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See detailOn the Laser Cladding of Ti Alloy Ti-6Al-4V with Low Laser Power
Mertens, Anne ULg; Paydas, Hakan ULg; Tchuindjang, Jérôme Tchoufack ULg et al

in Pilchak, Adam (Ed.) Proc. of Ti 2015: 13th World Conference on Titanium, Vol. 6: Additive and Near Net Shape Manufacturing (in press)

Laser cladding is an economic layer-by-layer near-net-shape process for the production and the repair of metallic parts. In this process, a metallic powder is projected onto a substrate while being molten ... [more ▼]

Laser cladding is an economic layer-by-layer near-net-shape process for the production and the repair of metallic parts. In this process, a metallic powder is projected onto a substrate while being molten by a laser beam. Laser sources with fairly high power – i.e. typically 2kW − are often used to ensure short building times and high productivity. However, this approach has limitations. Indeed, it is very difficult to produce thin walls at high laser power. Moreover, an increase of the incident energy may give rise to a relatively coarser microstructure, and this will in turn affect the mechanical properties of the component. In order to address these issues, this paper aims at assessing the potential of a laser source with a lower maximum power of 300W to enhance the flexibility of the process. Two types of samples – i.e. thin walls or bulk deposits − were produced at low laser power from alloy Ti-6Al-4V. Their geometry, microstructures and local hardness are characterised and correlated with the thermal history experienced during fabrication. [less ▲]

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See detailDetermination of Stress and Strain Fields in Cast and Heat Treated Bimetallic Rolling Mill Rolls
Neira Torres, Ingrid; Tchuindjang, Jérôme Tchoufack ULg; Sinnaeve, Mario et al

in Proceedings of the Iron & Steel Technology Conference and Exposition (AISTech 2015 & ICSTI) (2015, May)

Efficient work rolls for Hot Strip mill roughing stands are usually produced as bimetallic spun cast rolls with a core material made of Spheroidal Graphite Iron (SGI) and a shell material made of High ... [more ▼]

Efficient work rolls for Hot Strip mill roughing stands are usually produced as bimetallic spun cast rolls with a core material made of Spheroidal Graphite Iron (SGI) and a shell material made of High Chromium Steel alloy, semi-High speed steel or adapted High Speed steel chemistry. In this paper, the evolution of stress fields and microstructure during post casting cooling and subsequent heat treatment of a standard high chromium steel is targeted. This knowledge is a first step to analyze the different events that could happen during these production stages and provides the residual stress fields as well as the final roll microstructure which are interesting data for roll service life. As far as roughing mill work rolls for roughing mills are concerned, current trends in terms of work roll design are forcing the roll producer to go towards higher usable shell thicknesses or increased residual shell thickness after scrap diameter in order to delay potential fatigue phenomena at the shell-core interface. One important parameter could not be evaluated in this study, it concerns the pollutions of the core material by alloying elements of the shell during production, which could affect to some extent the mechanical properties and microstructure of the core. The macroscopic thermo-mechanical-metallurgical Finite Element model used to perform simulations, takes into account coupled effects. Input data parameters are identified by experimental tests such as compression tests at constant strain rate and numerical procedures such as inverse method. After the model presentation, the material data set is commented. Whole experimental campaign could not be presented, however interested readers are referred to [1] where more details on the material study of High Chromium Steel alloy can be found. The section of simulation results show the phase transformation histories and stress profiles of a typical roll of diameter 1.2 m and shell thickness of 0.08 m. An additional sensitivity analysis of the results to some material data such as induced plasticity transformation coefficient and shift of the martensitic transformation start temperature parameters is reported. Finally, some conclusions analyze the interest and drawbacks of the described model and its results. [less ▲]

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See detailModelling of stress field evolution in bimetallic rolling mill rolls during the manufacturing process
Gilles, G.; Neira Torres, I.; Tchuindjang, Jérôme Tchoufack ULg et al

in Proceedings of the 5th Conference on rolling mill rolls for metals processing Rolls 5 2015 (2015, April 22)

This paper presents a study of the phase transformation histories and stress profiles in a typical bimetallic roll subjected to a post-casting cooling followed by a tempering heat treatment. The ... [more ▼]

