Assessment of the degradation in mild structural steel using electron backscatter diffraction (EBSD) technique

This paper reports the degradation assessment of mild steel during the plastic tensile process. The electron backscatter diffraction (EBSD) technique was adopted in this study. The orientation maps showed that with the increase of tensile strain, the grain surface become wrinkled, and the deviation level of intragranular orientation also increased. Meanwhile, the parameters based on the image quality of the Kikuchi bands (i.e. BC and MAD) as well as the crystallographic orientation (i.e. LAGBs content, GND density, GOS, and GROD) can be used to evaluate the degradation degree of the mild steel. The results showed that the change of BC and MAD was significant at the end of plastic stage, but was not sufficiently distinctive at the early stage; Meanwhile, the LAGBs content and GND density increased evidently during the plastic tensile. Compared with the former, the GND density exhibited stronger regularity and better evaluation effect; Besides, a general upward trend of GOS and GROD was observed at this tensile process. However, the GROD changed less at the certain plastic stage. Compared with GROD, the GOS exhibited a relatively better evaluation effect; To sum up, the GND density and GOS are the better indicators for evaluating the degradation degree of mild steel.

Redistribution of Grain Boundary Misorientation and Residual Stresses of Thermomechanically Simulated Welding in an Intercritically Reheated Coarse Grained Heat Affected Zone

A study of the migration of the grain boundary misorientation and its relationship with the residual stresses through time immediately after the completion of a thermomechanical simulation has been carried out. After physically simulating an intercritically overheated welding heat affected zone, the variation of the misorientation of grain contours was observed with the electron backscatter diffraction (EBSD) technique and likewise the variation of the residual stresses of welding with RAYSTRESS equipment. It was observed that the misorientation of the grain contours in an ASTM DH36 steel was modified after the thermomechanical simulation, which corresponds to the measured residual stress variation along the first week of monitoring, with compressive residual stresses ranging from 195 MPa to 160 MPa. The changes in misorientation indicate that the stress relaxation phenomenon is associated with the evolution of the misorientation in the microstructure caused by the welding procedure. On the first day, there was a fraction of 4% of the kernel average misorientation (KAM) values at 1° misorientation and on the fourth day, there was a fraction of 7% of the KAM values at 1° misorientation.

Effect of Microstructure on Low-Temperature Fracture Toughness of a Submerged-Arc-Welded Low-Carbon and Low-Alloy Steel Plate

This study investigated the low-temperature fracture behavior of an 80-mm-thick low-carbon steel plate welded by submerged arc. The relationship between impact absorbed energy and ductility–brittle transition temperature (DBTT) based on the microstructures was evaluated through quantitative analysis on grain size and complex constituent phases using advanced EBSD technique. The microstructure formed differently depending on the heat affections, which determined fracture properties in a low-temperature environment. Among the various microstructures of the heat-affected zone (HAZ), acicular ferrite has the greatest resistance to low-temperature impact due to its fine interlocking formation and its high-angle grain boundaries.

EBSD Characterization of the Microstructure of 7A52 Aluminum Alloy Joints Welded by Friction Stir Welding

The microstructure and texture of materials significantly influence the mechanical properties and fracture behavior; the effect of microstructure in different zones of friction stir-welded joints of 7A52 aluminum alloy on fracture behavior was investigated in this paper. The microstructural characteristics of sections of the welded joints were tested using the electron backscattered diffraction (EBSD) technique. The results indicate that the fracture is located at the advancing side of the thermomechanically affected zone (AS-TMAZ) and the stir zone (SZ) interface. The AS-TMAZ microstructure is vastly different from the microstructure and texture of other areas. The grain orientation is disordered, and the grain shape is seriously deformed under the action of stirring force. The grain size grows unevenly under the input of friction heat, resulting in a large amount of recrystallization, and there is a significant difference in the Taylor factor between adjacent grains and the AS-TMAZ–SZ interface. On the contrary, there are fine and uniform equiaxed grains in the nugget zone, the microstructure is uniform, and the Taylor factor is small at adjacent grains. Therefore, the uneven transition of microstructure and texture in the AS-TMAZ and the SZ provide conditions for crack initiation, which become the weak point of mechanical properties.

