Cf／SiO2复合材料的组织性能与强韧化机理

采用真空热压烧结工艺制备了高致密的短C纤维（Cf)补强增韧SiO2基复合材料,研究了其组织结构、力学性能和强韧化机制。10％Cf/SiO2复合材料非晶态基体SiO2只发生部分晶化,Cf在基体中分布较均匀,并呈层状分布。复合材料强度、断裂韧性和断裂应变均基体显著改善,分别达到74MPa,2.4MPa.m^1/2和0．144％。压痕裂纹扩展行为和断口分析表明,Cf的桥接、拔出和诱导裂纹传转等是复合材料的强韧化机制。     

Room—temperature mechanical properties of WSi2／MoSi2 composites

Five Kinds of WSi2/MoSi2 composites were successfully prepared by mechanical alloying,IP and high temperature sintering techniques.And their hardness and fracture toughness were measured by the Vickers indentation fracture mode through an Hv-10A type sclerometer.The microstructure and morphology were investigated by a JSM-5600IV scanning electron microscope.Results show that the addition of 50% WSi2(in mole fraction)has remarkable hardening and toughening effects on the MoSi2 matrix.whose hardness value and fracture toughness value are increased about 60% and 86%,respectively.For WSi2/MoSi2 comosite,the hardening mechanisms are fine-grain and the second phase particles strengthening,and the toughening mechanisms include fine-grain,grain drawing,crack deflection,microbridge and bowing toughening.     

高强度高韧性铝合金基复合材料的制备和断裂机制

为解决金属基复氏韧性的缺点,采用宏观结构设计方法制备了断裂韧性达到相应铝合金水平的ＳｉＣｐ－ＬＤ２／ＬＤ２复合材料,与同体积分数的普通ＳｉＣｐ／ＬＤ２复合材料比较,其强化效果得以保持,并提高了材料的断裂力,断裂过程表明现出阶段性,避免了普通复合材料灾难性失效突然发生的缺点,高体积分数的ＳｉＣｐ－ＬＤ２复合材料棒之间未增强基体的塑性变形以及其对裂纹的阻断,使裂纹沿（ＳｉＣｐ－ＬＤ２）／（ＬＤ２）界面     

Fracture behavior of α-zirconium phosphate-based epoxy nanocomposites

The fracture behaviors of α-zirconium phosphate (α-ZrP) based epoxy nanocomposites, with and without core-shell rubber (CSR) toughening, were investigated. The state of exfoliation and dispersion of α-ZrP nanofiller in epoxy were characterized using X-ray scattering and various microscopy tools. The level of enhancement in storage moduli of epoxy nanocomposite against neat epoxy is found to depend on the state of exfoliation of α-ZrP as well as the damping characteristics of the epoxy matrix. The fracture process in epoxy nanocomposite is dominated by preferred crack propagation along the weak intercalated α-ZrP interfaces, and the presence of α-ZrP does not alter the fracture toughness of the epoxy matrix. However, the toughening using CSR can significantly improve the fracture toughness of the nanocomposite. The fracture mechanisms responsible for such a toughening effect in CSR-toughened epoxy nanocomposite are rubber particle cavitation, followed by shear banding of epoxy matrix. The ductility and toughenability of epoxy do not appear to be affected by the incorporation of α-ZrP. Approaches for producing toughened high performance polymer nanocomposites are discussed.     

Fabrication and fracture toughness of macro-toughening-designed composite

lINTR0DUCTIONParticleReinforcedMetalMatrixC0mp0s-ites(PMMCs)havehighspecificstrength,spe-cificmodulus,elevatedtemperatureproperties,res1stancetowearandlowcost.However,com-paniedlowductilityandtoughnessisonemainobstacletotheirapplicationforengineeringL','j.ManystudiesonSiCparticlereinforcedalu-.minum.ll.y.['v']showthattheadditionofpar-ticlenotonlyrefinesmatrixgrainbutalsoresultsinhighdensitydislocationsinthematrixneartheinterface.Particlesblocklong-distance-slipofthedislocationsinthema…     

