铝合金-环氧树脂叠层复合材料中界面相的形貌和应力破坏

环氧树脂与铝合金界面粘附之后,发生类纤维状的界面相形貌,然后逐步过渡进入环氧树脂类网状结构的基础相。环氧树脂在叠层复合材料中的连接层就是由界面相-基础相-界面相这三个层面组成的。当连接层受剪切应力作用后,界面相类纤维组织的形变速度和形变量均大于基础相中的情况,因此,类纤维组织的蠕变、损伤和破坏强烈地影响着聚合物连接层的力学性能和使用寿命。      

碳化硅颗粒增强铝基复合材料的无压浸透反应机理探讨

为探讨SiCp/Al基复合材料无压浸渗反应机理,利用XPS鉴定了SiC预制体浸渗前沿界面上的反应产物结构.采用HRTEM研究了SiCp/Al基复合材料的界面结构.结果表明,浸渗与未浸渗部分之间的界面上存在MgO.Al2O3和ZnO诸化合物,没有发现氮的化合物.在SiC相与铝相的界面上仅存在MgAl2O4相,MgAl2O4相几乎连续地包敷在SiC颗粒上.这表明,高温下SiC与熔Al合金接触后,SiC颗粒表面上的SiO2与Al,Mg,Zn诸元素发生了放热反应,从而降低了表面张力,提高了湿润性.促进了自发浸渗.     

碳化硅颗粒增强铝基复合材料的无压浸渗反应机理探讨

为探讨SiCp/Al复合材料无压浸渗反应机理,利用XPS鉴定了SiC预制体浸渗前沿界面上的反应产物结构,采用HRTEM研究了SiCp/Al基复合材料的界面结构。结果表明,浸渗与未浸渗部分之间的界面上存在MgO,Al2O3和ZnO诸化合物,没有发现氮的化合物,在SiC相与铝相的界面上仅存在MgAl2O4相,MgAl2O4相几乎连续地包敷在SiC颗粒上,这表明,高温下SiC与熔Al合金接触后,SiC颗粒表面上的SiO2与Al,Mg,Zn诸元素发生了放热反应,从而降低了表面张力,提高了湿润性,促进了自发浸渗。     

单丝拔出实验研究芳纶－环氧树脂界面相

用单丝拔出实验研究了以有机硅表面处理剂处理的Ｋｅｖｌａｒ－４９－环氧树脂体系界面相。从力一位移曲线可得到界面破坏强度、界面破坏能、界面摩擦功等界面参数。硅表面处理剂对三者的贡献不同，以２￣＃处理剂处理的综合效果最好。     

基体合金元素对SiC/Al界面结合影响的第一性原理及实验研究

采用基于密度泛函理论的第一性原理及实验相结合的方法, 探讨了Al基体中分别掺杂Mg、Si、Cu合金元素对SiC/Al界面结合的影响, 重点考察了合金元素在界面偏聚时的电子结构和成键情况。研究表明: 在未掺杂Al/SiC体系界面结构优化时, 以Si原子为终止面的Brigde结构是最稳定的结合方式; 当合金元素分别替换界面处的Al原子后, 界面处原子的分波态密度、Muliken电荷及成键原子集居数等电子结构参数均有不同程度的变化, 这不仅增加了界面处 Si与Al原子结合, 同时也增强了界面处和亚界面处的Al基体和SiC增强相原子之间的相互作用, 使体系更加稳定, 界面黏着功均有不同提升; 其中掺Mg提升效果最明显, 其次为掺Cu和掺Si; 利用第一性原理计算的掺杂Al/SiC体系黏着功和实验值较为接近且变化规律相同。     

