Study of dynamic grain growth by electron microscopy and EBSD

The effect of hot deformation on fully recrystallized aluminium–copper alloys (Al-4wt%Cu and Al-33wt%Cu) with different volume fractions of CuAl₂ has been studied. The alloys are Zener pinned systems with different superplastic properties. Strain-induced grain growth, observed in both alloys, was quantitatively estimated by means of electron microscopy and EBSD and compared with the rate of static grain growth. Surface marker observations and in situ hot-deformation experiments combined with EBSD were aimed at clarifying the mechanisms responsible for the changes in the deformed microstructures. A sequence of secondary and backscattered electron images and EBSD maps was obtained during in situ SEM deformation with different testing conditions. Overlaying EBSD maps for the Al-4wt%Cu with channelling contrast images showed that grain boundary motion occurred during deformation, creating a layered structure and leading to an increase in size of some grains and shrinkage of others. Of a particular interest are results related to behaviour of CuAl₂ in superplastic Al-33wt%Cu during deformation, including several problems with the use of EBSD in this alloy.     

The application of a hot deformation SEM stage, backscattered electron imaging and EBSD to the study of thermomechanical processing

The technique of combining in situ hot‐deformation and high resolution electron backscattered diffraction (EBSD) has been applied to study the mechanisms operating during the thermomechanical processing of metals. A simple hot tensile‐straining stage is installed in a field emission gun scanning electron microscope equipped with an EBSD system and has been used successfully for a number of preliminary investigations. These investigations include substructure formation, dynamic subgrain and grain growth, superplastic deformation in aluminium alloys, and dynamic recrystallization in copper. Despite the surface topography, which inevitably increases during plastic deformation, channelling contrast backscattered electron micrographs have been successfully obtained after strains of up to ～50%. Good quality EBSD maps have been obtained after strains of up to 100%. Most observations and measurements from the in situ experiments are consistent with what is known about the mechanisms occurring in the bulk. The microstructures revealed in the centre of the in situ samples after later repolishing are generally similar to those at the surface.     

Is fast mapping good mapping? A review of the benefits of high‐speed orientation mapping using electron backscatter diffraction

Orientation mapping using automated electron backscatter diffraction (EBSD) is now a common technique for characterizing microstructures. Improvements in software and hardware have resulted in high‐speed mapping capabilities above 80 000 points h^?1. For ‘routine’ microstructural analyses of materials such as steel and aluminium (e.g. texture and grain size measurements and high angle boundary characterization), high‐speed orientation mapping is an ideal approach with minimal penalty on the final statistics. However, for the accurate analysis of very low angle boundaries and for routine analyses of more difficult materials (e.g. most rock samples), we advocate a more patient approach to orientation mapping with an emphasis on data accuracy and reliability. It is important that the objectives of any EBSD analysis are carefully considered before starting – in this way the maximum potential of an EBSD system can be achieved.     

The degradation of EBSD-patterns as a tool to investigate surface crystallized glasses and to identify glassy surface layers

Surface crystallized samples of glass-ceramics containing cordierite, rhombohedral BaAl₂B₂O₇ and fresnoite were analyzed using electron backscatter diffraction (EBSD). The first two materials were chosen because surface crystallized samples of these materials have previously been shown to contain crystals covered by a very thin layer of glass. In all materials, EBSD pattern degradation occurs if the step size of a scan is chosen to be small. It is shown that the minimum step size enabling an evaluable EBSD-scan increases notably, if the crystals are covered by a thin layer of glass. It is also shown that pattern degradation may be utilized to prove the existence of such a thin glass or otherwise thermally sensitive layer. This provides significant information concerning the nucleation process of glasses also with respect to nucleation theory of glass-ceramics. It is also possible to describe the quantity of crystalline surface covered by the thermally sensitive layer.     

Modeling surface roughness for polishing process based on abrasive cutting and probability theory

The surface roughness is a variable used to describe the quality of polished surface. This article presents a surface roughness model based on abrasive cutting and probability theory, which considers the effects of abrasive grain shape, grit and distribution feature, pressure on surface roughness. The abrasive grain protrusion heights are thought to close to Gaussian distribution, and then the relationship between the indentation depth and the pressure based on Hertz contact theory is obtained. Surface roughness prediction model is established by calculating indentation depth of the abrasive grains on workpiece surface. The maximum surface profile height (R_y) is approximately equal to the maximum indentation depth of the abrasive grain. The arithmetic average surface roughness (R_a) is equal to the average indentation depth of the abrasive grain. The effects of process parameters such as pressure and grit on R_y and R_a were simulated and analyzed in detail.     

