Use of EBSD to study electropulsing induced reverse phase transformations in a Zn-Al alloy (ZA22)

Multi‐phase identification and phase transformations in electropulsing treated Zn–Al based alloy wire specimens were studied using electron back‐scattered diffraction, back‐scattered scanning electron microscopy and X‐ray diffraction techniques. By using electron back‐scattered diffraction, two phases: η′_S and η′_T with a small difference of about 1% in lattice parameters (c₀/a₀) were identified, based on the determined lattice parameters of the phases, and the reverse eutectoid phase transformations: η′_T+?′_T+α′_T→η′_S and ?+α→T′+η were successfully detected. Electron back‐scattered diffraction appeared to be an effective technique for studying complex electropulsing induced phase transformations.     

Electron backscattered diffraction characterization technique for analysis of a Ti2AlNb intermetallic alloy

This investigation was conducted to ascertain the benefits of electropolishing after mechanical polishing for electron backscattered diffraction of a Ti₂AlNb intermetallic Ti−21Al−29Nb (at.%) alloy containing the orthorhombic (O) and body-centered-cubic (BCC) phases. Electropolishing was performed at −40 °C in 6% H₂SO₄ methanol solution. Atomic force microscopy was used to measure the surface topography in attempt to correlate nano-scale surface roughness with electron backscatter diffraction pattern quality. The results suggest that mechanically polishing with colloidal silica (SiO₂) or alumina followed by electropolishing is a sufficient surface preparatory technique for producing quality electron backscattered diffraction patterns for O + BCC microstructures. However, poor pattern quality results after mechanically polishing without electropolishing. High-quality orientation maps for O-dominated O + BCC microstructures were only possible through mechanical polishing followed by electropolishing. The data also suggest that surface roughness, on the order of 50 nm, has less effect on pattern quality than subsurface deformation. Overall, removing the near-surface damage was more critical than reduction of topography.     

Crystalline phases found in rapidly quenched Ni–Nb–Zr alloys

The properties of metallic alloys can be significantly improved by developing non‐equilibrium phases in the microstructures through rapid solidification techniques, thus the characterisation of these unusual structures is extremely important. In this research, the microstructures of three rapidly quenched alloys, namely Ni_65.2Nb_33.8Zr_1.0, Ni_54.8Nb_31.1Zr_14.1 and Ni_54.8Nb_21.6Zr_23.6 (at. %) were investigated in greater detail in order to determine the structures and compositions of their crystalline phases. These crystalline phases were characterised using a combination of scanning electron microscopy, energy dispersive x‐ray spectroscopy, x‐ray diffraction and transmission electron microscopy techniques. The phases were compared to the crystalline structures reported in the literature. Our results indicate some agreement with the Ni–Nb phase diagram and an isothermal section of the Ni–Nb–Zr phase diagram; however, it is detected zirconium solubility in the Ni₃Nb phase, as well as, the absence of expected crystalline phases.     

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.     

Backscattered electron SEM imaging of cells and determination of the information depth

Backscattered electron imaging of HT29 colon carcinoma cells in a scanning electron microscope was studied. Thin cell sections were placed on indium‐tin‐oxide‐coated glass slides, which is a promising substrate material for correlative light and electron microscopy. The ultrastructure of HT29 colon carcinoma cells was imaged without poststaining by exploiting the high chemical sensitivity of backscattered electrons. Optimum primary electron energies for backscattered electron imaging were determined which depend on the section thickness. Charging effects in the vicinity of the SiO₂ nanoparticles contained in cell sections could be clarified by placing cell sections on different substrates. Moreover, a method is presented for information depth determination of backscattered electrons which is based on the imaging of subsurface nanoparticles embedded by the cells.     

