The characterization of low-angle boundaries by EBSD

A method of accurately measuring misorientations by electron backscatter diffraction (EBSD), which is an extension of that proposed by Wilkinson and based on the comparison of diffraction patterns, is described. The method has been applied to linescans, and found to improve the angular resolution by a factor of more than 30. The consequent improvement in determining misorientation axes is also analysed. Small changes of orientation very close to some low-angle boundaries were investigated and found to be artefacts of the analysis. Measurements of the area from which diffraction patterns are generated show this to be much larger than the effective spatial resolution of EBSD, and it is concluded that this may be a limiting factor in the use of EBSD for microstructural characterization.     

Effect of electron beam parameters on simulated CBED patterns from edge-on grain boundaries

Convergent beam electron diffraction (CBED) at vertical grain boundaries (parallel to the electron beam) can be applied to determine the symmetry of bicrystals. It can also be used to investigate the structure of the boundary region itself when subnanometre probe sizes are employed. In this paper it is shown that (sub)nanometre-probe CBED patterns are largely influenced by the electron-beam geometry. In particular, simulations of coherent CBED patterns based on the multislice algorithm show that the CBED pattern of an edge-on interface depends on the defocus distance between the probe position and the specimen midplane, the probe size and the beam-convergence angle. The pattern symmetry may be lower than the theoretically predicted symmetry in case of large spherical aberration. This effect increases with smaller accelerating voltages. An increase in the beam-convergence angle also increases the possibility of a non-optimum symmetry due to spherical aberration of a coherent probe. Thus, for the determination of an interface structure using subnanometre (coherent) probes, the imaging conditions play an important role.     

Quantitative HREM observation of the Σ11(113)/[1¯10] grain-boundary structure in aluminium and comparison with atomistic simulation

Quantitative high-resolution electron microscopy (QHREM) involves the detailed comparison of experimental high-resolution images with image simulation based on a model and weighted by the estimated uncertainty in the experimental results. For simple metals, such as Al, models have been systematically improved using nonlinear least-squares methods to obtain simulated images that are indistinguishable from experimental images within the experimental error. QHREM has been used to study the atomic structure of the Σ11(113)/[1¯10] in Al. In this paper, we focus on the method of refining electron-optical imaging parameters and atomic structure to bring the simulated HREM image into agreement with the experimental result to within the experimental error and thus yield a result more useful to the materials scientist. Uncertainties in fitted parameters are studied using the conditional probability distribution function. We discuss experimental results for atomic column locations compared with atomistic simulations of the structure of the grain boundary.     

On the orientations of abnormally grown grains in nanocrystalline Ni and Ni–Fe

The scanning electron microscopy–based electron backscatter diffraction technique has been used to determine grain orientations of abnormally grown grains upon annealing in nanocrystalline Ni and Ni–20 at.% Fe electrodeposits. The results show that in nanocrystalline Ni and Ni–Fe, the first grown grains that can be detected are 〈411〉 oriented with respect to the normal direction (〈411〉//ND). Upon annealing, further grain growth occurs and the dominant orientation of the abnormally growing grains changes from 〈411〉//ND to 〈111〉//ND. Twinning is found to be the mechanism responsible for the orientation change and is for the first time described in connection with abnormal grain growth in nanocrystalline materials. This means that well‐known models for the formation of annealing twins (initially introduced in connection with recrystallization) also seem to apply in nanocrystalline materials.     

叶片疲劳应力幅的断口特征形貌判断

归纳总结了叶片疲劳断口的特征形貌。宏观疲劳断口的特征形貌主要有宏观疲劳源或疲劳源区的疲劳沟线、疲劳扩展距离、疲劳断口的粗糙度,微观疲劳断口的待征形貌主要有微观疲劳条带间隔、二次疲劳裂纹和韧窝形貌等。然后讨论了通过疲劳断口特征形貌的定性分析或定量分析诊断疲劳应力幅大小的可能性和值得注意的问题。     

The effect of vacancies on the annular dark field image contrast of grain boundaries: a SrTiO(3) case study

The analysis of grain boundary structure in high resolution electron microscopy is often hindered by contrast variation within the grain boundary region which is not explained by simple models of the grain boundary structure. Recent work suggests that structural disorder along the beam direction and the presence of vacancies contribute significantly to this effect. One might expect a significant reduction in contrast in a Z-contrast image of a grain boundary would imply that vacancies present must result from the absence of heavier elements. Using a [001](210) Σ5 grain boundary in SrTiO₃ as a test case and first principles structure relaxation to calculate stable defect structures, we show that the reduction in the intensity from fully occupied Sr columns due to the structural distortion resulting from a nearby O vacancy can be as great as that due to introducing a Sr vacancy in the column itself. The effect on energy dispersive X-ray spectroscopy signals is also considered, but found to be smaller than that on Z-contrast images.     

The quantitative analysis of thin specimens: a review of progress from the Cliff-Lorimer to the new ζ-factor methods

A new quantitative thin‐film X‐ray analysis procedure termed the ζ‐factor method is proposed. This new ζ‐factor method overcomes the two major limitations of the conventional Cliff‐Lorimer method for quantification: (1) use of pure‐element rather than multielement, thin‐specimen standards and (2) built‐in X‐ray absorption correction with simultaneous thickness determination. Combined with a universal, standard, thin specimen, a series of ζ‐factors covering a significant fraction of the periodic table can be estimated. This ζ‐factor estimation can also provide information about both the detector efficiency and the microscope–detector interface system. Light‐element analysis can also be performed more easily because of the built‐in absorption correction. Additionally, the new ζ‐factor method has several advantages over the Cliff‐Lorimer ratio method because information on the specimen thickness at the individual analysis points is produced simultaneously with compositions, thus permitting concurrent determination of the spatial resolution and the analytical sensitivity. In this work, details of the ζ‐factor method and how it improves on the Cliff‐Lorimer approach are demonstrated, along with several applications.     

