Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A18: Metals Modeling Phase Transitions and Application |
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Sponsoring Units: DCMP Chair: Oleg Matveev, Georgetown University Room: 277 |
(Author Not Attending)
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A18.00001: Pressure-induced core-level crossing transitions in 5d metals. Igor Abrikosov Considering hexagonal closed-packed Os compressed to over 770 GPa, we discuss the anomaly observed experimentally in the behavior of the unit cells parameters ratio c/a at about 440 GPa. We argue that the anomaly is related to a new type of electronic transition, the core level crossing (CLC) transition, associated with interactions between the core electrons induced by pressure [1]. By carrying out a systematic theoretical study for all metals of the 5d series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at $\approx $1500 GPa, at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements [2]. [1] L. Dubrovinsky \textit{et al.}, Nature 525, 226--229 (2015). [2] A. A Tal \textit{et al.}, Phys. Rev. B 93, 205150 (2016). [Preview Abstract] |
Monday, March 13, 2017 8:12AM - 8:24AM |
A18.00002: Finite Size Scaling of the First Order Transition of Molecular Systems Ka Ming Tam, Brian Novak, Nicholas Walker, Dorel Moldovan, Mark Jarrell The calculation of the melting temperature remains an important challenge in the simulation of molecular systems. The conventional method based on stabilizing the co-existence of liquid and solid phases requires rather large system sizes. This is problematic for ab-initio simulations as they are often restricted to small systems of a couple hundreds of atoms. The first order transition, which melting is a prominent example, has been studied in the context of other statistical physics models. We employ some of these techniques to predict the melting point. A key concept of understanding the phase transition is in the energy distribution. We study the energy distribution of molecular systems by calculating the ratios of different cumulants. They show behaviors expected for the first order transition and thus finite size scaling can be used to extract the transition temperature. In contrast to the conventional co-existence method, large system sizes are not necessary. The prediction can be systematically improved by better sampling of the energy distribution, and efficiently utilizes parallel simulations. [Preview Abstract] |
Monday, March 13, 2017 8:24AM - 8:36AM |
A18.00003: Resolving the structure and properties of $\tau_1$-Cr-Ni-Al for high temperature protective applications J. W. Simonson, J. E. Nicasio, H. Ilyas, J. Pabla, K. Horvat, J. C. Misuraca Increasing the temperature of the steam in turbine power plants enhances thermal efficiency while reducing CO$_2$ emissions. Exposed steel components, however, must be coated to withstand the harsh environments present in next-generation advanced ultra-supercritical plants. Proposed coating materials must exhibit low density, high hardness, high toughness, excellent oxidation resistance, and low thermal conductivity. With an eye towards satisfying this diverse array of requirements, we report the properties of the so-called $\tau_1$ phase of Cr-Ni-Al. We resolve the previously controversial composition and crystal structure of this material. The complex structure is composed of distorted icosahedra and octahedra of Al, with nearest-neighbor transition metal-Al bond lengths as short as 2.4 $\AA$, far shorter than typical distances in Ni-Al and Cr-Al binaries. Accordingly, Vickers hardness is $6.88\pm0.13$ GPa, as hard as extra-high-hardness armor plating at only 45\% the density. We discuss these properties in light of the result of transport and oxidation resistance measurements. The apparent dependencies of these properties on crystal structure suggests new criteria for materials research. [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 8:48AM |
A18.00004: Sensitivity of Force Fields on Mechanical Properties of Metals Predicted by Atomistic Simulations Seyed Moein Rassoulinejad-Mousavi, Yuwen Zhang Increasing number of micro/nanoscale studies for scientific and engineering applications, leads to huge deployment of atomistic simulations such as molecular dynamics and Monte-Carlo simulation. Many complains from users in the simulation community arises for obtaining wrong results notwithstanding of correct simulation procedure and conditions. Improper choice of force field, known as interatomic potential is the likely causes. For the sake of users' assurance, convenience and time saving, several interatomic potentials are evaluated by molecular dynamics. Elastic properties of multiple FCC and BCC pure metallic species are obtained by LAMMPS, using different interatomic potentials designed for pure species and their alloys at different temperatures. The potentials created based on the Embedded Atom Method (EAM), Modified EAM (MEAM) and ReaX force fields, adopted from available open databases. Independent elastic stiffness constants of cubic single crystals for different metals are obtained. The results are compared with the experimental ones available in the literature and deviations for each force field are provided at each temperature. Using current work, users of these force fields can easily judge on the one they are going to designate for their problem. [Preview Abstract] |
