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Severe plastic deformation (SPD) is a widely used technique to obtain superior material properties specially mechanical properties. Constrained groove pressing (CGP) is found to be the most attractive SPD technique for the deformation of sheets and plates. However, this technique results in microstructural inhomogeneity during processing. The microstructural inhomogeneity can be alleviated by employing a thermal cycle, which assists in controlled recovery and recrystallisation. The current work focuses on, the microstructure evolution of one pass as‐deform CGP sample followed by a short heat‐treated (SHT). A correlative imaging technique of transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM) showed the presence of dislocation cell structure in an as‐deformed condition. The short heat treatment resulted in the transformation of the dislocation cell wall to high‐angle boundaries, with a further increase in heat‐treatment time resulting in grain growth. [ABSTRACT FROM AUTHOR]

Selective laser-melted (SLM) Ti-6Al-4V alloy was quasi-statically compressed in the transverse and longitudinal directions at a strain rate of 1 × 10−3 s−1 at room temperature. The twinning, in-grain misorientation axis (IGMA) distribution and active slip modes of individual grains in the deformed SLM Ti-6Al-4V alloy were studied in detail via transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The α'/α phase was textured with the c-axis oriented either at ~45° or perpendicular to the building direction (BD). A combined analysis of the IGMA distribution and Schmid factor revealed that the prismatic slip or pyramidal slip was easily activated in the soft grains with their c-axes perpendicular to the BD (or the loading direction) in the longitudinal compressed sample, while slip was hardly activated in the transverse compressed sample due to the lack of soft grains. Prismatic slip with IGMA around <0001> Taylor axis also occurred in {10–11} twins. The observations revealed that the prismatic slip played a key role in accommodating the external strain and, thus, well explained the anisotropy of mechanical properties in the SLM Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

Deformed polycrystalline rocks show various crystallographic textures reflecting their imposed deformation histories. However, the textures of ultrafine grains, which are in the submicrometer to nanometer order, may be overlooked depending on the analytical technique used. Thus, we report the first application of transmission Kikuchi diffraction (TKD), which is capable of high-spatial-resolution crystallographic texture analysis, to a fine-grained ultramylonitic peridotite sample in a scanning electron microscope. We successfully obtained TKD maps with an effective spatial resolution of ~ 80 nm and with highly reliable indexing using a conventional W-filament scanning electron microscope with a standard electron backscattered diffraction (EBSD) system. Olivine grains, which were clearly visualized by TKD, were slightly elongated in a direction subparallel to the macroscopic lineation texture. Their shapes were nonuniform with serrated grain boundaries, strongly indicating that the sample has been deformed dominantly by dislocation activity, even though the grain size is in the order of several micrometers or smaller. The combined TKD–transmission electron microscope (TEM) analysis indicated that a slip-system transition from the [100] slip to the [001] slip might have occurred, although the crystals' preferred orientation patterns were not completely overwritten. The transition might have been sufficiently affected by water infiltration, high differential stress, or both along the transform fault. Thus, TKD efficiently analyzed the crystallographic textures and characterized the subgrain boundaries of polycrystalline rocks consisting of submicrometer-order grains. Moreover, combining the EBSD, TKD, and TEM methods allowed us to perform multiscale analyses of the crystallographic textures of ultrafine-grained deformed rocks, seamlessly linking the millimeter- to nanometer-order scales. [ABSTRACT FROM AUTHOR]

We have investigated the microstructural and crystallographic evolution of nanocrystalline zirconia under heavy ion irradiation using in-situ transmission electron microscopy (TEM) and have studied the atomic configurations of defect clusters using aberration-corrected scanning transmission electron microscopy (STEM). Under heavy ion irradiation the monoclinic-ZrO 2 is observed to transform into cubic phase, stabilised by the strain induced by irradiation-induced defect clusters. We suggest that the monoclinic-to-cubic transformation is martensitic in nature with an orientation relationship identified to be (100) m ∥(100) c and [001] m ∥[001] c. By increasing the damage dose, both the formation of voids and irradiation-induced grain growth were observed. A model for the formation of voids is proposed, taking defect interactions into consideration. The study has also demonstrated that high resolution orientation mapping by transmission Kikuchi diffraction (TKD) combined with in-situ irradiation in a TEM is a powerful method to probe the mechanisms controlling irradiation-induced processes, including grain boundary migration, phase transformations and texture evolution. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• New method for nanoscale analysis of hydroxyapatite crystallites in dental enamel. • Dynamic template matching method is combined with TKD in the SEM. • Many HAp crystallites have significant internal orientation variation. • Frequent low angle boundaries and possible twin boundaries between crystallites. • Measuring only 〈0001〉 orientations will miss key microstructural features in HAp. The remarkable physical properties of dental enamel can be largely attributed to the structure of the hydroxyapatite (HAp) crystallites on the sub-micrometre scale. Characterising the HAp microstructure is challenging, due to the nanoscale of individual crystallites and practical challenges associated with HAp examination using electron microscopy techniques. Conventional methods for enamel characterisation include imaging using transmission electron microscopy (TEM) or specialised beamline techniques, such as polarisation-dependent imaging contrast (PIC). These provide useful information at the necessary spatial resolution but are not able to measure the full crystallographic orientation of the HAp crystallites. Here we demonstrate the effectiveness of enamel analyses using transmission Kikuchi diffraction (TKD) in the scanning electron microscope, coupled with newly-developed pattern matching methods. The pattern matching approach, using dynamic template matching coupled with subsequent orientation refinement, enables robust indexing of even poor-quality TKD patterns, resulting in significantly improved data quality compared to conventional diffraction pattern indexing methods. The potential of this method for the analysis of nanocrystalline enamel structures is demonstrated by the characterisation of a human enamel TEM sample and the subsequent comparison of the results to high resolution TEM imaging. The TKD – pattern matching approach measures the full HAp crystallographic orientation enabling a quantitative measurement of not just the c-axis orientations, but also the extent of any rotation of the crystal lattice about the c-axis, between and within grains. Results presented here show how this additional information highlights potentially significant aspects of the HAp crystallite structure, including intra-crystallite distortion and the presence of multiple high angle boundaries between adjacent crystallites with rotations about the c-axis. These and other observations enable a more rigorous understanding of the relationship between HAp structures and the physical properties of dental enamel. [ABSTRACT FROM AUTHOR]

