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Featured researches published by Anne Mertens.


Philosophical Magazine | 2001

On the sources of work hardening in multiphase steels assisted by transformation-induced plasticity

Pascal Jacques; Quentin Furnemont; Anne Mertens; Francis Delannay

The mechanisms effectively responsible for the enhancement of the work-hardening capabilities of multiphase steels assisted by transformation-induced plasticity are highlighted. Different microstructures, some containing a proportion of retained austenite with various mechanical stabilities, are studied. The dislocation density generated within ferrite by the mechanically induced martensitic transformation of retained austenite is shown to scale with the incremental work-hardening exponent. The acoustic emission generated during tensile straining was also measured. The acoustic emission was revealed to result mainly from dislocation motion, especially from the motion of the additional dislocation density generated in intercritical ferrite by the strain-induced martensitic transformation.


Scripta Materialia | 2001

Comparison of the effects of silicon and aluminium on the tensile behaviour of multiphase TRIP-assisted steels

Etienne Girault; Anne Mertens; Pascal Jacques; Yvan Houbaert; Bert Verlinden; Jan Van Humbeeck

Ghent University,Laboratory for Iron and Steelmaking, Technologiepark 9, B-9052 Ghent, Belgium(Received July 12, 2000)(Accepted in revised form November 21, 2000)Keywords: TRIP-steels; Microstructure; Phase transformations; Mechanical propertiesIntroductionMultiphase TRIP-assisted steels are a new generation of low alloy high strength steels that exhibitexceptional formability [1]. The remarkable strength to ductility balance results from the occurrenceduring testing of the Transformation Induced Plasticity (TRIP) phenomenon [2], which involves thestrain-induced transformation of austenite to martensite. The presence of austenite in the initialmicrostructure appears to be critical to the achievement of the desired properties. The retention ofaustenite is usually obtained by the combined effect of an appropriate chemistry and a typicalheat-treatment. In this respect, it is known that silicon and aluminium may both retard the kinetics ofcarbide formation and thus favour the austenite stabilisation by a bainitic holding stage [3]. Despite thisqualitative knowledge, very little literature can be found that rigorously compares the effect of siliconand aluminium on the austenite retention, on the extent of the TRIP effect, and on the resulting tensilebehaviour, all other chemical constituents have been kept constant [4]. The objective of this paper is toquantitatively assess the influence of aluminium and silicon contents, in view of the development ofmultiphase TRIP-assisted steels.Materials and Experimental ProcedureThe chemical compositions of the steels studied in this work are given in Table 1. Specific care wastaken to keep the same carbon content for each alloy. The slabs were initially hot and cold-rolled tothicknesses between 0.8mm and 1.0mm, following classical processing routes.The desired multiphase microstructure was obtained as displayed in Figure 1. The cold-rolledmaterial was first annealed for 4 minutes in the (a1g) region at a temperature 25°C above its Ac1temperature. It was then rapidly cooled and held at an intermediate temperature (i.e. between 375°C and450°C), where bainite formation takes place and contributes to the stabilisation of the austenite. Theheat-treatment was eventually interrupted by quenching the samples to room temperature. After the


Materials Characterization | 2001

Characterization of TRIP-assisted multiphase steel surface topography by atomic force microscopy

Tanya Ros-Yáñez; Yvan Houbaert; Anne Mertens

Transformation-induced plasticity (TRIP)-assisted multiphase steels have a complicated microstructure consisting of different phases, mainly ferrite, retained austenite, bainite and martensite. Atomic force microscopy has been used for the phase identification and characterization of the phases in this kind of steel. A series of tests has been made on a C-Mn-Si and a C-Mn-Al TRIP-assisted steel after two different heat treatments: intercritical annealing followed by quench, and intercritical annealing followed by aging. After the aging process, the C-Mn-Al alloy was tempered in order to make metallographic observation easier, except the samples for mechanical testing, XRD or Mossbauer spectroscopy. It has been possible to identify the different phases and their topographic characteristics and to study their morphology using atomic force microscopy. The fine and complex microstructures of TRIP-assisted multiphase, steels require improvements of the existing observation techniques, like electron backscattered diffraction and atomic force microscopy. Results of these techniques are presented


Journal of Materials Science | 2002

Quantitative dilatometric analysis of intercritical annealing in a low-silicon TRIP steel

