聚乙二醇增塑PLA/La-OMMT纳米复合材料的制备及性能研究

为改善聚乳酸(PLA)性脆、断裂形变小、韧性差、热稳定性差等问题,采用稀土镧表面改性有机蒙脱土(La-OMMT)对聚乳酸(PLA)进行熔融插层改性,并利用聚乙二醇400(PEG-400)进行增塑改性,最终制备出聚乙二醇增塑聚乳酸/蒙脱土纳米复合材料PLA/La-OMMT/PEG-400.实验结果表明,La-OMMT的加入,提高了复合材料的拉伸强度、弯曲强度和无缺口冲击强度,而PEG-400的加入,在保证复合材料具备一定强度的前提下,显著提高了复合材料的韧性和断裂伸长率.XRD,TEM和SEM结果表明,La-OMMT主要以剥离状态分散在PLA基体中,且La-OMMT和PEG-400的加入,使材料拉伸断面由脆性断裂向韧性断裂转变,由此扩大了PLA的应用范围.     

金属纳米多层膜力学性能研究进展

新型功能材料及器件向小型化,集成化和复合化发展的趋势,使得尺寸在纳米尺度的层状材料和柔性多层器件在使用过程中的服役行为成为其发展的关键科学问题。本文结合作者近几年对Ag/M系列和Cu/M系列多层膜力学性能的研究工作,对金属纳米多层膜的微结构特征及其对力学性能的影响进行了回顾和总结,主要包括多层膜的晶粒形貌对其强化机制和塑性变形行为的影响,组元强度错配对多层膜硬化行为的影响,界面结构与其强度极值的关系、不对称界面结构引起的异常弹性模量增强和多层膜的室温蠕变机制及界面结构对蠕变性能的影响等几个方面,并对多层膜的力学性能研究进行了展望。     

TiN/Ti多层膜韧性对摩擦学性能的影响

考察了TiN/Ti多层膜韧性对其摩擦学性能的影响.采用磁过滤阴极弧沉积的方法制备了具有不同Ti子层厚度的TiN/Ti多层膜.用透射电镜对其层状结构及子层厚度进行了观察和分析,分别用Rockwell硬度计和UMT摩擦磨损试验机,进行了压痕测试和摩擦磨损实验.结果表明,TiN/Ti多层膜中Ti子层的加人显著提高了多层膜的韧性,相对TiN单层薄膜,当载荷较大时,多层膜的耐磨性有明显的改善.结合实验结果,讨论了TiN/Ti多层膜韧性对其耐磨性的影响.     

微观组织结构对C/C复合材料力学行为的影响

采用快速化学液相气化渗透法制备了2D-C/C复合材料,沉积温度为1200-1250℃, 系统压力约0.1MPa.利用偏光显微镜及扫描电子显微镜观察了不同沉积温度制备的基体热解碳的微观组织结构及断口形貌.实验结果表明,1200℃沉积的基体热解碳中粗糙层组织占大多数,其弯曲强度较高、韧性较低; 1250℃的基体热解碳呈现为光学各向异性程度不同的光滑层/粗糙层交替层状组织,其弯曲强度较低、韧性较高,具有非脆性断裂行为.不同微观结构的材料具有不同的强度及断裂模式,除了纤维/基体间界面结合强度不同外,不同温度沉积得到的热解碳微观结构的不同引起裂纹在不同微观结构碳层内的扩展阻力也会不同.此外,裂纹在光滑层/粗糙层界面处的偏转会导致断裂面的高低不平,从而使后者韧性增强.     

界面涂层与基体对先进CVI-SiC/SiC复合材料性能的影响

对含有几种典型界面结构和SiC纳米线的CVI-SiC/SiC复合材料的弯曲性能和断裂韧性进行了比较研究. 研究表明: 界面涂层对SiC/SiC的力学性能至关重要, 120nm厚的碳界面涂层使材料的强度与韧性都增加一倍; 在用140nm厚的SiC层将该碳层分为更薄的两层, 形成C/SiC/C多层界面涂层时, 材料的强度没有明显的变化, 而断裂韧性则略有提高. 对基体中弥散分布有SiC纳米线的SiC/SiC的力学性能研究表明, SiC纳米线具有非常高的强化效率, 使SiC/SiC复合材料具有更高的强度和韧性.     