SiCW／Y—TZP／Al2O3复合陶瓷的显微结构及其力学性能

研究了ＳｉＣＷ／Ｙ－ＴＺＰ／Ａｌ２Ｏ３系复合陶瓷的显微结构及其力学性能，通过透射电镜拉伸试样中的裂纹扩展形态与组织变化，分析了晶须与ＺｒＯ２相变增韧机制。结果表明，陶瓷体内各相结合致密，分布较为均匀，其室温强度和断裂韧度分别为１１００ＭＰａ和１１．９ＭＰａ．ｍ＾１／２，晶须拔出，裂纹偏转及ＺｒＯ２ｔ－ｍ相变是该复合材料的主要增韧机制。ＳｉＣ晶须和Ｙ－ＴＺＰ的共同作用，对复合材料强度和断裂韧性的提高     

Aging and fracture of human cortical bone and tooth dentin

Mineralized tissues, such as bone and tooth dentin, serve as structural materials in the human body and, as such, have evolved to resist fracture. In assessing their quantitative fracture resistance or toughness, it is important to distinguish between intrinsic toughening mechanisms, which function ahead of the crack tip, such as plasticity in metals, and extrinsic mechanisms, which function primarily behind the tip, such as crack bridging in ceramics. Bone and dentin derive their resistance to fracture principally from extrinsic toughening mechanisms, which have their origins in the hierarchical microstructure of these mineralized tissues. Experimentally, quantification of these toughening mechanisms requires a crack-growth resistance approach, which can be achieved by measuring the crack-driving force (e.g., the stress intensity) as a function of crack extension (“R-curve approach”). Here this methodology is used to study the effect of aging on the fracture properties of human cortical bone and human dentin in order to discern the microstructural origins of toughness in these materials.     

Influence of AlN addition on thermal and mechanical properties of cordierite-based glass/ceramic composites

Cordierite-based glass/ceramic composites doped with different volume fractions of AlN particles were successfully prepared by hot-pressing process. Thermal and mechanical properties of the composites were also investigated. Results show that the thermal conductivity, the flexural strength and fracture toughness of cordierite-based glass/AlN composites increase with increasing AlN content. The thermal conductivity of the composite doped with 50 vol.% AlN reaches 6.5 W/m K. By incorporation of 40 vol.% AlN, the flexural strength and fracture toughness of the composites increase 81 and 139% compared to the unreinforced cordierite-based glass matrix, respectively. XRD analysis indicated that no chemical reaction occurred between cordierite-based glass and AlN. The main strengthening and toughening mechanisms is load transfer and crack deflection.     

改善颗粒增强金属基复合材料塑性和韧性的途径与机制

评述了影响颗粒增强金属基复合材料塑性和韧性的各种因素,在此基础上深入研究了颗粒形状对ＳｉＣｐ／ＬＤ２复合材料塑性和断裂韧性的影响规律。采用有限单元法分析不同形状的ＳｉＣ颗粒增强的ＬＤ２复合材料的微区力学环境和整体力学行为,结果表明颗粒的尖锐化导致基体内应变集中和颗粒尖端断裂的可能性加剧,因而降低材料的塑性;而在外加载荷的作用下,由于复合材料基体整体均处于较高的加工硬化状态,因此颗粒形状对材料断裂韧     

