ZrO2晶粒聚集态和粉末特性对增韧的影响

用 TEM 研究了热压 ZrO_2增韧 Al_2O_3(ZTA)的样品中,ZrO_2晶粒聚集态对四方相→单斜相相变的影响。以 Y_2O_3为稳定剂的四方 ZrO_2多晶体(Y-TZP)原料中加入同样组份的团聚粉末或粗粉末,对 ZrO_2的相变有很大影响。讨论了实验结果。对改善材料性能提出了建议。     

Al-Y-TZP陶瓷的抗热震行为与相变的关系

研究了不同 Y_2O_3添加剂含量的2mol% Al_2O_3-ZrO_2陶瓷的相变增韧和强化以及热震损伤行为。分析了材料的抗热震性和断裂参数(K_(1c),σ_f,γ_f)之间的关系。在实验的基础上阐明了四种 ZrO_2材料的热震损伤行为由抗热震参数(R′,R″,R_(8t))控制,并分别受到下述因素的影响:a.应力诱发相变的增韧和强化;b.抑制四方 ZrO_2相变的内约束力所起的强化作用;c.与无外应力下的相变开裂相关的增韧和强度衰减;d.热震裂纹成核引起的增韧。     

氧化锆增韧陶瓷（ZTC）的晶界结构

本文用 JEM200CX 超高分辨型透射电子显微镜对 ZTC 陶瓷的晶界结构进行了研宄。发现 Al_2O_3与ZrO_2之间的晶界存在共格点、共渗和无序结构形式,并发现晶界处常为 ZrO_2相变的成核区。ZrO_2(m)和ZrO_2(t)之间的晶界,既能成为 ZrO_2相变的成核区,也能阻止 ZrO_2相变的延续发展。只有当两个 ZrO_2晶粒的同类型晶面取向相近时,ZrO_2的相变才容易通过晶界而发展。ZrO_2(t)和 ZrO_2(t)之间的晶界具有较好的共格点结构,形成交错的锯齿状,这是 TZP 陶瓷具有高强和高韧的原因之一。     

3Y-TZP/mullite-Alumina复合陶瓷的韧性及增韧机制

为了研究3Y TZP为基体的3Y TZP/mullite Alumina复合陶瓷的断裂韧性及其增韧机制,将3Y TZP、mullite、Alumina3种粉料球磨混合,经干压、等静压成型,在1480℃,4h无压烧结,通过改变Alumina/mullite体积比,得到了不同断裂韧性的陶瓷复合材料,利用XRD与SEM技术分析了复合材料的成分及微观结构.研究结果表明:Al2O3/mullite体积比影响复合材料中四方氧化锆(t ZrO2)向单斜氧化锆(m ZrO2)转变的相变量、复合材料的微观结构和t ZrO2晶面间距,进而影响材料的断裂韧性;用单边切口梁法测试复合材料断裂韧性(KIC)为9 26～10 4MPa·m1/2;此系统中存在ZrO2相变增韧、非相变第二相颗粒增韧等机制.     

氧化锆中相变和位错

本文研究了 Y_2O_3-ZrO_2和 Al_2O_3-ZrO_2材料中四方相(t)ZrO_2向单斜相(m)相变过程,确定两相之间的取向关系,并证实在相变过程中相界处存在反相畴界。同时也对四方相中位错对相变影响进行了研究。     

PHASE TRANSFORMATION AND DISLOCATION IN ZrO_2

本文研究了Y_2O_3-ZrO_2和Al_2O_3-ZrO_2材料中四方相(t)ZrO_2向单斜相(m)相变过程,确定两相之间的取向关系,并证实在相变过程中相界处存在反相畴界。同时也对四方相中位错对相变影响进行了研究。     

液相包覆制备Ce-TZP陶瓷的力学性能与稳定行为

采用XRD、SEM、TEM等分析手段对由液相包覆工艺制备的Ce—TZP陶瓷的微结构进行了研究，并和共沉淀粉体制备的Ce—TZP陶瓷进行了对比分析．力学性能表明，同共沉淀粉体制备的Ce—TZP陶瓷相比，由液相包覆工艺制备的Ce—TZP陶瓷虽硬度下降，但断裂韧性改善；液相添加少量Al2O3硬度随之增加、断裂韧性显著提高．电镜分析表明，液相包覆工艺制备的Ce—TZP陶瓷晶粒尺寸分布宽化，一部分晶粒尺寸较大但CeO2含量低、易发生马氏体相转变晶粒的存在是断裂韧性改善的主要原因．陶瓷体中单斜相大晶粒与四方相之间的残余应力、添加少量Al2O3在晶界上易形成薄的非晶包裹层，是增加可相变四方相数量，提高断裂韧性的其它机制。     