Making EBSD on water ice routine

Electron backscatter diffraction (EBSD) on ice is a decade old. We have built upon previous work to select and develop methods of sample preparation and analysis that give >90% success rate in obtaining high‐quality EBSD maps, for the whole surface area (potentially) of low porosity (<15%) water ice samples, including very fine‐grained (<10 μm) and very large (up to 70 mm by 30 mm) samples. We present and explain two new methods of removing frost and providing a damage‐free surface for EBSD: pressure cycle sublimation and ‘ironing’. In general, the pressure cycle sublimation method is preferred as it is easier, faster and does not generate significant artefacts. We measure the thermal effects of sample preparation, transfer and storage procedures and model the likelihood of these modifying sample microstructures. We show results from laboratory ice samples, with a wide range of microstructures, to illustrate effectiveness and limitations of EBSD on ice and its potential applications. The methods we present can be implemented, with a modest investment, on any scanning electron microscope system with EBSD, a cryostage and a variable pressure capability.     

Sampling error in ad conversion of the surface profile signal

A fundamental problem in a/d conversion of a measurment signal of surface profile id discussed from the viewpoint of a limit of sampling error in the time domain. A comparison is also made of the results of autocorrelation function, power spectrum and profile parameters such as R_max, R_a etc, obtained from the sampled surface profile in the time domain and in the longitudinal domain. It is suggested that the minimization of sampling error may be attained by the use of a digital displacement transducer attached to the usual surface measurement instrument.     

Sampling error in conversion of the surface profile signal

A fundamental problem in a/d conversion of a measurment signal of surface profile id discussed from the viewpoint of a limit of sampling error in the time domain. A comparison is also made of the results of autocorrelation function, power spectrum and profile parameters such as R_max, R_a etc, obtained from the sampled surface profile in the time domain and in the longitudinal domain. It is suggested that the minimization of sampling error may be attained by the use of a digital displacement transducer attached to the usual surface measurement instrument.     

Orientation effects on indexing of electron backscatter diffraction patterns

Automated Electron Backscatter Diffraction (EBSD) has become a well-accepted technique for characterizing the crystallographic orientation aspects of polycrystalline microstructures. At the advent of this technique, it was observed that patterns obtained from grains in certain crystallographic orientations were more difficult for the automated indexing algorithms to accurately identify than patterns from other orientations. The origin of this problem is often similarities between the EBSD pattern of the correct orientation and patterns from other orientations or phases. While practical solutions have been found and implemented, the identification of these problem orientations generally occurs only after running an automated scan, as problem orientations are often readily apparent in the resulting orientation maps. However, such an approach only finds those problem orientations that are present in the scan area. It would be advantageous to identify all regions of orientation space that may present problems for automated indexing prior to initiating an automated scan, and to minimize this space through the optimization of acquisition and indexing parameters. This work presents new methods for identifying regions in orientation space where the reliability of the automated indexing is suspect prior to performing a scan. This methodology is used to characterize the impact of various parameters on the indexing algorithm.     

Low-angle subgrain misorientations in deformed NaCl

The development of subgrain boundary misorientations with strain in NaCl polycrystals has been investigated. At low strains, a power law relationship exists between strain and average misorientations. The accuracy of this relationship is assessed in terms of material and electron backscattered diffraction (EBSD) processing parameters and is found to hold for a material of constant grain size deformed in compression, providing EBSD mapping and processing conditions were similar. Average misorientations are strongly influenced by grain orientation, suggesting that the misorientation–strain relationship may also be texture dependent in materials with high plastic anisotropy. A slight grain size dependency of the average misorientations was observed.     

Electron backscatter diffraction characterization of inlaid cu lines for interconnect applications

Automated electron backscatter diffraction (EBSD) techniques have been used to characterize the microstructures of thin films for the past decade or so. The recent change in strategy from an aluminum‐based interconnect structure in integrated circuits to one based on copper has necessitated the development of new fabrication procedures. Along with new processes, complete characterization of the microstructures is imperative for improving manufacturability of the Cu interconnect lines and in‐service reliability. Electron backscatter diffraction has been adopted as an important characterization tool in this effort. Cu microstructures vary dramatically as a function of processing conditions, including electroplating bath chemistry, sublayer material, stacking sequence of sublayers, annealing conditions, and line widths and depths. Crystallographic textures and grain size and grain boundary character distributions, all of which may influence manufacturability and reliability of interconnect lines, are ideally characterized using EBSD. The present discussion presents some results showing structural dependence upon processing parameters. In addition, the authors identify an in‐plane orientation preference in inlaid Cu lines {111} normal to the line surface and 〈110〉 aligned with the line direction. This relationship tends to strengthen as the line width decreases.     

