纤维体积分数对W纤维/Zr基非晶合金复合材料压缩性能的影响

采用渗流铸造法制备了含不同体积分数W纤维的W_f/Zr基非晶合金复合材料,其中W_f体积分数分别为47%、66%、77%和86%。研究了W_f体积分数对Zr基非晶复合材料室温准静态压缩力学性能以及变形行为的影响。结果表明:随W_f体积分数的增加,W_f/Zr基非晶复合材料的屈服强度单调增大,塑性应变先增大后减小,W_f体积分数为66%时塑性应变最大,W_f/Zr基非晶复合材料塑性应变的变化主要取决于非晶基体和W_f相互作用的程度。随着应变量的增大,基体中剪切带的数量和密度也随之增大,主剪切带向大于45°方向偏转。由于压头的影响,W_f/Zr基非晶复合材料压缩过程中样品端部和中部的受力状态不同,导致两部分的剪切带方向也明显不同。随W_f体积分数的增大,W_f/Zr基非晶复合材料的断裂方式由剪切断裂向纵向劈裂转变,断裂行为符合摩尔库伦准则。     

玻璃包覆钴基非晶丝巨磁阻抗的长度效应

通过测量长度不同的玻璃包覆钴基非晶丝在频率为100kHz时的GMI值,近似计算出玻璃包覆钴基非晶丝的圆周磁导率.玻璃包覆钴基非晶丝圆周磁导率下降随着长度增加而变得剧烈,导致GMI变化更剧烈.利用玻璃包覆钴基非晶丝的磁畴模型,分析不同长度时玻璃包覆钴基非晶丝的磁化过程,合理解释了GMI效应随玻璃包覆钴基非晶丝长度增加而明显的现象.     

块体非晶合金韧塑性研究现状

提高室温塑性和断裂韧性是块体非晶合金作为先进结构材料应用亟待解决的关键科学问题,理解应力加载时的室温塑性变形机制是提高其韧塑性的前提。块体非晶合金通过高度局域化的剪切带形成和扩展而产生塑性变形,提高其室温塑性取决于剪切带的均匀化分布程度。研究者们在该领域做了深入细致的研究工作,如喷丸、设计高泊松比的非晶、设计具有微观起伏结构的铸态相分离非晶以及引入晶相增韧等,使块体非晶合金的韧塑性得到有效改善。从第二相韧塑化非晶基复合材料、泊松比判据、尺寸效应、非晶表面涂层增韧、通过预变形预制多重剪切带改善塑性、冷热循环处理抗非晶合金老化等方面,综述了块体非晶合金韧塑化的研究热点,韧塑性判据,控制剪切带形成、扩展和分布的方法,指出获得良好拉伸塑性和断裂韧性仍是不同体系非晶合金的研究目标和重要发展方向,推动着块体非晶合金作为新型功能结构材料的应用和产业化。     

镁基非晶复合材料制备、性能及应用的研究进展

综述了镁基非晶复合材料的制备,主要包括内生复合法和外加复合法;介绍了用这2种方法制得的镁基非晶复合材料的力学性能;讨论了其塑性变形机理,认为其综合力学性能得到很大改善的原因是在复合材料中的纳米相或第二相限制了剪切带的增殖和扩展.通过介绍其腐蚀性能发现,目前这方面的研究还较少,并介绍了镁基非晶复合材料目前的工程应用,提出将来的研究重点应是镁基非晶复合材料的制备和耐腐蚀性能.     

Zr-Al-Cu-Ni-Ag非晶复合材料的显微硬度和剪切带形貌

使用差氏扫描量热仪、维氏显微硬度计和扫描电子显微镜研究了过冷液相区内不同温度等温退火处理对Zr-Al-CuNi-Ag块体非晶合金的显微硬度和剪切带形核、扩展的影响。结果表明,等温退火处理后非晶合金的初晶相为二十面体准晶相(I-相),其体积分数随着退火温度的升高呈现上升的趋势;复合材料的显微硬度随着晶化体积分数的升高呈现增大的趋势;界面压痕下方剪切带密度随着晶化体积分数的升高则呈现下降的趋势。这是等温退火导致非晶合金发生结构弛豫和第二相析出综合作用的结果。     

W丝/Zr基非晶合金复合材料动态拉伸断裂模式研究

采用霍普金森杆拉伸技术研究了W丝体积分数为80%的W丝/Zr基非晶合金复合材料的动态拉伸性能,通过扫描电镜研究了该复合材料动态拉伸断裂模式.结果表明:随着打击速度增加,复合材料动态拉伸强度和断裂应变总体呈上升趋势;复合材料的动态拉伸断裂模式以钨丝解理断裂为主导,伴随非晶合金基体产生脉纹状花样和钨丝劈裂;脉纹状花样的形态不同于在动态压缩条件下所形成的,不存在"尖脊"形貌.     

