颗粒增韧陶瓷裂纹扩展微观过程

对于第二相颗粒增韧的复相陶瓷，颗粒热膨胀系数ａｐ与基体热膨胀系数ａｍ之间的匹配关系是决定增韧效果的主要因素。当两相弹性模量相当，颗粒粒径小于应力诱导微开裂的粒径，且ａｐ〉ａｍ时，残余热应力场的存在将会使扩展的裂纹在颗粒周围基体中产生较大的裂纹偏转，由此产生明显的增韧效果；而当ａｐ〈ａｍ时，扩展的裂纹将首先达到两相的界面，此时裂纹有可能沿两相界面偏转，也有可能穿过颗粒，这取决于颗粒的表面能、粒径、形     

TiB2／SiCw复合材料增韧机理的微观分析

在ＴｉＢ２／ＳｉＣｗ基体中加入适量的ＳｉＣｗ可以明显地提高其断裂韧 性ＫＩＣ，其它机械性能也有不同程度的改善。ＳＥＭ、ＴＥＭ微观分析表明：在具有较高ＫＩＣ值的ＴｉＢ２／ＢｉＣｗ陶瓷复合材料中，ＳｉＣｗ与ＴｉＢ２晶粒之间有较适宜的界面结合，两相之间未发现有明显的界面化学反应用，当该复合材料发生断裂时，其内部出现晶须拔出，裂纹桥连，裂纹偏转三种增韧机制。     

不同基体材质的Sm_2Ce_2O_7涂层热冲应力的数值模拟

采用ANSYS软件对Ni、45钢、SiC_f/SiC、2Cr13、1Cr13Ni9Ti五种不同基体Sm_2Ce_2O_7涂层的热冲击应力进行了计算,系统研究了基体材质对热应力的影响规律。结果表明,不同基体材质涂层均存在较大的热应力,最大热应力绝对值出现在热冲击瞬间,35 s后趋于稳定,径向应力的影响远大于轴向与剪切方向;径向应力在横向距离小于12mm时保持稳定,横向距离在12～18 mm范围内,应力梯度逐渐增大;SiC_f/SiC基体在表面及表面层/粘结层界面的应力状态为压应力,且表面径向、表面及表面层/粘结层界面的轴向应力梯度均低于其他基体涂层,有利于界面的结合及防止横向裂纹的扩展;热膨胀系数的差异造成SiC_f/SiC基体涂层与其他金属基体涂层的体积形变方向不一致,同时粘结层/基体界面应力绝对值及应力梯度略大于2Cr13基体涂层,基体的热膨胀系数是影响热冲击性能的关键因素之一。     

纤维增强复合材料中桥联纤维对裂纹的阻裂机理

基于应力强度因子K叠加原理，在考虑纤维桥联和拔出两种主要增韧机理的前提下，建立了裂纹尖端附近桥联纤维对复合材料基体微裂纹扩展的阻滞作用的理论模型；从裂纹扩展、纤维桥联及纤维断裂拔出的实际破坏的物理过程出发，推导出桥联纤维对裂纹扩展阻滞效应的简单实用的解析计算公式；解析公式及算例计算结果表明：纤维的体积分数、纤维和基体界面间的摩擦力大小等对微裂纹扩展的阻滞作用具有明显的影响，纤维的体积分数及界面摩擦力越大，对微裂纹扩展的阻滞效应越好。     

碳化硅晶须增强氮化铝复合材料的机械性能和界面研究

本研究应用热压工艺制备了致密ＳｉＣｗ／ＡｌＮ复合材料，其晶须的质量含量为１０％～３０％。当复合材料中晶须的质量含量达到３０％时，其弯曲强度增加了８５％，韧性提高了５０％。用ＳＥＭ和ＴＥＭ观察了材料的显微结构，指出弯曲强度增加是由于荷载从基体转移到晶须。断裂韧性的增加是由于裂纹偏转、裂纹分支和钉扎等作用引起。用ＨＲＥＭ对ＡｌＮ基体与ＳｉＣ晶须界面进行了初步分析和研究。     

晶须长径比对复合材料力学行为影响的模拟

在单向晶须增强树脂基复合材料的轴对称模型和已有研究成果基础上,利用有限元分析方法,研究该类复合材料中晶须长径比的变化对材料整体力学行为的影响.结果表明:1)晶须长径比对晶须应力作用明显大于对基体的影响;2)晶须的长径比h/r≤30时,随着晶须长径比的增大,发生在晶须端部处的集中应力急剧增加;但当长径比h/r≥30时,长径比的进一步增加对集中应力影响不大;3)随着晶须长径比的增大,界面剪切应力减小,分布曲线下移;但当长径比h/r≥30时,长径比的进一步增加对剪切应力影响不大;4)随着晶须长径比的增加,复合材料的拉伸强度逐渐增大.     