层合轧压SMAT纳米化304不锈钢复合材料的渐进损伤模拟

基于表面机械研磨处理技术(SMAT)和温轧工艺,可以加工出具有高强度和理想韧性的层合纳米化结构复合材料。为了研究层合轧压SMAT纳米化304不锈钢的变形行为以及随后的损伤起始与演化过程,采用内聚有限元方法,建立了用于预测该复合材料力学性能的有限元模型。基于这个模型,评估了材料中纳米晶层性质,包括法向内聚强度、切向内聚强度、损伤演化断裂能和体积含量对于材料整体强度和韧性的影响。通过数值仿真结果和实验结果的比较,验证了模型的合理性和准确性,同时预测结果表明增加纳米晶层的内聚强度和减小其断裂能都能提高材料的韧性;增加纳米晶层的体积含量,材料的整体韧性降低,但是强度会增加。     

Zr基氮化物／金属Cu纳米多层膜的强韧化研究

多层结构可以提高材料的强度、弹性模量和韧性。当尺寸减小到纳米量级时,性能将产生飞跃变化。首先探讨了多层结构提高强度、弹性模量和韧性等性能的基本原理,然后阐明了纳米尺度效应及理论,重点以过渡族金属氮化物ZrN纳米多层膜为例,研究了氮化物／金属（ZrN／Cu）纳米多层膜、ZrAIN纳米复合膜以及ZrAIN／Cu纳米多层膜的强韧化性能。结果表明,ZrN／Cu纳米多层膜的断裂韧性约是二元ZrN薄膜的2倍。当纳米多层膜的Cu单层厚度为2013131时,多层膜的K1C值最高。ZrAIN复合膜的断裂韧性与Al含量密切相关,当Al原子分数为23％时,薄膜的KIc值达3．17MPa·m^1/2,其硬度〉40Gpa,Al原子分数为47％的薄膜的K1C值则降低到1．13MPa·m…。,其硬度降低至17．1GPa。与z州／cu纳米多层膜和ZrAlN复合膜相比,以ZrAIN层和cu层为调制结构制备的ZrAlN／Cu纳米多层膜具有最高的硬度和最好的韧性。     

钛-钢爆炸复合板熔焊对接过渡层焊接材料

通过设计TA1-X80爆炸复合板熔焊连接过渡层焊接材料及焊接工艺,结合复合板对接实验及接头组织、成分及性能测试实验,研究钛-钢复合板熔焊对接的过渡层焊接材料及工艺。结果表明:开Y型坡口并采用近钛层+近钢层双层过渡,且近钛层采用Ti-Ni-Al合金系、近钢层采用Ni-Cr-Fe合金系,可实现钛-钢复合板的冶金对接。焊缝组织由钛层粗大等轴晶逐渐转变为过渡层细小等轴晶或树枝晶,并与钢层组织相互交织连接;所得接头抗拉强度及屈服强度分别为501.1,373.0MPa,均达到了复合板接头等强匹配效果,塑/韧性稍有不足,需通过减小过渡层厚度、调整焊材中细化晶粒元素等改善焊缝塑/韧性。     

纳米多层膜塑性变形及其Hall—Petch表征

采用直流磁控溅射制备了不同调制波长的Ni/Al多层膜，利用X射线衍射技术（XRD）和纳米亚痕仪对薄膜微结构及力学性能进行了系统研究。结果表明，Ni/Al多层膜呈现纳米晶结构特征；同时，随调制波长减小，多层膜的硬度与“软”相的微结构特征参量具有相似变化规律，表明多层膜的变形机制对软膜的微结构约束存在敏感性。随薄膜特征尺度的减小，通过提出一个与软膜相关的新的表征参量（Lsub/d，L表示亚层厚，d表示晶粒尺寸，下标代表亚层），对多层膜晶界强化和膜界强化两种机制进行了协调统一，使薄膜变形在整个尺度范围内较好的符合Hall—Petch关系。     

合金元素对Sn-57Bi无铅钎料组织及韧性的影响

研究了添加不同含量的合金元素Ag,Ge,Cu,Sb,Zn,Ce,P,Ni对Sn-57Bi钎料的熔化温度、润湿性能、冲击韧性和显微组织的影响。研究结果表明,合金元素的添加对于钎料的熔化特性的影响不大,P,Ni的加入会导致出现硬脆的Bi,削弱了钎料的性能,Ag3Sn和富锌相则在形状合适时可以强化钎料的性能。单独加入合金元素Ag,Ge,Zn,Cu可以改善钎料的塑韧性,Ag,Ge还可以提高钎料的屈服强度和接头的剪切强度。合金元素Sb,Ce,P,Ni的加入会弱化钎料的塑韧性。而在同时添加多种合金元素的钎料合金中,43Sn-Bi-1Ge-1Ag的改善效果最好。     

Introducing a hierarchical structure for fabrication of a high performance steel

The multifunctional diversities existing in nature provide clues to speculate the structure–property–function relationships. A hierarchically structured steel is designed by using principles derived from nature and fabricated in situ by a one-step method of surface mechanical attrition treatment (SMAT). The microstructure of the processed steel is characterized by multilayered structure with hard nanocrystalline surface and compliant inner-layer, in particular with a smooth mechanical gradient induced by dual-phase constituents and multiscale grain size distribution. The hierarchically structured steel exhibits simultaneously high stiff, strong and large ductility, which originate from the joint deformation mechanisms of distinct reinforcing layers. The four layers present their own unique deformation mechanisms, including second-phase hardening, transformation induced plasticity and twin strengthening. The unique spatial form of gradation can release stress concentration and improve energy-dissipation leading to exceptional mechanical properties compared with the uniform materials.     