热处理对不同基体表面镀铝相结构的影响

研究了热处理对不同钢铁基体表面镀铝相结构的影响。分别以Q235低碳钢,1Cr17铁素体不锈钢和201奥氏体不锈钢为基体,在摩尔比2∶1的酸性AlCl3-EMIC(1-甲基-3-乙基咪唑氯化物)室温熔盐中电沉积均匀致密的铝镀层,然后对试样在670℃下进行热处理,并用EDS,SEM和XRD等对热处理后的试样界面进行微观分析。结果表明,试样经热处理后,镀层与基体之间均发生互扩散形成合金层。Q235表面合金层呈舌状形貌向基体生长,而1Cr17和201表面的合金层平直。Q235上内外合金层为FeAl和Fe2Al5,并以Fe2Al5为主;而1Cr17的内外合金层为含Cr的Fe2Al5和FeAl3相;201不锈钢经短时间热处理可保留纯Al层,30min后主要由含Cr,Ni,Mn的Fe2Al5和FeAl3相组成,也形成少量的FeAl2和FeAl相。     

激光熔覆制备Fe3Al金属间化合物覆层的组织结构

为了研究激光熔覆工艺条件下Fe3Al金属间化合物合金层的组织结构特点,以纯Fe3Al粉 1%Y2O3为原料在钢基体表面激光熔覆Fe3Al金属间化合物,利用扫描电镜、能谱仪、X射线衍射试验方法等对熔覆合金层、合金层与钢基体的结合界面等进行了显微组织与相结构的分析.试验获得了致密、无肉眼可见气孔、夹杂的合金层,合金层与基体间完全冶金结合,但存在裂纹现象;熔覆合金层主要由单相Fe3Al构成,覆层组织为粗大等轴状晶团,等轴状晶团由大量极细小的条状Fe3Al晶粒构成,一些相邻的条状晶粒之间具有基本一致的晶体学取向.     

SiCp/Al复合材料界面调控研究进展

SiCp/Al复合材料具备一系列优异的物理性能,是航空航天、电子封装、装备、核电、汽车、轨道交通等国家重大需求和国民经济装备制造所需的关键材料.但是,工业精密仪器关键零部件对SiCp/Al复合材料的性能要求相对较高,导致复合材料在诸多高端领域的应用受到了严重限制,因而提升SiCp/Al复合材料的整体性能是当前亟需解决的重要难题.对于给定的增强体与基体,界面相具有的微观结构和物化性质是影响SiCp/Al复合材料性能的决定因素.然而,界面相在形成过程中通常会出现润湿性差、结构缺陷多以及生成不良界面产物等问题,对SiCp/Al复合材料的性能产生了严重的负面影响.因此,有效实现界面的可控设计成为提升复合材料性能的关键.根据近几年关于SiCp/Al复合材料界面调控的研究工作来看,增强体颗粒表面改性在抑制增强体与基体之间的相互扩散以及减缓化学反应速率等方面发挥着重要作用,而表面改性处理的方式通常包括酸洗、高温氧化和添加涂层等.在基体中添加合金元素能够有效降低铝液的表面张力,改善SiCp/Al复合材料界面相的润湿性,同时可抑制不良界面反应的发生.目前合金化处理添加的元素通常包括Mg、Si、Cr、Ti、Fe等.在SiCp/Al复合材料的制备过程中,烧结温度、保温时间、冷却速率、成型压力、球磨时间以及烧结气氛等成型工艺参数均会影响界面的反应程度,因而对成型工艺的优化改进同样能够有效调控复合材料的界面信息,以实现对SiCp/Al复合材料性能的提升.本文结合SiCp/Al复合材料界面相具有的微观结构和物化性质,从增强体颗粒表面改性、基体合金化和成型工艺优化改进三个角度综述了SiCp/Al复合材料界面调控的研究现状,并对其未来发展的整体趋势进行了展望.     

