Electron Backscattering Pattern Technique Research Articles

Development of visualization method of grain boundaries in stainless steel by using white X‐ray micro‐beam and image detector

AbstractA visualization method of grain boundaries in a polycrystal was developed at BL28B2 in SPring‐8. By combining a scanning type white X‐ray micro‐diffraction system with high‐energy synchrotron X‐rays we non‐destructively obtained images to visualize grain boundaries and grains in stainless steel by simple data processing. The images were comparable to those obtained by electron back scattering pattern technique. It was shown that the new method can be applied to bulky plate sample as thick as 300 µm containing grains with size of 100 µm.

Effects of an external electric field on cube texture development of rolled pure nickel during recrystallization

The effects of an external electric field on cube texture development have been studied by means of electron backscatter pattern technique, using rolled nickel sheets of 99.999% purity. Samples were annealed at 300 °C for different times both without and with an external electric field, of intensity 2000 V/cm. Results show that the application of an external electric field has decreased the volume fraction of cube texture and the grain size of cube oriented grains.

The Effect of Grain Boundaries on the Surface Rearrangement during Wuestite Reduction within its Range of Existence

Dense polycrystalline wüstite samples equilibrated with 50%CO-CO2 gas mixture for 432 ks has been reduced at 1073 K using 60%CO-CO2 gas mixture to study the effect of grain boundaries on the surface rearrangement process. Orientations of surface grains on the wüstite specimens are measured by applying electron backscattering pattern technique. The development of the surface arrangement away from grain boundaries is significantly larger than that near grain boundaries. Quick establishment of the equilibrium with the reacting gas in the region near grain boundaries at the early stage of the reduction makes it difficult to continue the transportation of Fe2+ ions into deep interiors of wüstite by the volume diffusion process. As a result, the surface rearrangement is retarded at the surface near grain boundaries after the equilibration of the surface. The transportation of Fe2+ ions at the surface layer away from grain boundaries by volume diffusion is small but not negligible so that the surface rearrangement away from the grain boundary is possible to continue until almost the whole sample is equilibrated.

Effects of electrical field treatment on recrystallization of copper single crystal

Abstract The effects of an electrical field on recrystallization of Cu have been investigated. A 12° off exact (1 1 2) [1 1 1 ¯ ] copper single crystal was rolled to 80% reduction. Samples cut from the deformed material were then annealed for 1 h at temperatures of between 200 °C and 400 °C. For each temperature, samples were annealed either with or without the presence of an electrical field of intensity 1500 V/cm. The microstructures were investigated in the longitudinal plane by using the electron backscatter pattern technique. Results show that the application of an external electric field might promote the grain growth rate, and also promote the formation of Σ3 twin boundary.

Dynamic recrystallization in Al-single crystals revealed by synchrotron radiation Laue technique

An experimental study on the microstructure development and stress–strain behavior during high temperature deformation of aluminum (Al) single crystals was made by using the synchrotron radiation Laue technique and the electron backscatter pattern technique. The main purpose was to clarify the process of dynamic recrystallization (DRX). The measured stress–strain curves with large stress peaks and the in situ observed new Laue spots without streaks at around the stress peaks confirmed the occurrence of DRX. Crystallographic analysis shows that the common axis between the DRX grain and the matrix is close to 〈1 1 2〉. The unrecrystallized region near the DRX grain consists of subgrains adjoined each other with 〈1 1 2〉 tilt boundaries and the size of subgrains becomes smaller and the misfit at subgrain boundaries becomes larger as the DRX grain boundaries are approached. These experimental results suggest that DRX grains are nucleated through the development of subgrains.

Effects of trace element on crystal growth of calcite in aquatic system: Morphology analysis using electron back-scattering pattern technique

Effects of trace element on crystal growth of calcite in aquatic system: Morphology analysis using electron back-scattering pattern technique

Orientation Dependence of Dynamic Recrystallization Behavior of Al Single Crystals

An experimental study on the microstructure development and stress–strain behavior during high temperature deformation of aluminum (Al) single crystals was made by using X-ray Laue technique and the electron backscatter pattern (EBSP) technique. The main purpose was to clarify the process of dynamic recrystallization (DRX). The measured stress-strain curves with large stress peaks and the new Laue spots without streaks at around the stress peaks confirmed the occurrence of DRX in Al single crystals with initial compression axis <111>, <011> or <001>. Crystallographic analysis by the Laue technique and EBSP technique show that the DRX grain and the matrix have an <121> axis in common in the <111> crystal, an <101> axsis in the <011> and <001> crystals. For the <111> crystal, the unrecrystallized region near the DRX grain consists of subgrains adjoined each other with <112> tilt boundaries and the size of subgrains becomes smaller and the misfit at subgrain boundaries becomes larger as the DRX grain boundaries are approached. These results suggest that DRX grains are nucleated through the development of subgrains.

