References of "Lecomte-Beckers, Jacqueline"
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See detailExtrusion tests of 7075 aluminium alloy at high solid fraction
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Pierret, Jean-Christophe ULg et al

in International Journal of Material Forming (2008), 1(1), 1019-1022

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. Higher solid fraction of 7075 alloy is less sensitive to a drop in temperature, avoids metal splash at high speed, allows laminar flow at high speed. Hot tool is used to slow down the solidification rate of the high solid fraction metal by decreasing thermal exchanges. To determine the best parameters to achieve maximum mechanical properties in thixoforging of 7075 aluminum alloy, we need to consider the impact of some parameters such as tool temperature, shear rate. For this, we use extrusion tests with constant speed [1] where these parameters are known. The result of this study is that each parameter has its level of impact on the thixoforging: the temperature of the tool and the deformation rate shouldn't be high to avoid cracks. Thermal exchanges between the material flow and the tool have to be reduced to avoid high solidification rate [2]. [less ▲]

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See detailSteel thixoforming, influence of forming parameters on the microstructure
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in International Journal of Material Forming (2008), 1(1), 1011-1014

Forming of parts in the semi-solid state is quite a complex process, especially for high melting point alloys such as steel. A reason for this complexity is the amount of parameters involved in the ... [more ▼]

Forming of parts in the semi-solid state is quite a complex process, especially for high melting point alloys such as steel. A reason for this complexity is the amount of parameters involved in the process. Among these we could quote liquid fraction, shear rate, shape factor, contiguity, tool temperature, agglomeration level, heating rate, protecting gas, temperature distribution, lubricant. Of course all of these parameters don’t have the same order of importance. In this paper we show the influence of a set of chosen parameters and we highlight their effects on the microstructure and so, on the deformation behavior. The studied parameters are the heating conditions, the tool temperature, the part temperature, the thermal exchanges between the part and the dies and the forming rate. [less ▲]

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See detailOptimization of the formulation and post-treatment of stainless steel for rapid manufacturing
Vaneetveld, Grégory ULg; Clarinval, A. M.; Dormal, T. et al

in Journal of Materials Processing Technology (2008), 196(1-3), 160-164

Rapid prototyping process called Optoform shapes functional parts from a photocurable paste. This paste contains metal powder, resin, UV photoinitiator and wetting agent. After processing on the Optoform ... [more ▼]

Rapid prototyping process called Optoform shapes functional parts from a photocurable paste. This paste contains metal powder, resin, UV photoinitiator and wetting agent. After processing on the Optoform machine, a post-treatment is applied (debinding+sintering). During the post-treatment, the residual carbon coming from the resin modifies the composition of the metal and its melting point. This modification affects densification mechanisms, which leads to a residual porosity that lowers mechanical characteristics. We will present theoretical consideration leading to the optimization of the formulation. To improve the process, bimodal powder is used and thermal treatment is adapted. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailRobustness of a thixoforming production line
Pierret, Jean-Christophe ULg; Rassili, Ahmed ULg; Vaneetveld, Grégory ULg et al

in Solid State Phenomena (2008), 141-143

The development of the thixoforming process made great progress since its beginning. But whereas thixoforming of aluminium and other low melting point alloys is now an industrial reality, thixoforming of ... [more ▼]

The development of the thixoforming process made great progress since its beginning. But whereas thixoforming of aluminium and other low melting point alloys is now an industrial reality, thixoforming of high melting point alloys, as steel, is still at the research level. High temperature issues, die wearing and production rate are problems that must be solved and are more and more investigated. This work is a study of the robustness of a complete thixoforming unit dealing with steel. This flexible unit allows parts of various shapes be formed in conditions close to industrial ones. The study focus on the heating strategy, heat exchanges between the slug and the tool, the feeding and the cycle time. In this work, modelling has been used to simulate heating and feeding. In parallel, experiments have been made to obtain the needed parameters, to validate the modelling and to evaluate the capacities of such a line. [less ▲]

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See detailInvestigation on retained delta ferrite occurrence and its influence on HSS and Semi HSS Strengthening after thermomecanical routes
Tchuindjang, Jérôme Tchoufack ULg; Lecomte-Beckers, Jacqueline ULg

in Proceedings of Abrasion 2008 (2008)

