References of "Mertens, Anne"
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See detailLaser cladding as repair technology for Ti6Al4V alloy: Influence of building strategy on microstructure and hardness
Paydas, Hakan ULg; Mertens, Anne ULg; Carrus, Raoul et al

in Materials & Design (in press)

Laser cladding is a metal deposition technique used to fabricate or repair components made from high value metallic alloys. In the present work Ti-6Al-4V deposits with variable thickness are made to ... [more ▼]

Laser cladding is a metal deposition technique used to fabricate or repair components made from high value metallic alloys. In the present work Ti-6Al-4V deposits with variable thickness are made to assess the use of laser cladding as a repair technology. Both the effect of the building strategy (BS) and the incident energy (IE) on the metallurgical characteristics of the deposits in relation to their complex thermal history have been studying. It is shown that for the configuration consisting in a decreasing track length (DTL) under high IE, a gradient of cooling rate exists that leads to the presence of different phases within the microstructure. Conversely homogeneous microstructures are present either for the configuration with a constant track length (CTL) under high IE, and for the strategy obtained from a DTL under low IE. Depending on the possible heat accumulation the nature of the phases are determined together with hardness maps within the deposits. Some qualification criteria are set prior to tensile tests to selected the adequate candidate-deposit that does not weaken the cladded material when it is stressed. A thermo-metallurgical scheme is proposed that helps understanding the effect of both the BS and the IE on the microstructure. [less ▲]

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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 detailTipTopLam - Rapid manufacturing laser de pièces en titane (2008-2015), volet 1: Caractérisation microstructurale
Carton, Marc; Contrepois, Quentin; Mertens, Anne ULg et al

Report (2015)

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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 detailInfluence of Fibre Distribution and Grain Size on the Mechanical Behaviour of Friction Stir Processed Mg-C Composites
Mertens, Anne ULg; Simar, Aude; Adrien, Jérôme et al

in Materials Characterization (2015), 107

Short C fibres-Mg matrix composites have been produced by friction stir processing sandwiches made of a layer of C fabric stacked between two sheets of Mg alloy AZ31B or AZ91D. This novel processing ... [more ▼]

Short C fibres-Mg matrix composites have been produced by friction stir processing sandwiches made of a layer of C fabric stacked between two sheets of Mg alloy AZ31B or AZ91D. This novel processing technique can allow the easy production of large-scale metal matrix composites. The paper investigates the microstructure of FSPed C fibre-Mg composites in relation with the fragmentation of the C fibres during FSP and their influence on the tensile properties. 3D X-ray tomography reveals that the fibres orient like onion rings and are more or less fragmented depending on the local shear stress during the process. The fibre volume fraction can be increased from 2.3% to 7.1% by reducing the nugget volume, i.e. by using a higher advancing speed in AZ31B alloy or a stronger matrix alloy, like AZ91D alloy. A higher fibre volume fraction leads to a smaller grain size which brings about an increase of the composite yield strength by 15 to 25%. However, a higher fibre volume fraction also leads to a lower fracture strain. Fracture surface observations reveal that damage occurs by fibre/matrix decohesion along fibres oriented perpendicularly to the loading direction. [less ▲]

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See detailAl/stainless-invar composites with tailored anisotropy for thermal management in light weight electronic packaging
Ryelandt, Sophie; Mertens, Anne ULg; Delannay, Francis

in Materials & Design (2015), 85

Composite plates in which the low CTE phase has the shape of a honeycomb are anticipated to present optimum anisotropy of thermal expansion and thermal conductivity for baseplates in electronic packaging ... [more ▼]

Composite plates in which the low CTE phase has the shape of a honeycomb are anticipated to present optimum anisotropy of thermal expansion and thermal conductivity for baseplates in electronic packaging. This design is explored by choosing an invar alloy for the low CTE phase. In order to allow the formation of a passivation layer protecting from reaction with liquid Al during squeeze casting, the honeycomb is made of the Cr-rich alloy commonly called “stainless-invar”. Composite plates containing 20vol% and 38vol% stainless invar were processed using honeycombs with the same thickness over cell side ratio. Experimental CTE values are significantly lower than the predictions of three different thermo-elastic models. The very limited amplitude of the strain hysteresis precludes the occurrence of global plastic yielding in the matrix. It appears that, owing to the high contiguity of the low CTE phase, the low value of the experimental CTE results from void closing and opening by localised plastic flow. A honeycomb volume fraction of 38% is necessary for bringing the average CTE down to the level suitable for packaging applications. The ratio of transverse thermal conductivity to density then amounts to about half of the performance of the best Al/SiC composites. [less ▲]