L. Zhao; T.A. Kop; V. Rolin; Jilt Sietsma; Anne Mertens; Pascal Jacques; S. van der Zwaag

In this work, an evaluation method to calculate the austenite fraction during continuous heating and isothermal annealing from dilatometric data is proposed. By means of a single reference measurement to determine a scaling factor correcting for experimental errors, a framework is created to determine the austenite fraction as a function of time and temperature. In the evaluation of the dilatometric data the effect of the changing carbon concentration in austenite phase is taken into account. The method is applied to dilatometric data for a 0.16C-1.5Mn-0.4Si (wt%) low-silicon transformation induced plasticity (TRIP) multiphase steel. Three typical dilatometric data are obtained by heating the material to 750°C, 800°C or 900°C, which leads to three different microstructures consisting of (1) ferrite, cementite and austenite, (2) ferrite and austenite and (3) full austenite, respectively. The calculated results using the proposed new method are compared with the results from thermodynamic analysis and those from quantitative microscopic analysis. Significant inter-test discrepancies are observed.


Journal of Materials Engineering and Performance | 2012

Processing of Carbon Fibers Reinforced Mg Matrix Composites Via Pre-infiltration with Al

Anne Mertens; Henri-Michel Montrieux; Jacques Halleux; Jacqueline Lecomte-Beckers; Francis Delannay

Mg-C composites offer a suitable alternative to Al alloys while allowing for a significant weight reduction, but their production can be impaired by the poor wettability of C substrates by Mg. In this study, a new “liquid” processing route has been investigated. By making use of the well-known effect of a pre-treatment of the C fibers with an aqueous solution of K2ZrF6 in favoring spontaneous wetting of C with Al, C yarns have been pre-impregnated with Al and the feasibility of further using them as reinforcements in Mg matrix composites has been assessed. More particularly, it has thus been shown that the, under the thermal conditions involved in the process, C fibers did not suffer damage due to chemical reaction with Al, and also that special care should be taken to control the surface condition of the pre-infiltrated yarns.


Materials Science Forum | 2012

C Fibres - Mg Matrix Composites Produced by Squeeze Casting and Friction Stir Processing: Microstructure & Mechanical Behaviour

Anne Mertens; Aude Simar; Francis Delannay

Mg-Al-Zn alloys have been reinforced with carbon fibres using either the liquid state process of squeeze casting (SC), or friction stir processing (FSP), a solid state process developed more recently and that appears as a promising alternative for the large-scale production of C-Mg composites. Both processes have shown their ability to produce sound composites with enhanced strength compared to the non-reinforced alloys. In SC composites, the unsized woven C fabric remains intact while in the FSP composites the sized C fabric is fragmented in short fibres, with an aspect ratio typically equal to 4, homogenously distributed in the Mg alloy matrix.


Steel Research International | 2008

Relative Influences of Aluminium and Silicon on the Kinetics of Bainite Formation from Intercritical Austenite

Anne Mertens; Pascal Jacques; Jilt Sietsma; Francis Delannay

Bainite formation from intercritical austenite is of great practical importance for the production of TRIP-assisted steels. Silicon and aluminium play important roles during this transformation by delaying carbide precipitation, thus favouring the carbon enrichment of untransformed austenite, which makes its stabilisation down to room temperature possible. Previous studies have shown a strong dependence of bainite formation kinetics on both chemical composition and transformation temperature. In the present work, the effect of silicon and aluminium contents on bainite formation kinetics is investigated experimentally using dilatometry combined with microscopical observations. The experimental results are analysed by comparison with thermodynamic parameters, such as the activation energy G* for nucleation of bainite and the carbon content C-To corresponding to the T-o-curve. It is shown that the faster transformation kinetics induced by the substitution of silicon by aluminium can be ascribed (i) to a higher driving force for nucleation, (ii) to a higher carbon content C-To at the To-curve and (iii) to the precipitation of carbide in austenite in steels with a low At content.


Journal De Physique Iv | 2003

On the influence of aluminium and silicon contents on the kinetics of bainite transformation of intercritical austenite

Anne Mertens; Pascal Jacques; L. Zhao; Suzelotte O. Kruijver; Jilt Sietsma; Francis Delannay


Archive | 2011

Interfacial phenomena in carbon fibre reinforced magnesium alloys processed by squeeze casting and thixomolding

Henri-Michel Montrieux; Anne Mertens; Jacques Halleux; Francis Delannay; Jacqueline Lecomte-Beckers


Archive | 2002

Influence of aluminium on the phase transformations during the heat treatments for the processing of multiphase TRIP-assisted steels

Anne Mertens

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Francis Delannay

Université catholique de Louvain

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Pascal Jacques

Université catholique de Louvain

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Jilt Sietsma

Delft University of Technology

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L. Zhao

Delft University of Technology

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Etienne Girault

Katholieke Universiteit Leuven

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