Polarity Determination in EBSD Patterns Using the Hough Transformation

Currently, the automated electron backscatter diffraction (EBSD) technique only allows the differentiation of the Laue groups based on an electron backscatter pattern (EBSP). This article shows that information concerning the lattice plane polarity is not only stored in the EBSP, but also in the Hough transformed EBSP where it can be easily accessed for automated evaluation. Polar Kikuchi bands lead to asymmetric peaks during the Hough transformation that are dependent on the atomic number difference of the involved atoms. The effect can be strong enough to be detected when evaluating the intensities of the regular excess and deficiency lines. Polarity detection from the Hough transformation of an EBSP cannot only enhance the utility of the EBSD technique and expand the information gained from it, but also illustrates a path toward automated polarity determination during EBSD scans.

Microstructure Evaluation Study of Al5083 Alloy Using EBSD Technique after Processing with Different ECAP Processes and Temperatures

The temperature effects on the microstructural evolution of a coarse-grained Al5083 alloy during equal channel angular pressing (ECAP), were studied at ambient and high temperatures. The microstructural evaluation was done using an EBSD (electron backscattering diffraction) process. The grain refinement occurred as the number of passes increased, which had a positive effect on its strength. Additionally, increasing the pressing temperature leads to a decrease in the new grain’s formation and an increase in the normal grain size in the third pass. This can be ascribed to the unwinding of strain similarity between the grains because of the continuous activity of dynamic recuperation and the grain limit sliding occurring at a higher temperature. The attainment of grain refinement is examined exhaustively in this study.

Investigation into Microstructure Evolution of Co–Ni–Cr–W–Based Superalloy During Hot Deformation

Hot compression tests were conducted using a Gleeble 3500 thermomechanical simulator at temperatures ranging from 1,000 to 1,200°C with the strain rate ranging from 0.1 to 10 s−1. Electron backscatter diffraction (EBSD) technique was employed by investigating the microstructure evolution during hot deformation. Microstructure observations reveal that deformation temperatures and strain rates have a significant effect on the DRX process. It is found that the fraction and grain size of DRX increase with the decreasing deformation temperature, along with the increasing high-angle grain boundaries (HAGBs). The fraction of DRX first decreases and then increases with the increase of strain rates. It is noted that there are both the nucleation mechanisms of discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) during the DRX process for Co–Ni–Cr–W–based superalloys. DDRX and CDRX are the primary and subsidiary nucleation mechanisms of DRX, respectively. It is also found that deformation temperatures and strain rates have almost no effect on the primary and subsidiary nucleation mechanisms of DRX. At the temperature above 1,150°C, the complete DRX occurred with the average grain sizes of about 25.32–29.01 μm. The homogeneity and refinement of microstructure can be obtained by selecting the suitable hot deformation parameters.

Revealing microstructural properties of shocked and tectonically deformed zircon from the Vredefort impact structure: Raman spectroscopy combined with SEM microanalyses

ABSTRACT Finite deformation patterns of accessory phases can indicate the tectonic regime and deformation history of the host rocks and geological units. In this study, tectonically deformed, seismically deformed, and shocked zircon grains from a granite sample from the core of the Vredefort impact structure were analyzed in situ, using a combination of Raman spectroscopy, backscatter electron (BSE) imaging, electron backscattered diffraction (EBSD) mapping, electron probe microanalyses (EPMA), energy-dispersive X-ray spectroscopy (EDS) qualitative chemical mapping, and cathodoluminescence (CL) imaging. We aimed to reveal the effects of marginal grain-size reduction, planar deformation bands (PDBs), and shock microtwins on the crystal structure and microchemistry of zircon. Deformation patterns such as PDBs, microtwins, and subgrains did not show any significant effect on zircon crystallinity/metamictization degree or on the CL signature. However, the ratio of Raman band intensities B1g (1008 cm–1) to Eg (356 cm–1) slightly decreased within domains with low misorientation. The ratio values were affected in shocked grains, particularly in twinned domains with high misorientation. B1g/Eg ratio mapping combined with metamictization degree mapping (full width at half maximum of B1g peak) suggest the presence of shock deformation features in zircon; however, due to the lower spatial resolution of the method, they must be used in combination with the EBSD technique. Additionally, we discovered anatase, quartz, goethite, calcite, and hematite micro-inclusions in the studied zircon grains, with quartz and anatase specifically being associated with strongly deformed domains of shocked zircon crystals.