Estimation of stress corrosion cracking sensitivity of type 304 stainless steel by magnetic force microscope

An application of a magnetic force microscope (MFM) to the measurement of the chromium depleted regions of type 304 stainless steel is proposed to enable more effective evaluation of the material sensitization to stress corrosion cracking than the conventional methods. The MFM images of sensitized materials show that the magnetizations are induced along grain boundaries by the chromium depletion. The dependence of the magnetization on the sensitization condition conforms to the expected one from the behavior of chromium depletion. Furthermore, the phase identification was performed by electron backscattered pattern technique to reveal the magnetization mechanism due to sensitization. Then, it was found that the magnetization is caused by the transformation from austenite phase to martensite phase. From the discussion on the temperature at which martensitic transformation starts, we see that it seems to be possible to detect regions where the chromium concentration is under 14% by using an MFM.

The Effect of Grain Boundaries on Iron Nucleation during Wuestite Reduction Process

Dense polycrystalline wustite samples equilibrated with 50%CO-CO 2 gas mixture for 432 ks were reduced at 1 073 K using 75%CO-CO 2 to study iron nucleation process. Especially the effects of grain boundaries and grain orientations on the iron nucleation were focused. The orientation of surface grains in the wustite specimens was measured by applying electron backscattering pattern technique. The number of formed iron nuclei near grain boundaries was found to be significantly larger than that away from grain boundaries. The prevalence of the iron nucleation process near grain boundaries was mainly due to the fast transport process of holes and Fe divalent cation by surface and grain boundary diffusion. The dominant effect of the grain boundary on the iron nucleation was found on the all grains with different grain orientations.

Determining dislocation cell sizes for high-strain deformation microstructures using the EBSP technique.

The effect of several data collection and processing choices has been examined for high-resolution electron back-scatter pattern (EBSP) investigation of a highly deformed sample. The results were compared with a transmission electron microscope (TEM) investigation of the same sample. The estimated dislocation cell size was examined as a function of data cleaning strategy, line intercept vs. reconstruction method, critical misorientation angle definition and step-size. The best agreement with the TEM results was obtained using a modified relative reconstruction algorithm on fine step-size maps allowing some of the noise in the data to be overcome. Step sizes of up to one-quarter the average cell size yielded similar values for the estimated average cell size. As a result of the mixture of both high- and low-angle boundaries, single diffraction condition TEM images may give larger cell size estimates than the EBSP data. Orientation noise in the EBSP data, however, still limits the extent to which quantitative information can be extracted.

EBSP study of the annealing behavior of aluminum deformed by equal channel angular processing

Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500°C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300°C.

Intergranular strains and plastic deformation of an austenitic stainless steel

Intergranular strains due to tensile plastic deformation were investigated in a sheet material of austenitic stainless steel. The objective was to study the development of residual intergranular strains in samples unloaded from the intermediate and large plastic deformation regimes for which few theoretical and experimental studies were available. By using neutron diffraction, residual lattice strain distribution as a function of sample direction was mapped for a number of crystallographic planes. Deformation microstructures were examined by both transmission electron microscopy and the electron back scattering pattern technique. Residual intergranular strains were observed in samples deformed significantly beyond the elastic limit and the strains varied with sample directions as well as the amount of applied plastic strain. In addition, a different tendency of intergranular strain evolution was observed after large plastic deformation, which could be attributed to the change of dominant plastic deformation mode from slip to mechanical twinning. The results are discussed based on the observed deformation microstructure studies.

Heterogeneous deformation and recrystallisation of iron base oxide dispersion strengthened PM2000 alloy

The recrystallisation behaviour of PM2000 oxide dispersion strengthened ferritic alloy has been investigated for tube specimens which had been cold deformed after extrusion. The evolution of the recrystallisation temperature, defined as the minimum temperature at which the specimen begins to recrystallise, has been studied in detail as a function of the level of deformation. The microstructure was characterised using optical and transmission electron microscopy, together with microhardness measurements, and local texture measurements obtained using the electron backscattering pattern technique. The results can be interpreted if it is assumed that any procedure that produces a heterogeneous microstructure, stimulates recrystallisation. In this sense, larger strain gradients lead to more refined and more isotropic grain structures. The way in which these results can be exploited for commercial applications is discussed.

Dislocation structures in cyclically deformed nickel polycrystals

The effect of the grain orientation and the plastic strain amplitude ε pa on the saturated dislocation structure was studied on individual grains of cyclically deformed nickel polycrystals by means of scanning electron microscopy using the electron back scattering pattern technique and the channelling contrast of back scattered electrons. The main features of the dislocation configuration in a grain were found to be essentially determined by the crystallographic axial orientation of the grain. A labyrinth-like dislocation pattern is typical for grains with axial orientations near [001], a patch pattern exists in grains with a loading axis (LA) near [011] and fragmented dislocation walls are dominant in grains with LA near [1̄11]. Grains with axial orientations in the central part of the stereographic standard triangle contain a bundle arrangement of dislocation structures. All four types of dislocation structures, but mostly the bundle type, can occur together with the ladder structure of persistent slip bands. Cell patterns were found to be a result of a modification of the bundle and patch configuration at high deformation amplitudes. The mesoscopic dimensions of the dislocation patterns turned out to depend on ε pa in the same way for all grain orientations: while the thickness of regions with high dislocation density is reduced with increasing ε pa, the width of regions with low dislocation density remains roughly constant.