非晶合金中剪切温升的研究进展

区别于传统的晶态金属材料,非晶合金(BMGs)不具备长程有序结构,其塑性变形载体为剪切带。剪切带一旦形成,便很快发展成为裂纹,引发材料的灾难性断裂。剪切不稳定性的研究有助于非晶合金塑性变形机理的理解,并可为非晶合金塑性变形能力的提高提供设计思路。近年来,基于非晶合金的结构特点,科研工作者努力探究非晶合金的剪切不稳定性,主要提出了结构软化诱导的剪切不稳定性和热软化引发的剪切不稳定性两种机制。本文重点总结了非晶合金中剪切温升的研究进展,介绍了测试应变速率、外部约束、试验机刚度和测试温度对剪切温升的影响,指明非晶合金中剪切引入的热远低于玻璃转变温度,暗示热软化对剪切不稳定性的影响是微弱的。本文最后对非晶合金中剪切不稳定性机制的研究方向进行了展望。     

重庆仪表材料研究所1988年主要科技成果简介

一、非晶合金力传感器材料我所研制成功非晶合金力传感器用非晶合金圆丝及扁带。非晶圆丝在技术上有较大突破,Fe-Si-B-C 非晶圆丝的物理、机械性能见表1。研究成功的非晶合金圆丝及扁带,目前除已应     

非晶合金中锯齿流变动力学的研究

非晶合金在外力场的作用下会出现间接性的锯齿流,锯齿具有空间和时间的无序分布性,能够反映塑性变形过程中剪切带的演化过程。借助于混沌理论、自组织临界理论、统计分析、分形和平均场理论等数学方法进行了锯齿动力学研究。发现非晶合金的塑性流变行为与材料的本征结构、试样尺寸、加载试验机的刚度、温度和应变速率等密切相关,揭示了非晶合金的塑性变形过程中剪切带滑移不稳定性的演化特点。试样尺寸小、低温或高应变速率下加载的韧性非晶试样的塑性流变动力学呈现类自组织临界状态,锯齿的幅值分布具有无标度性特点,剪切带之间的交互作用强,剪切带过程相对稳定。低温下大的分形维数说明剪切带分叉速率快,触发了剪切带之间的交互作用。简单的平均场理论证实了非晶合金的塑性可受应变速率调控。这些结论为进一步探索非晶合金的塑性提供了新的思路。     

以W为中间层的C/W多层膜的微观结构及性能研究

利用非平衡磁控溅射技术在钢基体上制备以W为中间层的C/W多层膜,使用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和透射电子显微镜(TEM)对镀层的表面形貌,相组成及截面微观结构进行分析;测试镀层的膜基结合强度和摩擦性能.结果表明:C/W多层膜是由非晶碳和WC纳米晶组成的复合镀层,具有明显的层状结构,周期厚度为6.5...     

Microstructure and Mechanical Properties of Fe-based Amorphous Composite Coatings Reinforced by Stainless Steel Powders

In this study,a few Fe-based amorphous matrix composite coatings reinforced with various portions(4,8 and16 vol.%) of 31 6L stainless steel powders have been successfully produced through high velocity oxy-fuel(HVOF) spraying.The microstructure of the composite coatings was systematically characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The main structure of composite coatings remained amorphous while 31 6L stainless steel splats were distributed homogeneously in the amorphous matrix and well connected with surrounding amorphous phase.Bonding strength of coatings to the substrate was determined by "pull-off" tensile tests.The results revealed that the31 6L stainless steel phase effectively improved the bonding strength of amorphous coatings,which is mainly contributed by the strong metallurgical bonding between stainless steel and amorphous splats.The addition of31 6L stainless steel also enhanced the ductility and fracture resistance of the coatings due to the ductile stainless steel phases,which can arrest crack propagation and increase energy dissipation.     

Formation and characterization of NaCl-type FeC

Cubic FeC nanoparticles were observed in amorphous iron carbon matrix produced by pulsed laser deposition directly onto electron microscopy grids. The observed lattice constant is close to a theoretically predicted value.     

Amorphous and nanograins in the bonding zone of explosive cladding

The amorphous and nanograins in the bonding zone of the titanium/titanium explosive cladding were investigated by means of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The nanograins with perfect crystal structure range from 2 to 50 nm in diameter were in coherent with the matrix. While the amorphous were in the state of the long-range disorder and coexisted with the nanograins. The formation of the amorphous and the nanograins as well as their coexisting were due to the high cooling rate (range from 3.55 × 10⁶ to 7.8 × 10⁶ K/s at the amorphous transition temperature) within the bonding zone, and the high pressure as well as the high shear stress during the explosive cladding.     

Thin film and bulk deformation behaviour of poly(ether ether ketone)/poly(ether imide) blends

The deformation behaviour of amorphous thin films of poly(ether ether ketone) (PEEK)/poly(ether imide) (PEI) blends was investigated over a wide temperature range by optical and transmission electron microscopy. All the materials showed localized shear deformation at temperatures well below Tg. In pure PEI and in blends with up to 60 wt% PEEK content, a transition from shear deformation to disentanglement crazing occurred as the temperature was raised. However, this transition was absent in PEEK, which deformed by shear over the whole temperature range, and similar behaviour was found for PEI/80 wt% PEEK. It is argued that at high PEEK content disentanglement crazing is suppressed by strain-induced crystallization and some evidence for crystalline order in deformed regions of initially amorphous PEEK thin films was obtained by electron diffraction. The thin film deformation behaviour of the blends was also shown to be consistent with their bulk deformation behaviour, a high temperature ductile–brittle transition being observed at low PEEK content in tensile tests. This revised version was published online in November 2006 with corrections to the Cover Date.     