Selective laser-melted (SLM) Ti-6Al-4V alloy was quasi-statically compressed in the transverse and longitudinal directions at a strain rate of 1 × 10−3 s−1 at room temperature. The twinning, in-grain misorientation axis (IGMA) distribution and active slip modes of individual grains in the deformed SLM Ti-6Al-4V alloy were studied in detail via transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The α’/α phase was textured with the c-axis oriented either at ~45° or perpendicular to the building direction (BD). A combined analysis of the IGMA distribution and Schmid factor revealed that the prismatic slip or pyramidal slip was easily activated in the soft grains with their c-axes perpendicular to the BD (or the loading direction) in the longitudinal compressed sample, while slip was hardly activated in the transverse compressed sample due to the lack of soft grains. Prismatic slip with IGMA around Taylor axis also occurred in {10–11} twins. The observations revealed that the prismatic slip played a key role in accommodating the external strain and, thus, well explained the anisotropy of mechanical properties in the SLM Ti-6Al-4V alloy.

Spatial resolution is one of the key factors in orientation microscopy, as it determines the accuracy of grain size investigation and phase identification. We determined the spatial resolutions of on-axis and off-axis transmission Kikuchi diffraction (TKD) methods by calculating correlation coefficients using only the effective parts of on-axis and off-axis transmission Kikuchi patterns. During the calculation, we used average filtering to evaluate the spatial resolution more accurately. The spatial resolutions of both on-axis and off-axis TKD methods were determined in the same scanning electron microscope at different accelerating voltages and specimen thicknesses. The spatial resolution of the on-axis TKD was higher than that of the off-axis TKD at the same parameters. Furthermore, with an increase in accelerating voltage or a decrease in specimen thickness, the spatial resolutions of the two configurations could be significantly improved, from tens of nanometers to below 10 nm. At a voltage of 30 kV and sample thickness of 74 nm, both on-axis and off-axis TKD methods exhibited the highest resolutions of 6.2 and 9.7 nm, respectively. [ABSTRACT FROM AUTHOR]

• We have discussed the mechanisms influencing the depth resolution in 'on-axis' TKD. • Signals contributing to detectable Kikuchi bands in TKD originate from a volume of finite thickness (∼λ TDS) next to the bottom foil surface. • This existing surface sensitivity of TKD analysis can lead to the observation of different grain structures when opposite sides of a nano-crystalline foil are facing the incident electron beam. • A guideline for suitable sample thickness is suggested in order to achieve clear and indexable Kikuchi patterns for TKD analysis. In this paper, we have analyzed the depth resolution that can be achieved by on-axis transmission Kikuchi diffraction (TKD) using a Zr–Nb alloy. The results indicate that the signals contributing to detectable Kikuchi bands originate from a depth of approximately the mean free path of thermal diffuse scattering (λ TDS) from the bottom surface of a thin foil sample. This existing surface sensitivity can thus lead to the observation of different grain structures when opposite sides of a nano-crystalline foil are facing the incident electron beam. These results also provide a guideline for the ideal sample thickness for TKD analysis of ≤ 6λ TDS , or 21 times the elastic scattering mean free path (λ MFP) for samples of high crystal symmetry. For samples of lower symmetry, a smaller thickness ≤ 3λ TDS , or ≤ 10λ MFP is suggested. [ABSTRACT FROM AUTHOR]

