Linear chemically sensitive electron tomography using DualEELS and dictionary-based compressed sensing

We have investigated the use of DualEELS in elementally sensitive tilt series tomography in the scanning transmission electron microscope. A procedure is implemented using deconvolution to remove the effects of multiple scattering, followed by normalisation by the zero loss peak intensity. This is performed to produce a signal that is linearly dependent on the projected density of the element in each pixel. This method is compared with one that does not include deconvolution (although normalisation by the zero loss peak intensity is still performed). Additionaly, we compare the 3D reconstruction using a new compressed sensing algorithm, DLET, with the well-established SIRT algorithm. VC precipitates, which are extracted from a steel on a carbon replica, are used in this study. It is found that the use of this linear signal results in a very even density throughout the precipitates. However, when deconvolution is omitted, a slight density reduction is observed in the cores of the precipitates (a so-called cupping artefact). Additionally, it is clearly demonstrated that the 3D morphology is much better reproduced using the DLET algorithm, with very little elongation in the missing wedge direction. It is therefore concluded that reliable elementally sensitive tilt tomography using EELS requires the appropriate use of DualEELS together with a suitable reconstruction algorithm, such as the compressed sensing based reconstruction algorithm used here, to make the best use of the limited data volume and signal to noise inherent in core-loss EELS

WORKING GROUP ON NEPHROPS SURVEYS (WGNEPS ; outputs from 2020)

The Working Group on Nephrops Surveys (WGNEPS) is the international coordination group for Nephrops underwater television and trawl surveys within ICES. This report summarizes the na-tional contributions on the results of the surveys conducted in 2020 together with time series covering all survey years, problems encountered, data quality checks and technological improve-ments as well as the planning for survey activities for 2021.ICE

Microstructure, plastic flow and fracture behavior of ferrite-austenite duplex low density medium Mn steel

International audienceThis study addresses the microstructure, plastic flow and fracture behavior of a laboratory Al-containing low density Fe-0.3C-6.7Mn-5.9Al medium Mn steel, intercritically annealed at either 850 °C or 900 °C, after cold rolling. Both resulting materials present an unordinary bimodal duplex microstructure made of coarse δ-ferrite grains and fine-grained (FG) {α-ferrite + retained austenite} regions. Tensile tests at room temperature and at −50 °C and Charpy impact tests showed that for both materials, each microstructural region presents its own fracture mechanisms and a specific ductile-to-brittle transition. A transition from brittle cleavage to ductile fracture is observed for coarse δ-ferrite grains, while FG regions present a transition from interfacial fracture to ductile fracture. The overall impact behavior seems to be driven by that of δ-ferrite grains

Ferrite effects in Fe‐Mn‐Al‐C triplex steels

International audienceIn order to determine the ferrite effect on tensile properties of Fe-28.8Mn-9.4Al-C Triplex steels, four Triplex steel sheets with different carbon contents were solution treated under various conditions leading to different ferrite fractions ranging from 0 to 39 pct. This approach was used as it was very difficult to prepare samples with a wide range of ferrite contents from only one grade. However, in order to isolate the ferrite effect from this approach, it was necessary to precisely know the effect of the austenite carbon content and that of the austenite grain size on tensile properties of fully austenitic samples. This is why, a preliminary study was performed to assess these two effects, which required a thorough analysis of the microstructures of the investigated samples combining electron backscattered diffraction experiments and transmission electron microscopy observations. The study of fully austenitic samples led us to the conclusion that a decrease in the austenite grain size leads to higher strength and lower elongation and that the austenite carbon content has a greatly significant influence on tensile properties. However, this influence was difficult to estimate with a very good accuracy. Finally, the study of samples with different ferrite contents showed that ferrite had a positive effect on strength when its content was lower than 5 pct. In contrast, a higher content of ferrite (more than 30 pct) has a deleterious effect on mechanical properties

Ferrite effects in Fe‐Mn‐Al‐C triplex steels

International audienceIn order to determine the ferrite effect on tensile properties of Fe-28.8Mn-9.4Al-C Triplex steels, four Triplex steel sheets with different carbon contents were solution treated under various conditions leading to different ferrite fractions ranging from 0 to 39 pct. This approach was used as it was very difficult to prepare samples with a wide range of ferrite contents from only one grade. However, in order to isolate the ferrite effect from this approach, it was necessary to precisely know the effect of the austenite carbon content and that of the austenite grain size on tensile properties of fully austenitic samples. This is why, a preliminary study was performed to assess these two effects, which required a thorough analysis of the microstructures of the investigated samples combining electron backscattered diffraction experiments and transmission electron microscopy observations. The study of fully austenitic samples led us to the conclusion that a decrease in the austenite grain size leads to higher strength and lower elongation and that the austenite carbon content has a greatly significant influence on tensile properties. However, this influence was difficult to estimate with a very good accuracy. Finally, the study of samples with different ferrite contents showed that ferrite had a positive effect on strength when its content was lower than 5 pct. In contrast, a higher content of ferrite (more than 30 pct) has a deleterious effect on mechanical properties

Ferrite Effects in Fe-Mn-Al-C Triplex Steels

International audienceIn order to determine the ferrite effect on tensile properties of Fe-28.8Mn-9.4Al-C Triplex steels, four Triplex steel sheets with different carbon contents were solution treated under various conditions leading to different ferrite fractions ranging from 0 to 39 pct. This approach was used as it was very difficult to prepare samples with a wide range of ferrite contents from only one grade. However, in order to isolate the ferrite effect from this approach, it was necessary to precisely know the effect of the austenite carbon content and that of the austenite grain size on tensile properties of fully austenitic samples. This is why, a preliminary study was performed to assess these two effects, which required a thorough analysis of the microstructures of the investigated samples combining electron backscattered diffraction experiments and transmission electron microscopy observations. The study of fully austenitic samples led us to the conclusion that a decrease in the austenite grain size leads to higher strength and lower elongation and that the austenite carbon content has a greatly significant influence on tensile properties. However, this influence was difficult to estimate with a very good accuracy. Finally, the study of samples with different ferrite contents showed that ferrite had a positive effect on strength when its content was lower than 5 pct. In contrast, a higher content of ferrite (more than 30 pct) has a deleterious effect on mechanical properties