Papers by Author: Thierry Baudin

Abstract: This study was mainly oriented on the evolution of the crystallographic texture as a function of the deformation resulting from the industrial wire drawing process. This, in fact, will make it possible to establish a relationship between the microstructure and the crystallographic texture in the medium carbon steel wires obtained by industrial wire drawing process and used in the manufacture of spring mattresses in order to minimize the loss of material and to satisfy the users of this product.During this study, a medium-carbon steel wires was characterized by two analytical techniques. The scanning electron microscopy (SEM) to monitor the microstructure evolution and the electron backscatter diffraction (EBSD) for the crystallographic texture analysis. The EBSD results are processed with OIM (Orientation Imaging Microscopy) analysis software.

Abstract: Laser cladding of a Ni based powder on Cu-Ni-Al or cast iron was performed with a 4kW continuous Nd: YAG laser. The Cu-Ni-Al and cast-iron substrates are used for their thermal properties in glass mold industry. But the issue of these materials is their lack of resistance on corrosion and abrasion. The role of the Ni based alloy is to protect the mold without affecting its thermal properties (Heat Affected Zone (HAZ)). The purpose of this research is to produce a well bonded Ni based melted powder without pores or cracks on a non-planar surface (curvilinear section). An investigation of the impact of the processing parameters, power (1500-3200 W), scanning speed (2.5-10 mm/s) and powder feeding rate (24.5-32.5 g/min) on the bonding quality, the porosity propagation and HAZ appearance is performed. The used methods are neutronography, Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Electron BackScatter Diffraction (EBSD). These multi-scale techniques are obviously complementary. Neutronography is a well-adapted non-destructive method to observe the porosity in the volume thanks to the contrast between materials. EBSD analysis allows us to analyze the microstructural evolution of the coating notably by observing the dendrites growth. This same method also permits to observe the HAZ nature according to the laser cladding parameters. Those methods allowed to optimize the processing parameters in a way to obtain perfect bonding, to avoid porosity propagation and to limit the HAZ emergence.

Abstract: Selective laser melting (SLM) is one of the new additive manufacturing techniques in which complex parts can be created directly by selectively melting layers of powder. If the productivity of the process is too fast, defects (porosity, partially melted powder, spatters …) are generated inside the fabricated parts and can deteriorate the mechanical properties of the product. A new Laser Boost strategy with a larger melting area and a productivity of 43.20 cm3/h has been compared to a Linear Classic strategy. Ti-64 alloy samples were elaborated with both strategies to study their influence on microstructure and mechanical properties. Laser Boost strategy leads to the formation of Ti-64 prior β grains that are larger than the Linear Classic strategy. Mechanical properties obtains are similar with both strategies with a maximum strength average around 1250MPa and an elongation at failure between 3 and 9%. A thermal post-processing by Hot Isostatic Pressure have been carried out on samples made by Laser Boost to increase the ductility of the material up to 15%.

Abstract: In this paper, the evolution of texture in the ferrite phase and mechanical behavior of cold-drawn pearlitic steel wires produced for strand manufacturing at Trefisoud company was investigated. Wire drawing induces the development of dislocation density, reduction of interlamellar spacing and the refinement of grains size which leads to a strong hardening of the wires. That explains the increase of the tensile strength from 1242 MPa to 2618 MPa with higher deformation. Also, the cementite lamellae are rotated toward the drawing axis and the thickness of lamellae further decreases when strain level increases, this phenomenon leads to a somewhat fibrous structure. The quantitative analysis obtained by EBSD data shows the development of a strong (<110> // ND) texture of the ferrite phase leading to a structural transformation from isotropic to anisotropic.