The applications of Au thin films and their adhesion layers often suffer from a lack of sufficient information about the chemical states of adhesion layers and about the high-lateral-resolution crystallographic morphology of Au nanograins. Here, we demonstrate the in-depth evolution of the chemical states of adhesive layers at the interfaces and the crystal orientation mapping of gold nanograins with a lateral resolution of less than 10 nm in a Ti/Au/Cr tri-layer thin film system. Using transmission electron microscopy, the variation in the interdiffusion at Cr/Au and Ti/Au interfaces was confirmed. From X-ray photoelectron spectroscopy (XPS) depth profiling, the chemical states of Cr, Au and Ti were characterized layer by layer, suggesting the insufficient oxidation of the adhesive layers. At the interfaces the Au 4f peaks shift to higher binding energies and this behavior can be described by a proposed model based on electron reorganization and substrate-induced final-state neutralization in small Au clusters supported by the partially oxidized Ti layer. Utilizing transmission Kikuchi diffraction (TKD) in a scanning electron microscope, the crystal orientation of Au nanograins between two adhesion layers was non-destructively characterized with sub-10 nm spatial resolution. The results provide nanoscale insights into the Ti/Au/Cr thin film system and contribute to our understanding of its behavior in nano-optic and nano-electronic devices. [ABSTRACT FROM AUTHOR]

In this paper, severe plastic deformation (SPD) is applied to commercially pure aluminum. Monotonic high pressure torsion (HPT) processing is employed at room temperature, and the microstructure of samples deformed up to an equivalent strain of 50 is investigated by electron backscatter diffraction (EBSD). The distribution pattern and the density of geometrically necessary dislocations (GNDs) are evaluated by examination of transmission Kikuchi diffraction (TKD) maps. Three different methodologies are utilized for assessment of the GND density. It was observed that two distinct stages of grain fragmentation and steady-state occur during processing. During the first stage, a severe grain refinement was observed as the average grain size decreased from ~85 μm to ~1 μm at an equivalent strain of 10. Quantification of the density of dislocations in both deformation regimes showed that, independent of the choice of model, the GND density is greater in the fragmentation stage than in the steady-state stage. This observation was linked with the prevalence of the continuous dynamic recrystallization (CDRX) phenomenon in each stage. Furthermore, a significant presence of GNDs in the steady-state stage was characterized. Formation of microstructure, grain refinement and saturation of grain size are discussed in the light of statistics of GNDs. [ABSTRACT FROM AUTHOR]

Spatial resolution is one of the key factors in orientation microscopy, as it determines the accuracy of grain size investigation and phase identification. We determined the spatial resolutions of on-axis and off-axis transmission Kikuchi diffraction (TKD) methods by calculating correlation coefficients using only the effective parts of on-axis and off-axis transmission Kikuchi patterns. During the calculation, we used average filtering to evaluate the spatial resolution more accurately. The spatial resolutions of both on-axis and off-axis TKD methods were determined in the same scanning electron microscope at different accelerating voltages and specimen thicknesses. The spatial resolution of the on-axis TKD was higher than that of the off-axis TKD at the same parameters. Furthermore, with an increase in accelerating voltage or a decrease in specimen thickness, the spatial resolutions of the two configurations could be significantly improved, from tens of nanometers to below 10 nm. At a voltage of 30 kV and sample thickness of 74 nm, both on-axis and off-axis TKD methods exhibited the highest resolutions of 6.2 and 9.7 nm, respectively.

The present case study compares transmission Kikuchi diffraction (TKD) with electron back-scattering diffraction (EBSD) on the same area of an electron transparent cross-section of a twinning induced plasticity steel. While TKD expectedly provides better clarity of internal defect substructures in the band contrast map, EBSD returns orientation data that approaches the quality of the TKD map. This was rationalised by Monte Carlo simulations of the electron energy spreads, which showed that due to the geometry-based compromises associated with adapting a conventional EBSD detector (which is off-axis with respect to the incident electron beam) to TKD, a broadening in the electron energy distribution of the forward-scattered electrons collected on the detector phosphor screen, is unavoidable. In this circumstance, the values of the full-widths at half-maximum of the energy distributions for TKD and EBSD are of the same order. It follows that EBSD on electron transparent cross-sections may be a viable alternative to TKD when: (i) conventional EBSD detectors are adapted to TKD and, (ii) sample microstructures comprise features whose sizes do not mandate the application of TKD. [ABSTRACT FROM AUTHOR]

Automated orientation mapping in SEM, until now relying on EBSD solely, is currently being improved with the development of the TKD technique. As part of the development of TKD, we introduce a new, TEM-like geometric configuration, with a detector “on-axis” relative to the electron beam, while the detector was “off-axis” in its first form. This new technique produces a wide range of diffraction contrast (spots, lines, bands), varying with sample thickness, incident energy, atomic number and scattering angle. Some of the main trends are identified and discussed. In particular, a model based on the plasmon and phonon scattering is proposed to account for the disappearing of diffraction spots with thickness and incident energy. This work should help experimentalists determine which microscope and sample parameters to use in order to obtain a specific contrast. Finally, the strength and weakness of each diffraction feature for orientation mapping are also reviewed. [ABSTRACT FROM AUTHOR]