Effects of rate on crack growth in a rubber-modified epoxy

The rate-dependent fracture behavior of a 10-phr rubber-modified epoxy was investigated using double-cantilever-beam tests at various crosshead speeds. Dramatic rate effects were observed in the R-curve behavior and in the relationship between the applied energy-release rate and the crack velocity. Furthermore, a transition between fracture with toughening mechanisms operating (kinetic crack growth) and brittle behavior (dynamic crack growth) was observed. This transition depended on the crack velocity and applied energy-release rate. Such behavior is expected to depend on how the intrinsic toughness and/or the extrinsic toughening mechanisms are influenced by strain rate. It was shown that the size of the process zone was only weakly dependent on the crack velocity until the onset of dynamic fracture. Furthermore, the extent of void growth was virtually independent of the crack velocity in the kinetic regime. These results appear to rule out the notion that crack-tip shielding is significantly affected by rate effects in this rubber-modified epoxy. Rather, the rate effects may arise from a rate-dependent intrinsic toughness. It was observed that the intrinsic toughness decreased significantly with increasing crack velocity. The crack instability was shown to be associated with an abrupt cessation of the development of the process zone, with both cavitation and void growth being totally suppressed.     

Mechanical properties evaluation of hot-pressed Si3N4–SiC(w) composites

Silicon nitride based ceramic composites have been prepared using an alternative development route, aiming to reach properties for structural applications. The prepared compositions were silicon nitride based matrix with aluminum nitride and yttrium oxide, as sintering aids, reinforced with silicon carbide whiskers. The powders were grounded/homogenized directly as received. Samples were obtained by uniaxial hot-pressing and, physical (specific mass, X-ray diffraction and microstructural analysis) and mechanical (microhardness, fracture toughness and flexural strength) properties were determined. The resulting high fracture toughness values were related to crack deflection and crack bridging toughening mechanisms, observed by SEM.     

DESIGN AND PREPARATION OF SILICON NITRIDE COMPOSITE WITH HIGH FRACTURE TOUGHNESS AND NACRE STRUCTURE

ＤＥＳＩＧＮＡＮＤＰＲＥＰＡＲＡＴＩＯＮＯＦＳＩＬＩＣＯＮＮＩＴＲＩＤＥＣＯＭＰＯＳＩＴＥＷＩＴＨＨＩＧＨＦＲＡＣＴＵＲＥＴＯＵＧＨＮＥＳＳＡＮＤＮＡＣＲＥＳＴＲＵＣＴＵＲＥＹＨｕａｎｇ；Ｈ．ＮＨａｏ；Ｙ．Ｌ．ＣｈｅｎａｎｄＢ．Ｌ．Ｚｈｏｕ（１）Ｄｅ...     

ZrO2+SiC颗粒强韧化MoSi2复合材料的显微组织和性能

通过显微组织观察和力学性能测试 ,初步探讨了ZrO2 SiC颗粒对MoSi2 基体材料的强韧化效果和机制。结果表明 ,材料复合具有较好的强韧化协同效应 ,复合材料中ZrO2 相和少量SiC颗粒在基体的间层作用 ,可抑制MoSi2 晶粒长大 ;断口呈现晶粒细小、裂纹扩展曲折和沿晶与穿晶混合型断裂等特征 ;ZrO2 SiC颗粒通过弥散强化和细化晶粒使复合材料强度提高 ,通过晶粒细化、裂纹偏转和分支、微裂纹形成等机制的综合作用使复合材料增韧     

Sm_2Zr_2O_7/SiC复合材料及其断裂韧性的研究

以ZrOCl_2·8H_2O、Sm_2O_3为原料通过化学共沉淀法制备Sm_2Zr_2O_7粉体,并运用传统固相法,热压(1300 ℃,40 MPa)制备2.5%、5%、7.5%、10%SiCp(质量分数)的Sm_2Zr_2O_7/SiC块体复合材料.压痕法测定材料的断裂韧性并结合场发射扫描电镜观察,分析裂纹扩展方式.结果显示,随着复合材料中SiC_p含量的增加,裂纹偏转增加,材料的断裂韧性明显提高.裂纹偏转分叉机制为其主要的增韧机制.     

