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Michel Rappaz

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Publications associées (85)

Probability of twin boundary formation associated with the nucleation of equiaxed grains on icosahedral quasicrystal templates

Michel Rappaz, Güven Kurtuldu

Recently, we have shown that minute Cr additions (typically 0.1 wt%) to Al-Zn alloys solidified in a uniform temperature field lead to the formation of fine equiaxed fcc Al grains [1]. Furthermore, these grains exhibit an unexpectedly large number of twin, ...

Iop Publishing Ltd2015

Solid-liquid interdiffusion (SLID) bonding in the Au-In system: experimental study and 1D modelling

Aïcha Hessler-Wyser, Thierry Hessler, Michel Rappaz, Léa Deillon

Au-In bonds with a nominal composition of about 60 at.% In were fabricated for use in wafer-level packaging of MEMS. The microstructure of the bonds was studied by scanning electron microscopy. The bond hermeticity was then assessed using oxidation of Cu t ...

Institute of Physics2015

Thermodynamic Aspects of Homogeneous Nucleation Enhanced by Icosahedral Short Range Order in Liquid Fcc-Type Alloys

Michel Rappaz, Güven Kurtuldu

We have recently shown that minute solute element additions to liquid metallic alloys can strongly influence the nucleation of the fcc phase and act as a grain refinement method. Electron back-scattered diffraction observations revealed a concomitant incre ...

Springer2015

Growth of intermetallic compounds in the Au-In system: Experimental study and 1-D modelling

Aïcha Hessler-Wyser, Michel Rappaz, Léa Deillon

The gold indium system is of primary interest for bonding processes such as solid liquid interdiffusion bonding. In order to optimize the manufacturing parameters, it is essential to know which intermetallic compounds (IMCs) are formed when solid Au and li ...

Elsevier2014

Icosahedral quasicrystal-enhanced nucleation of the fcc phase in liquid gold alloys

Michel Rappaz, Güven Kurtuldu, Alberto Sicco

Although the grain refinement of yellow gold alloys with Jr has been used in industry and known for nearly half a century, the basic mechanism is still unknown. The present contribution shows that the mechanism is the same as that evidenced recently in Al- ...

Elsevier2014

Time-Resolved X-Ray Microtomography Observation of Intermetallic Formation Between Solid Fe and Liquid Al

Aïcha Hessler-Wyser, Michel Rappaz, Guillaume Pasche, Cécile Hébert

Time-resolved in situ X-ray tomography combined with scanning electron microscopy was performed on an Al-Fe diffusion system at 973 K (700 A degrees C) to study the formation of the main intermetallic compounds occurring at the interface. After nucleation ...

Springer US2013

Prediction of Hot Tear Formation in Vertical DC Casting of Aluminum Billets Using a Granular Approach

Jean-Marie Drezet, Michel Rappaz, André Phillion, Meisam Sistaninia

A coupled hydromechanical granular model aimed at predicting hot tear formation and stress-strain behavior in metallic alloys during solidification is applied to the semicontinuous direct chill casting of aluminum alloy round billets. This granular model c ...

Springer2013

Dendritic Growth Morphologies in Al-Zn Alloys-Part II: Phase-Field Computations

Michel Rappaz, Jonathan Friedli, Jonathan Dantzig, Paolo Di Napoli

In Part I of this article, the role of the Zn content in the development of solidification microstructures in Al-Zn alloys was investigated experimentally using X-ray tomographic microscopy. The transition region between dendrites found at low Zn content a ...

Springer Verlag2013

Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al-Zn-Cr alloys: Can icosahedral solid clusters play a role?

Michel Rappaz, Güven Kurtuldu

The equiaxed solidification of Al-20 wt.% Zn alloys revealed an unexpectedly large number of fine grains which are in a twin, or near-twin, relationship with their nearest neighbors when minute amounts of Cr (1000 ppm) are added to the melt. Several occurr ...

Elsevier2013

Dendritic Growth Morphologies in Al-Zn Alloys-Part I: X-ray Tomographic Microscopy

Michel Rappaz, Jonathan Friedli, Paolo Di Napoli

Upon solidification, most metallic alloys form dendritic structures that grow along directions corresponding to low index crystal axes, e.g., directions in fcc aluminum. However, recent findings[1,2] have shown that an increase in the zinc content in Al-Zn ...