The present work deals with use of DTA tests in order to understand the crystallisation behaviour of semi-HSS and HSS alloys, and to enhance their solid state transformations. Emphasis is laid on the ... [more ▼]

The present work deals with use of DTA tests in order to understand the crystallisation behaviour of semi-HSS and HSS alloys, and to enhance their solid state transformations. Emphasis is laid on the decomposition of the unexpected retained delta ferrite during thermal and thermomechanical treatment. [less ▲]

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See detailPhysique des matériaux : partim 1 métal
Lecomte-Beckers, Jacqueline ULg

Learning material (2008)

Notions sur le cristal métallique parfait : état liquide, gazeux, solide, forces interatomiques, réseaux cristallins. Propriétés des cristaux métalliques parfaits : propriétés physiques, mécaniques ... [more ▼]

Notions sur le cristal métallique parfait : état liquide, gazeux, solide, forces interatomiques, réseaux cristallins. Propriétés des cristaux métalliques parfaits : propriétés physiques, mécaniques (élasticité-plasticité et rupture), thermiques, électriques. Les imperfections dans les réseaux cristallins : défauts ponctuels, dislocations, polycristaux. Les alliages : les solutions solides (thermodynamique - nanostructure - propriétés), les combinaisons intermétalliques (thermodynamique - propriétés). Diagramme de phases. Applications à des alliages de base (acier-aluminium). Les propriétés mécaniques marquantes des métaux limite élastique, domaine élasto-plastique, rupture, fluage, fatigue) : aspects microscopiques. Structures hors d'équilibre : modifications de la microstructure des métaux au cours de la trempe. [less ▲]

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See detailSélection des matériaux
Lecomte-Beckers, Jacqueline ULg

Learning material (2008)

Description et usage des différents types de matériaux : métaux, céramiques, polymères et composites. Origine et optimisation des propriétés mécaniques et physiques des matériaux. Sélection d'un matériau ... [more ▼]

Description et usage des différents types de matériaux : métaux, céramiques, polymères et composites. Origine et optimisation des propriétés mécaniques et physiques des matériaux. Sélection d'un matériau optimal en fonction des propriétés mécaniques et/ou physiques recherchées. Démarche de sélection du matériau pour une application (haute température, optique,...). Cas pratiques de sélection de matériaux. [less ▲]

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See detailIngénierie des matériaux métalliques: Solidification des métaux et alliages - Traitement thermique
Lecomte-Beckers, Jacqueline ULg

Learning material (2008)

Solidification des métaux et alliages. Traitements thermiques et thermomécaniques des métaux et alliages. Corrosion des métaux. Traitements de surface.

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See detailASSESSMENT OF RETAINED AUSTENITIC PHASE IN INDEFINITE CHILL CAST IRON MICROSTRUCTURE TOWARDS VARIOUS TECHNIQUES
Tchuindjang, Jérôme Tchoufack ULg; Terziev, Liuben; Sinnaeve, Mario et al

Poster (2007, November 16)

Indefinite Chill Cast Irons also called ICDP when used as rolling mill rolls are high alloyed cast iron alloys belonging to the Fe-Cr-C system. ICDP exhibit improved properties regarding hot oxidation and ... [more ▼]

Indefinite Chill Cast Irons also called ICDP when used as rolling mill rolls are high alloyed cast iron alloys belonging to the Fe-Cr-C system. ICDP exhibit improved properties regarding hot oxidation and wear resistances as their microstructure is a mixture of a martensitic with bulky cementite (M3C) and lamellar graphite fully dispersed into the matrix. Mechanical properties involved depend either on the chemical composition of the alloy or the crystallisation behaviour and the heat treatments performed subsequently in order to lead to the desired microstructure. Thus hardenability of the matrix is of great concern as heat treatments sequence is intended to transform austenite in a more stable structure like martensite or even bainite, depending on Cr content. In fact austenite is known to be unstable during hot working conditions as hot temperature and external stresses could yield transformation of this phase into martensite with major volume distortions and even multiple cracks network on the component involved. To avoid such a hitch in service it is quite necessary to make sure all the austenite is completely transformed into martensite while performing subsequent heat treatments like quenching or tempering on the material obtained after casting process. Various techniques are allowable starting from classical ones (X-Ray Diffraction (XRD), Image Analysis, Vibrating Sample Magnetometer (VSM), Dilatometry) to more exotic one like Conversion Electron Mössbauer Spectroscopy (CEMS). From an industrial point of view, it is important to set a fast and reliable method to assess retained austenite presence into ICDP microstructure at the end of any step of the thermomechanical process. The present work is intended to compare different techniques used for retained austenite assessment in ICDP alloys as a first step prior to the calibration of a classical method like dilatometry. This calibration is to be set starting from complex XRD and CEMS spectrometers analyses. Dilatometry seems to overrate retained austenite volume fraction in the as-cast conditions while good agreements are made on the overall batch of techniques when considering heat treated material where retained austenite transformation occurred [less ▲]