This paper presents a study of the phase transformation histories and stress profiles in a typical bimetallic roll subjected to a post-casting cooling followed by a tempering heat treatment. The simulations are performed using the non-linear finite element code "Lagamine" and a thermo-mechanical-metallurgical model able to take into account coupled effects. The sensitivity of the finite element results to some parameters which are not accurately identified is investigated. [less ▲]

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See detailPhase Transformations and Crack Initiation in a High-Chromium Cast Steel Under Hot Compression Tests
Tchuindjang, Jérôme Tchoufack ULg; Neira Torres, Ingrid; Fores, Paulo et al

in Journal of Materials Engineering and Performance (2015), 24(5), 2025-2041

The mechanical behavior of the fully austenitic matrix of high-chromium cast steel (HCCS) alloy is determined by external compression stress applied at 300 and 700 C. The microstructure is roughly ... [more ▼]

The mechanical behavior of the fully austenitic matrix of high-chromium cast steel (HCCS) alloy is determined by external compression stress applied at 300 and 700 C. The microstructure is roughly characterized toward both optical and scanning electron microscopy analyses. Dilatometry is used during heating from room temperature up to austenitization to study the solid-state phase transformations, precipitation, and dissolution reactions. Two various strengthening phenomena (precipitation hardening and stress-induced bainite transformation) and one softening mechanism (dynamic recovery) are highlighted from compression tests. The influence of the temperature and the carbide type on the mechanical behavior of the HCCS material is also enhanced. Cracks observed on grain boundary primary carbides allow establishing a rough damage model. The crack initiation within the HCCS alloy is strongly dependent on the temperature, the externally applied stress, and the matrix strength and composition. [less ▲]

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See detailMetal matrix nanocomposite coatings for improving the usage properties of metallic materials
Mertens, Anne ULg; Lecomte-Beckers, Jacqueline ULg

Conference (2015, January)

The use of metal matrix nanocomposite is at the present time not as widespread as for their polymer-based counterparts. Yet, the addition of nanoparticles in a metallic matrix also allows to significantly ... [more ▼]

The use of metal matrix nanocomposite is at the present time not as widespread as for their polymer-based counterparts. Yet, the addition of nanoparticles in a metallic matrix also allows to significantly improve its usage properties, thus opening new and interesting prospects in terms of applications. This presentation aims at providing a broad overview of the various usage properties that can be enhanced by the addition of nanoparticles as illustrated by a number of examples taken from the scientific literature as well as from the researches carried out by the Metallic Materials Science Unit at the University of Liege. [less ▲]

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See detailTooling Materials and Solutions for Thixoforming: A key to the process industrialization
Rassili, Ahmed ULg; Lecomte-Beckers, Jacqueline ULg

in Solid State Phenomena (2015), 217-218

Investigations on steel thixoforming started in the early 90's and many developments were carried out, mainly driven by the industrialization of the process. After a series of basic investigations on ... [more ▼]

Investigations on steel thixoforming started in the early 90's and many developments were carried out, mainly driven by the industrialization of the process. After a series of basic investigations on adapted steels and materials as well as near-net shaping investigations, the issue of mass production raised and thus induced some other challenges mainly on die life and process automation and cycling. High working temperatures and components complexity were then the main locks to mass productions. In most of reported literature, none of the involved research group reached or real production and industrialization criteria. The euro group holds most of these research investigations [1]. We have reported many of these results in previous communications and this paper presents a continuity of what have already been presented. Some advanced tooling materials and solutions are presented and applied to a real complex industrial component. [less ▲]

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See detailHIGH TEMPERATURE CORROSION RESISTANCE OF METALLIC MATERIALS IN HARSH CONDITIONS
Novello, Frederic; Dedry, Olivier ULg; De Noose, Vincent et al

in Lecomte-Beckers, Jacqueline; Dedry, Olivier; Oakey, John (Eds.) et al Proceedings of the 10th Conference on Materials for Advanced Power Engineering 2014 (2014, September)

Highly efficient energy recovery from renewable sources and from waste incineration causes new problems of corrosion at high temperature. A similar situation exists for new recycling processes and new ... [more ▼]

