Mg74Zn25Y1三元合金中的准晶相

旨在研究高镁、低锌和低钇合金中准晶的形成和分布,降低材料的密度,研究制备准晶增强自生复合材料的可行性。用金相显微镜和SEM分析低Zn和低Y含量下,Mg74Zn25Y1合金普通凝固组织;EDS分析合金和凝固组织中各相的成分;XRD分析凝固组织的相组成;TEM确定准晶的结构。研究结果表明,Mg74Zn25Y1合金的凝固组织为?-Mg+MgZn+Zn60Mg30Y10。其中,Zn60Mg30Y10准晶为五次对称的20面体结构,微观形貌呈现出完整五瓣花瓣和没有完全长大的五边形。准晶晶粒尺寸小于50 ?m。     

五棱镜的运动误差对波前测量的影响

五棱镜使光束转向时,它的工作状态的改变会给测量带来一定的误差,分析了五棱镜由于机械运动引起的在三维方向有微偏角时使光束转向改变波前的复杂情况,计算机模拟实验证明了由机械运动引起的波前改变量是可分离的,以便减小五棱镜的运动误差对测量的影响,使五棱镜光束转向系统在测量中发挥最佳效能。     

Convergent-beam and small-area-parallel-beam electron diffraction of icosahedral quasicrystals of a melt-quenched Al-Mn alloy

Intensity distribution in convergent-beam electron diffraction (CBED) patterns obtained from icosahedral quasicrystas of a melt-quenched Al-Mn alloy reveal that the quasicrystals do not have fivefold, threefold and twofold rotation axes and have no inversion center, although ordinary diffraction patterns obtained thus far showed these rotation symmetries. CBED patterns taken from specimen areas of about 3 nm in diameter show a deviation in geometry in spot positions from the fivefold rotation symmetry. Ring patterns due to higher-order Laue zone reflections are not observed in CBED patterns. Kikuchi bands are composed of two sub-bands in the five equivalent directions, and each band has a different intensity profile. Parallel-beam (3 × 10^-5 rad) electron diffraction patterns obtained from specimen areas less than 100 nm in diameter also show a deviation from the fivefold symmetry in spot positions and make clear that each Bragg reflection consists of many fine spots which show no fivefold symmetry. It is proven experimentally that all the observed reflections occur already in the approximation of kinematical diffraction, although their intensities may be modified by dynamical diffraction effect.     

五角棱镜在大口径望远镜检测中的应用

提出了一种用子孔径拼接法检测大口径望远镜的方案,分析了五角棱镜由于机械运动引起的在三维方向有微小偏角时使光束转向改变波前的复杂情况;计算机模拟试验证明了由于机械运动引起的波前改变量是可分离的,有利于五角棱镜在大口径望远镜中发挥最佳效能。     

In situ dynamic HR-TEM and EELS study on phase transitions of Ge2Sb2Te5 chalcogenides

The phase transition phenomena of Ge2Sb2Te5 chalcogenides were investigated by in situ dynamic high-resolution transmission electron microscopy (HR-TEM) and electron energy loss spectroscopy (EELS). A 300kV field emission TEM and a 1250kV high voltage TEM were employed for the in situ heating experiments from 20 to 500 degrees C for undoped and 3wt% nitrogen-doped Ge2Sb2Te5 thin films deposited by DC sputtering. Crystallization of amorphous Ge2Sb2Te5 to its cubic structure phase started at 130 degrees C and then rapid crystal growth developed from cubic to hexagonal phase in the range of 130-350 degrees C; finally, the hexagonal crystals started to melt at 500 degrees C. For nitrogen-doped Ge2Sb2Te5, its crystallization from amorphous film occurred at higher temperature of ca. 200 degrees C, and the cubic and hexagonal phases were usually formed simultaneously without significant growth of crystals at further heating to 400 degrees C. EELS measurements showed that the electronic structures of Ge, Sb and Te stayed almost the same regardless of the amorphous, FCC and hexagonal phases. The nitrogen doped in Ge2Sb2Te5 was confirmed to exist as a nitride. Also, the doped nitrogen distributed homogeneously in both amorphous and crystalline phases. Localization of doped nitrogen was not found in the grain boundary of crystallized phases. The dynamic process of phase transition was enhanced by high-energy electron irradiation. Peeling of atomic layers in nitrogen-doped Ge2Sb2Te5 film was detected during heating assisted with electron beam irradiation.     

