Dr Christine Blanc, ENSIACET, Toulouse, France

Modelling the corrosion behaviour of copper-rich aluminium alloys: galvanic coupling between different aluminium-copper model alloys

Dr Søren Fæster Nielsen, Risø National Laboratory, Denmark

Tomography and Diffraction

Dr Paul Michael Weaver, University of Bristol, UK

Hierarchical Materials and Structures

Dr Paul A. Midgley, University of Cambridge, UK

3D TEM: a new Perspective for Materials Microscopy

Dr Benoit Devincre, Laboratoire d’Etude des Microstructures, CNRS-ONERA, Chatillon Cedex, France

From Dislocation to Strain Hardening: can Discrete Dislocation Dynamics simulations make it

Dr Aránzazu del Campo, Max-Planck-Institut für Metallforschung, Stuttgart, Germany

Tailored surfaces with tunable adhesion

Christine Blanc

ENSIACET ( School of Chemical Sciences and Engineering), Toulouse, France

Christine Blanc was born in 1971 in France. She studied Chemistry and Science of Materials at the School of Chemistry in Toulouse (graduated in 1994). She did her thesis work on the susceptibility to pitting corrosion of different aluminium alloys and received her PhD in 1997. She is now an Assistant Professor at the ENSIACET ( School of Chemical Sciences and Engineering) in Toulouse. She gives lectures on Material Sciences and she is the head of a teaching section for third year students "Durability of Materials and Structures". Her research focuses on the corrosion processes affecting the materials and she is also interested in the protection against corrosion. She was awarded the 2001 H.J. Engell Prize from The International Society of Electrochemistry (ISE) and the 2005 Jean Rist medal from the French Society of Metallurgy and Materials (SF2M).

Modelling the corrosion behaviour of copper-rich aluminium alloys: galvanic coupling between different aluminium-copper model alloys

In commercial aluminium-copper alloys, the presence of various alloying elements induces the formation of different metallurgical phases: among these phases, coarse copper-rich intermetallic phases are known to be initiation sites for corrosion in various corrosive media. The reactivity of copper-rich phases and the galvanic coupling between these phases and the adjacent matrix has often been studied in the litterature but further results are still necessary to better understand these phenomena. Here, aluminium-copper alloys were synthesized to model the matrix and the copper-rich intermetallics; this talk is devoted to analysis of the galvanic coupling between these model alloys.

In a first step, Al-Cu alloys, containing 0 to 100 at.% Cu, were deposited onto aluminium substrates using an Atom Tech Ltd magnetron sputtering. Galvanic coupling tests consisted of recording the variation of galvanic current with time resulting from coupling of two Al-Cu alloys in 0.1M Na 2SO 4 solution. Galvanic coupling between a and q phase-containing model alloys has revealed that the anodic a phase did not suffer corrosion and remained in the passive state. Conversely, sulphate ions induced pitting of the cathodic q phase. Further, the higher the copper content of a phase, the greater its susceptibility to pitting.

In a second step, local electrochemical impedance spectroscopy (LEIS) was used to characterize the corrosion behaviour of three systems: pure aluminium, Al-20at%Cu and Al-40at%Cu model alloys. Model couples were also synthesized with a first layer of pure aluminium partially covered by a second layer of binary Al-Cu alloy to simulate the couple matrix/intermetallic particles. For the model couple, LEIS allowed the electrochemical behaviour of each material constitutive of the couple to be individually followed. Further SEM observations and SIMS analysis showed the dissolution of copper from Al-Cu model alloys simulating intermetallic particles and a deposition of this element on pure aluminium, simulating the matrix in agreement with observations carried out on commercial Al-Cu alloys. Comparison of the results obtained on individual model alloys and on model couples allowed the coupling effect to be studied.

Søren Fæster Nielsen

Risø National Laboratory, Denmark

Dr. Søren Fæster Nielsen is a scientist with the Materials Research Department at Risø National Laboratory, Denmark, and was nominated as the FEMS Lecturer for 2005 by the Danish Metallurgical Society (DMS). He studied physics at the H.C. Ørsted Laboratory at Copenhagen University receiving his Ph.D. in 2000 for synchrotron X-ray radiation studies of deformation in metals. As a post-doctoral researcher he participated in developing the three dimensional X-ray diffraction microscope placed at the material science beamline at ESRF in France. He currently holds a Research Fellowship for two years funded by the Danish Technical Research Council. He has published 30 articles in international journals and conferences. His prize consists of a bursary of up to €1500 to cover the costs of presenting his lecture in three different countries and €1500 in cash on completing the series. His first presentation took place on Wednesday 7th September during EUROMAT 2005 in Prague, Czech Republic, where the award had been presented to him during the Opening Ceremony.