稀土氧化物La2O3/Y2O3增韧补强ZTA陶瓷材料及其耐磨性能研究

针对单一相ZrO_2增韧Al_2O_3(ZTA)陶瓷在提高韧性的同时不能合理兼顾其耐磨性能,利用稀土氧化物能促进复合陶瓷材料热压烧结的工艺特点,将La_2O_3/Y_2O_3添加到ZTA陶瓷材料中,XRD衍射图谱表明:La_2O_3/Y_2O_3的添加可以有效阻碍ZrO_2不稳态晶型相变,促进介稳态t-ZrO_2的形成。当添加量为4%(质量分数)时,烧结后晶粒分布最为均匀,致密程度高,其维氏硬度、抗弯强度、断裂韧性分别比相应未添加稀土氧化物的ZTA材料提高了8%、21%、33%,且La_2O_3与Al_2O_3会发生原位反应生成片状LaAl_(11)O_(18),这种片晶不仅可以阻碍Al_2O_3、ZrO_2颗粒长大,还可通过晶粒拔出等增韧机制提高材料韧性。摩擦磨损试验结果表明:稀土氧化物的添加能提高ZTA陶瓷材料的耐磨性能,添加量为4%时其磨损率最低。     

Mullite(W)/TZP陶瓷复合材料的显微结构与力学性能

研究了 mullite(w) 含量对 mullite(w)/TZP 复合材料显微结构和力学性能的影响。结果表明,当mullite(w)含量大于15 v.-%,热压温度超过1600℃时复合材料将开裂;原因是 Y_2O_3从 TZP 中脱溶进入玻璃相。mullite(W)含量在5-20 V.-%时,室温力学性能与基质 TZP 大致相同:σ_f=1200MPa,K_(IC)=12MPa2~(1/m);而1000℃时复合材料抗弯强度为360-430MPa,是基质 TZP 的1.8-2.1倍。     

Al_2O_3-ZrO_2-SiCw陶瓷复合材料的断裂特点和韧化机理

本文通过 XRD,SEM,TEM 以及三点弯曲试验技术研究了 Al_2O_3-25 v.-%ZrO_2(2mol%Y_2O_3)-25v.-% SiCw(AZS)三元陶瓷复合材料的断裂特点和韧化机理。结果表明,该材料的载荷-位移曲线因晶须的反复阻止作用呈锯齿状,ZrO_2与 SiC 晶须同时起增韧作用,材料的良好韧性是 ZrO_2的相变增韧、微裂纹增韧和裂纹偏转与分枝增韧以及 SiC 晶须的裂纹桥接与拔出效应共同作用的结果,但其综合效果不是简单叠加。本文还建立了 ZrO_2-SiC_W 的复合韧化模型,并进行了讨论。     

聚碳酸酯基智能电表壳耐低温专用料的研制

用聚碳酸酯（PC）、玻璃纤维和环保阻燃剂分别与两种不同的增韧剂经双螺杆挤出机熔融共混制备了两种智能电表外壳材料,再经注射机成型各类标准样条,对材料的力学、阻燃、绝缘和耐低温冲击性能进行了表征,并进一步与有类似应用的市售进口材料进行比较。结果表明,两种智能电表外壳材料的阻燃、绝缘、耐热和抗撕等特性都达到或超过进口同类产品的技术水平。     

The Fabrication and Properties of the Squeeze-Cast TiN/Al Composites

Co-continuous TiN/Al composites with different volume fractions of Al phase have been fabricated by the squeeze-casting method. TiN porous ceramics with different porosities were fabricated through carbothermal reduction by changing the content of TiN and were used as preforms. The outstanding mechanical properties were attributed to the absence of excessive interface reaction between TiN and Al for the co-continuous TiN/Al composites. With the increase of Al content in the composites, the flexural strength and the microhardness decreased, and the fracture toughness increased. The strengthening and toughening mechanism of composites included dislocation strengthening, ductile rupture, crack deflection, and secondary cracks.     

Pressureless sintering and characterization of cordierite/ZrO2 composites

Cordierite/ZrO₂ composites with 5 to 25 wt% ZrO₂ were fabricated by conventional powder mixing and pressureless sintering method. Their densification behavior, microstructure, mechanical and thermal properties were studied. By dispersing 25 wt% (9.57 vol%) ZrO₂, densified cordierite/ZrO₂ composite with a relative density of 98.5% was obtained at an optimum sintering condition of 1440 °C and 2 h. ZrO₂ particles were homogenously dispersed within matrix grains and at the grain boundaries. The intragranular particles were finer than 100 nm and the intergranular particles were coarser. Both fracture strength and toughness could be enhanced more than two times higher, compare to those of monolithic cordierite, by dispersing 25 wt% ZrO₂ into the cordierite matrix. The toughening mechanism in the present composites was mainly attributed to martensitic transformation due to ZrO₂ dispersion. Electronic Publication     

