三角帆蚌珍珠质层结构和珍珠质涂层的研究

利用扫描电镜和光学显微镜对三角帆蚌贝壳和珍珠的珍珠质层微观结构进行了分析研究, 发现贝壳的珍珠质层中存在异常的结构带, 主要有柱状珍珠质带, 针状晶体带以及棱柱状晶体带. 其中柱状珍珠质带中, 单片文石板片的厚度超过1μm, 是正常珍珠质中文石板片厚度的两倍. 而对正常珍珠的珍珠质层的大量观察却未发现类似的异常结构. 分析认为这可能是因为贝壳珍珠质的矿化微环境与珍珠的珍珠质矿化微环境不同导致的. 并利用圆柱形珍珠囊在钛金属牙种植体表面制备的珍珠质涂层具有沿整个圆周面均匀生长的特点.     

贝壳珍珠层的研究现状

贝壳中的珍珠层是由占壳重95%的CaCO3晶体和占壳重仅5%的有机体构成的一种优异的天然纳米复合材料.对珍珠层的研究现状和最新进展进行了评述.重点介绍了珍珠层形成机制中的隔室说、矿物桥说、模板说和多模板二步成因假说等4种学说,及裂纹的偏转、纤维的拔出、有机质的桥连、矿物桥机制和凹凸镶嵌结构等5种增韧机理,简述了珍珠层的组成和微结构,指出了珍珠层研究中有待解决的问题.     

TC4-DT钛合金疲劳裂纹扩展的微观机制

通过断口分析讨论了TC4-DT钛合金裂纹扩展的微观机制。从微裂纹的形成,疲劳裂纹初期、近门槛区以及稳态区的扩展,分析了不同组织形态的TC4-DT钛合金对应的裂纹扩展微观机制。分析结果表明,对于片层组织,循环载荷的作用导致断裂表面粗糙及塑性变形过程中相界面产生位错塞积而诱使裂纹萌生。等轴组织变形过程中晶粒产生的断裂表面成为裂纹的萌生源。在近门槛区,等轴组织变形过程中位错累积将导致沿晶界的开裂,从而加速裂纹扩展;双片层组织由于次生α相的尺寸效应会加速裂纹扩展。在稳态扩展区,断口表面由第Ⅰ阶段的锯齿状断裂模式过渡到辉纹断裂模式,表现为塑性条带断裂机制。     

SHS纳米/微米块体复相陶瓷微观结构与断裂

通过在(CrO3 Al)燃烧体系中添加一定量的ZrO2(2Y)粉末,利用SHS冶金技术直接制备出Al2O3-35vol%ZrO2纳米/微米结构块体复相陶瓷,研究该复相陶瓷的微观结构与断裂行为.研究发现:该复相陶瓷基体主要由纳米/微米相晶内型结构共晶体组织构成;Vickers压痕试验显示引发陶瓷裂纹扩展的压痕压制临界载荷为30 kg;ZrO2相所具有的应力诱发相变增韧机制和微裂纹增韧机制均很微弱;裂纹扩展主要受纳米/微米相晶内型结构共晶体控制,使该复相陶瓷在断裂过程中呈现出强烈的裂纹偏转绕过机制.     

脆性高聚物的银纹化增韧设计

银纹化是脆性高聚物的一种典型的非线性变形方式。银纹在其引发、生长和断裂过程中消耗大量能量，对高聚物的增韧设计十分重要。考虑银纹细观结构特征的银纹生长和断裂规律是研究银纹增韧机制的核心内容。根据国内外近期的若干进展，基于对承载高聚物中的银纹断裂及其与裂纹扩展的相互作用等问题的分析，从理论上探讨将材料断裂韧性与其微观控制参数（如分子量，缠结密度等）联系起来，寻求脆性高聚物进行微观增韧设计的途径和方法。     

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.     

低温镀铁层的微观结构和摩擦学性能

低温镀铁修复功能强大,其组成结构对机械零部件的摩擦学性能影响重大.为此,用直流低温方法制备了镀铁层;利用扫描电镜观测了镀铁层表面的超细晶粒形貌及断面形貌,用X射线能量色散谱仪对镀铁层进行了微区的成分分析;探讨了镀铁层微观组织形貌的形成机理;讨论了镀铁层中的表面形貌和组织结构与低温镀铁层摩擦性能的关系.结果表明,在低温下可获得晶粒细小的镀铁层;析氢则是造成镀铁层裂纹产生的直接原因,杂质和镀层的表面应力会加速裂纹的扩展;镀铁层的摩擦学性能比纯铁好.     