Highly efficient energy recovery from renewable sources and from waste incineration causes new problems of corrosion at high temperature. A similar situation exists for new recycling processes and new energy storage units. These corrosions are generally considered to be caused by ashes or molten salts, the composition of which differs considerably from one plant to another. Therefore, for the assessment of corrosion-resistance of advanced materials, it is essential to precisely evaluate the corrosion rate under conditions close to industrial conditions. To be able to advise their customers in selecting the right material or the right protective coating, the present authors are developing testing equipment and related procedures to assess the high temperature corrosion rate of metallic materials. This paper describes the testing equipment developed so far and presents the first results obtained in two corrosive environments: the aggressive condensates that affect waste incinerators (mixture of liquid/solid salts in oxidising conditions) and heat transfer fluids of electric power generating plants based on solar towers (mixture of liquid salts). Temperatures range from 400 to 650°C. Tested materials include 16Mo3 (0.3% molybdenum steel alloy), Inconel 625 (austenitic nickel-chromium-based superalloys), Nickel 200, Ni-57CrMoSiB (nickel-base coating with high chromium content and boron as additional element) and Grade 91 (9% chrome- 1% molybdenum steel alloy). [less ▲]

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See detailProceedings of the 10th Conference on Materials for Advanced Power Engineering 2014
Lecomte-Beckers, Jacqueline ULg; Dedry, Olivier ULg; Oakey, J. et al

Book published by FZ. Juelich (2014)

The 10th Liege Conference on Materials for Advanced Power Engineering presents the achievements of international materials related research for high e ciency, low-emission power plants. Furthermore the ... [more ▼]

The 10th Liege Conference on Materials for Advanced Power Engineering presents the achievements of international materials related research for high e ciency, low-emission power plants. Furthermore the new demands of the transition of electricity supply towards more and more regenerative power sources are reported. Resource preservation and maximization of economic success by improved plant e - ciency were the driving forces in past materials and power plant technology development. Fossil fuels will still play a considerable role for future energy security, even if renewables gain rising importance. The integration of uctuating renewable energy technologies poses great future challenges in terms of load exibility, thermal cycling capability and downtime corrosion resistance for the materials employed in new concentrated solar power, biomass red or gas to liquid plants and the backing conventional fossil red power plants. In order to balance erroneous availability forecasts of uctuating regenerative power sources (wind, solar) and vice versa to bridge short periods of low conventional power demand, the minimum load capability of conventional power plants will have to be decreased, while on the other hand start-up times and load ramps will have to be increased to ensure grid stability. Above all improved e ciency of plant, implying rising process temperatures and pressures remains of the utmost importance to ensure economic prosperity. All these issues will create even stronger demands for future materials research and development. The series of Liège Conferences on Materials for Advanced Power Engineering re ects the necessity of joint international material research and component development for critical components of power generation equipment by bringing together material scientists, design engineers, alloy producers and component manufacturers. To put European efforts into an international framework there are several invited research and review papers covering materials, component and process development in the USA and Asia. In addition there are more than 75 contributed papers from 22 countries which are presented as posters at the conference. [less ▲]

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See detailRapport Final - PROJET ULTRA CB - CONVENTION RW 6418 : Etude de faisabilité dans le développement de nano-revêtements sol-gels capables d’assurer une protection anticorrosion dans les applications soumises à des contraintes mécaniques et thermiques
Lecomte-Beckers, Jacqueline ULg; Dedry, Olivier ULg

Report (2014)

Ce rapport final s’inscrit dans le cadre du projet ULTRA-CB porté par Saint Roch Couvin SA. Le but de ce projet est de réaliser une étude de faisabilité dans le développement de nano-revêtements sol-gels ... [more ▼]

Ce rapport final s’inscrit dans le cadre du projet ULTRA-CB porté par Saint Roch Couvin SA. Le but de ce projet est de réaliser une étude de faisabilité dans le développement de nano-revêtements sol-gels capables d’assurer une protection anticorrosion dans les applications soumises à des contraintes mécaniques et thermiques. L’objectif pour Saint Roch Couvin (SRC) est d’appliquer les résultats de cette recherche industrielle sur un substrat de fonte au travers d’une étude de faisabilité d’une chaudière en fonte à condensation interne. [less ▲]