Ti_3Al金属间化合物的熔盐热腐蚀

采用电化学方法并结合扫描电镜、X 射线衍射、电子探针和能谱等物相分析技术研究了 Ti_3Al 金属间化合物在800℃熔融 NaCl-(Na,K)_2SO_4体系中的腐蚀行为。结果表明,Ti_3Al 合金耐熔盐腐蚀性能远低于 Ni 基 IN738合金。腐蚀时在合金表面形成外层为 TiO_2;内层为富 Nb 的Nb_2O_5,Al_2O_3,TiO_2的混合层和中间层为富 Al 的 TiO_2,Al_2O_3混合层的多层腐蚀层结构。Ti 快速向外扩散和氧向内扩散使合金表面腐蚀产物层迅速增厚。腐蚀产物内层的富 Nb 氧化物破坏了膜层与合金基体的粘附性。     

双相MlNi3.7Al0.4Cu0.4微晶贮氢合金的结构及活化性能

测试和分析了新型超声气体雾化双相复合MlNi3.7Al0.4Cu0.4微晶贮氢合金的微观组织结构及电化学活化性能.结果表明,这种贮氢合金的微观结构为双相复合结构,基体为AB5(A≡La,Ce,Nd,Pr,B≡Ni,Al,Cu)相,富稀土的AB相在基体中呈不连续网状分布,在相界面存在淬火裂纹.电化学活化性能优越,活化次数仅为1～3次.     

环氧沥青混凝土桥面铺装材料研究与应用进展

随着桥梁设计理念、结构分析、施工技术等不断更新发展与完善,目前桥梁正逐渐朝着大跨度、高强度、长寿命、高耐久等方向发展,同时,未来桥梁也将面临更复杂的建设环境、更多的功能需求,因此必须加强研发与新型桥梁设计体系相匹配的特种桥面铺装材料。环氧沥青混凝土桥面铺装材料以高强度、耐高温、抗疲劳、抗老化等优异路用性能脱颖而出,逐渐受到关注。然而,环氧沥青混凝土制备工艺复杂、施工条件严苛、耐久性不足等问题日益凸显,这些缺点使得其在桥面铺装领域的推广受到一定阻碍。为此,研究者们针对如何提升环氧沥青混凝土使用品质及耐久性进行了深入研究并取得了一定成果。这一系列成果先后在大量桥面铺装实体工程中得以应用,良好的使用效果也为环氧沥青混凝土的进一步推广奠定了基础。环氧沥青混凝土在桥面铺装领域的研究成果可以概括为三个方面:铺装结构组合优化、制备工艺优化、混凝土原材料优化。其中铺装结构组合从早期的单质单层结构逐渐过渡到单质双层、异质双层结构,趋于合理的铺装结构组合使环氧沥青混凝土材料的性能得以充分发挥。制备工艺从热拌法发展到温拌甚至冷拌,在保证环氧沥青混凝土使用性能的同时减少了对环境的污染,并且在一定程度上降低了施工难度。而在原材料应用方面,研究者们不断对双组分环氧沥青与三组分环氧沥青的性能进行对比分析;同时,环氧沥青的改性方式趋于多样化,从单独使用改性沥青发展到同步使用改性环氧树脂,改性剂从纤维发展到高分子聚合物、超支化聚合物等。这些措施不仅改善了沥青与环氧树脂的相容性,也增强了环氧沥青混凝土的相关性能。此外,为使环氧沥青混凝土具有更好的稳定性,在级配优化方面也进行了深入研究。然而目前环氧沥青混凝土的一系列研究成果较为散乱,缺乏对其系统的总结与梳理,且环氧沥青混凝土的性能评价指标及要求仍需深入研究与完善。为进一步确定环氧沥青混凝土桥面铺装材料科学合理的性能评价指标及要求,本文全面梳理了国内外环氧沥青混凝土相关规范,系统调查了大量实体工程及研究动态,对比分析了不同主要原材料的环氧沥青混凝土对其路用性能的影响,最终推荐了环氧沥青混凝土桥面铺装结构组合、原材料类型、级配范围和性能评价指标及要求,为环氧沥青混凝土桥面铺装材料规范完善与质量控制奠定了基础。     