Nanostructure of cupper thin film on polyimide flexible substrate is revealed by novel orientation imaging techniques. Copper and polyimide thicknesses play critical roles on what technique is successful in acquiring diffraction patterns while avoiding electron beam damage and blistering. Conventional electron backscattered diffraction as well as emerging higher resolution transmission orientation imaging were employed to resolve the grain structure. Spatial resolution is compared in terms of minimum detectable twin width. Experiments and simulations indicate that polyimide thicknesses below 1000 nm allow the electrons to scape; resulting in acceptable reflective or transmission patterns and lack of blistering. [ABSTRACT FROM AUTHOR]

A new configuration for Transmission Kikuchi Diffraction (TKD) in SEM was recently developed, with a scintillator perpendicular to the electron beam. This configuration, “on-axis” TKD, makes grains and twins below 10 nm well visible in orientation maps and with high indexation rate, as demonstrated with an electrodeposited nanocrystalline Ni. This high lateral spatial resolution is achieved by combining high accelerating voltage and low sample thickness to reduce the interaction volume. Among the advantages of the on-axis TKD, orientation mapping of particularly thin samples can be realized thanks to the advantageous axial position of the detector. Indeed, the reduction of the solid angle of the transmitted intensity around the beam axis with decreasing sample thickness is much less of a problem with an axial detector than with an off-axis detector. With an on-axis detector, the only condition for production of an orientation map is that the sample must be thick enough to produce Kikuchi diffraction in addition to spots. [ABSTRACT FROM AUTHOR]

A new configuration for Transmission Kikuchi Diffraction (TKD) in a scanning electron microscope is presented; called 'on-axis TKD'. Compared to the usual off-axis configuration, the scintillator is placed perpendicular to the incident beam under the electron-transparent sample, not in vertical position. In this way, the setup benefits from intense forward scattered electrons enabling short acquisition times. At equivalent diffraction pattern quality, the electron dose needed on the sample is estimated to be 20 times lower in comparison to the off-axis configuration. The technique is particularly suited to the characterisation of severe plastic deformation induced ultrafine grained microstructures. The evolution of the microstructure of an Al-Mg alloy deformed by high pressure tube twisting was analysed. It is shown that the grain refinement was in the steady state stage for a shear strain of 24 with a mean grain size of 120 nm. [ABSTRACT FROM AUTHOR]

Transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM) have been used to investigate the fragmentation of Mg 24 Y 5 intermetallic particles in an Mg-Zn-Y alloy during the equal channel angular pressing (ECAP). During the ECAP process, micro-cracks formed in large Mg 24 Y 5 particles and dynamic recrystallised Mg grains were observed inside the crack. The dynamic recrystallisation of the Mg 24 Y 5 also occurred and the particle size has been reduced. The recrystallised Mg 24 Y 5 particles assume either an irregular or necking shape contributing to the dispersion of the small particles. The fragmentation of the Mg 24 Y 5 particles also reduced the grain size of the surrounding magnesium grains. The refinement of the intermetallic particles is expected to improve the strength and ductility of the alloys. [ABSTRACT FROM AUTHOR]

In this work, metallic bonding in GaN-based vertical light-emitting diode (VLED) is systematically characterized by using combined methodology of transmission Kikuchi diffraction (TKD) and energy dispersive X-ray spectroscopy (EDS) in a scanning electron microscope (SEM). SEM-based TKD with EDS identifies chemical composition, grain morphology, orientation, and phases at metallic bonding, while transmission electron microscopy (TEM) provides nanoscale characteristics of metallic diffusion bonding, and its interface-related defects and nano-twinned boundaries. Our results from SEM-TKD and TEM techniques provide unparalleled insight into the metallic bonding, and its future optimization. [ABSTRACT FROM AUTHOR]

The microstructure and hardness of Custom 465® precipitation hardened stainless steel were characterized following 4 hours aging at temperatures ranging from 482 °C to 648 °C. Dilatometry measurements and thermodynamic calculations were used to understand the mechanism of martensite-to-austenite reversion. Three major stages of aging were observed. The first stage is the peak hardening at aging temperatures of 480–510 °C, where both η-Ni 3 Ti precipitation and austenite reversion begin independently of each other. The second stage is the initial stage of overaging observed above 538 °C as reduction in hardness is due to a slight increase in both the precipitate dimensions and the reverted austenite volume fraction. The third, progressive overaging stage occurs above 593 °C in which a dramatic hardness decrease is caused by a significant increase in both precipitate dimensions and reverted austenite volume fraction. Transmission Kikuchi diffraction orientation mapping revealed that globular austenite randomly nucleates at martensite grain boundaries, while acicular austenite nucleates along martensite lath boundaries. Thermodynamic calculations indicated that the dissolution of η-Ni 3 Ti precipitates does not govern the austenite reversion, although both phases are in competition for Ni. While the thermodynamic calculation predicts increase in the fraction of austenite with increase in aging temperature, the fraction of austenite found at room temperature in aged samples does not vary when the aging temperature, in which austenite reversion occurs, is increased above 593 °C. This is explained by the change in composition of the austenite as a function of aging temperature. [ABSTRACT FROM AUTHOR]

