优越性。简单介绍了Ti2AlC陶瓷的结构及其特性,同时叙述了其在制备TiAl基复合材料方面的研究进展,最后总结了其强化机制。     

陶瓷材料增韧机理的研究进展

脆性是制约陶瓷材料发展的主要因素,因此陶瓷的增韧是陶瓷材料研究领域的核心问题.本文重点介绍了陶瓷材料增韧技术,分析了陶瓷材料的增韧机理.最后,探讨了陶瓷材料增韧技术的研究现状和今后的发展方向.     

Strengthening and Toughening Mechanisms of Ceramic Nanocomposites

Crack-tip bridging by particles is considered to be one of the primary strengthening mechanisms of ceramic nanocomposites. Small, brittle particulate inclusions have been shown to cause crack-tip bridging at short distances behind the crack tip. This mechanism leads to modest toughness but a very steep R -curve, and it is the latter that produces the very high fracture strength of the ceramic nanocomposite. Localized high residual stress around the particles (particularly in the case of silicon carbide-alumina material) causes the strengthening mechanism to operate effectively, even at a small volume fraction of 5%. The present study predicts the magnitude of the toughness increase and the extent of R -curve behavior for the nanocomposite.     

Ceramic Composites with Multilayer Interface Coatings

Silicon carbide matrix composites have been fabricated from either ceramic-grade Nicalon^TM or Hi-Nicalon^TM fibers coated with an interface material consisting of six alternating carbon and silicon carbide layers. Initial efforts involved the use of chemical vapor infiltration to produce minicomposites (single tows of fibers). In subsequent work, forced-flow thermal-gradient chemical vapor infiltration was used to produce a single composite plate with a multilayer interface from ceramic-grade Nicalon fabric and two plates from Hi-Nicalon fabric, one with a single carbon layer and one with a multilayer interface. Tensile testing of the minicomposites and of specimens cut from the plates revealed typical composite behavior and strengths for the as-processed samples. Exposure of tensile specimens to 950°C air for 100 h resulted in large losses in strength and strain tolerance regardless of the interface coating. The results demonstrate that forced-flow thermal-gradient chemical vapor infiltration can be used to prepare multilayer interface material. The results also verified that relatively thick (>100 nm) single or multiple carbon layers are susceptible to oxidation that causes the loss of composite properties.     

玻璃纤维增强聚乳酸复合材料的增韧改性研究

通过双螺杆挤出共混的方式制备了玻璃纤维增强聚乳酸复合材料,并采用乙烯/醋酸乙烯共聚物(EVA)、马来酸酐接枝乙烯辛烯共聚物(POE-g-MAH)、马来酸酐接枝高密度聚乙烯(HDPE-g-MAH)增韧剂对该复合材料进行了增韧改性,系统研究了玻璃纤维添加量、增韧剂用量对复合材料力学性能的影响,并结合扫描电镜等仪器对其增强及增韧改性的机理进行了研究。结果表明:EVA,POE-g-MAH,HDPE-g-MAH不仅改善复合材料的冲击性能,而且所制备的复合材料的拉伸强度、弯曲强度也得到了一定程度的提高;与HDPE-g-MAH相比,EVA与POE-g-MAH对复合材料表现出更佳的增强增韧效果。     

Thermal Shock of Layered Ceramic Structures with Crack-Deflecting Interfaces

In this paper the influence of crack-deflecting interlayers on the thermal shock behavior of a ceramic body has been studied. It is observed that the presence of such interlayers inhibits the penetration of cracks into the body and that the magnitude of this effect is much greater than that of internal stresses or of possible increases in fracture energy of the layers, because cracking occurs in a manner different from that expected. A finite difference model has been used to estimate the temperature distribution in the body, from which the crack driving force and its variation with time and penetration into the body have been calculated. It is shown that these observations are consistent with quantitative predictions, if continued crack growth in the laminate requires that the stress in the outermost intact layer is equal to the failure strength of that layer, rather than the crack driving force for the overall penetrating crack being equal to the fracture energy of the material.     

聚合物基复合材料的增强增韧

介绍了聚合物基复合材料增强增韧的改性方法和机理,包括有机小分子、弹性体、刚性粒子、纤维以及碳纳米管增强增韧聚合物。并介绍了一些具有代表性的聚合物/增强增韧剂体系。并对聚合物基复合材料增强增韧的发展前景进行了展望。     

莫来石品体增韧泡沫陶瓷中晶体的生长过程

采用原位合成莫来石晶体增韧氧化铝质泡沫陶瓷。研究了原位合成莫来石晶体的生长过程。研究发现，在加热过程中，由硅溶胶引入的SiO2与泡沫陶瓷中的刚玉相发生反应，生成一种长约5μm纺锤状莫来石晶体，该反应在1220～1280℃温度范围内完成。     

层状硅酸盐改性的聚氨酯泡沫的制备及性能分析

在研究国内外现状的基础上,主要开展了探索聚氨酯泡沫制备最佳工艺配比及层状硅酸盐添加剂聚氨酯泡沫制备工艺并分析不同添加量对泡沫性能的影响两方面的实验研究。层状硅酸盐添加剂可改善聚氨酯的阻燃性,且随其添加量的增加聚氨酯的阻燃性能逐渐提高,但其压缩强度先上升后下降。加入层状硅酸盐是聚醚多元醇的2%时,聚氨酯复合材料的阻燃和力学的综合性能是最优的。     

Transformation Toughening in Composites Containing Dicalcium Silicate

By taking into account solid-state Compatibility relations in the system CaO-SiO₂-ZrO₂, a series of dense, tough CaZrO₃-β-Ca₂SiO₄ composites were obtained. The increase in K_IC and σ_f values observed is interpreted in terms of the β-Ca₂SiO₄→γ-Ca₂SiO₄ polymorphic transformation.