Dynamic crack initiation toughness of 4340 steel at constant loading rates

Determination of fracture toughness for metals under quasi-static loading conditions can follow well-established procedures and ASTM standards. The use of metallic materials in impact related applications requires the determination of dynamic crack initiation toughness for these materials. There are two main challenges in experiment design that must be overcome before valid dynamic data can be obtained. Dynamic equilibrium over the entire specimen needs to be approximately achieved to relate the crack tip loading state to the far-field loading conditions, and the loading rate at the crack tip should be maintained near constant during an experiment to delineate rate effects on the values of dynamic crack initiation toughness. A recently developed experimental technique for determining dynamic crack initiation toughness of brittle materials has been adapted to measure the dynamic crack initiation toughness of high-strength steel alloys. A Kolsky pressure bar is used to apply the dynamic loading. A pulse shaper is used to achieve constant loading rate at the crack tip and dynamic equilibrium across the specimen. A four-point bending configuration is used at the gage section of the setup. Results are presented which show a monotonically increasing rate dependence of crack initiation toughness for 4340 high-strength steel.     

Enhancing the mechanical properties of low-carbon steel by a graded dislocation microstructure

In the present paper, the microstructures and mechanical properties of a low-carbon steel processed by graded pre-torsion (PTO) and homogeneous pre-tension (PTE), respectively, have been investigated. Experimental results demonstrate that both PTO and PTE can improve the strength of the low-carbon steel, but at a loss of ductility and toughness. However, a much better strength–ductility–toughness synergy is achieved in samples processed by graded PTO than that in samples subjected to PTE. This enhancement of comprehensive mechanical properties is due to the formation of a graded microstructure, that is, the dislocation-density increases gradually with decreasing the depth from the sample surface. This study provides a strategy for enhancing the mechanical properties of metallic materials by graded plastic deformation.     

高强韧金属材料中微结构的研究和应用

金属结构材料中的共格界面强化近年来受到广泛关注,虽然,该方法被证明是一种可同时实现强度、韧性双增的有效途径,但该类材料的制备往往受到尺寸、设备或工艺的制约.近期,一种全新的原位纳米颗粒强化技术被提出,旨在通过弥散分布的共格纳米粒子实现材料微观组织的优化及综合性能的提升.文中以铁基合金、铜合金、铝合金为例,对原位纳米颗粒...     

高强度超细晶金属材料塑性行为及增塑研究进展

强度和塑性是金属结构材料最重要的力学性能指标,金属高性能化的关键是在高强度水平下保证良好的塑性,然而两者往往不能兼顾。在众多强化方法中,晶粒细化长期以来被认为是强化金属最理想的手段,在传统晶粒尺寸范围,细化晶粒既可以显著提高材料的强度,又能改善材料的塑韧性。因此,近几十年来超细晶/纳米晶金属得到了广泛研究和发展,出现了以大塑性变形(SPD)、先进形变热处理(ATMP)技术为代表的超细晶制备方法,所得晶粒可以细化到亚微米或纳米尺度,金属性能大大提高。然而,大量研究证实当晶粒细化到亚微米或纳米尺度时金属强度提高但塑性显著下降,与传统的细晶强化规律不符。对此,国内外学者进行了很多研究,试图阐明其机理、揭示晶粒超细化导致塑性降低的物理本质。此外,由于细化晶粒方法受到塑性的限制,新的高强度水平下增强塑性的方法成为钢铁材料高性能化的研究热点。针对塑性下降的事实,为了进一步提高超细晶金属材料性能,研究者开展了许多增强塑性的工作,获得了较好的效果,但仍存在一些不足。关于金属晶粒超细化导致塑性降低的普遍共性现象,目前广泛认可的理论主要有晶界捕获(吸收)位错的动态回复理论、位错运动湮灭理论、高初始位错密度以及位错源缺失机制等。前三者都主要关注超细晶金属材料低(无)加工硬化能力,并将其归结为延伸率降低所致。主要是因为低(无)加工硬化使材料在变形早期发生塑性失稳或局部变形从而表现出低塑性。超细晶金属增塑研究主要体现在增塑方法和机理方面,目前,增塑方法主要有(1)形成纳米孪晶;(2)获得粗晶-细晶双峰组织;(3)利用相变诱发塑性/孪生诱发塑性(TRIP/TWIP)效应;(4)引入铁素体软相;(5)利用纳米第二相粒子等。这些增塑方法的主要机理是利用组织结构的改变提高超细晶金属的加工硬化能力以维持良好的均匀塑性变形以及利用组织相变提高塑性。本文归纳了常用的超细晶金属制备方法,综述了超细晶金属材料塑性降低的研究进展,总结了超细晶金属增塑的研究结果,分析了目前研究中存在的不足,探讨了超细晶金属增强增塑的发展趋势,以期为超细晶金属塑性降低理论及增强增塑研究提供参考。     