Commercially pure aluminium was selected as a model fcc material for a detailed investigation of the microstructural and textural evolution during processing by high pressure torsion (HPT). Vickers hardness measurements reveal that: the hardness is the lowest where the lowest strain is imposed and increases with increasing strain until saturation hardness is obtained. The microstructural evolution is investigated by means of electron backscattered diffraction and transmission Kikuchi diffraction. During HPT a grain fragmentation process takes place: within the original grains dislocations aggregate, resulting in the creation of very fine grains separated first by low and later by high angle grain boundaries. At a strain level of a simple shear texture of fcc structure was observed. This paper is part of a Themed Issue on Aluminium-based materials: processing, microstructure, properties, and recycling. [ABSTRACT FROM AUTHOR]

This work analyzes the influence of several microscope settings, namely, sample-forescattered electron detector (FSD) distance, and tilting conditions on the characteristics of the dislocation contrast imaged in transmission forescattered electron imaging (t-FSEI). The dislocation contrast behaviors of characteristic dislocation configurations of two Fe-based alloys, namely an α'-martensitic (body-centered cubic, bcc) Fe 33Ni alloy (wt%), and an austenitic (face-centered cubic, fcc) Fe-30Mn-6.5Al-0.3C alloy (wt%) were investigated on thin foil samples by using different on-axis transmission Kikuchi diffraction (TKD) configurations, namely t-FSEI, bright-field (BF) t-FSEI and electron channeling contrast imaging (ECCI). The set-ups use transmission Kikuchi electron patterns to orient the crystal into controlled diffraction conditions. Imaging parameters such as dislocation contrast intensity and information depth are analyzed and compared to those obtained in the ECCI mode under the same microscope conditions. These effects are associated with the attenuation of Bragg scattering by high-angle scattering processes and the electron channeling mechanism, respectively. The experimental analysis sets the microscope settings for optimum dislocation imaging in t-FSEI. • Analysis of the influence of microscope settings on the characteristics of the dislocation contrast imaged in t-FSEI. • Analysis of the microscope settings (range of optical axis-FSD distance) for optimum dislocation imaging in t-FSEI. • Comparative analysis of channeling effects on dislocation contrast in (BF) t-FSEI and ECCI. • Comparative analysis of the information depth in t-FSE and ECCI for imaging of dislocations in thin foils. [ABSTRACT FROM AUTHOR]

A detailed analysis has been conducted of Ti–6Al–4V processed by metallic shot peening and laser shock peening. Analysis by incremental hole drilling, electron backscattered diffraction microscopy, transmission electron microscopy and transmission Kikuchi diffraction microscopy is evaluated and discussed. The results of this analysis highlight the very different dislocation structures in surfaces processed by these two techniques. Transmission Kikuchi diffraction also has been used to evaluate sub-grains generated by laser shock peening. A notable feature of material processed by laser shock peening is the almost complete absence of deformation twinning, contrasting with the frequent observation of extensive deformation twinning observed in the material processed by metallic shot peening. [ABSTRACT FROM AUTHOR]

An attempt has been made to investigate Fe-rich fragments and surrounding intermetallic compounds in aluminum-steel friction stir welds using conventional EBSD + EDS as well as advanced Transmission Kikuchi Diffraction (TKD). Results indicate that the fragments are covered by a layer of orthorhombic Al 5 Fe 2 . This layer is surrounded by a mixed region composed of sub-micrometer Al 3 Fe crystals in a matrix of Al nano grains. Employing high beam current TKD on electron-transparent samples enables investigation of sub-micrometer grains in the mixed region with a higher spatial resolution than conventional EBSD. As a result, nano-twinning in Al in the mixed region has been observed. Microstructural and texture results imply that Fe-rich fragments travel through the Al matrix under extreme shear forces, severely refining Al grains, and inducing nano-twinning. Due to extreme shear forces and Fe outward diffusion, fine steel fragments dissolve in the surroundings leading to the nucleation of nano Al 3 Fe crystals particularly along Al grain boundaries. Al 3 Fe crystals consume the Al matrix as they grow in size and fraction. [ABSTRACT FROM AUTHOR]

This is the first transmission Kikuchi diffraction (TKD) study to report the indexing of nano-sized cementite as distinct structures and its orientation relationship with the body-centered cubic matrix in a quenched and tempered steel. Crystallographic analysis via TKD and selected area diffraction returned the well-known Bagaryatskii and Isaichev orientation relationships. However, the indexing of nano-sized cementite via TKD was sensitive to the thickness of the electron transparent region such that TEM remains the most precise method to characterise such precipitates. [ABSTRACT FROM AUTHOR]

