Half-cycle slip activity of persistent slip bands at different stages of fatigue life of polycrystalline nickel

The slip activity of persistent slip bands (PSBs) in polycrystalline nickel was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The half-cycle slip activity as well as the local shear strain amplitudes was investigated after half-cycle deformation at different numbers of cycles in the domain of stress saturation. Moreover, the fraction of grains containing cumulated PSBs and the accumulated volume fraction of PSBs was estimated depending on the number of cycles during fatigue life. The volume fraction of active PSBs during half-cycle deformation is significantly lower than the cumulated PSB volume and decreases with increasing number of cycles. Additionally, an increasing localization of cyclic plastic strain within the PSBs was observed. However, with increasing number of cycles the average local shear strain amplitude remains almost unchanged. Thus, PSBs in polycrystals are subjected to a life history which is characterized by active and inactive periods of their half-cycle slip activity during cyclic deformation at different stages of the saturation state.     

扫描电子显微镜成像信号分析

介绍了扫描电子显微镜（SEM）的基本工作原理,着重分析了在SEM初始电子束作用下,各种成像信号产生的方式及其特点,确定二次电子信号因成像分辨率高、携带成像信息丰富而成为SEM的最终信号源。针对此信号在实际应用中暴露出的缺陷,介绍了解决办法,从而使SEM的成像性能得以大幅提高,使用范围大为扩展。     

Evaluation of annular pupil for scanning transmission electron microscope formed by focused ion beam technique

Annular pupils for electron optics were developed using a focused ion beam (FIB) technique to realize an increase in the depth of focus, aberration-free imaging and separation of amplitude and phase images under scanning transmission electron microscopy (STEM). A tantalum plate 30 μm thick was used as the annular pupil material in the present experiment. The annular pupils were designed with various outer diameters from ?120 μm to ?40 μm. The inner diameter was designed at 60 to 80% of the outer diameter. The fabricated annular pupils were inspected by scanning ion beam microscopy and scanning electron microscopy. Annular pupils were successfully obtained at the designed size, although the slits of the pupils were slightly tapered by the ion beam etching process. These annular pupils were loaded on a STEM and confirmed to display no charge-up phenomenon by observation of the projection image on a scintillator using a CCD camera. We confirmed the image taken by annular pupil with narrow width was able to suppress the influence of the normal illumination.     

Calibrating a scanning electron microscope in two coordinates by the use of one certified dimension

A method is proposed for calibrating a scanning electron microscope that corresponds completely to national standards providing unification of measurements in nanotechnology. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 18–20, June, 2008.     

Determination of displacements around fatigue cracks using image analysis of in‐situ scanning electron microscope images

A technique to in‐situ measure the displacements in the vicinity of the crack tip during fatigue crack propagation has been developed. High‐resolution images of the crack tip were taken continuously throughout the fatigue load cycles with a scanning electron microscope (SEM), and an image analysis program was used to determine the displacements at different positions with respect to the crack tip. The displacements were then used to determine crack shapes and compliance curves. The measured crack shapes show a general √r dependence versus the distance to the crack tip. However, close to the crack tip the crack shape is clearly affected by plastic deformation, even in cases when small scale yielding prevails. The compliance curve measurements close to the crack tip can be used to determine the global stress level when the crack surfaces are separated, so that the exact opening and closure stresses can be determined.     

The application of neutron activation analysis, scanning electron microscope, and radiographic imaging for the characterization of electrochemically deposited layers of lanthanide and actinide elements

Lanthanide and actinide targets are prepared at the University of Mainz by molecular plating, an electrochemical deposition from an organic solvent, for heavy-ion reaction studies at GSI. To acquire information about deposition yield, target thickness, and target homogeneity, the following analysis methods are applied.With neutron activation analysis (NAA) the deposition yield and the average thickness of the deposited material is determined. We report on the analytical procedure of NAA performed subsequent to the molecular plating process.Scanning electron microscope (SEM) is used to determine the morphology of the target surfaces. In combination with energy dispersive X-ray spectrometer (EDS), we also could obtain qualitative information about the chemical form of the deposited material. So far, gadolinium, samarium, holmium, and uranium targets have been investigated with SEM/EDS.With radiographic imaging (RI), targets of uranium prepared by molecular plating and by vacuum vaporization are investigated. This method is suitable to obtain information about the spatial distribution, the homogeneity, and the thickness of the target layer deposition.     