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See detailTHIXOFORMAGE DES METAUX: Mise en forme rapide de pièces fonctionelles “near-net-shape” à design complexe dignes du forgeage!
Rassili, Ahmed ULg; Vaneetveld, Grégory ULg; Pierret, Jean-Christophe ULg et al

Poster (2007, June 14)

Présentation du laboratoire de thixofomage de métaux.

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See detailFractography survey on high cycle fatigue failure: Crack origin characterisation and correlations between mechanical tests and microstructure in Fe-C-Cr-Mo-X alloys
Tchuindjang, Jérôme Tchoufack ULg; Lecomte-Beckers, Jacqueline ULg

in International Journal of Fatigue (2007), 29(4), 713-728

Raw materials were cast from different specific processes in order to produce cleaner steels with a reduced amount of inclusions. Studied materials that are HSS hardened alloys belonging to the Fe-Cr-C-X ... [more ▼]

Raw materials were cast from different specific processes in order to produce cleaner steels with a reduced amount of inclusions. Studied materials that are HSS hardened alloys belonging to the Fe-Cr-C-X system were shared out in four groups depending on the tempering temperature and the presence of secondary and primary carbides. Both inclusions and carbides were roughly assessed by means of Image Analysis. Forging was done on all studied materials with different reduction ratios in order to highlight the texture influence oil mechanical properties. High cycle fatigue tests were made using the boundary method to allow a quick evaluation of results. Fractographic analyses carried out on broken samples led to the definition of four failure modes depending on the nature and the location of the point from which the crack was initiated in one hand, and the roughness of striations in the propagating area over and around the initiation point. Internal and surface crack initiation points were found, the latter being more harmful than the first ones. Though oxides appeared to be more detrimental than other inclusions, primary carbides were also found to be both crack initiation candidates and crack propagation enhancers. Various parameters likely to influence high cycle fatigue failures were finally defined, the most significant one dealing with the nature and location of embedded precipitates and the forging reduction ratio. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailImprovement in HSS grade for early stands of hot strip mills - Metallurgical features and mechanical properties assessment
Ernst, Roger; Breyer, Jean-Pierre; Tchuindjang, Jérôme Tchoufack ULg et al

in Proceedings of the 43rd Seminar of Rollings (2007)

Aurora and Kosmos grades are HSS alloys belonging to the complex Fe-Cr-C-X system, where X is a strong carbide former element of the V, Mo or W type. Both alloys were metallurgically characterised prior ... [more ▼]

Aurora and Kosmos grades are HSS alloys belonging to the complex Fe-Cr-C-X system, where X is a strong carbide former element of the V, Mo or W type. Both alloys were metallurgically characterised prior to their comparison. Metallurgical analyses involved phases identification and carbides quantification by using Scanning Electron Microscopy and Energy Dispersive X rays. Differential Thermal Analysis was performed to allow a better understanding of the solidification sequence of studied alloys while mechanical tests performed were compressive at room temperature and bulk hardness at usual service temperatures. An attempt was made in order to connect experimental results to the good behaviour in operation of Aurora grade. In fact Aurora grade appeared to exhibit strong metallurgical differences when compared to Kosmos grade, especially as concern in nature and amount of carbides. [less ▲]

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See detailStudy of transformations and microstructural modification in Ti-LCB and T-555 alloys using Differential Scanning Calorimetry
Carton, Marc ULg; Pascal, Jacques; Clement, Nicolas et al

in Proceedings of Ti-2007 Science and technology - 11th World Conference on Titanium (JIMIC 5) (2007)

The aerospace industry is the single largest market for titanium products primarily due to the exceptional strength to weight ratio, elevated temperature performance and corrosion resistance. Titanium ... [more ▼]

