Scientific Events

Intermetallic fascinated high temperature materials community for the last five decades. Starting with gamma TiAl, both Ti based and Ni based single phase intermetallics have been subject of extensive investigation. It took five decades for actual application in latest generation GE engine. However, very little attention has been given to multiphase multicomponent intermetallics. These, in particular eutectics, are abundant in the central regions of phase diagrams of ternary and higher components. With a hypothesis that they represent exciting opportunity, this talk will present the outline of our fairly extensive efforts in developing high temperature intermetallic composites based on a novel design of materials through microstructural engineering of intermetallics at nano scale. We shall concentrate on the Ni-Al-Zr system and show that unique complex multiphase microstructures could be developed containing intermetallics of Ni3Al, Ni5Zr, Ni7Zr2 and NiAl. The microstructures contain single or multiple coupled eutectics that are distributed seamlessly along the entire samples. For example, for an alloy Ni-12At%Al-11at%Zr, two intermetallic phases (Ni₃Al and Ni₅Zr) are seamlessly distributed along the entire sample with two different length scales and morphologies. Often these microstructures can be visualised by a 3D analysis that shows variations of connectivity among phases. Many of these alloys show strength in excess of 2GPa This architecture exhibits excellent high temperature microstructural stability, exceptional high strength with reasonable tensile ductility at high temperature. We show that this can be derived from an approach designed to exploit eutectic reactions that combine Intermetallics in a microstructural scale that restricts slip lengths to obtain both strength and ductility. Some of these alloys also have exceptional oxidation resistance that is retained up to a temperature of 973K. Finally we shall present some results of creep strength of these alloy that hints at the stress induced transformation. [more]

The design of Atom probe tomography (APT) at Oxford and Rouen universities for 25 years ago has been an outstanding breakthrough in the microscopy world. APT is the only analytical microscope able to provide 3D images of a material at the atomic scale [1]. Because of its ultimate spatial resolution (0.1 nm in depth, a few tenths of a nm at the sample surface), combined with its quantitativity of composition measurements, APT has played a major role in the investigation of the early stages of phase separation in solids. APT has also been the first instrument to show Cottrell atmospheres (tiny clouds of impurity atoms around dislocations in crystals) at the atomic-scale in the three dimensions of space [2]. A new breakthrough has been achieved ten years ago with the implementation of ultrafast pulsed laser (duration < 1ps) to atom probe tomography [3]. This new generation of laser-enhanced atom probe tomograph, designed in our lab and at Madison, USA, has opened the instrument to semi-conductors and oxides that are key materials in micro-electronics and nanosciences [4,5]. Correlative approaches combining TEM with APT has been shown to be crucial for more accurate APT reconstructions of microelectronics devices [6]. A key force of APT is that 3D reconstructions can be confronted at the same scale to kinetic Monte-Carlo simulations conducted on rigid lattice. This dual approach has been recently applied to phase separation in self-organised GeMn magnetic thin films [5]. In this talk, APT results will be confronted to simulations but also to analytical models dealing with precipitation kinetics (non-classical nucleation [7], coarsening in ternary systems, influence of precipitate size on their composition [8]). A recently developed analytical model dealing with nucleation, growth and coarsening in ternary systems including diffusion coupling between chemical species has revealed that the kinetic pathway does not necessarily follow the tie lines of phase diagram in agreement with APT experiments on model nickel base superalloys [9]. [1] D. Blavette, A. Bostel, J.M. Sarrau, B. Deconihout and A. Menand, 1993, Nature 363, 432 [2] D. Blavette, E. Cadel, A. Fraczkiewicz, A. Menand, 1999, Science 17, 2317 [3] B. Gault, F. Vurpillot, A. Vella, M. Gilbert, A. Menand, D. Blavette, B., 2006, Rev. Sci. Instr. 77, 043705 [4] S. Duguay, T. Philippe, F. Cristiano, D. Blavette, Applied Physics Letter (2010) 97, 242104 [5] I. Mouton, R, Larde, E. Talbot, C. Pareige, D. Blavette, JAP 115, 053515 (2014) [6] A. Grenier, R. Serra, G. Audoit, Jp Barnes, S. Duguay, D. Blavette, N. Rolland, F. Vurpillot, P. Morin, P. Gouraud, Applied Physics Letters 106, 213102 (2015) [7] T. Philippe, D. Blavette, Journal Of Chemical Physics, 135, 134508 1-3 (2011) [8] M. Bonvalet, T. Philippe, X. Sauvage, D. Blavette, Phil. Mag Vol. 94, N°26, 2956-2966 (2014) [9] M. Bonvalet, T. Philippe, X. Sauvage, D. Blavette, Acta Materialia 100 (2015) 169-177 [more]