In situ scanning electron microscopy study of fatigue crack propagation

The fatigue crack propagation rate is influenced by various mechanisms at the very vicinity of the crack tip, e.g., local plasticity and/or creep, microcracking, crack branching, and crack closure induced by plasticity and roughness. To study these mechanisms and their influence on crack propagation rate during different loadings, in situ scanning electron microscope studies have been performed. Throughout the load cycles images were taken and analyzed with an image analysis technique to measure the displacements around the crack tip. The obtained data can be used to determine compliance curves at any point along the crack, crack shapes, and the displacement field in the crack tip vicinity. The technique has been used to analyze which mechanisms of crack propagation are realized during, e.g., fatigue with overloads, and thermomechanical fatigue. The results were compared with results from measurements using the direct current potential drop technique, and it was found that various load conditions promote different mechanisms for crack propagation. __________ Translated from Problemy Prochnosti, No. 1, pp. 159–162, January–February, 2008.     

环境扫描电子显微镜的成像特点

环境扫描电子显微镜(ESEM)中所指的环境并非真正意义上的大气环境(760 Torr),与传统扫描电子显微镜(SEM)样品室高真空度相比,ESEM样品室的真空度可以很低(约达20 Torr)。ESEM是在传统的SEM样品室中多一个GSED探头,因此,它在传统的SEM基础上增添了新的功能。其主要的特点是,可以观察含适量水分的样品和非导体材料样品,比如植物的叶片、动物中的昆虫、作物的籽粒、含结晶水的固体材料等。     

Compression test of a single carbon fiber in a scanning electron microscope and its evaluation via finite element analysis

A longitudinal compression test for a single polyacrylonitrile-based carbon fiber (T300) was performed using a scanning electron microscope. The compressive stress/strain behavior was initially linear, but subsequently became nonlinear. The longitudinal tangent modulus decreased with increasing compressive strain. A cyclic compression test revealed that the T300 carbon fiber deformed elastically up to ~90% compressive strength. The variability in the compressive strength was evaluated using Weibull analysis. The representative compressive strength of the T300 carbon fiber was nearly the same as the tensile strength. The compressive strength of the T300 carbon fiber was almost same as that of the high-tensile strength T800S carbon fiber. Finite element analysis was performed to investigate the validity of the test method. The results showed that the longitudinal compressive stress on the carbon fiber varied during longitudinal compressive loading. The maximum longitudinal compressive stress in the carbon fiber was slightly higher than the average compressive strength applied at the end. However, the variability in the measured compressive strength was much higher than that in the longitudinal compressive stress on the carbon fiber, which does not affect the former.     

扫描电子显微镜图像漂移的实时矫正方法

为解决扫描电子显微镜(SEM)由于电子束漂移、电磁干扰等原因导致的图像漂移问题,提出基于ORB结合PROSAC的图像漂移矫正算法。首先采用ORB算法对基准图像和实时图像进行特征检测,然后利用汉明距离与交叉匹配实现特征的初匹配,再结合RANSAC的优化算法PROSAC计算帧间的单应矩阵,利用单应矩阵映射剔除外点后重新迭代计算出最终的精确单应矩阵,最后利用单应矩阵的透视变换实现SEM图像漂移实时矫正。通过实验证明,该算法不仅精度高,而且能够满足SEM实时处理的要求。     

Immobilization of phenol in cement-based solidified/stabilized hazardous wastes using regenerated activated carbon: leaching studies

In this research, we investigated the use of an inexpensive thermally regenerated activated carbon as a pre-adsorbent in the solidification/stabilization of phenol-contaminated sand. Our results show that even the addition of very low amounts of regenerated activated carbon (1%–2% w/w sand) resulted in the rapid adsorption of phenol in the Chemical solidification/stabilization (S/S) matrix, with phenol leaching reduced by as much as 600%. Adsorption studies indicated that the adsorption of phenol on the reactivated carbon was found to be partially irreversible over time in the S/S waste form, indicating possible chemical adsorption. Pore-fluid analyses of the cement paste containing phenol suggested the formation of a calcium–phenol complex, which further reduced the amount of free phenol present in the pores. Studies using several micro-structural techniques, including field emission scanning electron microscopy, X-ray diffraction, fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy, indicated significant morphological changes in the cement matrix upon the addition of phenol and reactivated carbon. The hydration of cement in the presence of phenol was retarded concomitant with formation of amorphous portlandite.     

Classification of test objects for use in calibration of scanning electron microscopes in the nanometric range

A classification of test objects for use in calibration of scanning electron microscopes in the nanometric range is created. The shape of the relief profile of the elements of the test objects and the relationship of the profile to the physical mechanisms underlying the formation of the signal generated by a microscope functioning in a mode for the collection of secondary slow electrons is used as the basis of the classification. Translated from Izmeritel’naya Tekhnika, No. 2, pp. 22–26, February, 2009.     