Processing and characteristics of TiB_2 toughened B-Ti-C composites

1　INTRODUCTIONBoroncarbidehasmanyoutstandingproperties ,suchasextremelyhighhardness (385 0kg·mm- 2 ,loweronlytodiamondandcubicboronnitride) ,ex cellentstabilitytowardtheeffectofvariousacids ,highmeltingpoint (2 4 5 0℃ ) ,highvalueofelasticmodulus (4 5 0GPa)andlowdensity(2 .5 2 g·cm- 3) .Allthesepropertiesallowboroncarbidetocoverawiderangeoftechnologicalapplicationsincludingcut tingtools ,wearresistantcomponentsandlightarmormaterials[14 ] .However ,owingtothestrongcovalentbondsinitslat…     

Fracture processes and mechanisms of crack growth resistance in human enamel

Human enamel has a complex micro-structure that varies with distance from the tooth’s outer surface. But contributions from the microstructure to the fracture toughness and the mechanisms of crack growth resistance have not been explored in detail. In this investigation the apparent fracture toughness of human enamel and the mechanisms of crack growth resistance were evaluated using the indentation fracture approach and an incremental crack growth technique. Indentation cracks were introduced on polished surfaces of enamel at selected distances from the occlusal surface. In addition, an incremental crack growth approach using compact tension specimens was used to quantify the crack growth resistance as a Junction of distance from the occlusal surface. There were significant differences in the apparent toughness estimated using the two approaches, which was attributed to the active crack length and corresponding scale of the toughening mechanisms.     

热处理对多层复合增韧涂层的微观结构及力学性能的影响

AT40 陶瓷涂层与黏结层界面裂纹萌生、扩展是导致涂层失效的主要原因,制备多层陶瓷 / 金属低应力涂层为陶瓷涂层增韧的方法之一。利用 APS(大气等离子喷涂)在 Q235 上制备 AT40-NiAl-AT40-NiAl 四层复合多层涂层并对复合多层进行热处理。使用 SEM、EPMA、3PB 等表征手段研究热处理对四层复合金属-陶瓷涂层的微观结构及涂层断裂韧性的影响。结果表明,热处理过程中陶瓷层-黏结层界面、陶瓷层富 Al 相富 Ti 相界面均发生了元素扩散;热处理后陶瓷层硬度增加 30%,复合涂层断裂韧性提高。热处理过程中元素扩散形成的氧化物一方面在黏结层与陶瓷层之间形成钉扎效应增强黏结性,另一方面填充涂层中的孔隙、裂纹等缺陷提高涂层的硬度,降低裂纹扩展的面积从而提升涂层的断裂韧性。多层金属陶瓷沉积形成的复合陶瓷涂层及对其使用热处理的方法能有效提升 AT40 等陶瓷涂层的断裂韧性,对解决铁基零部件表面耐磨陶瓷容易脆断失效和扩展陶瓷涂层的应用范围提供了新的思路。     

MICROSTRUCTURE AND FRACTURE FEATURE OF ZTA-SiC_W COMPOSITE

A ZTA-SiC_W ceramic composite of room temperature strength 935—1110 MPa and frac-ture toughness 9.7MPa·m~(1/2) was prepared using the sol-gel proeess.Its microstructure andfracture feature have been examined by means of X-ray diffraction analysis and electron mi-croscope observations.The results show that the whiskers are well dispersed and the matrixhas an obvious texture character.Between the whisker and matrix,there is a great number oftranscrystalline and transcrystalline connective relation other than part of conventionalpolycrystalline connective ones.Certain secondary cracks closely related with local whiskergroup are found on the fracture surface.It may be a new reinforcing and toughening mecha-nism by whisker group,of which the whiskers in the local whisker group arrest synergeticallythe crack propagation accompaning with the formation of secondary cracks.     

TOUGHENING OF IN SITU SYNTHESIZED MoSi_2-SiC COMPOSITE AT ROOM TEMPERATURE

二．InttodttCt1OllMoslZ meets thebaslc requirements for ahlgh temperature structuralmaterlal．凡reXampk,nhas a hi吵一king pdntd2030”C,rd扒IV*y high re幻s枯nCe扣high比m－perature。ldatlon,alow density of6．249/cm’,ahlgh modulus,adequate strength at1200－