Tomography and Diffraction

This lecture explains how 3D strain distributions in composite material can be studied by applying synchrotron X-ray tomography on samples with embedded marker particles.

Paul Weaver

University of Bristol, UK

Paul Weaver is Senior Lecturer in Aerospace Structures, and an EPSRC Advanced Research Fellow. He studied Materials Engineering at Newcastle University, UK where he obtained a First class degree for which the Institute of Materials awarded him its Royal Charter Prize. He worked on 3-D composites for his PhD before undertaking a postdoctoral role under Prof. MF Ashby at Cambridge University. Here, he studied the interactions between materials properties and section shape on structural performance. For the last 5 years he has had a lecturing post at the Aerospace Department of Bristol University, UK. He has close working relationships with Agusta-Westland Helicopters , Airbus UK and NEG-Nicon, with whom contracts approaching 1 million Euros have been secured. His interests remain in the area of exploiting structural efficiency for design purposes through materials tailoring. As such he is developing new predictive techniques for buckling of anisotropic plates and shells. This work has caught the interest of NASA Langley where Weaver has spent the last 3 summers consulting on structural design issues making use of the inherent anisotropic properties of composite materials. He has published in excess of 50 scientific papers in international journals and conferences.

Hierarchical Materials and Structures

The seminar discusses two key aspects of the interrelationship between material and geometric properties on structural performance. The first part concerns the boundaries between structured materials and efficient structures. In particular, at what length scale is it more appropriate to think of the material as a structure. The second half of the talk introduces concepts for innovative structural response using elastically - tailored orthotropic and anisotropic materials. Applications include manufacture of complex shapes to morphing structures.

A. When is a material a structure and vice-versa?

It is well-known that adding porosity to a material increases its structural efficiency. This is done by making the material cellular in structure - (honeycomb in 2- and foam in 3- dimensions). Depending on the length scale the result is either thought of as a material, such as polymeric foams or just an efficient structure (space frame structures such as the Eiffel Tower). When the length scale is small the efficiency gain is best described in terms of Ashby's shape factor. However, at large length scales the description is less clear. Issues regarding the development of a general taxonomy that is independent of length scale will be discussed.

B. Structural Utopia or something for nothing!

Materials stretch if you pull them or indeed develop curvature when subject to bending. Isotropic materials do this and little else. However, anisotropic materials can do much more! Essentially, it is possible to develop a material with up to 21 independent elastic constants meaning that such a material may bend, twist and shear as well as stretch, when pulled. Polymeric laminated composite materials give scope for tailoring the specific response of a material by changing the fibre orientation of a ply, layer-by layer through its thickness. In this sense, high-performance polymeric composites may be thought of as structured materials or indeed hierarchical materials. Convention dictates that much of the anisotropic response is designed out of the composite. However, this talk takes the perspective that such response may actually be desirable. Examples are drawn from the aerospace and natural worlds to demonstrate many unique positive advantages of anisotropic composites.

Paul Midgley

University of Cambridge

Dr Paul Midgley is a University Senior Lecturer and Director of the Electron Microscopy Facility at the Department of Materials Science and Metallurgy. He studied Physics at the H.H. Wills Physics Laboratory at the University of Bristol, receiving his PhD in 1991 for electron microscopy studies of high Tc superconductors. He then held two Research Fellowships, the first funded by The Royal Commission for The Exhibition of 1851, the second by The Royal Society. He moved to Cambridge in 1997. He has studied a wide variety of materials by electron microscopy and developed a number of novel electron microscopy techniques. He and his research group have developed new analytical techniques using EFTEM, STEM and electron holography and applied these to materials systems at the nanometer level. Recently, he has worked on the development of electron tomography using a new STEM-based approach that has wide applicability in materials science. He has written over 100 articles and is invited regularly to speak at conferences around the world.

3D TEM: a new Perspective for Materials Microscopy

The push for nanotechnology and the increasing use of nanoscale materials brings with it the need for high spatial resolution imaging and analysis. The transmission electron microscope (TEM) is a remarkably powerful and versatile instrument and in many ways ideal for such characterisation. Conventional use of a TEM is to section the object of interest and examine 2D slices assuming either uniformity in the 3rd dimension or speculating on the 3D structure from the projection. However, as the lateral dimensions of a feature approach that of its depth, as is happening in modern semiconductor fabrication, the electron microscopist will be required to examine truly 3-dimensional objects and a single projection will not be adequate for a complete description.

Stereo microscopy offers some insight into the 3D nature of an object but for true quantitative 3D analysis, one has to turn to tomography as a way to reconstruct the 3D object from a tilt series of 2D projections. Electron tomography has been used with great success in the biological sciences for about 30 years: the 3D structure of viruses and macromolecules have been determined with remarkable accuracy using tomography based on series of bright field images. However, in materials science, for a general crystalline object, diffraction (and Fresnel) contrast prohibits the use of (coherent) BF images for electron tomographic reconstruction. Other (incoherent) signals must be used.