In this work a carbide-free bainitic steel was examined by a novel correlative microscopy approach using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The individual microstructural constituents could be identified by TKD based on their different crystal structure for bainitic ferrite and retained austenite and by image quality for the martensite–austenite (M–A) constituent. Subsequently, the same area was investigated in the TEM and a good match of these two techniques regarding the identification of the area position and crystal orientation could be proven. Additionally, the M–A constituent was examined in the TEM for the first time after preceded unambiguous identification using a correlative microscopy approach. The selected area diffraction pattern showed satellites around the main reflexes which might indicate a structural modulation. [ABSTRACT FROM AUTHOR]

Molybdenum is an eligible material for high performance applications. However, its applicability is limited because of a brittle-to-ductile transition around room temperature, depending on the grain size and the content of interstitial impurities present at grain boundaries. The total amount of impurities in the current quality of molybdenum has become very small in the last decades. Therefore, the atom probe with its atomic resolution is the only suitable site-specific analysis technique. Nevertheless, a site-specific specimen preparation by focused ion beam (FIB) is required to study the grain boundary chemistry effectively. With a novel method, which combines re-sharpening of pre-electro-polished tips by FIB with transmission Kikuchi diffraction (TKD), a grain boundary can easily be positioned in the first 200 nm of an atom probe sample. Furthermore, the high resolution technique of TKD gives the opportunity to get crystallographic information of the mapped area and, therefore, an analysis of the grain boundary character to support the interpretation of the atom probe data files. In the present study, APT specimens of technically pure molybdenum which contain grain boundaries were prepared by FIB in support of TKD and subsequently were measured in the atom probe. The difference of segregation content at unequal types of grain boundaries in the as-deformed and recrystallized state is discussed. [ABSTRACT FROM AUTHOR]

This study applies the recently developed transmission Kikuchi diffraction technique to investigate the microstructures and micro-textures of a multi-phase Fe-17Mn-3Al-2Si-1Ni-0.08C wt% steel that concurrently exhibits twinning- and transformation-induced plasticity effects. The steel was cold rolled to 66% thickness reduction and subsequently annealed at 625 °C for 300 s. The cold-rolled microstructure mainly consisted of α′ martensite interspersed with blocky ϵ martensite and remanent nanometer-sized grains of γ. Annealing at 625 °C led to the partial transformation of α′ → γ and the reversion of ϵ → γ such that the microstructure comprised predominant nanometer-sized γ grains interspersed with a smaller α′ phase and a trace fraction of nanometer-sized ϵ along γ grain boundaries. During deformation via cold rolling and reverse transformation during annealing, micro-texture analysis indicated the operation of the Shoji-Nishiyama, Kurdjumov-Sachs, and Burgers ORs between γ ↔ ϵ, γ ↔ α′, and ϵ ↔ α′, respectively. [ABSTRACT FROM AUTHOR]

We report the first application of the emerging transmission Kikuchi diffraction technique in the scanning electron microscope to investigate nano-grain structures in polycrystalline MgB 2 superconductors. Two sintering conditions were considered, and the resulting differences in superconducting properties are correlated to differences in grain structure. A brief comparison to X-ray diffraction results is presented and discussed. This work focusses more on the application of this technique to reveal grain structure, rather than on the detailed differences between the two sintering temperatures. [ABSTRACT FROM AUTHOR]

Atom probe tomography (APT) is a suitable technique for chemical analyses with almost atomic resolution. However, the time-consuming site-specific specimen preparation can be improved. Recently, transmission electron backscatter diffraction (t-EBSD) has been established for high resolution crystallographic analyses of thin foils. In this paper we present the first successful application of a combined focused ion beam (FIB)/t-EBSD preparation of site-specific APT specimens using the example of grain boundary segregation in technically pure molybdenum. It will be shown that the preparation of a grain boundary can be substantially accelerated by t-EBSD analyses in-between the annular milling FIB procedure in the same microscope. With this combined method, a grain boundary can easily be recognized and positioned in the first 220nm of an APT sample much faster than e.g. with complementary investigations in a transmission electron microscope. Even more, the high resolution technique of t-EBSD gives the opportunity to get crystallographic information of the mapped area and, therefore, an analysis of the grain boundary character to support the interpretation of the APT data files. To optimize this newly developed technique for the application on needle-shaped APT specimens, a parameter study on enhanced background correction, acceleration voltage, and tilt angle was carried out. An acceleration voltage of 30kV at specimen surface tilt angles between -45° and -35° from horizontal plane leads to the best results. Even for molybdenum the observation of crystal orientation data up to about 200nm specimen thickness is possible. [ABSTRACT FROM AUTHOR]