Diffraction effects and inelastic electron transport in angle‐resolved microscopic imaging applications

We analyse the signal formation process for scanning electron microscopic imaging applications on crystalline specimens. In accordance with previous investigations, we find nontrivial effects of incident beam diffraction on the backscattered electron distribution in energy and momentum. Specifically, incident beam diffraction causes angular changes of the backscattered electron distribution which we identify as the dominant mechanism underlying pseudocolour orientation imaging using multiple, angle‐resolving detectors. Consequently, diffraction effects of the incident beam and their impact on the subsequent coherent and incoherent electron transport need to be taken into account for an in‐depth theoretical modelling of the energy‐ and momentum distribution of electrons backscattered from crystalline sample regions. Our findings have implications for the level of theoretical detail that can be necessary for the interpretation of complex imaging modalities such as electron channelling contrast imaging (ECCI) of defects in crystals. If the solid angle of detection is limited to specific regions of the backscattered electron momentum distribution, the image contrast that is observed in ECCI and similar applications can be strongly affected by incident beam diffraction and topographic effects from the sample surface. As an application, we demonstrate characteristic changes in the resulting images if different properties of the backscattered electron distribution are used for the analysis of a GaN thin film sample containing dislocations.     

Microscopy and microanalysis of crystalline glazes

Crystalline glazes on ceramic plates produced commercially in the U.K. and on ceramic pots produced commercially in Taiwan and Spain have been examined by X‐ray diffraction, conventional and polarized light microscopy, and scanning electron microscopy in order to identify the crystalline phases present in the glazes and to ascertain through X‐ray microanalysis the partitioning behaviour of the transition metal ions used to colour the glazes and the crystals within them. In each case examined, the macroscopic two‐dimensional spherulites within the glazes clearly seen by the naked eye were found to consist of large numbers of radially orientated acicular crystals each 5 µm or less in width embedded within the silica‐rich glaze. Energy dispersive X‐ray microanalysis and X‐ray diffraction of these crystals identified these crystals as willemite, α‐Zn₂SiO₄. The strong [001] texture of these crystals within the glaze evident from the X‐ray diffraction patterns was consistent with polarized light microscopy observations of the willemite crystals. In addition to willemite, small iron‐doped gahnite (ZnAl₂O₄) crystals were found in a honey‐coloured crystalline glaze and acicular rutile (TiO₂) crystals were found in the Portmeirion Pottery plates examined. Transition metal ions with a preference for tetrahedral coordination were observed to substitute for Zn²⁺ ions in willemite and to partition preferentially to the willemite crystals, whereas ions preferring octahedral coordination preferred to remain in the glaze.     

Scanning and transmission electron microscopy microstructure characterization of mechanically alloyed Nb–Ti–Al alloys

Results are presented of an investigation of the microstructure development during mechanical alloying and following consolidation of an Nb15Ti15Al alloy. The alloy was synthesized from elemental as well as pre‐alloyed powders. The microstructure of this material was examined by transmission electron microscopy, scanning electron microscopy and X‐ray diffraction. The use of pre‐alloyed TiAl powder for synthesis of the Nb15Ti15Al alloy meant that a much shorter time was required to complete the mechanical alloying process compared with the synthesis of elemental powders. The investigation indicates that three phases were present in the consolidated materials: the Nb solid solution, the Nb₃Al intermetallic phase and the dispersoid.     

Backscattered electron imaging and electron backscattered diffraction in the study of bacterial attachment to titanium alloy structure

The application of secondary electron (SE) imaging, backscattered electron imaging (BSE) and electron backscattered diffraction (EBSD) was investigated in this work to study the bacterial adhesion and proliferation on a commercially pure titanium (cp Ti) and a Ti6Al4V alloy (Ti 64) with respect to substrate microstructure and chemical composition. Adherence of Gram‐positive Staphylococcus epidermidis 11047 and Streptococcus sanguinis GW2, and Gram‐negative Serratia sp. NCIMB 40259 and Escherichia coli 10418 was compared on cp Ti, Ti 64, pure aluminium (Al) and vanadium (V). The substrate microstructure and the bacterial distribution on these metals were characterised using SE, BSE and EBSD imaging. It was observed that titanium alloy‐phase structure, grain boundaries and grain orientation did not influence bacterial adherence or proliferation at microscale. Adherence of all four strains was similar on cp Ti and Ti 64 surfaces whilst inhibited on pure Al. This work establishes a nondestructive and straight‐forward statistical method to analyse the relationship between microbial distribution and metal alloy structure.     