高温高压双金属片式疏水阀的设计

介绍了高温高压双金属片式疏水阀的工作原理以及特殊结构的设计,论述了双金属片材料和组合结构的选择,优化了阀门在恶劣工况下阻汽排水性能。     

Formation process of β-FeSi2 from amorphous Fe-Si synthesized by ion implantation: Fe concentration dependence

Formation processes of β-FeSi₂ from amorphous Fe-Si layers have been investigated using transmission electron microscopy (TEM). Si(111) substrates were irradiated with 120 keV Fe ions at −150°C to fluences of 1.0 × 10¹⁷ and 4.0 × 10¹⁷ cm^–2. An amorphous Fe-Si layer embedded in an amorphous Si was formed in the low-fluence sample, whereas an amorphous Fe-Si surface layer on an amorphous Si was obtained in the high-fluence one. The amorphous Fe-Si layers were crystallized to β-FeSi₂ after thermal annealing at 800°C for 2 h. Cross-sectional and plan-view TEM observations revealed that, prior to the formation of β-FeSi₂, the amorphous Fe-Si layers crystallized to α-FeSi₂ in the low-fluence sample and to ɛ-FeSi in the high-fluence one. The absence of metastable γ-FeSi₂ which is considered as a precursor of epitaxially grown β-FeSi₂ on Si was attributed to the instability of γ-phase in an amorphous matrix.     

柴油机高压喷油泵凸轮弹性流体润滑设计

对柴油机高压喷油泵中凸轮与滚轮摩擦副的润滑情况进行分析研究,用弹性流体润滑设计方法,计算出凸轮曲率半径,为柴油机高压喷油泵凸轮的设计提出了一种新型的设计思路,减少了传统设计中通过实验得出结论的即复杂又缺少理论依据的状况.     

The students of the “systematic deviations from ordinary rectilineal construction” in the Athenian Parthenon

Certain small “systematic deviations from the straight line” were engineered by Athenian architects of the 5th c B.C. with the aim of attaining visual aesthetic excellence for certain sacred buildings on the Acropolis. Here, we describe more-or-less in chronological order, the work of the 18th and 19th c architects such as Stuart and Pennethorne who measured and then attempted to rationalise such deviations. Buildings where aesthetic appeal somewhat based on mathematics precedes fitness for structural function, are rare. This paper is to be read in conjunction with Ref. ^[1].     

基于可靠性的大型数控铣齿机故障综合分析

分别用传统故障频次分析和故障比重比分析,对所采集的某大型数控铣齿机现场故障数据进行了统计分析,找出了影响该数控铣齿机可靠性的薄弱环节,弥补以往只通过故障频次图分析故障信息的缺陷,为机电类产品的故障分析研究提供较实用的方法。     

The quantitative measurement of magnetic moments from phase images of nanoparticles and nanostructures—I. Fundamentals

An approach that can be used to measure the magnetic moment of a magnetized nanoparticle or nanostructure from an electron-optical phase image is introduced. The measurement scheme is based on integration of the gradient of the measured phase image within a circular boundary that contains the structure of interest. The quantity obtained is found to be directly proportional to the magnetic moment of the particle, with a constant of proportionality that does not depend on the particle's shape or magnetization state. The measurement of magnetic moments from both simulated and experimental phase images is demonstrated, and strategies are presented that can be utilized to overcome sources of error associated with, for example, the presence of neighboring magnetic particles and the perturbation of the holographic reference wave.     

The ‘corpuscle’ stereological problem—re-evaluation using slab fragment volumes and application to the correction of DNA histograms from sections of spherical nuclei

A new category of stereological size distribution unfolding models is introduced. It is based on the use of the volumes of particle slab fragments, in addition to their profile dimensions. When spheres are cut by a slab of known (constant) thickness, an estimation of discrete sphere sizes from section data is then possible, as only one parent sphere solution exists for any slab fragment, given the latter's projection size and volume. The unfolding algorithm consists in sequentially testing a set of equations: only one of the solutions satisfies various constraints on bounds. A precise determination of the section thickness is required. Truncation parameters, instead of being troublesome inputs as in classical unfolding models, become valuable outputs. This model offers the first stereologically valid solution to the important problem of correcting DNA-amount histograms obtained from sectioned spherical nuclei. Under the (biologically reasonable) assumption that the nuclear volume is proportional to the DNA amount, it is possible to estimate the DNA concentration and, subsequently, compute discrete slab fragment volumes from corresponding DNA values. An application to Feulgen-stained rat liver sections is shown. Measurements of hepatocytic nuclear-profile areas and integrated optical densities are obtained by automated image analysis (IBAS), and the model is used to unfold the section-obtained DNA histogram. A maximum likelihood fitting of the final distribution with chi functions allows a parametric estimation of ploidy frequencies. This model can only be used for acceptably spherically shaped particles.     

CX6112车铣复合机床设计方案的研究与探讨

文章较系统地论述了车铣复合机床设计方案的形成过程，同时分析了该设计方案的持点，并简要介绍了该产品的主要技术参数和用途，简评了该产品的技术水平。