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See detailModification de la microstructure des métaux après déformation plastique : Restauration et recristallisation
Mertens, Anne ULg

Learning material (2014)

Cette présentation powerpoint vient compléter et illustrer les notes du cours MECA0473-1 "Ingénierie des matériaux métalliques" traitant de l'évolution de la microstructure des métaux suite à une ... [more ▼]

Cette présentation powerpoint vient compléter et illustrer les notes du cours MECA0473-1 "Ingénierie des matériaux métalliques" traitant de l'évolution de la microstructure des métaux suite à une déformation plastique telle que celle imposée typiquement par un procédé de mise en forme comme le laminage. Les phénomènes de restauration et de recristallisation sont discutés en détails du point de vue tant de leurs mécanismes que de leurs cinétiques. Le vieillissement des aciers après déformation est également abordé. [less ▲]

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See detailAn Introduction to the Additive Manufacturing of Metallic Materials - Two Case Studies on the Processing of Stainless Steel 316L and of Ti Alloy Ti-6Al-4V
Mertens, Anne ULg

Learning material (2014)

This powerpoint presentation was used as teaching material in a seminar given as part of the course “Ingénierie des matériaux métalliques” at Université de Liège. It outlines important current issues in ... [more ▼]

This powerpoint presentation was used as teaching material in a seminar given as part of the course “Ingénierie des matériaux métalliques” at Université de Liège. It outlines important current issues in the developments of additive technologies for the processing of metallic materials by discussing two case studies from researches carried out by the Metallic Materials Science Unit (ULg). In particular, two different metallic alloys, i.e. stainless steel 316L and Ti-6Al-4V, have been processed by laser beam melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the investigated conditions, Ti-6Al-4V exhibits a more complex behaviour than stainless steel 316L with respect to the occurrence of microstructural and mechanical anisotropy. Moreover, Ti-6Al-4V appears more sensitive to the build-up of internal stresses when compared with stainless steel 316L, whereas stainless steel 316L appears more prone to the formation of “lack of melting” defects. This correlates nicely with the difference in thermal conductivity between the two materials. Thermal conductivity was also shown to increase strongly with increasing temperature. [less ▲]

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See detailAdditive Manufacturing of Metallic Materials: Case Studies in the Processing of Stainless Steel 316L and of Alloy Ti-6Al-4V by Laser Beam Melting
Mertens, Anne ULg

Learning material (2014)

This powerpoint presentation was used as teaching material in a seminar given as part of the course “Compléments de fabrication mécanique et FAO” at Université catholique de Louvain. It outlines important ... [more ▼]

This powerpoint presentation was used as teaching material in a seminar given as part of the course “Compléments de fabrication mécanique et FAO” at Université catholique de Louvain. It outlines important current issues in the developments of additive technologies for the processing of metallic materials by discussing two case studies from researches carried out by the Metallic Materials Science Unit (ULg). In particular, two different metallic alloys, i.e. stainless steel 316L and Ti-6Al-4V, have been processed by laser beam melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the investigated conditions, Ti-6Al-4V exhibits a more complex behaviour than stainless steel 316L with respect to the occurrence of microstructural and mechanical anisotropy. Moreover, Ti-6Al-4V appears more sensitive to the build-up of internal stresses when compared with stainless steel 316L, whereas stainless steel 316L appears more prone to the formation of “lack of melting” defects. This correlates nicely with the difference in thermal conductivity between the two materials. Thermal conductivity was also shown to increase strongly with increasing temperature. [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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See detailProcessing of alloy Ti-6Al-4V and of stainless steel 316L by Laser Beam Melting
Mertens, Anne ULg; Paydas, Hakan ULg; Reginster, Sylvie ULg et al

Conference (2014, May)

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic ... [more ▼]

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic materials such as Ti alloys and stainless steels. Practically, in SLM, a metallic powder is deposited layer-by-layer in a powder bed and then molten locally according to the desired shape. An important feature of this process is that the structure undergoes an ultra-fast cooling once the beam leaves the working zone, thus giving rise to strongly out-of-equilibrium microstructures. In the case of Ti alloy Ti-6Al-4V, in particular, the microstructural anisotropy resulting from the epitaxial growth of the newly deposited layer on the material previously solidified has been shown to exert a very strong influence on the mechanical properties [1] In the present work, the thermophysical behaviour of Ti-alloy Ti-6Al-4V and of stainless steel 316L has been characterised in details, in order to reach a better understanding of the phenomena controlling the microstructures and mechanical properties of parts. In particular, the thermal conductivity of Ti-alloy Ti-6Al-4V and of stainless steel 316L at high temperature has been determined by combining dilatometry, Differential Scanning Calorimetry (DSC) and laser flash diffusivimetry based on Laplace’s equation. Since Ti-alloy Ti-6Al-4V and stainless steel 316L exhibit quite different physical behaviours, their careful comparison is shown to shed more light into the role of phenomena such as epitaxial growth, out-of-equilibrium phase transformations and/or internal stresses in the additive manufacturing of metallic materials. [less ▲]