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See detailCharacterization of the Solidification Path, the Solid State Transformations and the Mechanical Behavior of a High Chromium Cast Steel
Tchuindjang, Jérôme Tchoufack ULg; Neira Torres, Ingrid; Habraken, Anne ULg et al

in Proceedings of the 5th Abrasion Conference - 2014 (2014, August)

The mechanical behavior of the fully austenitic matrix of a High Chromium Cast Steel (HCCS) alloy has been determined under external compression stress applied at 300°C and 700°C. The solidification path ... [more ▼]

The mechanical behavior of the fully austenitic matrix of a High Chromium Cast Steel (HCCS) alloy has been determined under external compression stress applied at 300°C and 700°C. The solidification path and the microstructure have been studied, including the nature and the critical temperature ranges for carbides formation, while using Differential Thermal Analysis and both Optical and Scanning Electron Microscopes. The microstructure has been characterized towards both Optical and SEM analyses. Differential Thermal Analysis and Dilatometry were used to study the solid state phase transformations on the one hand, and precipitation and dissolution reactions on the other hand, especially during heating from room temperature up to austenitization, and subsequent cooling down to room temperature. Dilatometry also helps setting the parameters for the preliminary thermal treatments to perform prior to compression tests, in order to allow more or less transition carbides within the stressed microstructure, the other carbides remaining undissolved. Flow stress curves and related work hardening rates were determined for both temperatures. From the compression tests, various strengthening phenomena, such as precipitation hardening and stress induced bainite transformation, and one softening mechanism such as recovery, have been highlighted, while enhancing at the same time the influence of the temperature and the carbide type on the mechanical behavior of the HCCS material. Cracks observed on grain boundaries primary carbides allow establishing a rough damage model. The crack initiation within the HCCS alloy seems to be strongly dependent on the temperature, the external applied stress and the matrix toughness. [less ▲]

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See detailProcessing metallic materials by additive technologies - Specificities of the thermal history and microstructures
Mertens, Anne ULg; Lecomte-Beckers, Jacqueline ULg

Conference given outside the academic context (2014)

Additives technologies currently attract a growing interest as they are particularly versatile and well adapted for the production of small series e.g. of metallic parts. Beyond the great diversity of the ... [more ▼]

Additives technologies currently attract a growing interest as they are particularly versatile and well adapted for the production of small series e.g. of metallic parts. Beyond the great diversity of the concerned processes (laser beam melting, electron beam melting, laser cladding…) and metallic alloys, some common features may be highlighted: (1) the strong directionality of additive processes, due to the fact that parts are fabricated “layer-by-layer”; (2) the ultra-fast heating and cooling cycles, following the displacement of the beam(s) away from the working zone. The present paper aims at illustrating these two major features of additive techniques through case studies involving the most common metallic alloys (steels, Al- or Ti-based alloys…), thus highlighting the opportunities pertaining to additive technologies for the optimisation of materials microstructures and of the resulting properties. [less ▲]

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See detailLes composites à matrice métallique/céramique – De nouveaux procédés de fabrication pour de nouvelles applications
Mertens, Anne ULg; Lecomte-Beckers, Jacqueline ULg

Conference (2014, May 20)

A l’heure où la plupart des matériaux composites essentiellement structuraux sont faits d’une matrice à base polymère, les matériaux composites à matrice métallique ou céramique offrent de nouvelles ... [more ▼]

A l’heure où la plupart des matériaux composites essentiellement structuraux sont faits d’une matrice à base polymère, les matériaux composites à matrice métallique ou céramique offrent de nouvelles perspectives en termes de performances et de durabilité. Le présent exposé s’attache plus particulièrement à retracer les possibilités offertes par de nouvelles méthodes de mise en oeuvre telles que la friction-malaxage et les techniques d’impression 3D, aussi bien en termes d’amélioration des propriétés mécaniques des matériaux composites que des fonctionnalités inédites qui peuvent leur être conférées. [less ▲]

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