SiC晶须增韧氧化铝复合材料的韧性和温度的关系

研究了ＳｉＣ晶须增韧氧化铝复合材料在空气中80 0℃ ,10 0 0℃ ,130 0℃和 140 0℃下的增韧机理。结果表明 ,在室温时 ,其增韧机理主要是由于裂纹面晶须的桥接作用。随着温度的升高 ,由于ＳｉＣ晶须和氧化铝基质介面残余应力的减小 ,桥的牵引作用被削弱。最终 ,高于 130 0℃时 ,复合材料的Ｒ 曲线几乎是平坦的 ,表明桥的牵引力消失。10 0 0℃以上 ,主裂纹周围发现一个微裂纹带。形成原因认为是ＳｉＣ晶须和氧化铝基质颗粒介面发生的氧化反应 ,导致了空洞的扩散 ,并且界面的空洞与穿晶的空洞联接起来 ,在应力增强时 ,微裂纹带对主裂纹起盾护…     

几种瓷砖铺贴方法简介

在瓷砖铺贴施工时，瓷砖层和基体面之间能作微小相对移动，对于避免瓷砖层受应力破坏是十分必要的。几百年前，欧件队发明了一种铺贴瓷砖的方法，即在基体和瓷砖层之间铺一层破，使基体和瓷砖层能作自由的相对移动，如图1所示。这种方法现在仍在一些国家广泛应用。但由于铺贴层厚度较大，费工费料，该法已逐渐被淘汰。人们根据纤维（晶须）增韧陶瓷的原理，又发明了一种新的铺贴瓷砖方法，把作为中间过渡层的砂子用水泥砂浆代替，并在砂浆中埋设了裂纹阻断膜（图2），以阻止应力产生的裂纹向砖层扩展。但是，埋有裂纹阻断膜的砂浆层本身也是…     

偶联剂对T-ZnO晶须/环氧树脂复合材料的影响

研究了偶联剂KH－560对T－ZnO晶须／环氧树脂复合材料的影响。结果表明：偶联剂KH－560分子一端通过化学键进入环氧树脂的大分子中，另一端与T－ZnO晶须形成较强的氢键，在晶须与基体之间形成有效界面层，起到桥接基体与晶须和吸收能量的作用，有利于T－ZnO晶须起增韧增强作用。偶联剂在晶须表面形成薄层有利于提高材料的拉伸和弯曲强度，而较厚层可形成柔性的缓冲区，有利于吸收应力，提高压缩和冲击性能。     

碳化硅晶须改性反应烧结碳化硅陶瓷的显微结构及性能

以碳化硅晶须为增强体、碳化硅--碳为基体制备晶须增强反应烧结碳化硅复合材料,研究了碳化硅晶须、碳含量对复合材料显微结构与性能的影响。结果表明:碳化硅晶须经高温反应烧结后仍保持表面的竹节结构,且晶须增强体与反应烧结碳化硅基体间形成适中的界面结合强度;材料断口处有明显的晶须拔出,当碳黑含量为6%(质量分数)时,随着晶须含量的增加,材料的抗弯强度从200MPa提高到310MPa(晶须含量15%),当碳黑含量为18%时,随着晶须含量的增加,材料断裂韧性从3.3MPa·m1/2提高到4.3MPa·m1/2;碳化硅晶须含量过高时,晶须的"搭桥"效应导致材料中含有较多的游离硅,限制了材料力学性能进一步提高;微氧化处理使材料表面形成致密、均匀的氧化膜,可显著提高反应烧结碳化硅的抗弯强度和断裂韧性。     

Effects of Interfacial Films on Thermal Stresses in Whisker-Reinforced Ceramics

Toughening of whisker-reinforced (or fiber-reinforced) ceramics by whisker pullout requires debonding at the whisker/matrix interface. Compressive clamping stresses, which would inhibit interface debonding and/or pullout, are expected in composites where the matrix has a higher thermal expansion coefficient than the whisker. Because such mismatch in thermomechanical properties can result in brittle composites, it is important to explore approaches to modify the thermal stresses in composites. As a result, the effects of a film at the whisker/matrix interface on the stresses due to thermal contraction mismatch upon cooling are considered in this study. Analysis of various properties of the film are considered for the whisker/matrix systems, in particular for SiC/Al₂O₃, SiC/cordierite, and SiC/mullite composites. Reduction of thermomechanical stresses is shown to occur when the interfacial film has a low Young's modulus. Also, when the whisker has a lower thermal expansion coefficient than the matrix (e.g., SiC/Al₂O₃), the interfacial stresses generated during cooling decrease as the thermal expansion coefficient of the film increases.     