Determination of pigments in colour layers on walls of some selected historical buildings using optical and scanning electron microscopy

For successful restoration of painted walls and painted coloured finishing coats it is necessary to determine the composition of the original colour layers. Identification of the pigments used in The Cistercian Abbey of Stična and The Manor of Novo Celje was carried out using optical and scanning electron microscopy. Selected samples of wall paintings were inspected by the combined application of an optical microscope and a low-vacuum Scanning Electron Microscope to determine their colour and structural features and to identify the position of individual pigment grains. Energy dispersive spectroscopy was used to determine the elemental distribution on selected surfaces and elemental composition of individual pigments. It was found that the most abundantly used pigments were iron oxide red, cinnabar, green earth, umber, calcium carbonate white, ultramarine, yellow ochre and carbon black. These identifications have allowed us to compare the use of various pigments in buildings from different historical periods.     

Dynamic observation of vortices in superconductors using a holography electron microscope

Individual vortices in superconductors are directly observed with our holography electron microscope. Vortices cannot be viewed as an electron micrograph, but only as a holographic interference micrograph or a defocused micrograph (Lorentz micrograph), since vortices are phase objects to the illumination electron beam. Since the flux itself, and not its replica, is detected, even the dynamic behavior can be observed. The dynamics of vortices in a Nb thin film can be observed in real time when the sample conditions, such as the temperature or the applied magnetic field, change.     

微孔聚合物皮层厚度测量的扫描声显微方法

微孔发泡是一种有广泛应用前景的聚合物改性方法。皮层的存在对微孔结构材料的性能有很大的影响,皮层厚度的测量、工艺控制和理论计算是微孔材料加工中的主要问题。文章介绍了一种测量微孔聚合物皮层厚度的新的有效方法——扫描声显微(SAM)方法,并测量了微孔聚苯乙烯和微孔聚碳酸酯的皮层厚度。     

In situ investigation of small fatigue crack growth in poly-crystal and single-crystal aluminium alloys

Abstract   In situ scanning electron microscope observations of short crack growth in both a poly-crystal and a single-crystal alloy revealed that fatigue cracks may grow in a shear decohesion mode over a length that is several times the grain size, far beyond the conventional stage I regime. In the poly-crystal aluminium alloy 2024-T351, fatigue cracks were found to continue to grow along one shear band even after two mutually perpendicular shear bands had formed at the crack tip. For the single-crystal alloy specimen with the loading axis being nearly perpendicular to its main shear plane, mode I fatigue cracks were found to grow along the shear band. These two types of fatigue crack growth pose a significant challenge to the existing fatigue crack growth correlating parameters that are based on crack-tip opening displacement. In particular, it has been found that the cyclic crack-tip opening displacement, which accounts for both large-scale yielding and the lack of plasticity-induced crack closure, is unable to unify the growth rates of short and long cracks in aluminium 2024-T351, suggesting a possible dependence of crack growth threshold on crack length.     

Applications of scanning transmission electron microscope microanalysis in the study of materials

The dedicatedstem equipped with field emission electron source, affords opportunities for the acquisition of microchemical and microstructural data on a scale approaching the nanometer level. In this presentation, a number of applications of microchemical analysis and microdiffraction to engineering materials will be discussed, with major emphasis on high-strength low-alloy steels, steels for high formability in automotive applications, and aluminium alloys. Some advantages and limitations of the technique are noted, especially for application to analysis of electrochemically prepared thin foils, and to the analysis of extracted particles.     

电子背散射衍射的测试技术进展

电子背散射技术(EBSD)因可以获得晶体结构和取向信息而成为SEM的重要补充,在金属、半导体、矿物和陶瓷材料等领域的作用日益重要.更高的分辨率、更高的速度和效率是对EBSD技术提出的发展需求.本文在简述EBSD技术基础原理的基础上,重点评述了其在提高空间分辨率(透射菊池衍射(TKD))及提升处理速度和表征效率(CMOS...     

Evaluation of hydrogen effect on the fatigue crack growth behavior of medium-Mn steels via in-situ hydrogen plasma charging in an environmental scanning electron microscope

Fatigue crack growth(FCG)tests were conducted on a medium-Mn steel annealed at two intercritical annealing temperatures,resulting in different austenite(γ)to ferrite(α)phase fractions and different γ(meta-)stabilities.Novel in-situ hydrogen plasma charging was combined with in-situ cyclic loading in an environmental scanning electron microscope(ESEM).The in-situ hydrogen plasma charging increased the fatigue crack growth rate(FCGR)by up to two times in comparison with the reference tests in vacuum.Fractographic investigations showed a brittle-like crack growth or boundary cracking manner in the hydrogen environment while a ductile transgranular manner in vacuum.For both materials,the plastic deformation zone showed a reduced size along the hydrogen-influenced fracture path in comparison with that in vacuum.The difference in the hydrogen-assisted FCG of the medium-Mn steel with different microstructures was explained in terms of phase fraction,phase stability,yielding strength and hydrogen distribution.This refined study can help to understand the FCG mechanism without or with hydrogen under in-situ hydrogen charging conditions and can provide some insights from the applications point of view.