Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H46: Metals I |
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Sponsoring Units: DCMP Chair: Duane Johnson, Ames Laboratory Room: 311 |
Tuesday, March 15, 2016 2:30PM - 2:42PM |
H46.00001: Multiscale modelling of gallium induced embrittlement in aluminium Venkata Sai Pavan Kumar Bhogireddy, Mira Todorova, Robert Spatschek, J\"org Neugebauer Liquid metal embrittlement is a degradation phenomenon in which a solid metal undergoes brittle failure when it is stressed while in contact with a liquid metal. The transition from ductile to brittle metal failure manifests itself by rapid crack propagations which reduces the elongation to failure ratio. Combining density functional theory calculations with continuum methods, we study the liquid metal embrittlement of aluminium in contact with gallium. Comparing ab initio calculated energies for a $\Sigma 3$ and a $\Sigma 5$ Al grain boundary and their corresponding surface energies in the presence and absence of Ga, we identify critical Ga concentrations which result in a weakening of the mechanical strength of aluminium. Parametrising the DFT results in continuum model we obtain the concentration as a function of the strain in the system. In a final step we extend this approach and compute the stress field induced by cracks in bulk and at grain boundaries. The stress field explains the large segregation of gallium atoms at the crack tip and the crack tip\textquotesingle s subsequent propagation. [Preview Abstract] |
Tuesday, March 15, 2016 2:42PM - 2:54PM |
H46.00002: Corrosion Thermodynamics of Magnesium and Alloys from First Principles as a Function of Solvation Krista Limmer, Kristen Williams, Jan Andzelm Thermodynamics of corrosion processes occurring on magnesium surfaces, such as hydrogen evolution and water dissociation, have been examined with density functional theory (DFT) to evaluate the effect of impurities and dilute alloying additions. The modeling of corrosion thermodynamics requires examination of species in a variety of chemical and electronic states in order to accurately represent the complex electrochemical corrosion process. In this study, DFT calculations for magnesium corrosion thermodynamics were performed with two DFT codes (VASP and DMol3), with multiple exchange-correlation functionals for chemical accuracy, as well as with various levels of implicit and explicit solvation for surfaces and solvated ions. The accuracy of the first principles calculations has been validated against Pourbaix diagrams constructed from solid, gas and solvated charged ion calculations. For aqueous corrosion, it is shown that a well parameterized implicit solvent is capable of accurately representing all but the first coordinating layer of explicit water for charged ions. [Preview Abstract] |
Tuesday, March 15, 2016 2:54PM - 3:06PM |
H46.00003: Role of defect coordination environment on point defects formation energies in Ni--Al intermetallic alloys Emrys Tennessen, James Rondinelli We present a relationship among the point defect formation energies and the bond strengths, lengths, and local coordination environment for Ni--Al intermetallic alloys based on density functional calculations, including Ni$_3$Al, Ni$_5$Al$_3$, NiAl, Ni$_3$Al$_4$, Ni$_2$Al$_3$ and NiAl$_3$. We find the energetic stability of vacancy and anti-site defects for the entire family can be attributed primarily to changes in interactions among first nearest neighbors, owing to spatially localized charge density reconstructions in the vicinity of the defect site. We also compare our interpretation of the local coordination environment with a DFT-based cluster expansion and discuss the performance of each approach in predicting defect stability in the Ni--Al system. [Preview Abstract] |
Tuesday, March 15, 2016 3:06PM - 3:18PM |
