Electron backscatter diffraction of CdTe thin films: Effects of CdCl2 treatment

Constructing micro-mechanical representative volume element of medium Mn steel from EBSD data

Herein, micromechanical simulations for three different states of spheroidized steel (C45EC) are conducted under quasi‐static tensile loading based on the actual texture and crystallographic orientation from electron backscatter diffraction (EBSD) data. Data denoising is conducted with MTex (open‐source Toolbox with MATLAB) for cleaning up the EBSD data. Crystal plasticity‐based full phase numerical simulations are performed on these constructed representative volume elements (RVEs) to analyze the local stress and strain evolution in C45EC steels. The local results of the simulations exhibit important insights into deformation evolution influenced by the size and clustering of cementite particles as well as crystallographic orientations of ferrite grains. It is observed that the full phase simulation model helps predict the local microstructural details for overall mechanically improved properties of the steels. Spheroidized steel samples (97%) show the most favorable mechanical response as adequate strain hardening with extended elongation is desired for cold‐working of parts. The current work is another step forward to fine‐tune the microstructural attributes of medium carbon steels for an improved mechanical response.

Electron backscatter diffraction (EBSD) data yield plentiful information on microstructure and texture of natural as well as experimentally produced mineral and rock samples. For instance, the characterization of microstructures and textures by EBSD allows for the evaluation of phase equilibria. Furthermore, determination of the preferred orientations of crystals using EBSD yields constraints on deformation mechanisms and history of the minerals/rocks. The latter affects bulk-rock properites, for example, through the relation between lattice preferred orientation and electrical conductivity and seismic anisotropy. EBSD is also applied to advance our understanding of various phenomena such as seismic wave attenuation in the Earth deep interior and its relation to the presence of interfacial small degrees of melt fractions, or free fluid phases. In standard EBSD software solutions, the original EBSD patterns are rarely saved and indexing routines result in many artifacts, such as pseudo-symmetry or unindexed pixels at interfaces that may be misinterpreted as amorphous material, such as a melt. Here we report the first application of the dictionary indexing (DI) approach proposed by Chen et al. (2015), an alternative indexing routine, which we extended to be applicable to multiphase geologic materials. The DI method is independent of the EBSD system, and thus of the used detector/software. The DI routine generates simulated EBSD patterns for all possible crystal orientations, taking the sample composition and experimental setups into account. The resulting pattern database is called a dictionary. The experimental electron backscattering pattern (EBSP) images are indexed by comparing them to the dictionary using a dot-product algorithm. We evaluate the new DI method in comparison to standard routines and highlight advantages and disadvantages. To test and compare the DI’s reliability and performance, we apply the routine to two scientifically challenging samples: (1) A nominally anhydrous (“dry”) residual eclogite composed of garnet (cubic), clinopyroxene (monoclinic) and an amorphous melt, where the different degrees of hardness of the phases cause surface topology; and (2) a pure forsterite (olivine) polycrystalline sample produced by vacuum sintering. The acquired EBSD patterns are of low quality for the latter as a result of fast data acquisition to reduce the on-line machine time. We conclude that the new DI method is highly precise and surpasses the performance of previously available methods, while being computer time and computer memory consuming. We find that the DI method is free of pseudo-symmetry-related problems. Interpolation of data becomes obsolete and high reproducibility is obtained, which minimizes the operator impact on the final data set. The latter is often caused by applying several cleaning steps on EBSD maps with low indexing fraction. Finally, much higher scientific integrity is ensured by image collections as described above, which requires that all patterns are saved. This in turn allows later re-analyses if required. The DI routine will help to achieve more reliable information on interface properties of geological samples, including amorphous materials, and thus in the long run help to improve the accuracy of large-scale Earth mantle process models.