五角棱镜的角度制造误差对波前测量的影响

从光学平行差入手,导出了有角度制造误差的五角棱镜的像方坐标系和作用矩阵,分析了角度制造误差引起的扫描激光束转向的波前误差,提出了调整五角棱镜的依据,有利于减小角度制造误差对大口径透镜望远镜波前测量的影响。     

大型望远系统波前检测中的波前误差修正

在大型望远系统的波前检测中,固定着五角棱镜的运动平台沿并非严格平面的导轨平台移动时,五角棱镜会发生微偏转产生扫描激光束转向的波前误差。用渥拉斯顿棱镜型双频激光干涉仪实时测量五角棱镜的运动误差,计算扫描激光束入射望远系统子孔径时的波前误差,修正此波前误差得到子孔径范围内望远系统自身的波前。     

CR扫描仪激光扫描光学系统的设计

设计了一种适合于计算机X射线扫描仪的新型激光扫描系统,其空间分辨率为10lp/mm。针对常用扫描机构的不足,用五角棱镜和聚焦物镜组成扫描臂取代传统的Fθ镜头,利用成像板的柔韧性实现圆弧形进片,扫描臂同时作为接收器收集激发出的荧光,从而简化系统结构,提高系统性能。利用所设计的光学系统,分析了激光光点大小对分辨率的影响,结果显示光点越小,系统分辨率越高。分析了系统中影响激光光点大小的因素,在高转速条件下对扫描臂进行了有限元仿真,计算了当入射光与五角棱镜入射面不垂直及五角棱镜存在安置误差时,对激光光点大小的影响。结果显示光点直径最大相对变化量为0.07%,表明所设计的激光扫描光学系统具有一定的容差性和实用性。通过实验验证了所研制扫描仪的性能,结果表明图像具有良好的视觉效果,能够满足工业检测要求。     

Characterization of self-assembling isolated ferroelectric domains by scanning force microscopy

Lead zirconate titanate (PZT) thin films were prepared by a sol–gel process on platinized Si substrate. Their microstructure and surface morphology were characterized by XRD and Scanninn Force Microscopy. Phase transformation of the prepared PZT films from pyrochlore to ferroelectric was observed by XRD and PFM (piezoresponse force microscopy), respectively. Self-assembling nano-structured ferroelectric phases are fabricated by solution deposition technique followed by the controlling kinetics of the transformation. Complex structures of ferroelectric domains in the isolated ferroelectric phases were found in the furnace annealed PZT films in the temperature range of 400–500°C. Single ferroelectric domain structure in the isolated ferroelectric phases could be found in thinner PZT films and used to study the size effect of laterally confined ferroelectric domains.     

Dental gallium alloy composites studied by SEM and TEM

Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium alloys have been carried out. The Ga alloys were made by triturating a LU powder (Ag–Sn–Cu rich alloy powder) and a GF powder (Ag–Sn–Cu–Pd rich alloy powder) with a liquid Ga alloy containing Ga, In and Sn. The dental materials were found to be composites consisting of remaining, undissolved particles from the Ag-based alloy powders in a matrix of reaction products with the Ga alloy. SEM studies have been carried out to give an overview of the composites. The distribution of the elements was found by the X-ray mapping technique. The phases in the matrix and the remaining alloy particles have been identified by electron diffraction, high-resolution electron microscopy and energy-dispersive X-ray spectroscopy. The following phases were identified in the LU alloy: orthorhombic Ag₃Sn, cubic Ag₉In₄, tetragonal β-Sn and hexagonal Ag₂Ga. In addition to these well-known phases Ga-rich regions were observed consisting of an intergrowth of tetragonal CuGa₂ and one of the cubic γ-Cu₉Ga₄ phases. In addition to these phases cubic Ga₇Pd₃ was found in the GF alloy. The anomalous setting expansion of the GF alloy may be explained by the presence of Ga₇Pd₃.     