H46.00004: A high-throughput search for new ternary superalloys Chandramouli Nyshadham, Jacob Hansen, Corey Oses, Stefano Curtarolo, Gus Hart In 2006 an unexpected new superalloy, Co$_{3}$[Al,W], was discovered[1]. This new alloy is cobalt-based, in contrast to conventional superalloys, which are nickel-based. Inspired by this new discovery, we performed first-principles calculations, searching through 2224 ternary metallic systems of the form A$_{3}$[B$_{0.5}$C$_{0.5}$], where A = Ni/Co/Fe and [B, C] = all binary combinations of 40 different elements chosen from the periodic table. We found 175 new systems that are better than the Co$_{3}$[Al, W] superalloy. 75 of these systems are brand new---they have never been reported in experimental literature. These 75 new potential superalloys are good candidates for further experiments. Our calculations are consistent with current experimental literature where data exists.\\ \\ {\tiny \raggedright {\footnotesize [1] Sato $et$, $al$., ``Cobalt-base high temperature alloys. Science 2006; 312 (5770):90-1."} \\ } [Preview Abstract] |
Tuesday, March 15, 2016 3:18PM - 3:30PM |
H46.00005: High-throughput study of crystal structures and stability of strengthening precipitates in Mg alloys Dongshu Wang, Maxmilian Amsler, Vinay Hegde, James Saal, Ahmed Issa, Xiaoqin Zeng, Christopher Wolverton Age hardening, in which precipitates form and impede the movement of dislocations, can be applied to magnesium alloys in order to increase their limited strengthening behavior. To help clarify the energetics of precipitation hardening of Mg alloys, we employed first principles density functional theory calculations to elucidate both crystal structures and energetics of a very large set of precipitates in Mg alloys. We find the enthalpy changes of (stable and metastable) observed precipitates during the age hardening process are consistent with the experimental sequence of formation for many Mg binary alloys (Mg- \textbraceleft Nd, Gd, Y, Sn, Al, Zn\textbraceright ). For cases where the metastable precipitate crystal structure is unavailable, we search over several prototypes and predict structures/stoichiometries for several ternary precipitates. In addition, high-throughput calculations are performed to construct hcp-based based convex hulls, which assist the identification of coherent GP zones and new metastable phases in age-hardened hcp systems. [Preview Abstract] |
Tuesday, March 15, 2016 3:30PM - 3:42PM |
H46.00006: High hardness and superlative oxidation resistance in a pseudo-icosahehdral Cr-Al binary J. W. Simonson, R. Rosa, A. K. Antonacci, H. He, A. D. Bender, J. Pabla, W. Adrip, D. E. McNally, A. Zebro, P. Kamenov, G. Geschwind, S. Ghose, E. Dooryhee, A. Ibrahim, M. C. Aronson Improving the efficiency of fossil fuel plants is a practical option for decreasing carbon dioxide emissions from electrical power generation. Present limits on the operating temperatures of exposed steel components, however, restrict steam temperatures and therefore energy efficiency. Even as a new generation of creep-resistant, high strength steels retain long term structural stability to temperatures as high as $\sim973$ K, the low Cr-content of these alloys hinders their oxidation resistance, necessitating the development of new corrosion resistant coatings. We report here the nearly ideal properties of potential coating material Cr$_{55}$Al$_{229}$, which exhibits high hardness at room temperature as well as low thermal conductivity and superlative oxidation resistance at 973 K, with an oxidation rate at least three times smaller than those of benchmark materials. These properties originate from a pseudo-icosahedral crystal structure, suggesting new criteria for future research. [Preview Abstract] |
Tuesday, March 15, 2016 3:42PM - 3:54PM |
H46.00007: Ordering Transformations in High-Entropy Alloys Prashant Singh, Duane D. Johnson The high-temperature disordered phase of multi-component alloys, including high-entropy alloys (HEA), generally must experience segregation or else passes through partially-ordered phases to reach the low-temperature, fully-ordered phase. Our first-principles KKR-CPA-based atomic short-range ordering (SRO) calculations (analyzed as concentration-waves) reveal the competing partially and fully ordered phases in HEA, and these phases can be then directly assessed from KKR-CPA results in larger unit cells [Phys. Rev. B 91, 224204 (2015)]. For Al$_x$CrFeNiTi$_{0.25}$, Liu et al. [J Alloys Compd 619, 610 (2015)] experimentally find FCC+BCC coexistence that changes to BCC with increasing Al (x from 0-to-1), which then exhibits a partially-ordered B2 at low temperatures. CALPHAD (Calculation of Phase Diagrams) predicts a region with L2$_1$+B2 coexistence. From KKR-CPA calculations, we find crossover versus Al from FCC+BCC coexistence to BCC, as observed, and regions for partially-order B2+L2$_1$ coexistence, as suggest by CALPHAD. Our combined first-principles KKR-CPA method provides a powerful approach in predicting SRO and completing long-range order in HEA and other complex alloys. [Preview Abstract] |