A charge-coupled device camera of an electron backscattered diffraction system in a scanning electron microscope was positioned below a thin specimen and transmission Kikuchi patterns were collected. Contrary to electron backscattered diffraction, transmission electron forward scatter diffraction provides phase identification and orientation mapping at the nanoscale. The minimum Pd particle size for which a Kikuchi diffraction pattern was detected and indexed reliably was 5.6 nm. An orientation mapping resolution of 5 nm was measured at 30 kV. The resolution obtained with transmission electron forward scatter diffraction was of the same order of magnitude than that reported in electron nanodiffraction in the transmission electron microscope. An energy dispersive spectrometer X-ray map and a transmission electron forward scatter diffraction orientation map were acquired simultaneously. The high-resolution chemical, phase and orientation maps provided at once information on the chemical form, orientation and coherency of precipitates in an aluminium-lithium 2099 alloy. [ABSTRACT FROM AUTHOR]

The microstructure of heavily deformed pure nickel processed by accumulative roll bonding to a von Mises strain of 6.4 has been investigated using both transmission electron microscopy and transmission Kikuchi diffraction in a scanning electron microscope. By monitoring the microstructure in one region during in-situ annealing in a transmission electron microscope, it is found that 9% of all triple junctions present in this region have migrated over more than 40 nm. Junctions formed by three high angle boundaries are observed to be more prone to motion during recovery than any other junctions. The extent of triple junction motion in the Ni sample is compared to that in heavily deformed aluminum. [ABSTRACT FROM AUTHOR]

Due to their good mechanical properties and corrosion resistance, Ferritic Martensitic and ODS steels are widely studied for applications in the next generation of nuclear reactor. Under irradiation, migration of point defects leads to different mechanisms including radiation-induced segregation (RIS). This type of segregation affects defect sinks such as grain boundaries (GB). Many parameters influence the amplitude of the RIS such as temperature, dose and chemical composition of the alloy. This paper presents the quantification of GB plane variation on RIS. Two different near Σ3 (60° 〈111〉) GB were investigated using EBSD and TKD for structural characterization and APT and STEM/EDXS for chemical quantification. This work revealed W-shaped profiles of Cr across GBs and a heterogeneous precipitation of Cr C rich particles in GBs planes after irradiation. Our work shows that not only the amplitude but also the sign of the Gibbsian Excess may be affected by the GB habit plane. • After irradiation segregation of Cr and C was obtained on near ∑3 in Fe-13%Cr. • Difference in orientation of habit plan has an effect on segregation profile. • Heterogeneous precipitation of Cr C rich phase was observed on the habit plan of near ∑3. • W shape profile was observed with Cr across each grain boundary after irradiation. [ABSTRACT FROM AUTHOR]

A novel approach using focused ion beam (FIB) and electron backscatter diffraction (EBSD) or transmission Kikuchi diffraction (TKD) was developed to characterize all five parameters of the individual grain boundary. With this approach, the grain orientations and the grain boundary trace angles on two perpendicular surfaces can be measured. Then the grain boundary plane normal in the sample coordinate system can be determined and transformed to plane indices in the two crystal coordinate systems. FIB-TKD is a viable alternative to FIB-EBSD when EBSD measurement can't be conducted on the sample surface which is degraded by oxidation or corrosion. This approach was verified on a coherent twin boundary in alloy 690. The accuracy of the present FIB-EBSD method is better than 3°. This approach provides a convenient and efficient solution for measuring all five parameters of a site-specific grain boundary during FIB sample preparation. [Display omitted] • The grain boundary character can be investigated by focused ion beam (FIB) and electron backscatter diffraction (EBSD) or transmission Kikuchi diffraction (TKD). • The measurement accuracy of the FIB-EBSD method is better than 3º. • The FIB-TKD method provides a feasible way to index grain boundary plane when the surface of sample cannot meet the conventional EBSD test requirement. [ABSTRACT FROM AUTHOR]

The presence of intermetallic constituent particles strongly influences the deformation and fracture characteristics of as-cast magnesium alloys. The present study investigates the two-dimensional (2D) and three-dimensional (3D) microstructure of these intermetallic particles in a direct chill as-cast AZ91 alloy and their effect on the tensile deformation of the alloy. Electron backscattered diffraction (EBSD) was employed to characterize the non-equilibrium eutectic β-Mg 17 Al 12 phase, which further assisted in hypothesizing the solidification process of the alloy. Transmission Kikuchi diffraction (TKD) indicated the small-sized spherical Mg 17 Al 12 precipitates, formed adjacent to the non-equilibrium eutectic precipitate, did not exhibit any orientation relationship reported in the literature. Further, micron-sized Al Mn inclusions were observed to be single phase γ 2 -Al 8 Mn 5 particles exhibiting a cyclically twinned structure with 20 2 ¯ 1 habit plane. Additionally, optical microscopy (OM) in the dark-field (DF) and differential interference contrast (DIC) mode, in assistance with high resolution – transmission electron microscopy (HR-TEM) confirmed that the nano-sized γ 2 -Al 8 Mn 5 particles resulted in a bimodal grain size distribution of the alloy. The three-dimensional (3D) spatial distribution of these intermetallic constituent particles along with fractography facilitated in understanding the damage process of the alloy in uniaxial tension. • 2D and 3D microstructures of intermetallic particles in as-cast Mg-Al-Zn have been characterized. • Correlation between microstructure-solidification process has been established. • Nano-sized γ 2 -Al 8 Mn 5 resulted in a bimodal grain size distribution of α-Mg matrix. • Damage of the as-cast alloy depends predominantly upon the Mg 17 Al 12 precipitates. [ABSTRACT FROM AUTHOR]