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See detailTechniques additives vs techniques conventionnelles-les microstructures
Mertens, Anne ULg; Lecomte-Beckers, Jacqueline ULg

Conference given outside the academic context (2014)

Très flexibles et particulièrement bien adaptées à la production de petites séries, les techniques additives suscitent un intérêt croissant, notamment pour la mise en oeuvre de matériaux métalliques. Par ... [more ▼]

Très flexibles et particulièrement bien adaptées à la production de petites séries, les techniques additives suscitent un intérêt croissant, notamment pour la mise en oeuvre de matériaux métalliques. Par-delà la diversité des techniques que ce terme recouvre (laser beam melting, electron beam melting, laser cladding…) et par-delà la variété des alliages qu’elles permettent de mettre en oeuvre, quelques caractéristiques récurrentes se dessinent: 1) La nature fortement directionnelle des procédés additifs, lié au fait que la pièce est fabriquée “couche par couche” 2) Des cycles de chauffe et de refroidissement ultra-rapides, en fonction des déplacements du/des faisceau(x) La présente communication s’attache à illustrer ces deux caractéristiques essentielles des techniques additives au moyen d’exemples touchant aux principaux alliages métalliques (aciers, alliages d’aluminium ou de titane…), et à en dégager les risques et les opportunités qu’offrent les techniques additives du point vue du contrôle et de l’optimisation des microstructures et des propriétés d’usage qui en découlent… [less ▲]

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See detailDating Metallic Reinforcements in Roof Frames
Maggi, Christophe; Pagès, Gaspard; Hoffsummer, Patrick ULg et al

in Bolle, Caroline; Coura, Geneviève; Léotard, Jean-Marc (Eds.) L'archéologie des bâtiments en question. Un outil pour les connaître, les conserver et les restaurer (2014)

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See detailMicrostructures and Mechanical Properties of Stainless Steel AISI 316L Processed by Selective Laser Melting
Mertens, Anne ULg; Reginster, Sylvie ULg; Contrepois, Quentin et al

in Materials Science Forum (2014), 783-786 (2014)

In this study, samples of stainless steel AISI 316L have been processed by selective laser melting, a layer-by-layer near-net-shape process allowing for an economic production of complex parts. The ... [more ▼]

In this study, samples of stainless steel AISI 316L have been processed by selective laser melting, a layer-by-layer near-net-shape process allowing for an economic production of complex parts. The resulting microstructures have been characterised in details in order to reach a better understanding of the solidification and consolidation processes. The influence of the processing parameters on the mechanical properties was investigated by means of uniaxial tensile testing performed on samples produced with different main orientations with respect to the building direction. A strong anisotropy of the mechanical behaviour was thus interpreted in relation with the microstructures and the processing conditions. [less ▲]

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See detailRapport Final, Projet FEDER Programmation 2007-2013, portefeuille de projets SINUS : Simulation Numérique Haute Performance
Lecomte-Beckers, Jacqueline ULg; Mertens, Anne ULg; Carton, Marc et al

Report (2014)

Le portefeuille de projets SINUS : Simulation Numérique Haute Performance, s'inscrit dans le cadre des mesures 2.2 de valorisation du potentiel des centres de recherche en Wallonie. Trois projets ... [more ▼]

Le portefeuille de projets SINUS : Simulation Numérique Haute Performance, s'inscrit dans le cadre des mesures 2.2 de valorisation du potentiel des centres de recherche en Wallonie. Trois projets composent le portefeuille SINUS: une action 2.2.1 Équipements technologiques exceptionnels, une action 2.2.2 Projets de recherche transversaux en partenariat, une action 2.2.4 Optimisation de l'offre de services technologiques des centres de recherches agréés.Ce rapport s'inscrit dans l'action 2.2.2 des projets de recherche transversaux en partenariat. Cette action vise à développer des méthodes numériques de nouvelle génération en collaboration avec des centres de recherche universitaires et agréés et des entreprises répondant aux besoins de l’industrie. Les domaines couverts sont la modélisation des processus de fabrication, des matériaux et des structures, la mécanique des fluides et l’optimisation multidisciplinaire. Au sein de cette action, différents lots ont été définis : Lot 1 Modélisation avancée d'écoulements complexes multi-physiques, Lot 2 Modélisation avancée multi-échelles des matériaux et des structures, Lot 3 Modélisation avancée des procédés de fabrication, Lot 4 Optimisation multidisciplinaire. [less ▲]

