Project-Group ESRF-Beamline (ROBL-CRG), Bi-Annual Report 2001/2002, Wissenschaftlich-Technische Berichte

The third report from the Project-Group ESRF-Beamline of the Forschungszentrum Rossendorf covers the period from January 2001 until December 2002. The Rossendorf BeamLine (ROBL) at the European Synchrotron Radiation Facility (ESRF) in Grenoble performed again well during this time - although we had major staff fluctuations, including two times a change in the project-management: Dr. W. Matz became head of the Technical Infrastructure at FZR, and Dr. T. Reich had been offered a professorship at the University of Mainz. We congratulate both of them. In the beamtime used by the FZR and collaborating institutes 77 different experiments were scheduled, while in the ESRF scheduled beamtime 21 experiments were performed by external groups. Additionally, a distinct amount of beamtime was devoted to commissioning of new equipment. The report is organised in three main parts. The first part contains extendet contributions on results obtaines at ROBL. The second part gives an overview about the general experimental possibilities, scheduled experiments, publications, guests having visited ROBL with support of the EC, an staff information. Finally, the third part collects the experimental reports of the user groups received

On the Oscillating Course of dhkl^{hkl}−sin2^{2}ψ Plots for Plastically Deformed, Cold-Rolled Ferritic and Duplex Stainless Steel Sheets

This work deals with non-linear dhkl−sin2ψ distributions, often observed in X-ray residual stress analysis of plastically deformed metals. Two different alloys were examined: duplex stainless steel EN 1.4362 with an austenite:ferrite volume ratio of 50:50 and ferritic stainless steel EN 1.4016. By means of an in situ experiment with high-energy synchrotron X-ray diffraction, the phase-specific lattice strain response under increasing tensile deformation was analysed continuously with a sampling rate of 0.5 Hz. From Debye–Scherrer rings of nine different lattice planes {hkl}, the dhkl−sin2ψ distributions were evaluated and the phase-specific stresses were calculated. For almost all lattice planes investigated, oscillating courses in the dhkl−sin2ψ distributions were observed, already occurring below the macro yield point and increasing in amplitude within the elasto-plastic region. By comparing the loaded and the unloaded state after deformation, the contribution of crystallographic texture and plastically induced intergranular strains to these oscillations could be separated. For the given material states, only a minor influence of crystallographic texture was observed. However, a strong dependence of the non-linearities on the respective lattice plane was found. In such cases, a stress evaluation according to the sin2ψ method leads to errors, which increase significantly if only a limited ψ range is considered

Comparison between experimental data and thermodynamic predictions

Funding Information: JPO and JS acknowledge Fundação para a Ciência e a Tecnologia (FCT - MCTES) for its financial support via the project UID/00667/2020 (UNIDEMI). JS acknowledges the China Scholarship Council for funding the Ph.D. grant (CSC NO. 201808320394). JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P. in the scope of the projects LA/P/0037/2020, UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Beamtime was allocated for proposal I-20210899 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. CF and ACM gratefully acknowledge partial financial support for this research by the Institute of Materials Research (IMR) at The Ohio State University under a 2017 Exploratory Materials Research Grant, and by the American Welding Society (AWS) under an AWS Graduate Research Fellowship Grant. Electron microscopy was performed at the Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State University. Funding Information: JPO and JS acknowledge Fundação para a Ciência e a Tecnologia (FCT - MCTES) for its financial support via the project UID/00667/2020 (UNIDEMI). JS acknowledges the China Scholarship Council for funding the Ph.D. grant (CSC NO. 201808320394 ). JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects LA/P/0037/2020, UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Beamtime was allocated for proposal I-20210899 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. CF and ACM gratefully acknowledge partial financial support for this research by the Institute of Materials Research (IMR) at The Ohio State University under a 2017 Exploratory Materials Research Grant, and by the American Welding Society (AWS) under an AWS Graduate Research Fellowship Grant. Electron microscopy was performed at the Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State University. Publisher Copyright: © 2022 The AuthorsThe development of multi-principal element alloys is currently on the rise. While there is significant fundamental work being performed to understand microstructure-property relationships, the processability of these novel alloys is yet incipient. In this work, the microstructure evolution in two arc-welded multi-principal element alloys, Al10Co25Cr8Fe15Ni36Ti6 and Al10.87Co21.74Cr21.74Cu2.17Fe21.74Ni21.74, was evaluated by electron microscopy and high energy synchrotron X-ray diffraction coupled with thermodynamic calculations. By correlating microhardness maps across the welds to results from microstructure characterization, it was possible to identify the strengthening phases across the welded materials, which can aid in fine tuning the alloy microstructure to achieve targeted strengths. Moreover, a comparison between the thermodynamically predicted microstructure evolution and that present in the welded joints was performed, highlighting the difficulty of such predictions in complex, scarcely studied multi-principal element systems.publishersversionpublishe

Phase Transformation Induced by High Pressure Torsion in the High-Entropy Alloy CrMnFeCoNi

The forward and reverse phase transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) in the equiatomic high-entropy alloy (HEA) CrMnFeCoNi has been investigated with diffraction of high-energy synchrotron radiation. The forward transformation has been induced by high pressure torsion at room and liquid nitrogen temperature by applying different hydrostatic pressures and large shear strains. The volume fraction of hcp phase has been determined by Rietveld analysis after pressure release and heating-up to room temperature as a function of hydrostatic pressure. It increases with pressure and decreasing temperature. Depending on temperature, a certain pressure is necessary to induce the phase transformation. In addition, the onset pressure depends on hydrostaticity; it is lowered by shear stresses. The reverse transformation evolves over a long period of time at ambient conditions due to the destabilization of the hcp phase. The effect of the phase transformation on the microstructure and texture development and corresponding microhardness of the HEA at room temperature is demonstrated. The phase transformation leads to an inhomogeneous microstructure, weakening of the shear texture, and a surprising hardness anomaly. Reasons for the hardness anomaly are discussed in detail