Study of two tungstates Ca0.5Cd0.5WO4 and Ca0.2Cd0.8WO4 by transmission electron microscopy

To better understand the role of crystal structures and local disorder in the photonic properties of the system (1 ? x)CaWO₄ ? xCdWO₄ with 0 < x < 1, two specific phases with compositions x = 0.5 (scheelite phase) and 0.8 (wolframite phase) have been studied by scanning and transmission electron microscopies. High‐resolution electron microscopy images and image simulations, associated with X‐ray diffraction data, allowed confirming the lattices and space groups I4₁/a and P2/c of the two scheelite and wolframite phases, at the local scale. The electron microscopy data show the existence of a high degree of crystallization associated with statistical distribution of Ca or Cd atoms on a Ca_1?xCd_x site in each lattice.     

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.     

Quantitative measurements of Kikuchi bands in diffraction patterns of backscattered electrons using an electrostatic analyzer

Diffraction patterns of backscattered electrons can provide important crystallographic information with high spatial resolution. Recently, the dynamical theory of electron diffraction was applied to reproduce in great detail backscattering patterns observed in the scanning electron microscope (SEM). However, a fully quantitative comparison of theory and experiment requires angle-resolved measurements of the intensity and the energy of the backscattered electrons, which is difficult to realize in an SEM. This paper determines diffraction patterns of backscattered electrons using an electrostatic analyzer, operating at energies up to 40 keV with sub-eV energy resolution. Measurements are done for different measurement geometries and incoming energies. Generally a good agreement is found between theory and experiment. This spectrometer also allows us to test the influence of the energy loss of the detected electron on the backscattered electron diffraction pattern. It is found that the amplitude of the intensity variation decreases only slowly with increasing energy loss from 0 to 60 eV.     

Application of the EBSD technique to describe the initiation and growth behaviour of microstructurally short fatigue cracks in a duplex steel

Up to 90% of the fatigue life of engineering alloys results from the initiation and propagation of microstructurally short cracks. Owing to their strong interactions with microstructural features, e.g. grain and phase boundaries, they exhibit substantially non‐uniform propagation kinetics as compared with the growth rate of long cracks, which can be well described using a power‐law function of the range of the stress‐intensity factor ΔK. In the present paper interactions between the crystallographic misorientation of grain and phase boundaries and microcracks in an austenitic/ferritic stainless steel are discussed and quantified by means of fatigue experiments in combination with the electron backscattered diffraction technique. In the second part a numerical model for the simulation of microcracks is introduced, which is capable of taking real microstructural arrangements into consideration.     

Microstructural analysis of iron aluminide formed by self-propagating high-temperature synthesis mechanism in aluminium matrix composite

An aluminium matrix composite with iron aluminide formed in situ as a result of self‐propagated high‐temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle‐like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self‐propagating high‐temperature synthesis consisted only of the Al₃Fe phase.     

A multimodal microcharacterisation of trace‐element zonation and crystallographic orientation in natural cassiterite by combining cathodoluminescence,EBSD, EPMA and contribution of confocal Raman‐in‐SEM imaging

