Hume-Rothery Award Symposium: Alloy Phase Chemistry at the Atomic Level - Opportunities and Challenges: Session II
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

Monday 2:00 PM
February 27, 2017
Room: 31C
Location: San Diego Convention Ctr

Session Chair: Dieter Isheim, Northwestern University; Duc Nguyen-Manh, Culham Centre for Fusion Energy

2:00 PM  Invited
Arranging Atoms for Fun and Profit: A Tale of Two Smiths: Greg Olson1; 1Northwestern University
    In the early 1980s, Morris Cohen’s dream of establishing the long-sought structural mechanism of early aging phenomena in ferrous martensites was brought to fruition through a collaboration with G.D.W. Smith whose atom-probe microanalysis confirmed the theoretical prediction of a Zener-order-induced spinodal instability of the BCT Fe-C solution, showing for the first time that the composition of the resulting high C modulations is of Fe8C stoichiometry. DFT calculations have since confirmed that this is the ground state of the BCT solution. Combining the atomic capability of G. D. W. Smith with the systems vision of C. S. Smith, a Materials Design Initiative was undertaken, where G. D. W. Smith extended the analysis of multicomponent alloys down to the nm scale of efficient strengthening dispersions. Smith’s leadership in 3D atom-probe development ultimately enabled full validation of the first commercial alloys to emerge from this design technology, now known as the Materials Genome.

2:30 PM  Invited
Solute Segregation to Migrating Ferrite/Austenite Interfaces: Hatem Zurob1; Brian Langelier1; Hugo Van Landeghem2; Andreas Korinek1; Baptiste Gault3; Gianluigi Botton1; 1McMaster University; 2SIMaP; 3Max-Planck Institut für Eisenforschung
    Recent developments of Electron Energy Loss Spectroscopy and Atom Probe Tomography techniques have allowed increasingly more accurate quantification of interface chemistry at the atomic level. The above techniques have recently been used to evaluate the segregation of substitutional alloying elements to ferrite/austenite interfaces during the austenite to ferrite transformation in steel. In the case of stationary and quasi-stationary interfaces, accurate quantitative measurements of solute segregation were obtained for a wide range of Fe-C-X systems. Efforts to evaluate solute segregation to moving interfaces proved to be much more difficult due to the evolution of contact conditions during quenching. Some of the difficulties encountered, including the breakaway of the interface from its solute atmosphere, will be discussed. Examples in which interface segregation was successfully evaluated as a function of the velocity of the moving interface will also be discussed.

3:00 PM  
Microstructural Characterization of Mn-Ni-Si Precipitates in Reactor Pressure Vessel Steels from the High Fluence Intermediate Flux UCSB ATR-2 Irradiation: Nathan Almirall1; Peter Wells1; Takuya Yamamoto1; G. R. Odette1; Randy Nanstad2; Keith Wilford3; Tim Williams3; Lynne Ecker4; David Sprouster4; 1University of California Santa Barbara; 2Oak Ridge National Laboratory; 3Rolls Royce; 4Brookhaven National Laboratory
    Some initial results from the UCSB Advanced Test Reactor (ATR-2) neutron irradiation experiment (high fluence, intermediate flux) will be discussed. UCSB ATR-2 fills a critical gap in embrittlement data and understanding, especially since current models systematically underpredict ductile-to-brittle transition temperature shifts at high fluence. Recent research has demonstrated the existence of high volume fractions of intermetallic Mn-Ni-Si precipitate (MNSP) phases which contribute to embrittlement at high fluence and has generated significant insight into their character. This presentation covers microstructural characterization of MNSPs in a new subset of alloys procured by Rolls Royce for UCSB ATR-2 with varying levels of Ni, Mn, and Si, designed to expand RPV composition range and explore potential for tougher and higher strength steels in advanced reactors. A wide range of techniques were used including atom probe tomography (APT); (b) small angle neutron scattering (SANS); (c) small angle x-ray scattering (SAXS) and X-ray diffraction (XRD).