Load-adaptive crystalline–amorphous nanocomposites

Advances in laser-assisted deposition have enabled the production of hard composites consisting of nanocrystalline and amorphous materials. Deposition conditions were selected to produce super-tough coatings, where controlled formation of dislocations, nanocracks and microcracks was permitted as stresses exceeded the elastic limit. This produced a self-adjustment in the composite deformation from hard elastic to quasiplastic, depending on the applied stress, which provided coating compliance and eliminated catastrophic failure typical of hard and brittle materials. The load-adaptive concept was used to design super-tough coatings consisting of nanocrystalline (10–50 nm) TiC grains embedded in an amorphous carbon matrix (about 30 vol%). They were deposited at near room temperature on steel surfaces and studied using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, Raman spectroscopy, nanoindentation and scratch tests. Design concepts were verified using composition–structure–property investigations in the TiC–amorphous carbon (a-C) system. A fourfold increase in the toughness of hard (32 GPa) TiC–a-C composites was achieved in comparison with nanocrystalline single-phase TiC.     

Analytical electron microscope study of the dissolution of the Fe3C iron carbide phase (cementite) during a graphitisation anneal of carbon steel

The evolution of microstructure and composition of the Fe₃C iron carbide phase (cementite) during a graphitisation anneal of a quenched, medium carbon steel has been studied by analytical electron microscopy, including energy dispersive X-ray spectroscopy (EDX), electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM) imaging. During heat treatment at 680 °C, dissolution of the cementite particles dispersed in the martensitic matrix was completed within a time period of 1.5 h, during which time graphite nodules began to form. However, a non-graphitic carbon-rich amorphous phase was also detected during this heat treatment. It is postulated that these amorphous particles could be an intermediate stage during the overall graphitisation process.     

In situ transmission electron microscopy observation of microstructure and phase evolution in a SnO₂ nanowire during lithium intercalation

Recently we have reported structural transformation features of SnO(2) upon initial charging using a configuration that leads to the sequential lithiation of SnO(2) nanowire from one end to the other (Huang et al. Science2010, 330, 1515). A key question to be addressed is the lithiation behavior of the nanowire when it is fully soaked into the electrolyte (Chiang Science2010, 330, 1485). This Letter documents the structural characteristics of SnO(2) upon initial charging based on a battery assembled with a single nanowire anode, which is fully soaked (immersed) into an ionic liquid based electrolyte using in situ transmission electron microscopy. It has been observed that following the initial charging the nanowire retained a wire shape, although highly distorted. The originally straight wire is characterized by a zigzag structure following the phase transformation, indicating that during the phase transformation of SnO(2) + Li ? Li(x)Sn + Li(y)O, the nanowire was subjected to severe deformation, as similarly observed for the case when the SnO(2) was charged sequentially from one end to the other. Transmission electron microscopy imaging revealed that the Li(x)Sn phase possesses a spherical morphology and is embedded into the amorphous Li(y)O matrix, indicating a simultaneous partitioning and coarsening of Li(x)Sn through Sn and Li diffusion in the amorphous matrix accompanied the phase transformation. The presently observed composite configuration gives detailed information on the structural change and how this change takes place on nanometer scale.     

Hardness and the nature of microplasticity of hydroxyapatite

The hardness of thin (1.0–4.0 μm) hydroxyapatite (HA) coatings with different structures (nanocrystalline, amorphous-crystalline, and amorphous) grown on Ti and Si by rf magnetron sputtering has been studied using nanoindentation. In all of the coatings, deformation was observed to have an elastoplastic nature. The hardness of the nanocrystalline coatings corresponds to medium hardness values of HA microcrystals. The structure of the nanocrystalline coatings has been studied by high-resolution transmission electron microscopy in the indent zone and away from it. Comparison of the hardness values of coatings with different structures and analysis of the intragranular structure leads us to assume a nondislocation mechanism of plastic deformation. Its nature is interpreted in terms of a cluster representation of the structure of HA and amorphous calcium phosphates and cluster-boundary sliding in the course of deformation.     

Micromechanical properties in lamellar heterophase polymer systems

Several nanoanalytical techniques based on electron and atomic force microscopy were used to analyse the micromechanical deformation mechanisms in different nanostructured lamellae forming heterogeneous polymers: in (semicrystalline) -modified isotactic polypropylenes and (amorphous) lamellar styrene/butadiene block copolymers. It was found that the deformation processes in these two entirely different classes of materials are governed by fundamentally similar mechanisms due to similar dimension and arrangement of the nanostructures. The basic mechanism shows two steps: The initial step is determined by a plastic deformation of the soft (amorphous or rubbery) phase with a reorganisation of the hard (crystalline or glassy) lamellae and their orientation towards the deformation direction. The second step is characterised by the intense plastic deformation (yielding) of the hard lamellae up to elongations of several 100%.