Monday, March 13, 2017 8:48AM - 9:00AM |
A18.00005: Properties of liquid Ti alloys from electrostatic levitation experiments and simulation Brian Novak, Jonathan Raush, Xiaoman Zhang, Dorel Moldovan, Wenjin Meng, Shengmin Guo Accurate thermophysical property data for liquid metals and alloys are important for the development of realistic simulations of laser-based 3D printing processes. We are using the container-less electrostatic levitation (ESL) method, molecular simulation, and CALPHAD calculations to obtain such data for Ti alloys. We performed vacuum ESL measurements of viscosity and surface tension with an oscillating drop technique at NASA MSFC on molten elemental Ti, Ti-xAl binaries (x $=$ 0-10 wt{\%}), Ti-6Al-4V, and Ti-6Al-4V-10Mo which showed improved mechanical properties compared with traditional $\beta $ Ti alloys. We also used classical molecular simulations to obtain viscosities and surface tensions for Ti-xAl. Pair distribution functions, diffusivities, and vapor pressures were also obtained from simulations. The simulated viscosities and surface tensions for pure Ti agree well with the ESL data while the Ti-xAl viscosities have the same trends as the ESL data, but not quantitative agreement. Chemical activity and Gibbs free energy of Ti-10Al were generated using the CALPHAD technique and compared to experimental values. [Preview Abstract] |
Monday, March 13, 2017 9:00AM - 9:12AM |
A18.00006: Residual Stress Analysis in Welded Component. Shahab Rouhi, Sanichiro Yoshida, Fumiya Miura, Tomohiro Sasaki Due to local heating, thermal stresses occur during welding; and residual stress and distortion result remain welding. Welding distortion has negative effects on the accuracy of assembly, exterior appearance, and various strengths of the welded structures. Up to date, a lot of experiments and numerical analysis have been developed to assess residual stress. However, quantitative estimation of residual stress based on experiment may involve massive uncertainties and complexity of the measurement process. To comprehensively understand this phenomena, it is necessary to do further researches by means of both experiment and numerical simulation. In this research, we conduct Finite Element Analysis (FEA) for a simple butt-welded metal plate specimen. Thermal input and resultant expansion are modeled with a thermal expansion FEA module and the resultant constitutive response of the material is modeled with a continuous mechanic FEA module. The residual stress is modeled based on permanent deformation occurring during the heating phase of the material. Experiments have also been carried out to compare with the FEA results. Numerical and experimental results show qualitative agreement.~ [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:24AM |
A18.00007: Grain boundary segregation in phase separating nanocrystalline alloys Fadi Abdeljawad, Ping Lu, Nicolas Argibay, Stephen Foiles Grain boundary (GB) solute segregation has been proposed as a route to mitigate grain growth in nanocrystalline (NC) metals and stabilize their structures. Based on a diffuse interface model, we examine grain growth dynamics in immiscible NC alloys, where an interesting effect emerges due to GB segregation and bulk phase separation processes. Analytical treatments identify regimes, where the reduction in GB energy is significant. Simulation results reveal that the stability and solute partitioning between bulk and GB regions are a manifestation of the competing effects of GB segregation and alloy phase separation. More specifically, in systems with low GB segregation, precipitation of solute-rich domains and associated GB pinning effects lead to sluggish grain growth rates. In contrast, GB solute segregation plays a more pronounced role as the heat of segregation increases in comparison with bulk heat of mixing. In broader terms, our treatment provides a framework to examine both bulk alloy and interfacial effects and their roles on the stability of NC metals. [Preview Abstract] |
Monday, March 13, 2017 9:24AM - 9:36AM |
