Hume-Rothery Award Symposium: Alloy Phase Chemistry at the Atomic Level - Opportunities and Challenges: Session V
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Nuclear Materials Committee, TMS: Phase Transformations Committee
Program Organizers: Wei Xiong, University of Pittsburgh; Shuanglin Chen, CompuTherm LLC; Frederic Danoix, Université de Rouen; Indrajit Charit, University of Idaho

Wednesday 8:30 AM
March 1, 2017
Room: 31C
Location: San Diego Convention Ctr

Session Chair: Frederic Danoix, CNRS - Université de Rouen; Michael Moody, University of Oxford

8:30 AM  Invited
Outlooks for Atom Probe Microscopy: Simon Ringer1; 1The University of Sydney
    The atom probe microscope provides a flexible platform for high resolution mass spectrometry, field desorption microscopy, field ion microscopy and atom probe tomography. Significantly, by combining various information from these modalities, it has recently become possible to discern local crystallographic information. This innovation changes the way that we use the instrument—from a tool that was primarily for microanalysis to one that serves as an holistic microscope. This lecture will present recent developments undertaken primarily at the University of Sydney in atom probe microscopy. The post-experimental data workflow is reviewed in detail. Frontiers in mass spectrometry, the tomographic reconstruction, analysis and visualisation will be discussed. On the basis of these developments, it is proposed that an exciting era of integration is opening up, where computational techniques such as density functional theory approaches, and atomic-resolution microscopy can solve problems that were previously difficult or impossible by one approach alone.

9:00 AM  Invited
Combining Small Angle Scattering, Atom Probe Tomography and Differential Calorimetry for a Better Characterization of Solid Solution Decomposition: Frederic De Geuser1; Rosen Ivanov1; Laurent Couturier1; Alexis Deschamps1; Baptiste Gault2; 1SIMAP - CNRS - Univ. Grenoble Alpes; 2Max-Planck Institut für Eisenforschung
    While spatial resolution may not be an issue anymore with modern instruments, there are still multiple challenges associated with the study of the early stages of supersaturated solid solution decomposition. Well-formed precipitates are easy to identify on an image, but early decomposition products (clusters, early spinodal stages,…) are even complex to define. With examples from clustering and precipitation in Al-Cu based alloys and from spinodal decomposition of Cr in a stainless steel, we will show that via a common formalism, the combination of local real space atom by atom information (atom probe tomography) and global reciprocal space information (small angle scattering) can help building a statistical description of the solid solution. Together with differential scanning calorimetry, it will be shown to give a more complete picture of the reaction.

9:30 AM  Invited
Kinetic Pathways in Phase Separation Processes: Atom-Probe Tomography versus Modeling: Didier Blavette1; Isabelle Mouton2; Thomas Philippe3; Manon Bonvallet4; 1Normandie University; 2CEA; 3CNRS; 4KTH
    Because of its 3D imaging capabilities at the atomic scale, atom probe tomography (APT) has played a major role in the investigation of the early stages of phase separation in solids. 3D reconstructions can be confronted at the same scale to kinetic Monte-Carlo simulations conducted on rigid lattice. This dual approach has been applied to phase separation in self-organised GeMn magnetic thin films. In this talk, APT results will be confronted to simulations but also to analytical models dealing with precipitation kinetics (non-classical nucleation showing enrichment of nuclei during nucleation process, non-classical kinetic pathway during coarsening in ternary systems…). 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.

10:00 AM Break

10:20 AM  Invited
Atomic Scale Modeling of Phase Separation in Fe-Cr Alloys: Frederic Soisson1; 1CEA Saclay
    Fe-Cr alloys are the base of ferritic steels, which are used in a wide range of high-temperature applications. Below 600°C, they undergo a coherent decomposition between Fe-rich (α) and Cr-rich (α’) phases. The kinetics of α-α’ phase separation has been extensively studied, because of its industrial relevance but also as a typical case of spinodal decomposition. However many open questions remains e.g. on the Cr solubility limit, on the composition of the phases during the α’ precipitation, and on the segregation and precipitation behaviors under irradiation. Most of them are related to the special magnetic properties of Fe-Cr alloys. We present an atomic scale modeling of phase separation in Fe-Cr alloys, using ab initio calculations and Monte Carlo simulations. It provides an atomic description of the α-α’ microstructure: the size, shape and composition of α and α’ domains are directly compared to experimental – especially tomographic atom probe – observations.

10:50 AM  Invited
Spinodal Decomposition in FeCr Alloys: From Fundamental to Applications: Frederic Danoix1; Alexander Dahlstrom1; Didier Blavette1; Helena Zapolsky1; 1CNRS - Université de Rouen
    Atom probe tomography is recognised as a key technique for exploring materials down to the subnanometer scale. Among the many systems studied since the late 1960’, iron-chromium has received a continuous attention. Because of its ablity to detect iron and chromium composition fluctuation,combined with its mass and spatial resolutions, atom probe is the ideal technique for investigating this system. Fe-Cr exhibit a fundamental interest, as one of the only systems showing isotropic spinodal decomposion over a large range of composition and temperatures. For this reason, and for industrial reasons (in particular because of the so called 475°C embrittlement phenomenon in ferritic and martensitic stainless steels), it has been extensively investigated as a model system for studiying this phase transformation mechanism, in particular by the Oxford group under the guidance of G. Smith. Some of the early and more recent results on this system will be presented in this contribution.

11:20 AM  Invited
Phase Decomposition in Fe-Cr Alloys under Irradiation: Mukesh Bachhav1; Elaina Anderson1; G. Robert Odette2; Emmanuelle Marquis1; 1University of Michigan; 2University of California - Santa Barbara
    The Fe-Cr system is the basis for most of structural steels currently considered for nuclear applications. While simple in appearance, it presents experimental and theoretical challenges that if solved would provide unique insights into the processes controlling microstructure evolution under irradiation. Specifically the precipitation of the Cr-rich α′ phase appears to be particularly susceptible to dose rate. Fe-Cr alloys that exhibit α′ precipitation upon neutron irradiation, fail to do so upon ion irradiation at typical dose dose rates of the order of 10-4 dpa/s. We will summarize atom probe tomography analyses of ion- and neutron-irradiated Fe-Cr alloys and discuss technical limitations and impact of the findings.

11:50 AM Concluding Comments