In Cambridge we have been developing electron tomography for materials science, using STEM HAADF and inelastic EFTEM images, both predominantly incoherent signals, as the basis for the tomography tilt series. Using a variety of examples, including a number of animations, I will show how the 3D structure and composition of nanoscale objects can be revealed using electron tomography. The spatial resolution and field of view of the new technique complements perfectly the ultra-high resolution technique of atom probe tomography and the much lower resolution X-ray micro-tomography.

Benoit Devincre

Laboratoire d’Etude des Microstructures, CNRS-ONERA, Chatillon Cedex, France

B. Devincre was born in France in 1965. He is married and father of two sons. He graduated from the Formation d’Ingénieur de l’Université Paris Sud Orsay, and did his PhD in Université d'Orsay. After a Post-Doc in the material department of Oxford University, he joined the Centre National de la Recherche Scientifique (CNRS) in 1994. He is currently at the Laboratoire d’Etude des Microstructures jointly run by the Office National d'Etudes et de Recherches Aérospatiales (ONERA) and CNRS. He and his collaborators developed original simulations based on Dislocation Dynamics (DD) at the meso-scale. His main interests are in linking the dynamical properties of crystal defects and the mechanical properties of material. His research is concerned with the plastic properties of pure metals, alloys and heterostructures like thin films or Metallic Matrix Composites. He has written over 40 articles. The title of his lecture is ‘What simulations of dislocation dynamics tell us that is not in textbooks?’

From Dislocation to Strain Hardening: can Discrete Dislocation Dynamics simulations make it?

The objective of the present work is to obtain a constitutive formulation con-taining a minimum number of free parameters and having a predictive value of the strain hardening properties of FCC crystals. The constitutive model used derives from an expanded form of the scalar Kocks-Mecking model. The key element is a hardening matrix, in which the matrix describing interactions between slip systems plays a major role. The early steps of modeling consisted in checking, via a com-parison between atomistic and Discrete Dislocation Dynamics (DDD) simulations, that contact reactions between dislocations can be computed at the mesoscale to a good approximation. Further, the domain of formation of junctions and locks was investigated in terms of geometrical parameters for each type of interaction. The coefficients of the interaction matrix were then determined from model DDD simulations, which led to two major results. The hierarchy of the different types of interactions shows the major role played by the collinear interaction, which surpris-ingly, has been ignored up to now. In addition, the apparent interaction coefficients were found to depend on forest density, due to line tension effects not being properly accounted for in the Taylor relation. The last step consists in setting the full con-stitutive model by integrating all the available information. Examples of predicted stress-strain curves for FCC crystals in single and multiple slip are presented and compared to experimental data. The reason why models based on uniform dislo-cation densities can reproduce single crystal behavior in monotonic deformation is discussed in the light of DDD simulations of dislocations patterning.

Aránzazu del Campo

Max-Planck-Institut für Metallforschung, Stuttgart, Germany

Born in 1972 in Coomonte (Spain), she studied Chemistry at the Universidad Complutense and Materials Engineering at the Universidad Politécnica in Madrid (Spain). She got her PhD degree in the Instituto de Ciencia y Tecnología de Polímeros (Madrid) in 2000 working in the field of liquid crystalline polymers. She then joined the Max-Planck-Institut für Polymerforschung in Mainz (Germany) as Marie Curie Fellow and started to work in the field of surface chemistry and nanotechnology. In 2003 she moved to the Universitá degli Studi di Urbino (Italy) and since 2004 she is leading the group “Complex, Multifunctional Surfaces” within the Department “Thin Films and biological Systems” at the Max-Planck-Institute in Stuttgart (Germany). Her group is mainly engaged in developing novel synthetic approaches for manufacturing hierarchical, chemically and topographically patterned surfaces. These are based on challengi5 papers in refereed journals and 4 book chapters.

Tailored surfaces with tunable adhesion

The interaction between two bodies in close proximity is strongly influenced by the chemical nature of their outmost molecular layer and their surface topography. The external control of these factors enables fine tuning of the resulting adhesion forces. Particular interesting are surface designs which enable strong but reversible attachment, or even selective adhesion. Biology provides spectacular examples which inspire our developments, eg. the hierarchical assembly of nanosized setae found in gecko’s feet which enable their effective locomotion, or the selective attachment or cells to surfaces with particular topographies and compositions. Artificial realisation of such properties requires the combination of materials and surface chemistry with micro and nanofabrication techniques to obtain complex and responsive surface designs. Novel developments based on wavelength sensitive materials and complex 3D topographies will be presented. These will allow us to control adhesion phenomena at different levels in multiple fields of modern technologies.