Microstructural and Tribological Characterization of Stainless Steel–Reinforced Aluminum Matrix Bimetal Composites Produced at Various Mold Burnout Temperatures

This study aims to identify the optimal burnout temperature (BT) of a plaster mold that was used in bimetal composite production. To achieve this goal, the mold was gradually heated up to 600, 650, 700, and 750?°C prior to melt infiltration casting. Molten A356 aluminum alloy was cast into mold at 730?°C for each casting process. Fifty percent porous 304 stainless steel (SS) preforms, obtained by assembling recycled SS shavings, were placed in a mold and infiltrated by A356 alloy until solidification was completed. The produced bimetal composites were subjected to a ball-on-disc tribometer with loads of 5, 10, and 15 N for 100 m sliding distance using an Al₂O₃ ball as a counterpart. θ-Fe₄Al₁₃ and η-Fe₂Al₅ phases were formed at A356 Al–304 SS interfaces for all samples. Wear rates increased with increasing load and decreased with increasing BT, except at 750?°C. At this temperature, interfacial phases with excessively increased layer thickness, hardness, and brittleness were fragmentized during the test, and these cracked particles decreased wear resistance by participating in the wear process. The most suitable BT of the mold was found to be 700?°C, considering the microstructure and wear results of bimetal composites.     

The Third International Conference on Scanning Tunnelling Electron Microscopy

The transition quasi-crystalline→crystalline is found to be very sluggish in the ternary alloy Al₆₀Mn₁₁Ni₄. This makes it possible to study in detail the relationship between the decagonal phase, obtained after furnace cooling, and two different crystalline phases, which result after long annealing at 400°C. Use is made of electron diffraction, high resolution electron microscopy and optical diffraction. The crystalline phases still exhibit features which are closely related to those of the decagonal phase. This can be concluded from a comparison of the electron diffraction patterns of the quasi-crystalline phase along a number of zones, with those of the crystalline phases along corresponding zones. The crystalline phases contain different types of defects which are analysed in detail using high resolution images and diffuse scattering in the electron diffraction patterns. The close relationship between the electron diffraction patterns of the crystalline and quasi-crystalline phases is explained in terms of general optical principles. Some characteristic features of a model of the quasi-crystalline phase are tentatively proposed.     

Structure determination of the hexagonal quasicrystal approximant micro'-(Al,Si)4Cr by the strong reflections approach

A number of different crystalline phases have been found in Al-rich Al-Cr-Si alloys by transmission electron microscopy (TEM). Among these, the new hexagonal phase micro'-(Al,Si)(4)Cr (a=2.01 and c=1.24 nm) often found coexisting with the hexagonal micro-(Al,Si)(4)Cr (a=1.998 and c=2.4673 nm, isostructural with micro-Al(4)Mn) and also with the hexagonal lambda-(Al,Si)(4)Cr (a=2.839 and c=1.239 nm, isostructural with lambda-Al(4)Mn). It is evident from their electron diffraction patterns that the structures of these three phases are related. The strong reflections in all three are distributed in a similar way. They all exhibit a pseudo-icosahedral symmetry. The structure factor amplitudes and phases for the strong reflections of the micro' phase could therefore be adopted from those of the lambda phase, according to the strong reflections approach. A structure model of the micro' phase is thus deduced from the known lambda-Al(4)Mn. micro' consists of chains of 3+3 or 4+2 interpenetrated icosahedra along the 100 directions. Similar to the lambda phase, there are two flat layers (F) and four puckered layers (P) in each unit cell of micro', stacked along the c-axis in a sequence of PFP(PFP)' where the (PFP)' block is related to the PFP block by a 6(3) screw.     