Deformation and recrystallisation studied by EBSP: breakthroughs and limitations

The use of microtexture investigations by the electron backscattering pattern (EBSP) technique in the SEM for investigations of plastic deformation and recrystallisation is described. The focus is on grain subdivision during deformation and on nucleation and growth during recrystallisation. Specific investigations in which the EBSP technique has been essential to achieve a scientific breakthrough are reviewed. Also the limitations of the EBSP technique are discussed and illustrated by examples of incorrect results which might have been accepted if the EBSP measurements had not been complemented by other methods.

Application of high-energy synchrotron radiation for texture studies

A novel experimental technique that employs high-energy synchrotron radiation is used for the investigation of through-thickness texture gradients in two aluminium plates, cold-rolled 40% with either intermediate or small draughts. In these two plates, crystallographic textures are inspected in a large number of layers. Texture maps of pole densities throughout the sample thickness are presented. A texture of the rolling type is developed through the plate thickness after intermediate draught rolling. Pronounced inhomogeneities associated with the shear texture are observed in the sample rolled with small draughts. For selected layers, direct pole figures are compared with those obtained by traditional low-energy X-ray diffraction and by the electron backscattering pattern technique using a scanning electron microscope. A good qualitative agreement between textures measured using the three different techniques is obtained. Experimental aspects and potentials of the new technique are discussed.

Unsupervised approval criteria for automated EBSP investigation of deformed metals.

Unsupervised approval criteria have been investigated for orientations gathered from cold deformed samples (medium to high strain range) using the electron backscattering pattern technique. For such samples, the dislocation cell-size is on the order of the available step-size and pattern quality is generally low. Approval criteria for assessing the validity of measured orientations under these conditions were determined using, as a calibration, channel die cold deformed single crystals of stable orientations. In all cases, approval criteria based on an indexing confidence measure are found to be preferable. Different criteria are suggested, depending on whether the orientation data are subsequently to be used for texture analysis, or for a misorientation angle-based analysis. The latter is illustrated by an investigation of the number of deformation generated high angle boundaries introduced during a 90% cold reduction of a polycrystalline sample.

Grain Size Analysis Using Automated-EBSP

This work discusses using the automated Electron BackScatter Pattern (EBSP) technique of electron diffraction in the Scanning Electron Microscope (SEM) for measuring grain size in polycrystalline materials. A quantitative analysis of 2-D grain size from a standard metallographic section can be made in less than one hour using an automated-EBSP system on a traditional SEM and dedicated analysis software. Thus, the automated EBSP technique provides a useful and cost-effective way to determine grain size. A common measure used to describe grain size is mean intercept length (MIL) and the present discussion will be limited to determining MIL using EBSP.Grain size analysis using optical microscopy is strongly influenced by sample preparation, which involves etching of the polished section to reveal boundaries. Boundaries that are to be avoided in determining MIL, such as sub-grain boundaries and twin boundaries, may be revealed and mistaken for random high angle boundaries.

Texture and transport in spray pyrolyzed TlBa2Ca2Cu3O9 thick films

The electron backscattering pattern technique has been applied to the microstructural investigation of Tl(1223) thick films formed by vapor-phase thallination of Ag-containing Ba–Ca–Cu–oxide precursors. For samples grown on polycrystalline YSZ, considerable biaxial alignment is found in localized, multigrain regions as wide a 100 μm or more. However, on scales above 1 mm the overall texture remains only uniaxial with the c-axes (i.e., [001]) aligned perpendicular to the plane of the substrate. On single-crystal KTaO3 an epitaxial relationship is evident which persists to the surface of a 3 μm thick film. Modest variations in the processing protocol yield films containing grains oriented with the c-axis in the plane, resulting in the degradation of transport properties. The data suggest a growth mode in which sparse nucleation occurs at the substrate followed by rapid lateral crystallization.

Misorientation measurements near grain boundary cracks after fatigue tests

Microcrack initiation and propagation in mechanical fatigued polycrystals are sensitive to crystallographic misorientation between grains. The analysis of factors affecting the propagation of microcracks requires quantitative knowledge about the crystallographic misorientations of the grain boundary segments in which microcracks have been observed. Such observations are possible using the electron back-scattering pattern technique in the scanning electron microscope. The principle of this method is explained and some examples of such investigations on nickel polycrystals in push-pull tests are presented.