High strength nanocrystalline Cu–Co alloys with high tensile ductility

A supersaturated single-phase Cu–26 at.% Co alloy was produced by high-pressure torsion deformation, leading to a nanocrystalline microstructure with a grain size smaller than 100 nm. The nonequilibrium solid solution decomposed during subsequent isothermal annealing. In situ high-energy X-ray diffraction was used to map changes linked to the separating phases, and the development of a nanoscale Cu–Co composite structure was observed. To gain further information about the relationship of the microstructure and the mechanical properties after phase separation, uniaxial tensile tests were conducted on as-deformed and isothermally annealed samples. Based on the in situ diffraction data, different isothermal annealing temperatures were chosen. Miniaturized tensile specimens with a round cross section were tested, and an image-based data evaluation method enabled the evaluation of true stress–strain curves and strain hardening behavior. The main results are as follows: all microstructural states showed high strength and ductility, which was achieved by a combination of strain-hardening and strain-rate hardening

Ferrite recrystallization and austenite formation during annealing of cold-rolled advanced high-strength steels: In situ synchrotron X-ray diffraction and modeling

Ferrite recrystallization and austenite formation occurring during annealing of cold-rolled advanced high-strength steels are key mechanisms as they largely determine the final microstructure and mechanical properties. However, the influence of processing parameters on these mechanisms and their interactions is still not fully understood. This is particularly the case for Dual-Phase steels having an initial cold-rolled microstructure con-sisting of ferrite and martensite before annealing, which were scarcely investigated compared to ferrite-pearlite initial microstructures. In situ synchrotron X-ray diffraction experiments together with post-mortem metallo-graphic analysis allowed clarifying both ferrite recrystallization and austenite formation during annealing of a ferrite-martensite initial microstructure depending on the process parameters of the annealing cycle. Results showed a major influence of recrystallization state on austenite formation, leading to an unexpected effect of heating rate on austenite formation kinetics. A modeling approach was undertaken to rationalize the influence of heating rate on austenite formation by taking into account the bi-phased ferrite-martensite initial microstructure and the effect of ferrite recrystallization state

Formation of lower bainite in a high carbon steel – an in-situ synchrotron XRD study

The microstructural evolution of and simultaneous dimensional changes in high-carbonSAE 52100 bearing steel were monitored continuously during austempering for 120 min atselected temperatures in the range of 210 C-270 C, and also during its subsequenttempering to 340 C for an additional 120 min, via high-energy X-ray diffraction in real timeand in-situ dilatometry. The austenite-to-bainitic ferrite transformation induces lattice defectsand internal lattice stresses that increase with austempering time and at lower austemperingtemperatures. These changes are evidenced by the increase in the full-width halfmaximumof the relevant reflections in X-ray diffraction. The lattice parameter of bainiticferrite takes its highest value during the early stages of austempering, and then graduallydecreases as the transformation progresses. This observation points to an initial state ofcarbon supersaturation in the ferritic lattice that is likely reducing due to carbon segregationclose to dislocations, fine carbide precipitation within the bainitic ferrite, and carbon partitioninginto the surrounding austenite. The carbon partitioning into austenite is evidencedin particular at the higher austempering temperatures of 240 C and 270 C, at which there isa noticeable increase in the lattice parameter of the remaining austenite at longer times. Thedimensions of the bearing steel specimens are governed by the volume change due to theformation of bainitic ferrite during austempering and by the relaxation of its lattice distortionduring tempering at 340 C in the absence of further phase transformation

Texture and lattice strain evolution during tensile loading of Mg–Zn alloys measured by synchrotron diffraction

To explore the effect of neodymium (Nd) on the deformation mechanisms of Mg–Zn alloys, texture and lattice strain developments of hot-rolled Mg–Zn (Z1) and Mg–Zn–Nd (ZN10) alloys were investigated using in situ synchrotron diffraction and compared with elasto-viscoplastic self-consistent simulation under tensile loading. The Nd-containing ZN10 alloys show much weaker texture after hot rolling than the Nd-free Z1 alloy. To investigate the influence of the initial texture on the texture and lattice strain evolution, the tensile tests were carried out in the rolling and transverse direction. During tension, the {002} texture components develop fast in Z1, which was not seen for ZN10. On the other hand, fiber // loading direction (LD) developed in both alloys, although it was faster in ZN10 than in Z1. Lattice strain investigation showed that // LD-oriented grains experienced plastic deformation first during tension, which can be related to basal slip activity. This was more apparent for ZN10 than for Z1. The simulation results show that the prismatic slip plays a vital role in the plastic deformation of Z1 directly from the beginning. In contrast, ZN10 plastic deformation starts with dominant basal slip but during deformation prismatic slip becomes increasingly important

Diffraction-based determination of single-crystal elastic constants of polycrystalline titanium alloys

Single-crystal elastic constants have been derived by lattice strain measurements using neutron diffraction on polycrystalline Ti-6Al-4V, Ti-6Al-2Sn-4Zr-6Mo and Ti-3Al-8V-6Cr-4Zr-4Mo alloy samples. A variety of model approximations for the grain-to-grain interactions, namely approaches by Voigt, Reuss, Hill, Kroener, de Wit and Matthies, including texture weightings, have been applied and compared. A load-transfer approach for multiphase alloys was also implemented and the results are compared with single-phase data. For the materials under investigation, the results for multiphase alloys agree well with the results for single-phase materials in the corresponding phases. In this respect, all eight elastic constants in the dual-phase Ti-6Al-2Sn-4Zr-6Mo alloy have been derived for the first time