Effect of multi-directional forging and ageing on fracture toughness of Al–Zn–Mg–Cu alloys

Strength, ductility and fracture toughness are the most important mechanical properties of engineering materials. In this work, an Al–Zn–Mg–Cu alloy was subjected to multi-directional forging (MF) and ageing treatment. Microstructural evolution was studied by optical and electron microscopy and strength, ductility and fracture toughness were researched. After MF, the dislocation density was increased and the microstructure was refined. The strength and fracture toughness were increased, while the ductility was decreased sharply. Without compromising the strength, the ductility was improved significantly after ageing. The fracture toughness was increased further. The coarse and discontinuously distributed grain boundary precipitates were found to be responsible for higher fracture toughness of the fine-grained structure Al–Zn–Mg–Cu alloy.     

Fatigue crack growth rates and fracture toughness in electroslag refined En 52 steel

En 52 steel has been electroslag refined and the resultant effects of refining on its mechanical properties have been assessed. It was found that refining caused a decrease in fatigue crack growth rates and increases in fatigue strength, fracture toughness, Charpy fracture energy and tensile ductility. Fatigue crack growth rates in region I and in region III were found to be considerably lower in the electroslag refined steel: they were unaffected in region II. The fracture toughness values for the electroslag refined steel are nearly twice those estimated for the unrefined steel. Measurements on heat-treated samples have shown that the electroslag refined steel has a better response to heat-treatment. The improvement in the mechanical properties is explained in terms of the removal of nonmetallic inclusions and a reduction in the sulphur content of the steel.     

Multi-length scale micromorphic process zone model

The prediction of fracture toughness for hierarchical materials remains a challenging research issue because it involves different physical phenomena at multiple length scales. In this work, we propose a multiscale process zone model based on linear elastic fracture mechanics and a multiscale micromorphic theory. By computing the stress intensity factor in a K-dominant region while maintaining the mechanism of failure in the process zone, this model allows the evaluation of the fracture toughness of hierarchical materials as a function of their microstructural properties. After introducing a multi-length scale finite element formulation, an application is presented for high strength alloys, whose microstructure typically contains two populations of particles at different length scales. For this material, the design parameters comprise of the strength of the matrix–particle interface, the particle volume fraction and the strain-hardening of the matrix. Using the proposed framework, trends in the fracture toughness are computed as a function of design parameters, showing potential applications in computational materials design.     

Alloy design by dislocation engineering

Ultra-high strength alloys with good ductility are ideal materials for lightweight structural application in various industries. However, improving the strength of alloys frequently results in a reduction in ductility, which is known as the strength-ductility trade-off in metallic materials. Current alloy design strategies for improving the ductility of ultra-high strength alloys mainly focus on the selection of alloy composition (atomic length scale) or manipulating ultra-fine and nano-grained microstructure (grain length scale). The intermediate length scale between atomic and grain scales is the dislocation length scale. A new alloy design concept based on such dislocation length scale, namely dislocation engineering, is illustrated in the present work. This dislocation engineering concept has been successfully substantiated by the design and fabrication of a deformed and partitioned (D&P) steel with a yield strength of 2.2 GPa and an uniform elongation of 16%. In this D&P steel, high dislocation density can not only increase strength but also improve ductility. High dislocation density is mainly responsible for the improved yield strength through dislocation forest hardening, whilst the improved ductility is achieved by the glide of intensive mobile dislocations and well-controlled transformation-induced plasticity (TRIP) effect, both of which are governed by the high dislocation density resulting from warm rolling and martensitic transformation during cold rolling. In addition, the present work proposes for the first time to apply such dislocation engineering concept to the quenching and partitioning (Q&P) steel by incorporating a warm rolling process prior to the quenching step, with an aim to improve simultaneously the strength and ductility of the Q&P steel. It is believed that dislocation engineering provides a new promising alloy design strategy for producing novel strong and ductile alloys.