We conducted correlated transmission Kikuchi diffraction and atom probe tomography measurements to investigate the relationship between the structure and chemistry of grain boundaries in Cu-rich and Cu-poor sulfide chalcopyrite CuInS 2 thin-films. We detect different elemental redistributions at random high‐angle grain boundaries, Σ9 twin boundaries and stacking faults in the Cu-rich and Cu-poor film but no chemical fluctuations at Σ3 twin boundaries. For the Cu-rich CuInS 2 thin-film, our atom probe tomography analyses reveal Cu enrichment as well as In and S depletion at random grain boundaries, Σ9 twin boundaries and stacking faults. Hence, we may observe a 'Cu on In' scenario, which is accompanied by co-segregation of Na and C. In contrast, for the Cu-poor CuInS 2 thin-film, our analyses show Cu depletion and In enrichment at random grain boundaries and at the vast majority of stacking faults. For S we do not observe a clear trend. Therefore, for the Cu-poor CuInS 2 thin-film we may observe a 'In on Cu' scenario, which is accompanied by co-segregation of Na, K and O at the random grain boundaries but not at stacking faults. The amount of impurity segregation varies from one grain boundary to another in both thin-films. Image 1 • Cu-rich CuInS 2 films show Cu enrichment, In and S depletion at RHAGBs, ∑9 TBs and SFs as well as segregation of Na and C. • Cu-poor CuInS 2 films show Cu depletion and In enrichment at RHAGBs as well as segregation of Na, K and O. • SFs in the Cu-poor CuInS 2 film show both Cu enrichment and Cu depletion and for In vice versa but no impurity segregation. • ∑3 twin boundaries in both Cu-rich and Cu-poor CuInS 2 films show no compositional changes. [ABSTRACT FROM AUTHOR]

The characterization of precipitates in bulk materials by Electron Backscatter Diffraction becomes challenging when the precipitate size falls below 200 nm. This is due to the drastic decrease of diffracted intensity with decreasing precipitate size and the rapidly growing signal generated by the surrounding matrix. A new technique is presented and allows determination of the structure and orientation of precipitates far below 100 nm directly in bulk samples in the Scanning Electron Microscope, normally requiring thin lamella extraction and Transmission Electron Microscopy analysis. The technique relies on the selective chemical etching of the matrix material of a sample, combined with the large tilt characteristic of the EBSD technique. As a result of the selective etching, precipitates protrude from the surface and emit what turns out to be a transmission diffraction signal instead of a backscatter diffraction signal, even though the sample remains massive. With this technique successful analysis of precipitates down to 30 nm was performed in a bulk Cu/Cr sample produced by Laser Powder Bed Fusion Additive Manufacturing with standard EBSD hardware. A Monte Carlo simulation confirms that the intensity of the transmission signal collected from a nanometer-sized precipitate protruding from the surface is much higher than the intensity of the backscatter signal collected from the same precipitate embedded right underneath the surface of a flat EBSD sample. Transmission signals emitted by bulk samples are a great opportunity to study features whose size are below the resolution limit of EBSD, like nanometer-sized precipitates, while keeping the possibility of exploring large areas and without the need to produce a thin lamella. • A new technique is presented to study the structure of nano-sized precipitates in SEM. • 30 nm precipitates could be analyzed in bulk samples with a conventional EBSD set-up. • Thanks to a selective chemical etch, precipitates emit diffraction in transmission. • The signal intensity generated this way is much higher than with a flat EBSD sample. [ABSTRACT FROM AUTHOR]

Transmission Kikuchi diffraction is an emerging technique aimed at producing orientation maps of the structure of materials with a nanometric lateral resolution. This study investigates experimentally the depth resolution of the on-axis configuration, via a twinned silicon bi-crystal sample specifically designed and fabricated. The measured depth resolution varies from 30 to 65 nm in the range 10-30 keV, with a close to linear dependence with incident energy and no dependence with the total sample thickness. The depth resolution is explained in terms of two mechanisms acting concomitantly: generation of Kikuchi diffraction all along the thickness of the sample, associated with continuous absorption on the way out. A model based on the electron mean free path is used to account for the dependence with incident energy of the depth resolution. In addition, based on the results in silicon, the use of the mean absorption coefficient is proposed to predict the depth resolution for any atomic number and incident energy.