纳米ZrO_2-微米Al_2O_3复合陶瓷中“内晶型”结构的形成与机理

考察了不同烧结状态的氧化错增韧氧化铝陶瓷(zirconia—toughened alumina,ZTA)的晶粒长大与“内晶型”形成的关系。烧结过程中,ZTA陶瓷中晶粒生长与温度、保温时间、第二相ZrO2含量有关,其中温度的影响最为显著。第二相粒子有沿主晶相晶界移动聚集的趋向。内晶结构的形成机理可概括为第二相粒子被夹在主相两晶粒之间不能移动,在随后的主晶相长大过程中,两晶粒共同晶界发生迁移或晶粒“合并”,将第二相粒子纳入晶粒内部。而没有被主相颗粒挤住的可移动的第二相粒子则聚集成较大的晶问第二相颗粒。

内晶型结构纳米复合陶瓷研究进展

本文概述了内晶型纳米复合陶瓷近年来的研究进展，并对内晶型结构的形成与制备工艺之间的关系以及内晶型结构的强韧化机制作了重点介绍。

Al_2O_3-ZrO_2陶瓷体系中晶粒生长模型的研究

研究了Al2 O3-ZrO2 陶瓷体系中两相晶粒生长 ,提出了双相体系的晶粒生长模型 ,并解释了“内晶型”结构是如何形成的。研究发现 ,两相结构的形成与温度、保温时间及ZrO2 第二相的数量有关系 ,其中温度的影响最为显著。内晶型ZrO2 结构的形成是基体晶粒急剧长大的结果 ,而不是以往研究的以纳米粒子为生长点 ,基体粒子的成核、长大。有利于基体晶粒急剧生长的条件也有利于内晶的形成 ;内晶的形成过程可概括为Ostwald生长与基体晶粒的快速长大。但值得注意的是 ,并不是ZrO2 的含量越多 。

Al_2O_3/SiC纳米陶瓷复合材料的制备及力学性能

采用一次粒径分别为 10nm和 15nm的α Al2 O3 和SiC粉体为原料 ,制备了Al2 O3 /SiC纳米陶瓷复合材料·纳米SiC颗粒明显抑制Al2 O3 基体晶粒的长大 ,SiC体积分数超过 4 %时 ,材料的断裂方式由沿晶断裂变为穿晶断裂·随SiC含量的增加 ,Al2 O3 /SiC纳米复合材料的硬度增大·材料的弯曲强度和断裂韧性在SiC体积分数为 5 %时达到最大值·最大三点弯曲强度和断裂韧性分别为 6 4 1MPa和 4 7MPam1/2 ,明显高于热压单相Al2 O3 陶瓷 (344MPa和 3 1MPam1/2 )

Al_2O_3/SiC_(nano)纳米复合材料微结构及强韧化机理研究

纳米颗粒复合材料的“内晶型”结构中，晶内纳米相和基体间存在的次界面对材料性能的改善有重要作用。本文系统观察了氧化铝陶瓷和Ａｌ２Ｏ３／ＳｉＣｎａｎｏ纳米复合材料的微结构，着重研究了弥散ＳｉＣ颗粒对Ａｌ２Ｏ３基体微结构的影响，讨论了“内晶型”结构、位错组态、纳米化效应和穿晶断裂之间的关系以及材料强韧化机理。

热压烧结制备Ti_3Al/TiC+ZrO_2陶瓷复合材料

采用机械合金化和热压烧结制备了Ti3Al/TiC+ZrO2复合材料。研究了不同烧结温度(1500,1550℃)及Ti3Al在TiC基体中不同的添加方式对烧结体力学性能的影响,并对烧结体的断口进行了SEM分析。结果表明:在Ti3Al和ZrO2协同增韧补强的作用下,得到的烧结体具有良好的力学性能,其断裂以穿晶和沿晶相结合方式进行,并且出现了内晶。