Investigation of properties of fiber/matrix interphase formed due to the glass fiber sizings

Sizings on glass fibers consist of a silane-based network that is chemically bound to the fiber and other compounds that are adsorbed onto the glass surface. Formation of interphase involves dissolution of adsorbed species and inter-diffusion of these compounds and resin monomers into the interphase region and chemical reaction of available functional groups. All these phenomena occur at the presence of the silane-based network. In this study, the effects of the silane-based network on the properties of the interphase region are investigated for an epoxy/amine resin system and compatible sized glass fibers. The composition of the sizing material bound to glass was determined using nuclear magnetic resonance (NMR) spectroscopy. Based on this information, model interphase materials were synthesized that were a blend of an epoxy/amine matrix and inclusions. The inclusions consist of an interpenetrating network of silane-based polymer and epoxy/amine thermoset that represents the interphase material formed during processing. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques were used to characterize the glass transition temperature and flexural modulus of the model materials. The properties of the model interphase material were obtained using the DMA results and established micromechanics models. The results show that the glass transition temperature of the model interphase is about –5°C, and its flexural storage modulus at room temperature is about 50% of that of the bulk matrix. This work has also shown that a reduction in the cross-link density of the bound network might significantly reduce the modulus within the interphase region by a factor of 5 to 8.     

Influence of an electric field on the hardening process and the properties of an epoxy composite discretely reinforced with phosphocarbon fibers

The influence of an electric field on the hardening process, the structure, and the properties of an epoxy composite in the presence of a phosphorus-containing carbon filler has been investigated. It has been shown that under the action of an electric field the process of formation of a three-dimensional epoxy polymer in the presence in the system of phosphocarbon fibers proceeds more intensively with the formation of a more rigidly bound structure of the polymer as compared to the same composition hardened in the absence of the field. It has been established that the fibrous filler-binder interface has a dominant role in the formation of a spatially cross-linked polymer and in the properties of the product hardened both under the action of the electric field and without it. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 47–54, May–June, 2007.     

Load carrying characteristics of short fiber composites containing a heterogeneous interphase region

A micromechanics finite element model has been developed for the stress transfer in short fiber composites, incorporating a heterogeneous interphase region. The specimen consists of a single fiber under stress embedded in an epoxy matrix. Considering a heterogeneous and compliant interphase, a generalized computational procedure has been developed that enables imperfect adhesion or loss of interphasial strength simulations. Varying the global variables of the problem, parametric studies were performed to study the influence of the model parameters on the load transfer characteristics from the fiber to matrix. Numerical results of the stress distribution have been determined as a function of geometric and material variables. The effect of both the imperfect adhesion between the fiber and the matrix, and the loss of interphase compliance on stress state were demonstrated and discussed. The results showed that the interphase plays a significant role in stress transfer characteristics of fibrous composites, and extension of the load transfer zone is restricted very close to the loaded fiber end.     

Characterization and micromechanical testing of the interphase of aramid-reinforced epoxy composites

The properties of the interphase between Twaron^® aramid fibres and polymer matrix systems can be optimized by a surface treatment process of the fibres. The relation between this surface treatment, the resulting chemical and physical surface structure, as measured with XPS, IGC and SFM, and the adhesion strength in fibre–epoxy systems, as measured with Raman spectroscopy and single-filament pull-out experiments, has been established and related to the macromechanical data of real composites. The concept of local bond strength was used and the fibre–epoxy failure mechanism investigated.     