Effect of the size of Sic whiskers on the toughness of alumina-based composite materials

The effect of the dimensions of SiC whiskers on the strength and toughness of hot-pressed composites with a 20% volume fraction of whisker reinforcement was studied. It was established that the mechanical properties of the composites were improved only on introducing whiskers with the diameters, within 1.5–2.5 μm. These materials also exhibited a higher resistance to crack propagation. Crystals of smaller diameter had a negative effect on the mechanical properties, which was explained by bundle formation. There is a definite critical content of whiskers ensuring their uniform distribution in the matrix, and this value decreases on reducing the whisker diameter. A correlation was established between composite toughness and the level of average residual compressive stresses in the whiskers.     

晶须补强陶瓷基复合材料界面研究进展

结合国内外的工作，介绍了晶须补强陶瓷复合材料界面研究的最新进展，包括：晶须表面化学；界面物理和化学相容性，界面应力和涂层对复合材料力学性能的影响；晶须涂层工艺，界面研究发展动向。     

Preparation and Mechanical Properties of SiC Whisker and Nanosized Mullite Particulate Reinforced TZP Composites

The influence of the addition of nanometer mullite particulates and SiC whiskers coated with alumina on the mechanical properties of tetragonal zirconia polycrystals (TZP) was studied. With increasing mullite( p ) content the high-temperature flexural strength increased, and a maximum value of 360 MPa at 1000°C was reached at 15 vol% mullite( p . Furthermore, 10 vol% SiC( w ) reinforced 15 vol% mullite/TZP composites improved the high-temperature strength up to 490 MPa at 1000°C, 2.7 times that of pure TZP matrix. This high-temperature strengthening is attributed to load transfer from TZP matrix to SiC( w ) and mullite particulates. Significant whisker pull-out and interface debonding were also observed on the fractured surfaces when SiC( w ) was coated with Al₂O₃ film.     

Effect of entropy penalty on selective distribution of aluminum borate whiskers in isotactic polypropylene (iPP)/syndiotactic polypropylene (sPP) blends

The selective distribution of aluminum borate whisker in isotactic polypropylene (iPP)/syndiotactic polypropylene (sPP) blends was studied. For iPP/sPP/whisker composites, whiskers are distributed in iPP phase, which follow the theory of interfacial tension. When Irganox 1010 is introduced into the composites, the distribution of whiskers is changed from iPP phase to sPP phase. The results of contact angle tests indicate that the characteristics of the whisker surface are modified by Irganox 1010 and the interactions between the whisker and the matrix are dominated by van der Waals type power law. An entropy-penalty process dominates the change of distribution of whiskers in the composites. The DMA tests show that the loss modulus of composites is improved when whiskers distribute in sPP phase.     

Formation of SiC whiskers/leucite-based ceramic composites from low temperature hardening geopolymer

In this study, SiC whiskers (SCWS) reinforced geopolymer composites (SCWS/KGP) and their ceramic products (SCWS/leucite) were prepared, and effects of SiC whiskers contents on the microstructure and flexural strength of the SCWS/KGP and SCWS/leucite composites were investigated. The results show that the whisker addition has little influence on both phase composition and thermal shrinkage of the KGP composites, but a suitable content of whisker will result in the improved flexural strength, and when the SCWS content is 2 wt%, flexural strength of the SCWS/KGP composite is enhanced by 95% compared with the neat geopolymer. The flexural strength of the composites can be further enhanced significantly after the composites being treated at 1100 °C and 1200 °C and flexural strength of the composite with SCWS content of 2 wt% was 107% and 125% higher than the untreated counterpart, respectively. The increase in flexural strength of the composites should be attributed to the strong leucite formation, whisker debonding and pulling out from matrix during the fracturing process based on the good interfacial bonding state between whisker and leucite matrix.     

Reinforcement of a Magnesium‐Ammonium‐Phosphate Cement with Calcium Phosphate Whiskers

Self‐setting resorbable phosphate cements are characterized by an excellent biocompatibility and bioactivity. However, poor mechanical properties restrict their application. Most studies which characterize phosphate cements mechanically focus on strength measurements. Examinations of mechanical reliability and facture toughness were hardly performed. In this study, calcium phosphate whisker‐reinforced magnesium‐ammonium‐phosphate (struvite) cements were examined at the whisker–matrix interface and the measured strength, reliability and toughness values were correlated to these observations. Moreover, the toughening mechanisms were evaluated. It was shown that whisker incorporation is not beneficial for material strength. It led to a strength decrease from 29.8 to 21.8 MPa by the incorporation of 15 vol% calcium‐deficient hydroxyapatite (CDHA) whiskers compared to the pure struvite cement. Weibull statistics and microstructural observations revealed that this is caused by the whisker–matrix interface, which acts as a flaw. In contrast with that, the reliability increases upon whisker incorporation. Furthermore, the critical stress intensity factor K_IC as well as the work‐of‐fracture γ_wof increase from 0.52 to 0.60 MPam^1/2 and from 9.5 to 12.9 J/m² by the addition of 15 vol% CDHA whiskers compared to the original struvite cement. It was shown that whisker pull‐out and crack deflection are the main mechanisms responsible for this increase.