烧结温度对20%ZrO_2(3Y)/Al_2O_3复相陶瓷力学性能和微观结构的影响

20%纳米ZrO2（3Y）粉末加入到高纯亚微米Al2O3粉中,采用高压干压成型方法和恒速升温多阶段短保温烧结方法制备出不同烧结温度下的复相陶瓷。研究烧结温度对复相陶瓷力学性能的影响,通过XRD,EDS和SEM对复相陶瓷进行元素组成和微观结构分析。结果表明：烧结温度在很大程度上影响着复相陶瓷的力学性能和微观结构,常压烧结1600℃保温8h时,相对密度、维氏硬度和断裂韧性达到最大,分别为98.6%,18.54GPa和9.3MPa·m1/2,而基体晶粒尺寸为1.4~8.1μm,ZrO2相变量为34.6%。1600℃下复相陶瓷具有优质的微观结构,断裂方式为沿晶-穿晶混合断裂模式。ZrO2（3Y）粉体的加入,从相变增韧、内晶型颗粒增韧和裂纹偏转等多个方面提高了复相陶瓷的断裂韧性。

纳米/微米CaB_6烧结体的形貌组织和力学性能

采用真空热压工艺,在烧结温度1750℃、烧结压力32MPa、保温时间5min的工艺条件下制备了添加不同量纳米六硼化钙(CaB6)粉末的微米烧结体,研究了纳米粒子含量对CaB6烧结体形貌组织和力学性能的影响.纳米粉末加入量为10wt%纳米/微米复合陶瓷的致密度和力学性能最佳,硬度、弯曲强度和断裂韧性分别为92.6 HRA、331.7MPa和3.06MPa.m1/2,优于微米烧结体和添加镍作为烧结助剂的烧结体.纳米粒子对微米颗粒晶界的填充和在复合烧结体中形成的"内晶型"晶粒结构是提高复合陶瓷致密度和力学性能的主要原因.

纳米复合陶瓷材料强韧化的研究进展

与传统陶瓷材料相比，纳米复合陶瓷材料断裂强度和断裂韧性得到了显著的提高。综述了纳米复合陶瓷材料强韧化机理的研究进展，主要包括弥散细化、混晶型结构强化、钉扎理论、残余应力场理论等。断裂模式从以传统复合陶瓷的以沿晶断裂为主转变为纳米复合陶瓷的以穿晶断裂为主，从而将导致断裂韧性和抗弯强度极大的提高。

Low temperature quasi-superplasticity of ZK60 alloy prepared by reciprocating extrusion

Fine-grained ZK60 alloy was prepared by 2-pass reciprocating extrusion, and the low temperature superplasticity was conducted in a temperature range from 443 to 523 K and an initial strain rate ranging from 3.3×10^-4 to 3.3×10-2^s^-1. The results show that the alloy has an equiaxed grain structure with an average grain size of about 5.0μm, and the sizes of broken secondary particles and precipitates are no more than 175 and 50 nm, respectively. The alloy exhibits quasi-superplasticity with a maximum elongation of 270% at 523 K and an initial strain rate of 3.3×10^-4 s^-1. The strain rate sensitivity m is less than 0.2 at 443 and 473 K, and it is 0.42 at 523 K. The apparent activation energies at temperature below 473 K and at 523 K are less than 63.2 and 110.6 kJ/mol, respectively At temperature below 473 K, mainly intragranular sliding contributes to superplastic flow. At 523 K, grain boundary sliding is the dominant deformation mechanism, and dislocation creep controlled by grain boundary diffusion is considered to be the main accommodation mechanism.

纳米复合陶瓷ZTA的强韧化机理

作者综述了纳米复合陶瓷ZTA的强韧化机理。包括 :弥散增韧机理、相变增韧机理、微裂纹增韧机理三种机理 ,其中弥散增韧机理又包括“内晶型”增韧机理和“晶界型”

Effect of Mg on nucleation process of recrystallization in Al-Mg-Si/SiC_p composite

The recrystallization nucleation processes of two cold-rolled Al-Mg-Si/SiCpcomposites with different contents of Mg are investigated mainly by dynamic mechanical analyzer （DMA） and electron microscopy including high angle annular dark field scanning transmission electron microscopy （HAADF-STEM） andhigh-resolution transmission electron microscopy （HRTEM）. Internal friction and electron microscopy results show that solute atom clusters are present in association with dislocationsin supersaturated cold-rolled composites. During recrystallization process, the internal friction peak position of Al-Mg-Si/3SiCp/2Mg （volume fraction,%） is higher than that of Al-Mg-Si/3SiCp（volume fraction,%） due to more solute atom clusters formed in association with the dislocations in the cold-rolled composite with a much higher Mg content, indicating a strongerresistance for the recrystallization nucleation.