基于EBSD技术构建弹性各向异性粗晶材料超声仿真模型的研究

针对弹性各向异性粗晶材料晶粒结构和取向定量描述困难,导致超声检测仿真结果与试验符合程度较差的问题,提出基于电子背散射衍射(Electron back-scatter diffraction,EBSD)技术确定晶粒形态及晶体取向的建模思路。利用EBSD技术实测得到了尺寸为96 mm×12 mm的离心铸造奥氏体不锈钢(Centrifugally cast austenitic stainless steel,CCASS)轴-径向截面的晶体取向图谱,选择15°取向相(差)角定义EBSD图谱的晶粒结构,并对晶体取向进行归一化处理。在此基础上借助Bond变换法赋以晶粒在对应晶体取向下的刚度矩阵,对模型中晶粒的弹性特征进行量化表征,建立CCASS超声检测模型。采用时域有限差分法进行数值计算,结果表明:利用该方法能够较好地重现CCASS超声检测特有的结构噪声和主频降低等现象,为揭示超声波在弹性各向异性粗晶结构中的散射机理提供了解决思路。     

Quantitative metallography by electron backscattered diffraction

Although electron backscattered diffraction (EBSD) in the scanning electron microscope is used mainly to investigate the relationship between local textures and microstructures, the technique has now developed to the stage where it requires serious consideration as a tool for routine quantitative characterization of microstructures. This paper examines the application of EBSD to the characterization of phase distributions, grain and subgrain structures and also textures. Comparisons are made with the standard methods of quantitative metallography and it is shown that in many cases EBSD can produce more accurate and detailed measurements than the standard methods and that the data may sometimes be obtained more rapidly. The factors which currently limit the use of EBSD for quantitative microstructural characterization, including the speed of data acquisition and the angular and spatial resolutions, are discussed, and future developments are considered.     

Polycrystal orientation maps from TEM

Determination of topography of crystallite orientations is an important technique of investigation of polycrystalline materials. A system for creating orientation maps using transmission electron microscope (TEM) Kikuchi patterns and Convergent beam electron diffraction patterns is presented. The orientation maps are obtained using a step-by-step beam scan on a computer-controlled TEM equipped with a CCD camera. At each step, acquired diffraction patterns are indexed and orientations are determined. Although, the approach used is similar to that applied in SEM/electron back scattered diffraction (EBSD) orientation imaging setups, the TEM-based system considerably differs from its SEM counterpart. The main differences appear due to specific features of TEM and SEM diffraction patterns. Also, the resulting maps are not equivalent. On these generated by TEM, the accuracy of orientation determination can be better than 0.1 degrees. The spatial resolution is estimated to be about 10nm. The latter feature makes the TEM orientation mapping system an important tool for studies at fine scale unreachable by SEM/EBSD systems. The automatic orientation mapping is expected to be a useful complement of the conventional TEM contrast images. The new technique will be essential for characterization of fine structure materials. To illustrate that, example maps of an aluminum sample produced by severe plastic deformation are included.     

Atomic force microscopy imaging of polycrystalline CuInSe2 thin films

In this study, atomic force microscopy (AFM) imaging has been used to study the structural properties of polycrystalline CuInSe₂ films, which are widely used as absorber materials in thin film solar cell devices. This technique demonstrated an excellent capability for the reproducible imaging of these rough polycrystalline materials. AFM imaging in combination with statistical analysis revealed distinct differences in the structural properties (i.e. grain width and height distributions, root‐mean‐square (RMS) and peak to valley (R_(p–v)) roughness values) as a function of the specific growth technique used and the bulk composition of the films. In the case of Cu‐rich films, prepared by the H₂Se/Ar treatment of Cu/In/Cu alloys, rough surface structures were in general observed. Statistical analysis revealed two distinct distribution of grains in these samples (1.0–2.5 μm and 3–5.5 μm) with large RMS and R_(p–v) roughness values of 380 nm and 2.6 μm, respectively. In‐rich films were characterized by the presence of much smaller, roughly circular clusters with a significant reduction in both the width and height distributions as well as RMS and R_(p–v) roughness values. The most successful growth techniques, in terms of producing homogeneous and dense films, were in the cases of H₂Se/Ar treated metallic InSe/Cu/InSe alloys and the coevaporation of all materials to form CuInSe₂. Both these techniques produced absorber films with very narrow grain width and height distributions as well as small roughness values. It was possible to establish that high efficiency devices are associated with the use of absorber films with narrow width distributions between 0.5 and 2 μm and small RMS (> 300 nm) roughness values. These values are used as a figure of merit in our laboratories to evaluate the structural properties of our CuInSe₂ thin films.     

