Microstructural Evolutions and Mechanical Properties of Drawn Medium Carbon Steel Wire

International audienceThis study focuses on the evolution in the microstructure, texture and mechanical properties of medium carbon steel wires obtained by wire drawing at Tréfissoud Company for the manufacturing of the spring mattress. Wire drawing induces elongation of grains in the direction of drawing with the development of the fibre texture parallel to the wire axis. Kinking and bending of cementite lamellae were observed during the drawing process. The work was carried out respectively on three states, wire rod and drawn states for two different amounts (ε %=43,6 and 60 %), using the optical and SEM microscopy, electron backscatter diffraction and X-ray diffraction analysis for examination of the microstructure and texture evolution, the hardness Vickers and tensile test to follow the curing of the studied wires

The Influence of the Back Stress (X) and the Hardening Rate (dX/Xεpqe) on Void Nucleation in α/β Titanium Alloys

The study of void nucleation in four α/β titanium alloys has provided nucleation criteria corresponding to voids at the α/β interface. This macroscopic nucleation criterion, written as ∑m=f(εpqe), was explained with the help of microscopic observations. Microscopic parameters such as plastic strain in the α-phase or local hydrostatic stress σm at the α/β interface have been linked to the damage initiation. Besides, the influence of the different heterogeneity levels on the macroscopic nucleation criterion was demonstrated using the macroscopic mechanical parameters : back stress (X) and hardening rate (dX/Xεpqe) which express the plastic strain incompatibilities and their evolution in such alloys

Monte Carlo simulation of primary recrystallization and annealing twinning

International audienceFormation of annealing twins has been studied from the beginning of 20 th century. The related mechanisms as growth accident, nucleation of twins and nucleation of partial Shockley loops were suggested. The simulation was also realized by molecular dynamics simulations at the atomic scale. In this paper, a microscopic scale simulation of primary recrystallization and twinning by Monte Carlo approach was realized for a nickel alloy. Different twin morphologies were simulated. It showed a possibility of dependence of grain growth direction on twin formation during annealing. The incoherent Σ3 and Σ9 boundaries formation is verified as the indirect outcome after coherent Σ3 formation

Compromise between magnetic shielding and mechanical strength of thin Al/Steel/Al sandwiches produced by cold roll bonding: Experimental and numerical approaches

International audienceElectromagnetic pollution become an issue these last years with growth of electrical and electronic industry. The shielding of electromagnetic fields is one solution to reduce effects of this pollution. This study proposes an Al/Steel/Al sandwich produced by cold roll bonding to shield low frequency magnetic wave in near field. The structure evolution of sandwich composite has been characterized in function of the reduction rate of thickness. The bonding quality of Al/Steel interfaces has been then quantified by Tensile Bond Strength Test. Finally, the magnetic shielding effectiveness of the composite and the initial Al and steel sheets have been evaluated experimentally and numerically. During cold roll bonding, plastic instability has been observed and causes steel necking and fragmentation. A numerical model has been developed to explain its origin. A good bond quality is attained when debonding of Al/Steel interfaces requires the deterioration of the composite. The composite takes both shielding behavior of steel and Al and can shield low frequency. However, steel fragmentation has a negative impact on shielding effectiveness. The optimal condition between shielding and mechanical properties is then obtained for a reduction rate of 62 % where only few fragmentations are observed

In-situ EBSD investigation of thermal stability of a 316L stainless steel nanocrystallized by surface mechanical attrition treatment

International audienceIn-situ Electron BackScatter Diffraction (EBSD) was used to study the thermal stability of a stainless steel nanocrystallized by Surface Mechanical Attrition Treatment (SMAT). A grain size gradient was generated after SMAT from the surface to the interior of the specimen. Observations at different temperatures were performed to study the thermal stability of the gradient microstructure. During the investigation, oxidation was detected which greatly affected the indexation quality especially for high temperatures. After an ionic polishing, the grains could be properly revealed. No obvious microstructure changes were highlighted up to 720°C, which indicated a good thermal stability of the nanocrystalline grains

Microstructure and microtexture evolution with aging treatment in an Al-Mg-Si alloy severely deformed by HPT

Experiments were conducted on an Al–0.6 % Mg–0.4 % Si alloy to evaluate the effect of different preliminary thermal treatments on the evolution of microstructure and microtexture during processing by High-Pressure Torsion (HPT). Disks of the alloy were solution-treated, then some disks were briefly aged at 473 K, and other disks were briefly aged at 523 K before processing by HPT for up to 20 complete revolutions. The processing by HPT refined the microstructure to an average grain size as small as ~0.25 ?m in the solution-treated alloy after 20 turns but preliminary aging led to slightly larger average grain sizes of ~0.35–0.40 ?m after 20 turns. For all processing conditions, there was a high fraction of high-angle grain boundaries after HPT and it is shown that aging introduces changes in the microtexture intensities.<br/

Experimental study of microstructure changes due to low cycle fatigue of a steel nanocrystallised by Surface Mechanical Attrition Treatment (SMAT)

International audienceElectron Backscatter Diffraction technique is used to characterize the microstructure of 316L steel generated by Surface Mechanical Attrition Treatment (SMAT) before and after low cycle fatigue tests. A grain size gradient is generated from the top surface to the interior of the samples after SMAT so that three main regions can be distinguished below the treated surface: (i) the ultra-fine grain area within 5 μm under the top surface with preferably oriented grains, (ii) the intermediate area where the original grains are partially transformed, and (iii) the edge periphery area where the original grains are just mechanically deformed with the presence of plastic slips. Fatigue tests show that cyclic loading does not change the grain orientation spread and does not activate any plastic slip in the ultra-fine grain top surface area induced by SMAT. On the opposite, in the plastically SMAT affected region including the intermediate area and the edge periphery area, new slip systems are activated by low cycle fatigue while the grain orientation spread is increased. These results represent a first very interesting step towards the characterization and understanding of mechanical mechanisms involved during the fatigue of a grain size gradient material

Turn the heat up – A first look at MESSENGER's near-infrared spectra of Mercury using new high-temperature emissivity measurements

Analyzing the surface composition of Mercury's regolith from remote-sensing measurements is a challenging task. In support of the National Aeronautics and Space Agency's MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission and especially in preparation for the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument on the BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency, we are developing a Planetary Emissivity Laboratory (PEL) at Deutsches Zentrum für Luft- und Rahmfahrt (DLR) in Berlin. The PEL allows measurement of the emissivity of Mercury-analogue materials at grain sizes smaller than 25 μm and at temperatures of more than 400°C, typical for Mercury's low-latitude dayside. The PEL development follows a multi-step approach. We have already obtained emissivity data at mid-infrared wavelengths that show significant changes in spectral behavior with temperature indicative of changes in the crystal structure of the samples. We are currently installing a new calibration target that will allow the acquisition of emissivity data over the full wavelength range from 1 to 50 micrometer with good signal-to-noise ratio. Here we present initial data in the range 1 to 1.4 micrometer, the near-infrared wavelength coverage of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on MESSENGER. Even these early PEL measurements have important implications for the analysis of the spectral observations obtained during MESSENGER's first Mercury flyby on 14 January 2008 as well as the data to be obtained during the probe's second Mercury flyby on 6 October