Stochastic analysis of the fracture toughness of polymeric nanoparticle composites using polynomial chaos expansions

The fracture energy is a substantial material property that measures the ability of materials to resist crack growth. The reinforcement of the epoxy polymers by nanosize fillers improves significantly their toughness. The fracture mechanism of the produced polymeric nanocomposites is influenced by different parameters. This paper presents a methodology for stochastic modelling of the fracture in polymer/particle nanocomposites. For this purpose, we generated a 2D finite element model containing an epoxy matrix and rigid nanoparticles surrounded by an interphase zone. The crack propagation was modelled by the phantom node method. The stochastic model is based on six uncertain parameters: the volume fraction and the diameter of the nanoparticles, Young’s modulus and the maximum allowable principal stress of the epoxy matrix, the interphase zone thickness and its Young’s modulus. Considering the uncertainties in input parameters, a polynomial chaos expansion surrogate model is constructed followed by a sensitivity analysis. The variance in the fracture energy was mostly influenced by the maximum allowable principal stress and Young’s modulus of the epoxy matrix.     

Epoxy modified with triblock copolymers: morphology, mechanical properties and fracture mechanisms

The morphology, fracture toughness and mechanical properties of an anhydride-cured diglycidylether of bisphenol-A epoxy polymer modified with poly(methyl methacrylate)-b-poly(butylacrylate)-b-poly(methyl methacrylate) (MAM) have been investigated. The addition of three different MAM triblock copolymers (M22N, M52N and M52) to the epoxy polymer gives two different microstructures. A nanostructure with well-dispersed worm-like micelles (or a bicontinuous gyroid structure if the micelles are connected into a network) was obtained using M22N. The addition of M52N or M52 gives dispersed micron-size particles in the epoxy matrix for ≤7 wt% MAM, and a co-continuous microstructure at higher MAM contents. These triblock copolymers toughen the epoxy polymer significantly, with only slight reductions in the mechanical and thermal properties of the epoxy polymer. The maximum values of fracture toughness and fracture energy (1.22 MPa m^1/2 and 450 J/m², respectively) were measured using 12 wt% M22N, which is an increase of 100 and 350%, respectively, compared with the unmodified epoxy. The M52- and M52N-modified materials show a maximum toughness when a co-continuous microstructure is formed. The potential toughening mechanisms are identified and discussed.     

Role of a gradient interface layer in interfacial enhancement of carbon fiber/epoxy hierarchical composites

To improve the interfacial properties of carbon fibers/epoxy composites, we introduced a gradient interphase reinforced by graphene sheets between carbon fibers and matrix with a liquid phase deposition strategy. Interlaminar shear strength and flexural strength of the composites are both improved. The interfacial reinforcing mechanisms are explored by analyzing the structure of interfacial phase with linear scanning system of scanning electron microscope and atomic force microscope. Results indicate that carbon element shows a graded dispersion in the interface region and a gradient interface layer with the modulus decreasing from fibers and matrix is found to be built. To verify the effect of gradient interphase on the interfacial properties of composites, the mixture of carbon fiber/graphene/epoxy is sonicated before curing to disperse graphene sheets in matrix homogeneously. As a result, gradient interphase structures are disappeared and interfacial performance of composites is found to be weakened. The role of gradient interface layers in enhancing interfacial performances is further proved from a different angle.     

Simulation of interphase percolation and gradients in polymer nanocomposites

Experimental data suggests that well dispersed nanoparticles within a polymer matrix induce a significant interphase zone of altered polymer mobility surrounding each nanoparticle, which can lead to a percolating interphase network inside of the composite. To investigate this concept and the nature of the interphase, a two-dimensional finite element model is developed to study the impact of interphase zones on the overall properties of the composite. Thirty non-overlapping identical circular inclusions are randomly distributed in the matrix with layers of interphase surrounding the inclusions. The simulation results clearly show that the loss moduli of composites are either broadened or shifted corresponding to the absence or presence of a geometrically percolating interphase network. Our numerical study correlates well with experimental data showing broadening of loss peaks for unfunctionalized composites and a large shift of the loss modulus for functionalized nanotube polymer composites. Further, our results indicate the existence of a gradient in properties of the interphase layer and that incorporating this gradient into modeling is critical to reflect the behavior of polymer nanocomposites.