In cassiterite, tin is associated with metals (titanium, niobium, tantalum, indium, tungsten, iron, manganese, mercury). Knowledge of mineral chemistry and trace‐element distribution is essential for: the understanding of ore formation, the exploration phase, the feasibility of ore treatment, and disposal/treatment of tailings after the exploitation phase. However, the availability of analytical methods make these characterisations difficult. We present a multitechnical approach to chemical and structural data that includes scanning electron microscopy (SEM)‐based imaging and microanalysis techniques such as: secondary and backscattered electrons, cathodoluminescence (CL), electron probe microanalyser (EPMA), electron backscattered diffraction (EBSD) and confocal Raman‐imaging integrated in a SEM (RISE). The presented results show the complementarity of the used analytical techniques. SEM, CL, EBSD, EPMA provide information from the interaction of an electron beam with minerals, leading to atomistic information about their composition, whereas RISE, Raman spectroscopy and imaging completes the studies with information about molecular vibrations, which are sensitive to structural modifications of the minerals. The correlation of Raman bands with the presence/absence of Nb, Ta, Fe (heterovalent substitution) and Ti (homovalent substitution) is established at a submicrometric scale. Combination of the different techniques makes it possible to establish a direct link between chemical and crystallographic data of cassiterite.     

A precession electron diffraction study of α, β phases and Dauphiné twin in quartz

Precession electron diffraction is used to distinguish between the hexagonal β high-temperature and the trigonal α low-temperature phases of SiO₂ quartz. The structures just differ by a kink of the SiO₄ tetrahedra arranged along spiraling chains, which induces a loss of the two-fold axis and subsequent twinning in the low-temperature phase. Conventional selected-area electron diffraction (SAED) does not enable the phases distinction since only the intensity of reflections is different. It becomes possible with precession that reduces the dynamical interactions between reflections and makes their intensity very sensitive to small variations of the electron structure factors. Distinction between the twinned individuals in the low-temperature phase is then easily made and the twin law is characterized using stereographic projections. The actual symmetry of precessed zone axis patterns is also examined in detail. Using dynamical intensity simulations, it is shown that under certain thickness conditions, the diffraction class symmetry can be observed on selected area patterns that are to be used in the case of beam sensitive materials such as quartz.     

Local structure studies of Fe-Nb-B metallic glasses using electron diffraction

Local atomic structures in Fe₈₄Nb₇B₉ and Fe₇₀Nb₁₀B₂₀ amorphous alloys were examined by means of electron diffraction with the help of computer calculation. Electron diffraction patterns were taken by using energy‐filtered transmission electron microscopy (TEM) to eliminate inelastic scattering. We constructed structure models with 5000 atoms fitting to experimental interference functions. Voronoi polyhedral analyses were performed for the obtained final structure models. Local atomic structures of the alloys were closely related to those of the crystalline phases that appeared on annealing. A difference of stability of two amorphous phases was discussed on the basis of structure models.     

Effect of prior deformation on microstructural development and Laves phase precipitation in high‐chromium stainless steel

This study investigated the influence of deformation on precipitation behaviour and microstructure change during annealing. Here, the prior deformation of high‐chromium stainless steel was tensile deformation of 3%, 6% and 10%, and the specimens were then annealed at 700?C for 10 h. The specimens were subsequently analyzed using backscattered electron image and electron backscattering diffraction measurements with SEM. Compared with the deformation microstructure, the grains revealed no preferred orientation. The precipitates of TiN and NbC were formed homogenously in the grain interior and at grain boundaries after annealing. Fine Laves phase precipitates were observed in grains and along subgrain boundaries as the deformation increased. Furthermore, the volume fraction of Laves phase increased, but the average particle diameter of precipitate was reduced as the deformation increased.     

Electron crystallography at atomic resolution: The structure of the odd-chain paraffin n-tritriacontane

The crystal structure of the odd-chain paraffin, n-tritriacontane, nC₃₃H₆₈, is determined directly by using low-dose electron microscope images and electron diffraction intensity data from epitaxially grown microcrystals. Phases of the most intense “polyethylene” reflections are determined from triplet structure-invariant relationships often used in X-ray crystallography. Low-dose electron microscopic images provide phases of the low-angle “lamellar” reflections and these can be used with one-dimensional structure-invariant relationships to determine other phases on the 00? reciprocal row. The phase set is sufficient to calculate an electrostatic potential map which is directly interpretable as a structure image at atomic resolution.