Cryofixation and ultra-low-temperature freeze-drying as a preparative technique for TEM

We have developed cryofixation and ultra-low-temperature molecular distillation drying as a method for preparing biological samples for electron microscopic analysis. To validate this approach, we have investigated the relationship between the drying characteristics and ice phases present within frozen samples. Two sample types were investigated. In the first, pure deuterium oxide (D₂O), or heavy water, was vapour condensed under vacuum conditions onto a gold-coated copper sample holder held at ?175 or ?110°C. Additionally, D₂O was slow-rate cooled from room temperature under an ultra-pure dry nitrogen gas atmosphere. The second sample type was rat liver biopsies from animals after 5 days of feeding with D₂O loaded water and ultra-rapid cooling by metal-mirror cryofixation. Ice forms present in the latter samples, determined by electron diffraction of frozen-hydrated cryosections, were amorphous, cubic, and hexagonal. Drying of samples was achieved using a molecular distillation configuration with continuous, microprocessor-controlled sample heating. The vacuum contents of the drying column were monitored by residual gas analysis (RGA) throughout the drying cycle. D₂O vapour in the vacuum chamber, as analysed by RGA, was found to increase in a phasic manner across a broad temperature range. These phases had characteristic onset temperatures and could be removed sequentially. For condensed D₂O samples, these onset temperatures were — 160, — 148, — 125 and — 90°C. Rat liver samples also demonstrated phasic drying patterns which were more complex than those detected with pure D₂O samples. Ultrastructural analysis of samples cryofixed and dried in this manner demonstrated a morphology consistent with the ice phases demonstrated in the frozen-hydrated cryosections. This, together with the RGA results, suggests the absence of devitrification or ice crystal growth during the drying procedure.     

Field emission from multiwall carbon nanotubes in controlled ambient gases,H2, CO,N2 and O2

Adsorption and desorption on clean pentagons at a tip of multiwall carbon nanotube (MWNT) have been investigated by field emission microscopy (FEM) in an atmosphere of various gases, i.e., hydrogen, carbon monoxide, nitrogen and oxygen. A MWNT with clean surface which is obtained by heat treatment gives FEM patterns consisting of six bright pentagonal rings. Adsorbates are recognized as bright spots in the FEM pattern. They reside preferentially on the pentagonal sites where the strong electric field is concentrated, and bring about stepwise increase in the emission current. Heat treatment of the MWNT emitter at about 1300K allows adsorbates to desorb. After the desorption of hydrogen and nitrogen, the original clean surface with pentagons is recovered, while the tip structure is destroyed after the desorption of oxygen.     

A study on the mechanical properties of ti-8ta-3nb alloy for biomaterials

Ti-8Ta-3Nb has been developed as a new biomaterial. The experimental specimens are as-cast and forged Ti-8Ta-3Nb alloys. Treatment in a solution, ranging from 760 to 960°C has carried out. The microstructural research has carried out after the solution treatment and the hardness was measured. The specific heat and the length variations of Ti-8Ta-3Nb were also measured. The optimum temperature for the solution heat treatment of Ti-8Ta-3Nb was found to be 880°C. This was based on the mechanical properties and the volume fraction of α phase and their phases shown from the results of the solution heat treatment. From the results, the β transition temperature of Ti-8Ta-3Nb was found to be between 860° and 880°C.     