贝壳珍珠层及其仿生应用

综述了贝壳珍珠层结构及其文石晶体的结晶学取向特征，并概述了珍珠层中参与调控生物矿化的有机基质的结构和功能方面的最新研究进展。从裂纹偏转、纤维拔出、有机基质桥连及矿物桥的作用等方面对珍珠层的高韧性机制进行了讨论。同时介绍了珍珠层的微结构特征及其特殊的组装方式在仿生材料制备方面的应用。     

BASCA热处理对TC10钛合金组织与断裂韧性的影响

本工作对TC10钛合金进行BASCA热处理(β退火+缓慢冷却+时效),通过改变BA温度(β退火温度),研究BASCA热处理对TC10钛合金微观组织与断裂韧性的影响。结果表明：BA温度对合金微观组织与断裂韧性起到决定作用,随着BA温度升高,合金微观组织类型由等轴组织转变为片层组织,断裂韧性不断增加,最大值为77 MPa·m^1/2。此外,研究了不同类型组织的裂纹尖端区域塑性变形量、裂纹扩展路径以及断口微观形貌,进一步揭示断裂机制。与片层组织相比,等轴组织的裂纹尖端区域塑性变形较大,裂纹扩展路径曲折程度较小。等轴组织的断口形貌光滑平顺,主要由韧窝构成;片层组织的断口形貌凹凸起伏明显,韧窝数量与尺寸均减小,并出现撕裂棱、空洞以及二次裂纹。     

EB-PVD工艺制备Ti/Ti-Al微层板的力学性能与增韧机制研究

为满足金属热防护系统面板材料的轻量化要求,以Ti-Al金属间化合物作为基体,以Ti作为增韧层,利用电子束物理气相沉积技术和双靶沉积方法,制备了Ti/Ti-Al微层板,并利用热压法对材料进行了致密化处理。采用纳米压痕法和常温拉伸试验对材料的力学性能进行了表征,根据断口形貌和结构特征,分析了材料的增韧机制。结果表明:添加金属韧化层使TiAl基合金的室温力学性能有所提高,微层板中的裂纹多次沿着层间界面或层中拐折,表现出良好的断裂延迟特性,其增韧机制则为韧化层的存在导致裂纹发生偏转、微桥接等使裂纹扩展阻力增加。     

鲍鱼壳珍珠层无机文石片的层状微结构研究

贝壳珍珠层是软体动物壳的最内层,经过若干世纪的自然进化,贝壳珍珠层形成了优良的微结构,并使贝壳具有了相当高的强度、刚度及断裂韧性.本文利用扫描电镜(SEM)观察了鲍鱼贝壳珍珠层的主要微结构特征,发现其是由层状的无机文石片和有机胶原蛋白质组成的生物陶瓷复合材料.根据发现的贝壳珍珠层层状微结构特征,建立贝壳珍珠层三维有限元模型,并用此模型分析了珍珠层的拉伸屈服极限与无机文石片拉伸屈服极限及其厚度的关系,研究表明珍珠层的屈服极限随无机文石片屈服极限的增加和无机文石片厚度的减小而增加.     

Observations of damage morphologies in nacre during deformation and fracture

The deformation, fracture and toughening mechanisms of nacre from a kind of fresh-water bivalve mollusc (Cristaria plicata) were studied by SEM, TEM and microindentation tests. Experimental results revealed a strong anisotropy of the damage behaviour reflecting the microstructural character of nacre. The fractured surface parallel to the cross-sectional surface of nacre was much more tortuous than that parallel to the platelet surface. The crack line on the cross-sectional surface was step-like, while that on the platelet surface was polygonal. Sliding of aragonite layer combined with the plastic deformation of organic matrix is the main plastic deformation mechanism of nacre. Three main toughening mechanisms have been found acting in concert: crack deflection, fibre pull-out and organic matrix bridging.     

On flaw tolerance of nacre: a theoretical study

As a natural composite, nacre has an elegant staggered ‘brick-and-mortar’ microstructure consisting of mineral platelets glued by organic macromolecules, which endows the material with superior mechanical properties to achieve its biological functions. In this paper, a microstructure-based crack-bridging model is employed to investigate how the strength of nacre is affected by pre-existing structural defects. Our analysis demonstrates that owing to its special microstructure and the toughening effect of platelets, nacre has a superior flaw-tolerance feature. The maximal crack size that does not evidently reduce the tensile strength of nacre is up to tens of micrometres, about three orders higher than that of pure aragonite. Through dimensional analysis, a non-dimensional parameter is proposed to quantify the flaw-tolerance ability of nacreous materials in a wide range of structural parameters. This study provides us some inspirations for optimal design of advanced biomimetic composites.     