Electron backscatter diffraction scans are an important experimental input for microstructure generation and homogenization. Multiple electron backscatter diffraction scans can be used to sample the uncertainty in orientation distribution function: both point to point within a specimen as well as across multiple specimens that originate from the same manufacturing process. However, microstructure analysis methods typically employ only the mean values of the orientation distribution function to predict properties, and the stochastic information is lost. In this work, analytical methods are developed to account for the uncertainty in the electron backscatter diffraction data during property analysis. To this end, a linear smoothing scheme is developed in the Rodrigues fundamental region to compute the orientation distribution function from the electron backscatter diffraction data. The joint multivariate probability distributions of the orientation distribution function are then modeled using a Gaussian assumption. The uncertainty in engineering properties that are obtained by homogenization are also computed. It is shown that the uncertainty in nonlinear properties can be analytically obtained using direct transformation of random variables in the homogenization approach.

Ten years ago electron backscatter diffraction (EBSD) became available to a wider group active in materials research. This paper highlights some of the more significant developments in camera technology and software developments that have arisen since then. The use of slow-scan charge couple device cameras for phase identification and rapid determination of orientation image micrographs is reviewed. The current limiting spatial resolution of the technique is shown to be less than 10 nm. A procedure for improving lattice spacing measurement by utilizing the full resolution of the camera is described with experimental measurements on silicon and nickel showing relative errors of plus/minus 3%. An investigation of partially recrystallized aluminium shows how the recrystallized fraction can be extracted with confidence but that the mapping of substructure in the highly deformed regions is questionable. Phase identification is described for complex cases in which the phase data tabulated in standard databases do not correspond to what is observed in the EBSD patterns. Phase mapping in a complex mineral in which chemical data and EBSD data are collected simultaneously is shown to be improved by recording both the chemical and the EBSD data into computer memory and proceeding with the phase discrimination and orientation measurement in off-line analysis.

Effect of unusual texture on tension-compression asymmetry for Mg-RE alloy by viscoplastic self-consistent modeling

Acoustical holography (volume 7) — Recent advances in ultrasonic visualization: Edited by Lawrence W. Kessler Plenum Press, New York and London (1977), xiii + 654 pp, $35.40

Texture evolution in deformed AZ31 magnesium sheets: Experiments and phase-field study

Influence of deposition time in CdTe thin film properties grown by Close-Spaced Sublimation (CSS) for photovoltaic application

Investigation of deformation mechanisms in an advanced FeCrAl alloy using in-situ SEM-EBSD testing

To improve component design, the fundamental understanding of the fatigue behaviour of gas turbine materials is essential. Since Ni-alloys exhibit pronounced elastic anisotropy, the local grain orientation strongly affects the stress and strain distribution in the material under mechanical loadings. This work addresses the characterisation of anisotropic elastic–plastic deformation and its consequences for crack initiation of nickel-base superalloy IN617 under tensile loading. Samples were loaded in situ in a scanning electron microscope (SEM) to correlate the deformation behaviour with the grain structure and the grain orientation determined by electron backscatter diffraction (EBSD) measurements. To calculate the resulting stresses and strains, the EBSD data were used to develop a model by finite element method (FEM) considering the grain structure and orientation. The results of the elastic–plastic finite element (FE) simulation were compared with the theories of the E⋅m model based on the Schmidt factor (m) and anisotropic Young’s modulus (E). A mathematical image registration method called “optical flow method” (OFM), which is capable to calculate the transformation of EBSD measuring points during deformation, was applied to the EBSD data. The strains calculated by the optical flow method and by FE simulation were compared for two samples. The findings revealed large strains in the later crack initiation area found in both the OFM and FEM. The developed FEM model was verified by the successful correlation of hypotheses of the E·m model with the simulated mechanical behaviour. Furthermore, the impact of the microstructural neighbourhood on the mechanical behaviour was emphasised.Graphical