Precision of area estimation: a numerical study

After listing some general formulae for sampling in n-dimensional space, the author considers the one-dimensional case: the estimation of the length of a line segment by counting the number of points that happen to fall within the segment. If the points are equidistantly located, the variance of the estimate is a strictly periodic function of the length of the segment. This systematic sample has a higher efficiency than simple and stratified random samples of the same intensity. With some modifications, the results carry over to the two-dimensional case: the estimation of the area of a plane figure by counting the number of sample points falling inside the figure. However, the strict periodicity of the variance in the one-dimensional systematic case is replaced by a ‘Zitterbewegung’. The magnitude of this oscillation is seen to be very different for figures of different shapes. Some results are presented also for the estimation of areas by line transects, and for the estimation of volumes by aid of lattices of points in R³, and R⁴. Some comments are also given on the practical implications of the results for sampling in the plane.     

Crystallographic orientation of ZrB2-ZrC composites manufactured by the spark plasma sintering method

The crystallographic grain orientation of ZrB₂‐ZrC composites manufactured using a spark plasma sintering (SPS) method, a new sintering technique in development for poorly sinterable ceramic materials, was analysed by the scanning electron microscopy‐electron backscattered diffraction (SEM‐EBSD) method. Their crystallographic features have been compared with those of a conventionally sintered specimen using a pressureless sintering (PLS) method. In the composite sintered by PLS, (0001) planes of ZrB₂ were orientated in the direction parallel to the specimen surface (RD) but (101 0) and (211 0) planes randomly orientated. In the case of SPS, (0001) planes of ZrB₂ were orientated normal to the specimen surface (ND) and weakly to the RD. In both cases of PLS and SPS, ZrC grains had a randomly orientated grain structure. The distribution of grain boundary misorientation of PLS and SPS‐processed composites showed the same tendency that high‐angle boundaries were more prevalent than low‐angle boundaries. But in the case of ZrC grains in the SPS sample, the proportion of CSL boundaries with low sigma value (3, 5, 7, 9, 11) was relatively larger.     

The interpretation of indexing of high Σ CSL grain boundaries from ceramics

Electron backscatter diffraction (EBSD) is a useful technique for measuring the orientation of individual grains and for determining grain boundary misorientations in polycrystals. However, its application to ceramics is more difficult than to metals, because the surface quality that can be achieved often makes the Kikuchi patterns blurred. As a consequence, it can be difficult, even for automated systems, to differentiate between different grain orientations, which have similar patterns. In this paper, we carry out EBSD analyses of SrTiO₃ polycrystalline material prepared with different polishing methods, and we consider the effect of different criteria in interpreting the EBSD patterns from them. In particular, we investigate the CSL statistics using both the Palumbo and Aust and the Brandon criteria in this situation.     

Electron backscatter diffraction of grain and subgrain structures — resolution considerations

Characterization of microstructures containing small grains or low-angle grain boundaries by electron backscattered diffraction (EBSD) is limited by the spatial and angular resolution limits of the technique. It was found that the best effective spatial resolution (60 nm) for aluminium alloys in a tungsten-filament scanning electron microscope (SEM) was obtained for an intermediate probe current which provided a compromise between pattern quality and specimen interaction volume. The same specimens and EBSD equipment when used with a field-emission gun SEM showed an improvement in spatial resolution by a factor of 2–3. For characterizing low-angle boundary microstructures, the precision of determining relative orientations is a limiting factor. It was found that the orientation noise was directly related to the probe current and this was interpreted in terms of the effect of probe current on the quality of the diffraction patterns.     

材质气孔率和气孔大小与表面粗糙度的数学模拟与特征

为提高光学系统的成像质量,研究了光学系统中镜片表面粗糙度与镜片材质中的颗粒大小、缺陷、气孔率、气孔大小的关系.通过几何方法,建立了气孔率与气孔大小和数量的关系模型,分别给出了单位体积和单位面积中气孔率与气孔大小和数量的关系表达式.最后用数学方法建立了材质中气孔率、气孔大小与表面粗糙度的定量模型,给出了表面粗糙度与材质气孔率和气孔大小的关系表达式,表明表面粗糙度近似与材质中的气孔率成正比,与气孔大小成正比.