Low frequency damping behavior associated with sintering process in Al powder compact

The internal friction behavior of Al green power compact duxing the sintering process was studied as a function of temperature. The internal friction measurements were performed from room temperature to 600 °C. Two typical internal friction peaks were detected corresponding to heating and cooling processes, respectively. The heating peak corresponds to a recrystallization process of deformed Al particles, which is influenced by many extrinsic parameters, such as measuring frequency, strain amplitude, heating rate, power particle size and compacting pressure. However, the intrinsic nature of the peak is originated from the micro-sliding of the weak-bonding interfaces between Al particles and increased dislocation density induced in compressing. The cooling peak with the activation energy of (1.64±0.06) eV is associated with the grain boundary relaxation, which can be interpreted as the viscous sliding of grain boundaries. The similar phenomena are also found in the Mg green powder compact.

追求是种美

1990年．在柴可夫斯基国际音乐比赛中，一位年仅18岁的女孩创下了这项赛事最年轻的冠军记录，她就是日本小提琴女子三杰之一的Akiko Suwanai（诹访内晶子）．后来她还摘取了意大利热那亚的帕格尼尼国际小提琴大赛的桂冠。这位清丽俊秀的音乐才女先后师从美同朱利亚音乐学院名师迪蕾、哥伦比亚音乐学院华裔小提琴家林昭亮等名家。

A modified constitutive model and hot compression instability behavior of Cu-Ag alloy

The hot compressive deformation behaviors of Cu-6wt.%Ag alloy were studied experimentally in the temperature range of 973.1123 K and the strain rate range of 0.01.10 s^-1.The stress increases and reaches the maximum value when the true strain is very small,and then the stress changes slowly and tends to be stable under the action of work hardening,dynamic recovery and recrystallization.The material parameters of the conventional Arrhenius constitutive model are only related to strain under different deformation conditions,and the prediction error is large,which cannot accurately characterize the hot deformation behavior of the alloy.To describe the hot deformation behavior of the alloy accurately,a modified constitutive model was established by considering the simultaneous influence of forming temperature,strain rate and strain.The results indicate that correlation coefficient(R)and the average absolute relative error(AARE)are 0.993 and 4.2%,respectively.The modified constitutive model can accurately describe the hot deformation behavior of Cu-6wt.%Ag alloy.

A Study of Rabbit Lens Epithelial Cells Survival and Growth on the Rabbit Capsular Bag in Vitro

Objective: To study the proliferation, migration and metaplasm of residual rabbit lens epithelial cells (LECs) after extracapsular cataract extraction(ECCE)based on the rabbit capsular bag model in vitro. Methods: Sham cataract surgery, including anterior capsulorhexis, nucleus hydroexpression and aspiration of lens fibers, was performed on 20 rabbit lens. The capsular bags were isolated and pinned to sterile non-toxic silicone rings on petri dishes. The capsular bags were incubated with Eagle's minimum essential medium (DMEM) supplemented with 10% fetal calf serum (FCS) and monitored for 3 weeks by phase-contrast microscopy, after which light microscopy was performed on them.Results: After a latent period of 2-3 d, outgrowth was observed across the posterior capsule. Growth proceeded rapidly so that the posterior capsule was totally covered by a confluent monolayer of cell at 6-8 day. Capsular wrinkles became increasingly apparent as time progressed, causing a marked rise in light scatter. An increase in capsular tension also came.Conclusion: This model exhibits many of the in vito characteristics of the lens capsule after extracapsular surgery and may prove useful in further elucidating the cellular mechanisms of posterior capsule opacification and developing strategies for inhibiting cell growth with this system.