Tuesday, March 15, 2016 3:54PM - 4:06PM |
H46.00008: KKR-DCA Thermodynamics for Cluster Short-Range Order with Full Charge Self-Consistency Dominic A. Biava, Duane D. Johnson The Dynamical Cluster Approximation (DCA) implemented in the Korringa-Kohn-Rostoker (KKR) electronic-structure method gives a systematically exact, \emph{course-grained} theory of the electronic states of substitutionally disordered alloys, including the effects of chemical short-ranged order (SRO). We implement the KKR-DCA within density functional theory (DFT) to calculate directly the charge self-consistent electronic contributions to the alloy grand potential. The KKR-DCA is combined with the chemical entropy from the Cluster Variation Method (CVM), which when minimized predicts the SRO directly. The calculated SRO has been tested in several metallic systems with agreement to measured values. For very large clusters, the KKR-DCA can be sampled, as done within Quantum Monte Carlo, and provides the charge self-consistent thermodynamic grand potential in complex alloys with SRO at finite temperature, at the same level as done for perfect ordered alloys in other electronic-structure methods at zero Kelvin. [Preview Abstract] |
Tuesday, March 15, 2016 4:06PM - 4:18PM |
H46.00009: The Effect of Disorder on Lattice Thermal Transport in Solid Solution Alloys Raina Olsen, Biswanath Dutta, German Samolyuk, Brian Sales, Ben Larson, Hongbin Bei, Eliot Specht, Malcolm Stocks Dramatic decreases in radiation damage for 3- and 4-component equiatomic single phase solid solution Ni-based alloys have been recently observed. The strongly decreased damage retention in these highly disordered materials is attributed to severe disruption of the pathways of energy dissipation away from atomic displacement cascades. Because the energy of an irradiating ion is primarily deposited into the lattice degrees of freedom, it is the lattice thermal conductivity that is most important to the dissipation of heat from damage events. Here we report measurements of phonon linewidths in NiCo, NiFe, and NiFeCoCr using inelastic neutron and X-ray scattering, showing a dramatic increase in phonon linewidth by a factor of 4 with increasing disorder. Measured phonon linewidths are shown in comparison to theoretical phonon linewidths originating from disorder calculated using the itinerant coherent potential approximation (I-CPA). Lattice thermal conductivity is calculated from the phonon properties, and compared to measurements of bulk thermal and electrical properties. The impact of the observed decrease in lattice thermal conductivity on damage resistance is discussed. [Preview Abstract] |
Tuesday, March 15, 2016 4:18PM - 4:30PM |
H46.00010: Extreme Chemical Disorder and the Electrical Transport Properties of Concentrated Solid Solution Alloys: From Binaries to High Entropy Alloys Replace this text with your abstract title G. Malcolm Stocks, German Samolyuk, Suffian Khan, Markus Daene, Sebastian Wimmer, Brian Sales, Hongbin Bei, Ke JIn We present the results of experimental and theoretical studies of electrical transport properties of a family of 2, 3, 4 and 5-component concentrated solid solution alloys (CSA) comprising subsets of the \textit{3d-} and \textit{4d}-transition metal elements Cr, Mn, Fe, Co, Ni and Pd. Many of this family of CSA show unusual mechanical, magnetic and transport properties as well as indications of increased radiation resistance that are clearly related to the underlying chemical disorder. Here we show the results of calculations of the electrical transport properties that are based on the \textit{ab initio} Korringa-Kohn-Rostoker coherent-potential-approximation (KKR-CPA) method for treating the effect of substitutional disorder, and necessary configurational averaging, on the underlying electronic structure. We compare calculated residual (T$=$0K) resistivities to corresponding experimental measurements and relate the variations in residual resistivity, which span almost two orders of magnitude, to the underlying electron structure. [Preview Abstract] |