The oxygen content during the intermediate and final stages of sintering can have a strong effect on the microstructural evolution of oxide fuels. Two depleted urania (d-UO2.0 and d-UO2.14) samples, sintered up to a theoretical density of 90%, were serial sectioned using a focused ion beam and characterized with electron backscatter diffraction (EBSD). The EBSD data were used to make three-dimensional reconstructions of the microstructures to evaluate their characteristics at an intermediate stage of sintering. The oxygen content was found to affect grain shape and grain boundary (GB) mobility, as curved and elongated grains were observed in UO2.0, as well as stronger pore-GB interactions, which is an indication that microstructure was less evolved in UO2.0. Both samples presented a similar fraction ([approximate]20%) of special, coincident site lattice boundaries, with larger amounts of Σ3n GBs, and a rather large fraction of Σ11 GBs for UO2.14. Crystallographic GB planes were also determined to study the distributions of all GB parameters. The UO2.0 sample had a large fraction of GB planes close to the Σ3 twinning planes, which suggests that lower-energy interfaces are used to minimize energy in this sample, potentially due to lower overall GB mobility as compared to UO2.14.

This article reports on recent progress in the effort to develop an automated, crystallographically based twin identification and quantification routine using large sets of spatially correlated electron backscattered diffraction (EBSD) data. The proposed analysis scheme uses information about the most probably occurring twin types and the macroscopic stress state, taken together with the crystallographic theory of deformation twinning, to identify and classify twinned areas in a scanned cross section of a material. The key features of the analysis are identification of potential twin boundaries by their misorientation character, validation of these boundaries through comparison with the actual boundary position and twin-plane matching across the boundary, and calculation of the Schmid factors for the orientations on either side of the boundary. This scheme will allow researchers to quantify twin area fractions from statistically significant regions and, in turn, estimate twinned volume fractions with reasonable reliability.

The dynamic recrystallization as well as meta-dynamic and static recrystallization of the nickel-based alloy 80A was investigated by means of electron backscatter diffraction (EBSD). Specimens were hot compressed at a temperature of 1120 degrees C and a strain rate of 0.1/s at varying strain and soak times to describe the recrystallization behaviour. Various approaches were tested in order to differentiate between recrystallized and deformed grains based on EBSD data. The grain orientation spread was clearly found to be the most reliable procedure. A high twinning of the recrystallized grains was observed, and as a consequence the measured grain size was strongly dependent on whether the coherent and incoherent twin boundaries were regarded as genuine boundaries or removed.

CdTe thin films were synthesized using CdTe nanoparticle precursors. Capped CdTe nanoparticles were prepared by injection of a mixture of Cd(CH3)2, (n‐C8H17)3PTe and (n‐C8H17)3P into (n‐C8H17)3PO at elevated temperatures and characterized by x‐ray diffraction, UV‐Vis spectroscopy, transmission electron microscopy, thermogravimetric analysis and energy dispersive x‐ray spectroscopy. CdTe thin film deposition was accomplished by forming a colloidal suspension of CdTe nanoparticles in a suitable organic solvent and then spraying the colloid onto SnO2‐coated glass substrates at variable susceptor temperatures (‘‘one‐step process’’). In addition, a two‐step process was performed where a low‐temperature spray deposition (T=150 °C) was followed by sintering in air, forming gas or argon at variable annealing temperatures. The one‐step process yielded smooth and dense CdTe thin films using growth temperatures approximately 200 °C less than conventional spray pyrolysis approaches. CdTe films were characterized by x‐ray diffraction, UV‐Vis spectroscopy, atomic force microscopy, Auger electron spectroscopy and electron probe micro analysis. An increase in crystallinity and average grain size as determined by x‐ray diffraction was noted as growth temperature was increased from 240 to 300 °C. This temperature dependence of film grain size was further confirmed by atomic force microscopy with no remnant nanocrystalline morphological features detected. The films obtained by the two‐step process showed a dependence of crystallinity on annealing temperature. Atomic compositions determined by Auger electron spectroscopy and electron probe microanalysis showed nearly stoichiometric Cd and Te for both one‐ (Tgr=300 °C) and two‐step (Tanneal≥400 °C) deposited films; however, C impurities, arising presumably from the capping agent, were also detected.