AN EXPERIMENTAL STUDY OF THE TUMOUR NECROSIS FACTOR LEVELSIN AQUEOUS HUMOR AFTER TRAUMATIC CATARACT AND INTRAOCULAR LENS IMPLANTATION

Purpose. This paper studies the tumour necrosis factor (TNF) levels in aqueous humor after traumatic cataract extraction and posterior chamber (PC) intraocular lens (IOL) implantation in rabbits,and discusses the effect of TNF on postoperative anterior ocular inflammation. Methods. Twenty seven pigmented rabbits were divided into three groups: for the first group, the IOL were placed in the capsular bag after traumatic cataract extraction; for the second, the Extracapsular cataract extraction without IOL implantation; and for the third, the control group without surgical intervention. On the 1st, 3rd, 7th and 14th day postoperatively, aqueous humor samples were obtained. A modified double antibodies indirect sandwich ELISA was used to detected for the presence of TNF. The data were studied by means of analysis of variance in SAS software. Result. The TNF level was increased in aqueous humor and reached its maximum on the 1st postoperative days after traumatic cataract extraction and PC IOLs implantation, and the TNF levels are significantly higher (P<0 05) on the 1st, 3rd, 7th and 14th day postoperatively in traumatic cataract extraction and PC IOL implanted group than that in the non surgical intervention group and extracapsular cataract extraction group. Conclusions. The increase of TNF levels had a close relationship with presence of the IOL itself which induces the secretion of TNF. This suggested that TNF as the principal mediators of immunological and inflammatory responses, so that may play critical role in anterior ocular inflammative response after traumatic cataract extraction and IOL implantation.

Deformation behavior of materials in micro-forming with consideration of intragranular heterogeneities

To describe the relationship between the whole material deformation behavior and each grain deformation behavior inmicro-forming,experimental and numerical modelling methods were employed.Tensile test results reveal that contrary to the valueof flow stress,the scatter of flow stress decreases with the increase of thickness-to-grain diameter(T/d)ratio.Microhardnessevaluation results show that each grain owns unique deformation behavior and randomly distributes in each specimen.The specimenwith less number of grains would be more likely to form an easy deformation zone and produce the concentration of plasticdeformation.Based on the experiment results,a size-dependent model considering the effects of grain size,geometry size,and thedeformation behavior of each grain was developed.And the effectiveness and practicability of the size-dependent model wereverified by experimental results.

Gate-Capacitance-Shift Approach and Compact Modeling for Quantum Mechanical Effects in Poly-Gates

A new approach,gate-capacitance-shift (GCS) approach,is described for compact modeling.This approach is piecewise for various physical effects and comprises the gate-bias-dependent nature of corrections in the nanoscale regime.Additionally,an approximate-analytical solution to the quantum mechanical (QM) effects in polysilicon (poly)-gates is obtained based on the density gradient model.It is then combined with the GCS approach to develop a compact model for these effects.The model results tally well with numerical simulation.Both the model results and simulation results indicate that the QM effects in poly-gates of nanoscale MOSFETs are non-negligible and have an opposite influence on the device characteristics as the poly-depletion (PD) effects do.

Phase Field Simulation of Intragranular Microvoids Evolution Due to Surface Diffusion in Stress Field

Based on the bulk free energy density and the degenerate mobility constructed by the quartic double-well potential function,a phase field model is established to simulate the evolution of intragranular microvoids due to surface diffusion in a stress field.The corresponding phase field governing equations are derived.The evolution of elliptical microvoids with different stressesΛ,aspect ratiosβand linewidths hˉis calculated using the mesh adaptation finite element method and the reliability of the procedure is verified.The results show that there exist critical values of the stressΛc,the aspect ratioβc and the linewidth hˉc of intragranular microvoids under equivalent biaxial tensile stress.When Λ≥Λ_(c),β≥β_(c) or h≤h_(c),the elliptical microvoids are instable with an extending crack tip.WhenΛ<Λ_(c),β<β_(c) or hˉ>h_(c),the elliptical microvoids gradually cylindricalize and remain a stable shape.The instability time decreases with increasing the stress or the aspect ratio,while increases with increasing the linewidth.In addition,for the interconnects containing two elliptical voids not far apart,the stress will promote the merging of the voids.