Abstract: In glass industry, laser cladding is an innovative surfacing technique allowing to deposit a layer of nickel to protect glass mold against corrosion, abrasion and thermal fatigue. This method (powder fusion by projection), well known in additive manufacturing represents a real technological leap for the glass industry. But during laser cladding of Ni-based powder on gray cast iron, cracks can be observed for some process conditions. These cracks are often due to the Heat Affected Zone that creates structural stresses linked to the development of a martensitic structure in the ferritic matrix of the lamellar graphite cast iron. The aim of this work is to observe the impact of laser cladding (without substrate pre-heating usually employed to limit cracking) on the coating behavior but also on the flake-graphite cast iron substrates. The microstructure and the mechanical properties were studied (SEM and microanalysis, microhardness) around the interface cladding/substrate. Also, the impact of the processing parameters (power P (1500-2300 W), scanning speed v (2.5-10 mm/s) and powder feeding rate PFR (24.5-32.5 g/min) was studied by using the ANOVA (ANalysis Of VAriance) technique. It has been observed that laser cladding on graphite cast iron is possible without cracks by limiting the linear energy induced by the process. Also, an optimization of the processing parameters (P, v, PFR) in order to obtain the industrial expected geometry of the coating has been proposed.

Abstract: This 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 <110> 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.

Abstract: The aim of the present work is to study the evolution of microstructure, texture and mechanical properties during drawing of mild steel wire of type F8Z used in the manufacture of welding electrodes TREFISOUD. It was found that the as received wire has a ferritic-pearlitic microstructure corresponding to an isotopic state (without texture). This microstructure is relatively heterogeneous in the wire section. On the other hand, after strong drawing structure appears relatively homogeneous, throughout the section of the drawn wire. Also the deformation process by drawing causes the hardening of wire as a function of deformation with a reinforcing component of the fiber texture <110> // ND (majority), typical for bcc materials. Characterization methods used in this work is: Optical microscopy (OM), Scanning Electron Microscopy (SEM), the Electron Back Scattered Diffraction EBSD, Vickers microhardness and the tensile tests.

Abstract: Copper destined for electrical cabling require a compromise of mechanical properties and electrical resistivity. The drawing process accompanied by the formation of crystalline defects, such as gaps and dislocations, which leads to the increase in hardness, and therefore to the increase in resistivity, a very important characteristic for the conductivity and the efficiency of the cable. The scope of this work is to investigate the phenomenon of deformation texture evolution while copper wire drawn destined for electric cable-making and to understand its relationship with the electrical conductivity. In this study, we notice that the hardness and the resistivity increase with an increase of the deformation level. On the other hand, a slight decrease in the resistivity of the wires was observed after a holding time of 30 min at 260°C. The annealing of wires at 260°C for 9 min of holding time leads to a recrystallisation especially for high deformations and a gradual return of the mechanical properties and of the microstructure towards a state close to the state of the wire rod with the extension of time . The recrystallization texture is composed of the same components as the drawing texture, fibers <111>//ND (Normal Direction) and <001>//ND. The decrease in the intensity of the fiber after annealing is observed. On the other hand, the fiber <001> // ND remains stable.

Abstract: The present study aims to study the texture heterogeneity of an AA5754/AA6061 composite processed by cross accumulative roll-bonding at room temperature. Both Al alloys were first roll-bonded with a 50% reduction and the product was cut in half. Then, both parts were stacked and finally another roll-bonding was carried out but the initial rolling direction was turned by 90°. As a result, a strong gradient appears in the thickness of the composite because of shearing but also due to the alloys composition dissimilarity. As a consequence, it appears each of the four resulted layers has its own texture. In the bulk, AA5754 layer promotes the ND-rotated Brass {011}<755> and S {123}<634> components while AA6061 develops the ND-rotated Brass and Dillamore {4 4 11}<11 11 8> components. On the surface, AA5754 favors the Dillamore component whereas AA6061 shows the rotated-Cube {001}<110> component.

Abstract: The microstructure and microtexture evolution of a Fe-36%Ni alloy processed by cross accumulative roll-bonding was investigated using Electron BackScatter Diffraction. Deformation led to the development of elongated ultrafine grains parallel to the rolling direction that subsequently became more equiaxed. The grains were more effectivelly refined after CARB than after ARB processing. The grain aspect ratio (l/L) decreased (which means a trend towards elongated sub-grain structure) after 2 and 3 CARB processing cycles and then increased (which means a trend towards equiaxed subgrain structure) from 4 to 5 cycles. The fraction of HAGB, CSL boundaries and the estimated deformed volume fraction gradually increased with increasing number of CARB cycles. Copper-type texture was observed after CARB odd cycles (RD//RD), while after even cycles (RD//TD) a new texture component named H ({012}<221>) was observed.