Springer Verlag2013

Modeling of peritectic coupled growth in Cu-Sn alloys

Michel Rappaz, Jonas Valloton, Jonathan Dantzig

In directional solidification experiments on hypoperitectic Cu-Sn alloys at low velocity and high thermal gradient, both lamellar and fibrous coupled peritectic growth patterns have been observed. Two phenomena that had not been observed in previous experi ...

Elsevier2013

Morphology and Growth Kinetic Advantage of Quenched Twinned Dendrites in Al-Zn Alloys

Michel Rappaz, Mario Alberto Salgado Ordorica, André Phillion

Twinned dendrites appearing in an Al-26 wt pct Zn alloy have been quenched during growth using a specifically designed setup that is positioned on top of a directional solidification experiment. X-ray tomography performed at the Swiss Light Source (SLS-bea ...

Springer Verlag2013

3-D granular modeling and in situ X-ray tomographic imaging: A comparative study of hot tearing formation and semi-solid deformation in Al-Cu alloys

Jean-Marie Drezet, Michel Rappaz, André Phillion, Meisam Sistaninia

The mechanical behavior of partially solidified Al-Cu alloys is investigated to assess the influence of mushy zone deformation on hot tearing. For this purpose, the results of a semi-solid tensile test conducted in situ using X-ray microtomography are comp ...

Elsevier2013

Three-dimensional chemical analysis of laser-welded NiTi–stainless steel wires using a dual-beam FIB

Aïcha Hessler-Wyser, Michel Rappaz, Marco Cantoni, Jonas Vannod, Pierre Burdet

The biomedical industry has an increasing demand for processes to join dissimilar metals, such as laser welding of NiTi and stainless steel wires. A region of the weld close to the NiTi interface, which previously was shown to be prone to cracking, was fur ...

Elsevier2013

A 3D coupled hydro-mechanical granular model for the prediction of hot tearing formation

Jean-Marie Drezet, Michel Rappaz, André Phillion, Meisam Sistaninia

A new 3D coupled hydro-mechanical granular model that simulates hot tearing formation in metallic alloys is presented. The hydro-mechanical model consists of four separate 3D modules. (I) The Solidification Module (SM) is used for generating the initial so ...

Iop Publishing Ltd2012

Competition of the primary and peritectic phases in hypoperitectic Cu-Sn alloys solidified at low speed in a diffusive regime

Michel Rappaz, Jean-Daniel Wagnière, Jonas Valloton

Directional solidification experiments on hypoperitectic Cu-Sn alloys have been performed at very low velocity in a high thermal gradient to ensure planar front growth of both phases. The diameter of the sample has been reduced to 500 mu m to strongly redu ...

Elsevier2012

A 3-D coupled hydromechanical granular model for simulating the constitutive behavior of metallic alloys during solidification

Jean-Marie Drezet, Michel Rappaz, André Phillion, Meisam Sistaninia

A three-dimensional (3-D) coupled hydromechanical granular model has been developed and validated to directly predict, for the first time, hot tear formation and stress strain behavior in metallic alloys during solidification. This granular model consists ...

Elsevier2012

Three-dimensional granular model of semi-solid metallic alloys undergoing solidification: Fluid flow and localization of feeding

Jean-Marie Drezet, Michel Rappaz, André Phillion, Meisam Sistaninia

A three-dimensional (3-D) granular model which simulates fluid flow within solidifying alloys with a globular microstructure, such as that found in grain refined Al alloys, is presented. The model geometry within a representative volume element (RVE) consi ...

Elsevier2012

Development of a laser-based heating system for in situ synchrotron-based X-ray tomographic microscopy

Michel Rappaz, Marco Stampanoni

Understanding the formation of materials at elevated temperatures is critical for determining their final properties. Synchrotron-based X-ray tomographic microscopy is an ideal technique for studying such processes because high spatial and temporal resolut ...

International Union of Crystallography2012

3D Phase-Field Simulation of Micropore Formation during Solidification: Morphological Analysis

Alain Jacot, Michel Rappaz, Hossein Meidani

A 3D multiphase-field (PhF) model has been developed in order to study the formation of a micropore constrained to grow in a solid network (i.e., pinching effect). The model accounts for the pressure difference due to capillarity between liquid and gas, th ...

Iop Publishing Ltd2012

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