环氧树脂增韧改性研究进展

本文对环氧树脂的增韧改性进行了总结,重点介绍了橡胶、热塑性树脂、无机纳米粒子、互穿网络、热致型液晶聚合物和核-壳结构聚合物的增韧机理和改性方法,并概括了环氧树脂增韧过程中存在的问题,最后对环氧树脂增韧改性的发展方向进行了展望。     

Strengthening mechanisms in Al2O3/SiC nanocomposites

A strengthening mechanism merely arising from internal (residual) microstresses due to thermal expansion mismatch is proposed for explaining the high experimental strength data measured in Al₂O₃/SiC nanocomposites. Upon cooling, transgranular SiC particles undergo lower shrinkage as compared to the surrounding matrix and provide a hydrostatic “expansion” effect in the core of each Al₂O₃ grain. Such a grain expansion tightens the internal Al₂O₃ grain boundaries, thus shielding both weakly bonded and unbonded (cracked) grain boundaries. It is shown that the shielding effect by intragranular SiC particles is more pronounced than the grain-boundary opening effect eventually associated with thermal expansion anisotropy of the Al₂O₃ grains, even in the “worst” Al₂O₃-grain cluster configuration. Therefore, an improvement of the material strength can be found. However, a large stress intensification at the grain boundary is found when intergranular SiC particles are present, which can produce a noticeable wedge-like opening effect and trigger grain-boundary fracture. The present model enables us to explain the experimental strength data reported for Al₂O₃/SiC nanocomposites and confirms that the high strength of these materials can be explained without invoking any toughening contribution by the SiC dispersion.     

脆性陶瓷材料的增韧方法及其应用现状

从陶瓷断裂的基本理论入手,对比了相变增韧、微裂纹增韧、纤维增韧和纳米颗粒增韧等技术应用到陶瓷领域的增韧机理及其实施方法,举例阐述了这些增韧方法的应用,并对其发展前景进行了展望。     

Mechanical properties and toughening mechanism of WC-doped ZrB2–ZrSi2 ceramic composites by hot pressing

WC-doped ZrB₂–ZrSi₂ ceramic composites were fabricated by hot pressing at temperatures ranging from 1450 °C to 1550 °C. The influence of ZrSi₂ content on the mechanical properties of the composites was investigated by means of three point bending test and single edge notched-beam test, respectively. The microstructure and phase composition were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. The results revealed that: (i) the highest relative density was 99.5% for the composite fabricated at 1550 °C; (ii) the doping of WC refined the grain size and led to an anisotropic grain growth which was evidenced by the occurrence of elongated grains; (iii) the highest strength and fracture toughness were 585 MPa and 6.87 MPa m^1/2, respectively; (iv) the main toughening mechanism was considered as the pull out of elongated grains and the deflection of cracks.     

氧化锆增韧陶瓷的相变及相变增韧

本文阐述了氧化锆增韧陶瓷（ＺＴＣ）的相变增韧机理，并探讨了热处理工艺对ＺＴＣ的相变及显微组织的影响规律。     

Fracture of porous materials - Influence of the pore size

The random distribution of pores in location, size and shape makes the fracture of porous materials a difficult problem. We address herein a simplified model of porous material as can be obtained for instance in ceramics by introducing organic or polymer particles prior to the sintering step. Resulting spherical pores are almost regularly located with a homogeneous distribution in size. A fracture criterion involving both toughness and tensile strength allows studying the competition between, on the one hand the crack blunting due to the pores and resulting in an apparent toughness enhancement, and on the other hand the weakening effect caused by an increasing volume fraction of pores.     

Epoxy nanocomposites - fracture and toughening mechanisms

This study focuses to provide information about reinforcing influences of nanoparticles exerted on the mechanical and fracture mechanical properties of epoxy resins, particularly with regard to fracture and toughening mechanisms. A comprehensive study was carried out on series of nanocomposites containing varying amounts of nanoparticles, either titanium dioxide (TiO₂) or aluminium oxide (Al₂O₃). Nanocomposites were systematically produced by applying high (shear) energy during a controlled dispersion process, in order to reduce the size of agglomerates and to gain a homogeneous distribution of individual nanoparticles within the epoxy resin. The mechanical performance of the nanocomposites was then characterized by flexural testing, dynamic mechanical analysis (DMA), and furthermore, by fracture mechanics approaches (LEFM) and fatigue crack growth testing (FCP). The microstructure of specimens and the corresponding fracture surfaces were examined by TEM, SEM and AFM techniques in order to identify the relevant fracture mechanisms involved, and to gain information about the dispersion quality of nanoparticles within the polymer. It was found that the presence of nanoparticles in epoxy induces various fracture mechanisms, e.g. crack deflection, plastic deformation, and crack pinning. At the same time, nanoparticles can overcome the drawbacks of traditional tougheners (e.g. glass beads or rubber particles) by simultaneously improving stiffness, strength and toughness of epoxy, without sacrificing thermo-mechanical properties.