Multivariate statistics applications in phase analysis of STEM-EDS spectrum images

Spectrum imaging (SI) methods are displacing traditional spot analyses as the predominant paradigm for spectroscopic analysis with electron beam instrumentation. The multivariate nature of SI provides clear advantages for qualitative analysis of multiphase specimens relative to traditional gray-scale images acquired with non-spectroscopic signals, where different phases with similar average atomic number may exhibit the same intensity. However, with the improvement in qualitative analysis with the SI paradigm has come a decline in the quantitative analysis of the phases thus identified, since the spectra from individual pixels typically have insufficient counting statistics for proper quantification. The present paper outlines a methodology for quantitative analysis within the spectral imaging paradigm, which is illustrated through X-ray energy-dispersive spectroscopy (EDS) of a multiphase (Pb,La)(Zr,Ti)O₃ ceramic in scanning transmission electron microscopy (STEM). Statistical analysis of STEM-EDS SI is shown to identify the number of distinct phases in the analyzed specimen and to provide better segmentation than the STEM high-angle annular dark-field (HAADF) signal. Representative spectra for the identified phases are extracted from the segmented images with and without exclusion of pixels that exhibit spectral contributions from multiple phases, and subsequently quantified using Cliff–Lorimer sensitivity factors. The phase compositions extracted with the method while excluding pixels from multiple phases are found to be in good agreement with those extracted from user-selected regions of interest, while providing improved confidence intervals. Without exclusion of multiphase pixels, the extracted composition is found to be in poor statistical agreement with the other results because of systematic errors arising from the cross-phase spectral contamination. The proposed method allows quantification to be performed in the presence of discontinuous phase distributions and overlapping phases, challenges that are typical of many nanoscale analyses performed by STEM-EDS.     

Effect of thermal activation on the tribological behaviours of serpentine ultrafine powders as an additive in liquid paraffin

The influence of thermal activation temperature on the tribological properties of surface-coated serpentine ultrafine powders as liquid paraffin additives was studied. It is found that the serpentine powders suspended in liquid paraffin present excellent tribological properties. Thermal activations in a temperature range from 300 to 600 °C increase the film forming ability and tribofilm completeness of the serpentine, keep the layer structure and accordingly further improve the tribological properties. However, the layer structure is destroyed and hard phases appear after thermal activated at or higher than 850 °C, as results in the aggravation of friction and wear.     

Characterization of ultrafine coal fly ash particles by energy-filtered TEM

In this study, energy-filtered transmission electron microscopy is demonstrated to be a valuable tool for characterizing ultrafine coal fly ash particles, especially those particles encapsulated in or associated with carbon. By examining a series of elemental maps (K-edge maps of C and O, and L-edge maps of Si, Al, Ti and Fe) recorded using the three-window method, considerable numbers of titanium and iron species with sizes from several nanometres to submicrometre were shown to be present, typically as oxides dispersed in the carbonaceous matrix. Crystalline phases, such as rutile and iron-rich oxide spinel, were also identified from electron diffraction patterns and high-resolution TEM images. Information about these ultrafine coal fly ash particles regarding their size, morphology, elemental composition and distribution, and crystalline phases, which has not been available previously in conventional ash studies, should be useful in toxicological studies and related environmental fields.     

多元陶瓷相在激光熔覆层中的溶解机制研究

激光熔覆层材料以铁基粉末为基础,添加有TiC、WC和SiC多元陶瓷增强相。依据自由能变理论,对激光熔覆过程中的涂层化学反应方向与反应程度进行了热力学分析,研究了所添加陶瓷增强相的溶解机制,结果表明：在设定的工艺参数和激光作用下,涂层表面可产生2 000~3 000 K的高温,通过显微组织分析可以发现,在上述温度范围内陶瓷物质发生了部分甚至完全溶解,且熔池中熔化游离的Fe、Cr、Ni等离子或颗粒先后与陶瓷物质中分解出的Ti、W、Si与C元素发生再反应与互溶,形成了具有一定金属性以及陶瓷相强度和硬度的物质,如FeNi2Ti、Fe-Cr-Ni-Si等新合金相或固溶体,并达到了强化涂层性能的效果。研究结果与理论模型分析结果规律相同。