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See detailMechanical properties of alloy Ti-6Al-4V and of stainless steel 316L processed by Selective Laser Melting: Influence of out-of-equilibrium microstructures
Mertens, Anne ULg; Reginster, Sylvie ULg; Paydas, Hakan ULg et al

in Powder Metallurgy (2014), 57(3), 184-189

Ti-6Al-4V and stainless steel 316L have been processed by selective laser melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the ... [more ▼]

Ti-6Al-4V and stainless steel 316L have been processed by selective laser melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under the investigated conditions, Ti-6Al-4V exhibits a more complex behaviour than stainless steel 316L with respect to the occurrence of microstructural and mechanical anisotropy. Moreover, Ti-6Al-4V appears more sensitive to the build-up of internal stresses when compared with stainless steel 316L, whereas stainless steel 316L appears more prone to the formation of “lack of melting” defects. This correlates nicely with the difference in thermal conductivity between the two materials. Thermal conductivity was shown to increase strongly with increasing temperature and the thermophysical properties appeared to be influenced by variations in the initial metallurgical state. [less ▲]

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See detailMicrostructure and Mechanical Properties of a Mixed Si-Al TRIP-Assisted Steel Subjected to Continuous Galvanizing Heat Treatments
Mertens, Anne ULg; Bellhouse, Erika M.; McDermid, Joseph R.

in Materials Science & Engineering : A (2014), 608

Heat treatments with an isothermal bainitic transformation temperature of 465°C compatible with the continuous galvanizing process were performed on a 0.2C-1.5Mn-1.0Si-0.5Al (wt%) TRIP-assisted steel. The ... [more ▼]

Heat treatments with an isothermal bainitic transformation temperature of 465°C compatible with the continuous galvanizing process were performed on a 0.2C-1.5Mn-1.0Si-0.5Al (wt%) TRIP-assisted steel. The effect of intercritical annealing temperature and isothermal bainitic transformation (IBT) time at 465C on mechanical properties and microstructure were determined. The best combination of strength and ductility was obtained for the lower intercritical annealing temperature of 750°C for an isothermal bainitic transformation time of 90 s at 465°C. However, after intercritical annealing at a higher temperature of 797°C, optimum mechanical properties were obtained for a shorter isothermal bainitic transformation time of 60 s at 465°C, likely due to the lower C content of the intercritical austenite bringing about faster transformation kinetics. It was concluded that varying the intercritical temperature and IBT time can play an important role in the development of a suitable process window to obtain the desired mechanical properties in low alloy TRIP-assisted steels given the constraints associated with the continuous galvanizing process. [less ▲]

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See detailFriction Stir Processing of Magnesium Matrix Composites Reinforced with Carbon Fibres or Carbon Nanotubes - A Comparative Study
Mertens, Anne ULg; Simar, Aude; Garray, Didier et al

Conference (2013, December 05)

The poor wettability of carbon substrates by liquid Mg and, in the case of carbon nanotubes (CNTs), their strong tendency to agglomerate, are major obstacles to the large-scale production of C-Mg ... [more ▼]

The poor wettability of carbon substrates by liquid Mg and, in the case of carbon nanotubes (CNTs), their strong tendency to agglomerate, are major obstacles to the large-scale production of C-Mg composites by classical ‘liquid-state’ processing routes such as squeeze casting. As an innovative ‘solid state’ process, Friction Stir Processing (FSP) hence appeared as a very promising alternative for the production of C-Mg composites, although the method for inserting the reinforcing phase - in grooves or holes machined in the matrix material - remained time-consuming and labour-intensive. More recently, the present authors proposed a new and easier technique for the insertion of C fibres in FSPed Mg-matrix composites i.e. FSP of a C fabric stacked between two metal sheets. In the current work, the feasibility of extending this latter method to the production of CNTs-Mg composites has been assessed. “Bucky papers” – thin disks made from agglomerated CNTs, thus ensuring for their safe handling – were stacked between two sheets of Mg alloy AZ31B, and the resulting sandwich was FSPed. The effect of FSP experimental parameters such as the rotational and advancing speeds or the number of passes on the microstructural changes occuring upon processing has been studied and compared with the case of C fibres-Mg composites. Moreover, a particular attention has been given to the distribution of the reinforcements in the Mg matrix and to the characterization of the resulting mechanical properties. [less ▲]

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