Crystal orientation,toughening mechanisms and a mimic of nacre

Based on the investigations of crystal structure of nacre using SEM, TEM and XRD, it is proposed that there exists a domain structure of crystal orientation in the nacre. The orientation domain consists of continuous 3–10 tablets along the direction perpendicular to nacreous plane, and 1–5 tablets in a single lamina. The tablets in a domain are crystallographic identical in three dimensions. From the crack morphologies, it is found that the crack deflection, fibre pull-out and organic matrix bridging are the three main toughening mechanisms acting on nacre. The organic matrix plays an important role in the toughening of this biological composite. The biomimetically synthesized composite made of alumina and kevlar showed significant increase in the fracture energy compared with the single ceramics. The soluble proteins extracted from nacre can induce aragonite and the one from prism can induce calcite grown with a preferred orientation of [104]. The insoluble proteins control the nucleation site and thus lead to a finer crystallization of CaCO₃.     

贝壳珍珠层中文石晶体择优取向研究

贝壳珍珠层中文石晶体的择优取向是其具有独特力学性能的重要原因．本文采用Ｘ射线衍射方法对我国主要育珠贝（蚌）的贝壳珍珠层中文石晶体的择优取向进行了较系统的研究,结果表明：海水马氏珍珠贝、大珠母贝及企鹅珍珠贝贝壳珍珠层中文石晶体ｃ轴垂直珍珠层面定向排列;淡水三角帆蚌壳珍珠层文石晶体有两种明显择优取向,一种ｃ轴垂直珍珠层层面,另一种ｃ轴与层面斜交,其（０１２）面网方向与层面平行．     

三角帆蚌贝壳的微结构及尺寸变化特征

天然生物经历了亿万年的不断进化,已经形成了近乎完美的结构。天然生物材料结构的研究是仿生研究的基础,本文以三角帆蚌贝壳为研究对象,利用SEM和AFM,描述了三角帆蚌贝壳的微结构特征,包括其角质层、棱柱层、珍珠层及界面和晶带的形貌,揭示文石晶片及各层间的尺寸变化规律。研究表明:角质层内部分布大量裂纹,珍珠层与棱柱层无明显过渡界面,珍珠层内发现条状晶带结构缺陷;贝壳壳体和珍珠层厚度随0生长线向外呈现先增大后减小的变化趋势,且单层文石晶片的厚度不均,最厚处可达最薄处的2倍多。对三角帆蚌贝壳的结构进行了深入研究,为其优异的力学性能提供了理论依据,为未来的仿生结构设计提供了新思路和新想法。      

Toughening mechanisms in bioinspired multilayered materials

Outstanding mechanical properties of biological multilayered materials are strongly influenced by nanoscale features in their structure. In this study, mechanical behaviour and toughening mechanisms of abalone nacre-inspired multilayered materials are explored. In nacre''s structure, the organic matrix, pillars and the roughness of the aragonite platelets play important roles in its overall mechanical performance. A micromechanical model for multilayered biological materials is proposed to simulate their mechanical deformation and toughening mechanisms. The fundamental hypothesis of the model is the inclusion of nanoscale pillars with near theoretical strength (σ_th ~ E/30). It is also assumed that pillars and asperities confine the organic matrix to the proximity of the platelets, and, hence, increase their stiffness, since it has been previously shown that the organic matrix behaves more stiffly in the proximity of mineral platelets. The modelling results are in excellent agreement with the available experimental data for abalone nacre. The results demonstrate that the aragonite platelets, pillars and organic matrix synergistically affect the stiffness of nacre, and the pillars significantly contribute to the mechanical performance of nacre. It is also shown that the roughness induced interactions between the organic matrix and aragonite platelet, represented in the model by asperity elements, play a key role in strength and toughness of abalone nacre. The highly nonlinear behaviour of the proposed multilayered material is the result of distributed deformation in the nacre-like structure due to the existence of nano-asperities and nanopillars with near theoretical strength. Finally, tensile toughness is studied as a function of the components in the microstructure of nacre.     

In situ observation of nanograin rotation and deformation in nacre

Nacre is a natural nanocomposite material with superior mechanical strength and toughness. What roles do the nanoscale structures play in the inelasticity and toughening of nacre? Can we learn from this to produce nacre-like nanocomposites? Here we report in situ dynamic atomic force microscope observations of nacre with aragonite nanograins (nanoparticles) of an average grain size of 32 nm, which show that nanograin rotation and deformation are the two prominent mechanisms contributing to energy dissipation in nacre. The biopolymer spacing between the nanograins facilitates the grain rotation process. The aragonite nanograins in nacre are not brittle but deformable.