Tuesday, March 15, 2016 4:30PM - 4:42PM |
H46.00011: Electronic origin of atomic-level stresses in High-Entropy Alloys Khorgolkhuu Odbadrakh, Takeshi Egami, Madhu Ojha, Don Nicholson, Malcolm Stocks High-entropy alloys are multi-component solid solutions in which four or more elements occupy the same crystallographic lattice sites with roughly equal compositions. The underlying chemical disorder gives rise to small local lattice distortions and atomic-level stresses, which are also disorders on their own. These disorders lead to radiation resistance and mechanical strength in high temperature environment, making HEAs alloys attractive candidates as nuclear materials. We report electronic origin of the atomic-level stresses based upon first-principles calculations using Locally Self-consistent Multiple Scattering theory method. Strong atomic-level stresses are present in HEAs due not only to the differences in the intrinsic atomic sizes but due to charge transfer among the elements. We suggest that the improved properties of HEAs originate mainly from the high magnitudes of atomic-level stresses in these complex disordered alloys. [Preview Abstract] |
Tuesday, March 15, 2016 4:42PM - 4:54PM |
H46.00012: ABSTRACT WITHDRAWN |
Tuesday, March 15, 2016 4:54PM - 5:06PM |
H46.00013: Ab Initio Investigation of He Bubbles at the Y$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$-Fe Interface in Nanostructured Ferritic Alloys Thomas Danielson, Eric Tea, Celine Hin Nanostructured ferritic alloys are promising materials candidates for the next generation of nuclear reactors due to their ability to withstand high temperatures, high pressures, high neutron flux and especially, the presence of high concentrations of transmutation product helium. As helium diffuses through the matrix, large number densities of complex oxide nanoclusters, namely Y$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$, Y$_{\mathrm{2}}$O$_{\mathrm{3}}$ and Y$_{\mathrm{2}}$TiO$_{\mathrm{5}}$, act as trapping sites for individual helium atoms and helium clusters. Consequently, there is a significant decrease in the amount of helium that reaches grain boundaries, mitigating the threat of pressurized bubble formation and embrittlement. In order to understand the helium trapping mechanisms of the oxides at a fundamental level, the interface between the nanoclusters and the iron matrix must be modeled. We present results obtained using density functional theory on the Y$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$-Fe interface where the structure has been modeled based on experimental observations. Helium has been added along the interface in order to investigate the influence of helium on the structure and to obtain thermodynamic and kinetic parameters of helium along the interface. [Preview Abstract] |
Tuesday, March 15, 2016 5:06PM - 5:18PM |
H46.00014: The impact of short-range forces on high-energy atom collisions in displacement cascades. German Samolyuk, Roger Stoller, Artur Tamm, Laurent Beland, G. Malcolm Stocks, Alfredo Caro, Lyudmila Slipchenko4, Yury Osetskiy, Alvo Aabloo, Mattias Klintenberg, Yang Wang Simulation of primary radiation damage formation in solid materials involves collisions between atoms with a few hundred keV of kinetic energy. As a result, during these collisions, the distance between two colliding atoms can approach 0.05 nm. For such small atomic separations, interatomic potentials significantly underestimate the potential energy. The common practice involves using a screened Coulomb pair potential to describe the high-energy interactions and to smoothly join this to the equilibrium potential. However, there is no standard method for choosing the joining parameters and defect production during cascade evolution has been shown to be sensitive to how the joining is done. We developed a new procedure, which includes the use of ab initio, calculations to determine the pair interactions at intermediate distances, together with systematic criteria for choosing the joining parameters. Results are presented for the case of nickel. [Preview Abstract] |
Tuesday, March 15, 2016 5:18PM - 5:30PM |
H46.00015: ABSTRACT WITHDRAWN |
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