A18.00008: Crystal gene: Common motifs transcending crystals, glasses, and liquids Feng Zhang, Yang Sun, Zhuo Ye, Yue Zhang, Xiaowei Fang, Zejun Ding, Cai-Zhuang Wang, Mikhail Mendelev, Ryan Ott, Matthew Kramer, Kai-Ming Ho We establish through typical metallic systems Cu-Zr and Al-Sm the concept of ``crystal gene'', that is, structural order in the short-to-medium range order that transcends crystals, liquids, and glasses. With such a connection between crystalline and amorphous phases, a mature toolset for treating crystals can be used to assist the identification of complicated structural order in amorphous systems, which is a fundamental difficulty in physics and materials science. In addition, as demonstrated in the example of the Al$_{90}$Sm$_{10}$ system, the crystal gene persists from liquid to crystalline phases during the crystallization processes observed in experiments. Therefore, the identification and quantification of the crystal gene bring new insight into the atomistic transformation mechanism from the amorphous to various metastable crystalline phases, which can ultimately lead to a better understanding of phase selection in metallic alloys. [Preview Abstract] |
Monday, March 13, 2017 9:36AM - 9:48AM |
A18.00009: Effect of sub-Tg annealing on CuZr and AlSm glasses: A molecular dynamics study Yang Sun, Feng Zhang, Yue Zhang, Zhuo Ye, Mikhail Mendelev, Cai-Zhuang Wang, Kai-Ming Ho Cu65Zr35 and Al90Sm10 glasses, which represent strong and marginal binary metallic glass formers, respectively, were developed with a sub-Tg annealing method [1--3] using Molecular Dynamics simulations. The short-range order (SRO) in both systems was characterized based on the concept of ``crystal gene'' that we established recently [4]. Furthermore, we found that while the local clusters representing the dominant short-range order form an ever-more pronounced interpenetrating network with slower cooling rates in Cu65Zr35 glasses, the interpenetration of SRO in Al90Sm10 glasses only shows a weak dependence on the cooling rate. This clear difference in the connectivity of the SRO, which can characterize the medium-range order (MRO), could contribute to the different glass forming abilities of both systems. [1] F. Zhang et al., Appl. Phys. Lett. 104, 61905 (2014). [2] Y. Zhang et al., Phys. Rev. B 91, 64105 (2015). [3] Y. Sun et al., J. Appl. Phys. 120, 15901 (2016). [4] Y. Sun et al., Sci. Rep. 6, 23734 (2016). [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:00AM |
A18.00010: Tuning the Second-Order Structural Transition in the Compound MnAs via Structural Anisotropy B. D. White, K. Huang, I. K. Lum, J. J. Hamlin, S. Jang, G. J. Smith, J. W. Simonson, C. S. Nelson, M. C. Aronson, M. B. Maple The second-order structural phase transition in MnAs is typically observed near $T_S$ = 400 K; however, magnetization and specific heat measurements on MnAs single crystals that were grown in a molten Sn flux revealed a significantly lower transition temperature of $T_S~\simeq$ 353 K. The structural phase transition at $T_S$ is thought to be governed by the dependence of a soft phonon mode on unit cell volume. Measurements of the thermal expansion on these single crystals uncovered several differences in the volume’s temperature dependence when compared to other reports for MnAs. While such differences might be partially responsible for the anomalously low value of $T_S$, we also observed a suggestive correlation between the ratio of hexagonal lattice parameters, $c/a$, and $T_S$. This second observation suggests that the degree of structural anisotropy in MnAs could play an important and heretofore unappreciated role in tuning $T_S$. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A18.00011: Thermodynamic properties by equation of state and from Ab initio molecular dynamics of liquid potassium under pressure Huaming Li, Yanting Tian, Yongli Sun, Mo Li In this work, we apply a general equation of state of liquid and Ab initio molecular-dynamics method to study thermodynamic properties in liquid potassium under high pressure. Isothermal bulk modulus and molar volume of molten sodium are calculated within good precision as compared with the experimental data. The calculated internal energy data and the calculated values of isobaric heat capacity of molten potassium show the minimum along the isothermal lines as the previous result obtained in liquid sodium. The expressions for acoustical parameter and nonlinearity parameter are obtained based on thermodynamic relations from the equation of state. Both parameters for liquid potassium are calculated under high pressure along the isothermal lines by using the available thermodynamic data and numeric derivations. Furthermore, Ab initio molecular-dynamics simulations are used to calculate some thermodynamic properties of liquid potassium along the isothermal lines. [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A18.00012: Magnetostriction of Liquid Metals Rishi Bhandia, Jason C. Cooley, Seth D. Imhoff The study of magnetic field-driven microstructural effects is in its infancy, but results have been promising. Previous work showed that these effects are easily observable in some systems, suggesting that magnetic fields could be used to control and engineer various micro-structural properties. The energy scales for crystallite rotation in the liquid and on the viscosity of the melt are known. However, the fundamental energy scale of the magnetic field interaction with the liquid and solid near the melting point is not. In this talk, we present magnetostriction data on liquid elements and alloys that will help us understand the energy scale of these processes and develop a theoretical understanding of solidification in magnetic fields. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A18.00013: Melting and stress response of metallic alloys using molecular dynamics Juana Moreno, Sarah Bartley Selective laser melting of powdered metals holds the promise of revolutionizing additive manufacturing. However, there are many unanswered questions about how the initial conditions of the melting and the composition of the powder determine the final alloy properties. In this study, we will run molecular dynamics simulations with an embedded-atom potential. Using different melting conditions for a range of compositions of NiAl alloys, we will explore the formation of different phases, grain structures, and segregation of impurities to interfaces and grain boundaries. We will identify the most promising structures and study their stress response to better understand the appearance of dislocations and the interaction between dislocations and interfaces in nanoscale metallic samples. We will apply uniaxial compression and nanoindentation to explore dislocation starvation and hardening and how the strength of the structure depends on diverse deformation process such as grain rotation, twinning, and stress-driven grain coarsening. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A18.00014: Electrophobic interaction induced impurity clustering in metals Guang-Hong LU, Hong-Bo ZHOU, J AGUIAR, Feng LIU Helium is a typical impurity in metals, which is produced from transmutation reactions in both fission and fusion. It is well known that He atoms are energetically favorable clustering with each other, resulting in mechanical property degradation of metals, which is originated from the self-trapping of He. Here, we introduce the concept of electrophobic interaction, analogous to hydrophobic interaction, for describing the behavior of impurity atoms in a metal, a “solvent of electrons”. We demonstrate that there exists a form of electrophobic interaction between impurities with closed electron shell structure, which governs their dissolution behavior in a metal. Using He, Be and Ar as examples, we predict by first-principles calculations that a clustering energy due to the electrophobic interaction follows a universal power-law scaling with the number of atoms (N) dissolved in a free electron gas, as well as W or Al lattice, as Ec $\propto $ (N\textasciicircum 2/3 -- N). This new concept significantly advances our fundamental understanding and capacity to predict the solute behavior of impurities in metals, a useful contribution to be considered in future material design of metals for nuclear, metallurgical, and energy applications. [Preview Abstract] |
Monday, March 13, 2017 10:48AM - 11:00AM |
A18.00015: Quantum Mechanics of Chemisorption on Palladium Clusters. Chloe Robinson, Ajit Hira, Jose Pacheco, Ruben Rivera In view of our interest in the chemisorption of different atomic and molecular species on small clusters of metallic elements, we present theoretical results on the interactions of H, H$_{2,}$ O and CO adsorbates with Pd$_{n}$ clusters (n $=$ 2 thru 60). Transition-metal clusters are specially suited for the study of quantum size effects, and for formation of metallic states, and are ideal candidates for catalytic processes. Hybrid ab initio methods of quantum chemistry (particularly the DFT-B3LYP model) are used to derive optimal geometries for the clusters of interest, including the influence of Jahn-Teller effects. We compare calculated binding energies, bond-lengths, ionization potentials, electron affinities and HOMO-LUMO gaps for the clusters. Of particular interest are the comparisons of binding strengths at the five important types of sites: edge (E), on-top (T), threefold sites, fourfold sites, and hexagonal sites. Effects of crystal symmetries corresponding to the bulk structures are investigated. Implications for the existing experimental results on icosahedral structures and cubic structures will be examined. The capacity of Pd clusters to adsorb H atoms will be compared to the capacity of other metallic clusters.. [Preview Abstract] |
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