The aerospace industry is the single largest market for titanium products primarily due to the exceptional strength to weight ratio, elevated temperature performance and corrosion resistance. Titanium applications are most significant in jet engine and airframe components that are subject to high temperatures. The studied Ti-LCB and Ti-555 titanium alloys must present good properties to fatigue damage as they are located in a low-pressure compressor. In order to avoid this damage, an optimized alloy microstructure is required. In our case, the optimal microstructure would be a beta matrix in which small alpha particles are uniformly distributed, obtained after a combination of thermomechanical and thermal treatments. The understanding of the mechanisms ruling the microstructure evolution is achieved through the study of phase transformations versus temperature. During heating, the ωath phase is transformed into the ωiso phase, allowing itself the appearance of the α phase. Then this α phase is transformed progressively into the β phase, and the structure becomes totally β when the transus temperature is reached. Therefore, a thermal analysis tool such as DSC (Differential Scanning Calorimetry) was used in order to characterise the phase transformations of the material during imposed controlled temperature programs. [less ▲]

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See detailCorrosion studies of different ferrous alloys for rolling cylinders
Martinez, L.; Gomez, C.; Lecomte-Beckers, Jacqueline ULg et al

in Materials & Design (2007), 28(1), 196-202

The aim of this work is to study the corrosion behaviour in chloride media of a high chromium iron alloy. The influence of the surface finishing as well as the heat treatment was analysed. The technique ... [more ▼]

The aim of this work is to study the corrosion behaviour in chloride media of a high chromium iron alloy. The influence of the surface finishing as well as the heat treatment was analysed. The technique employed for measuring the corrosion behaviour was the Electrochemical Impedance Spectroscopy, an electrochemical technique that allows the observation not only of the corrosion rates but also the changes on the corrosion mechanism of the alloy. The results showed that it is worth performing a double tempering and a having smoother surface finishing only for long exposure periods. A comparison between different oxidising conditions was also performed simulating the life in service of the hot rolling cylinders and revealed an increase in the protective properties as the oxidising time increased due to the chromium present on the alloy (18%). (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailStudy of a 2024 aluminium rod produced by Rotary Forging
Habraken, Anne ULg; Bouffioux, Chantal ULg; Carton, Marc ULg et al

in Journal of Materials Processing Technology (2007), 184

An investigation of the rotary forging process of a 2024 aluminium rod is summarised. Some dispersion in mechanical properties and chemical composition of the base material is permitted. Samples of two ... [more ▼]

An investigation of the rotary forging process of a 2024 aluminium rod is summarised. Some dispersion in mechanical properties and chemical composition of the base material is permitted. Samples of two material batches were selected: one just stays near the upper limit of tolerance and the other has mean properties. Tensile and compression tests confirm the different mechanical behaviours and allow the identification of constitutive laws parameters. Optical metallography after T3 and T10 thermal treatments and differential thermal analysis provide the grain size and precipitation characteristics of each material batch, which explain their different mechanical behaviours. The industrial rod studied is usually forged in two operations: a first forging process, then a T10 thermal treatment followed by a second forging step. Industrial practise shows that manufacturing the rod with one forging step fails. FEM simulations of the process coupled with a fracture criterion confirm the advantage of a two-step process compared to a single forging step. [less ▲]

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See detailMetallurgical assessment of two HSS rolls grades for Hot Strip Mill
Lecomte-Beckers, Jacqueline ULg; Delaunois, Fabienne; Breyer, Jean-Pierre et al

in AISTech-Proceedings of the Iron and Steel Technology Conference (2007)

Aurora and Kosmos grades are HSS alloys used for the manufacturing of rolling mill work rolls for early finishing stands of Hot Strip Mills. Both alloys were metallurgically assessed using Electron ... [more ▼]

Aurora and Kosmos grades are HSS alloys used for the manufacturing of rolling mill work rolls for early finishing stands of Hot Strip Mills. Both alloys were metallurgically assessed using Electron Microscopy, X Rays analysis on carbides and Differential Thermal Analysis. These methods allow a better understanding of the behaviour of the studied alloys during solidification and cooling. Some mechanical tests were also performed. A connection between the laboratory results and the performance in operation of both grades is performed. The strong metallurgical differences especially as concern the nature and amount of carbides allow to explain the good behaviour in service of Aurora. [less ▲]

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