3:20 PM Break

3:40 PM  Invited
Nanoalloys & Nanoparticles for Catalysis: Insights from Atom Probe Tomography & Complementary Techniques: Paul Bagot1; Eric Marceau2; Anne-Félicie Lamic-Humbolt3; Daniel Haley1; Tomas Martin1; Michael Moody1; George Smith1; Qifeng Yang1; Tong Li4; 1University of Oxford; 2Université Lille 1; 3Université Pierre et Marie Curie; 4Ruhr-Universität Bochum; Max-Planck-Institut für Eisenforschung
    Heterogeneous catalysts underpin a vast range of processes covering including chemical refining, pollution control and energy production. At the heart of these catalysts are metal particles/surfaces, often using a number of elements to give the desired performance, selectivity and stability. However the exact surface structure and composition of the alloys formed at the gas-metal interface is poorly understood, due to the inherent complexities of the reactive environment and catalyst form. Atom Probe Tomography has become a powerful tool to shed light on many of these details, offering new insights into how both model and real catalyst systems are engineered, along how they respond to their operating conditions. This talk will highlight progress in this vital field, outlining advances in both instrumental technologies and efforts to combine APT with a growing range of experimental and modelling tools to help develop better catalysts for future applications.

4:10 PM  
Grain Boundaries in Molybdenum. The Role of Segregation for an Improved Ductility: Katharina Babinsky1; Sophie Primig2; Wolfram Knabl3; Alexander Lorich3; Helmut Clemens1; Verena Maier-Kiener1; 1Montanuniversität Leoben; 2UNSW Australia; 3Plansee SE
    Combining mechanical properties with chemical information on the nanometer scale have become a key approach in recent characterization techniques of metals and their alloys. The availability of advanced high-resolution characterization techniques such as the three-dimensional atom probe facilitates a detailed investigation of material´s interfaces on the atomic level. For Molybdenum and its alloys it is shown how to correlate atom probe tomography with mechanical testing on different length-scales. The direct correlation of strength and ductility with segregation mechanisms significantly helps to understand the intergranular fracture of molybdenum. Therefore, high-angle grain boundaries of recrystallized and as-deformed molybdenum are studied and described by the interfacial excess values of the segregation over the disorientation of the grain boundaries. Furthermore, the grain boundaries of molybdenum model alloys, which are showing a fracture mode change, are analyzed and compared to pure molybdenum. An outlook for improved ductility of molybdenum focusing on segregated elements is given.

4:30 PM  
Prediction of Segregation Induced Precipitation at Dislocations via Atomistic Simulations: Chad Sinclair1; Evgeniya Dontsova2; Joerg Rottler1; 1University of British Columbia; 2University of Houston
    There are many problems in materials science for which mean-field models are inappropriate. An example is precipitation in the vicinity of a dislocation. The presence of the long-range strain field of the dislocation makes both the local thermodynamics and kinetics spatially and temporally complex and not easy to capture without information about the local details of the dislocation. In this work we have used a recent adaptation of the “diffusive molecular dynamics” (DMD) model to examine the precipitation of an ordered phase at edge dislocations in the Al-Mg system. It is found that segregation of Mg lowers the barrier for nucleation of the ordered phase to zero, allowing for a “barrierless” first order transition. It will be shown that this has similarities to, but is distinct from, dislocation induced precipitation in systems exhibiting a chemical spinodal. These results will be compared with experimental observations of ordered phase formation at dislocations.

4:50 PM  
Local Order and Lattice Dynamics in a Shape Memory Strain Glass Alloy: Paul Stonaha1; Michael Manley1; 1Oak Ridge National Laboratory
    The magnetocaloric effect describes the coupling between a materials temperature and its magnetic state. Modern magnetocaloric devices employ materials which undergo a change in magnetic order coinciding with a martensitic (first-order) phase transition. A drawback of the martensitic transformation is the requirement of large magnetic fields (>2T) and the accompanying structural hysteresis. In this talk, we discuss the magnetocaloric effect in the shape memory alloy Ni45Co5Mn36.6In13.4 near its Curie temperature. We present diffuse neutron and X-ray scattering measurements and discuss the corresponding implied local order within the material. We show this material has a large change in the phonon entropy across the transition driven by the low lying TO [H00] phonon, and that the energy of this phonon changes with an applied magnetic field. Finally, we present the results of frozen phonon calculations that show how the phonon couples to magnetism at the atomic level.