Computational Thermodynamics and Kinetics: Defects and Kinetics
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Nana Ofori-Opoku, Canadian Nuclear Laboratories; Jorge Munoz, University of Texas at El Paso; Sara Kadkhodaei, University Of Illinois Chicago; Vahid Attari, Texas A&M University; James Morris, Ames Laboratory
Tuesday 2:00 PM
February 25, 2020
Room: 33C
Location: San Diego Convention Ctr
Session Chair: David Strubbe, University of California, Merced; Haixuan Xu, University of Tennessee
2:00 PM Invited
Thermodynamics and Kinetics of Defects in Perovskite Oxide Superlattices: Haixuan Xu1; Lipeng Zhang2; Valentino Cooper3; Paul Kent3; 1University of Tennessee; 2Beijing University of Chemical Technology; 3Oak Ridge National Laboratory
Complex oxide superlattices sometimes exhibit novel physical properties that do not exist in the constituent oxides. In this talk, we focus on the fundamental properties of point defect in the prototypical superlattice systems. Particularly, the thermodynamics and kinetics of defects in perovskite oxide superlattice consisting of SrTiO3 and PbTiO3 are determined using first-principles calculations in combination with kinetic Monte Carlo (KMC) simulations. The effects of various structural distortion mode in the superlattices, including octahedral rotation, polar modes, and interfacial effects on the oxygen vacancy formation energies will be discussed. The defect trajectories obtained from KMC simulations reveal that defect dynamics can be confined within a few atomic layers of the superlattices, leading to two-dimensional planar diffusion. This study also shows that the dominant vacancy position may vary in the superlattices, depending on the superlattice structure and stacking period, contradicting the common assumption that point defects reside at interfaces.
2:30 PM
{11-21} Twin Nucleation in HCP Rhenium from < c+a > Edge Dislocations: Lu Jiang1; Velimir Radmilović2; Julian Sabisch3; Liang Qi4; Andrew Minor1; Daryl Chrzan1; Mark Asta1; 1University of California, Berkeley; 2University of Belgrade; 3Sandia National Laboratories; 4University of Michigan
Dislocation slip and twinning are two essential plastic deformation mechanisms in materials, which impact the mechanical properties. An anisotropic elasticity model is developed based on density functional theory calculated material parameters to understand the unique mechanical properties of rhenium relative to other HCP metals. Specifically, rhenium shows predominant twinning in the {11-21} system, and restricted < c+a > dislocation slip. The mechanism of {11-21} twin nucleation from < c+a > edge dislocation is predicted to be favored in rhenium regardless of the stress condition while limited or conditionally operative in other HCP metals. The model thus provides insights into the origins of the relatively unique deformation modes in rhenium, which are supported by high-resolution electron microscopy results. The elasticity model can be further used in alloy design for identifying possible replacements for rhenium in high-temperature structural applications. This research is supported by the Office of Naval Research under grant N00014-16-1-3124.
2:50 PM Invited
Molecular Dynamics Simulation of Diffusion, Dislocation and Grain Boundary Migration in Austenitic Steels: Mikhail Mendelev1; Valery Borovikov1; 1Ames Laboratory
While the austenitic steels have numerous applications, the atomistic simulation of their properties were rather limited until now due to the lack of reliable semi-empirical potentials. We recently developed a Finnis-Sinclair potential which correctly reproduces the key thermodynamic properties of the Fe-Ni-Cr alloys including high temperature elastic properties, melting temperatures of pure metals, high temperature fcc-bcc transformation and formation enthalpies of the fcc-based and liquid solutions. In the present talk, we will review the molecular dynamics (MD) simulations performed utilizing this potential. First, we will discuss the temperature and concentration dependences of the point defect formation energies and the effect of Ni and Cr on the vacancy formation energy and entropy obtained directly from MD simulation (without relying on quasiharmonic approximation). Next, we will discuss how the addition of Ni and Cr affect the dislocation migration. Finally, we will compare the grain boundary migration in fcc Fe and austenitic steels.
3:20 PM
Temperature-dependent Kinetic Pathways for Jog-pair Nucleation in FCC Metals: Anas Abu-Odeh1; Maeva Cottura2; Mark Asta1; 1University of California, Berkeley; 2Institut Jean Lamour, CNRS
The dislocation climb efficiency of a metal under a specific environment can dictate how it responds under creep, annealing, and irradiation conditions. Here we present energetics from classical atomistic simulations of jog-pair structures using molecular statics, simulated annealing, and the nudged-elastic band (NEB) method as inputs to a climb efficiency model for Al and Cu. Given the low stacking fault energy (SFE) of Cu, there exists a variety of kinetic pathways for jog-pair formation which can vary its climb efficiency. Our method presents possible pathways for a jog-pair spanning one climb plane, but can be extended to an arbitrary number of climb planes as well as the inclusion of stress. These generally neglected considerations are crucial for the development of predictive mesoscale models of dislocation climb of low-SFE metals.
3:40 PM Break
3:55 PM Invited
Atomistic and Mesoscale Modeling of Nanoscale Sintering: Applications to Additive Manufacturing: Maher Alghalayini1; Fadi Abdeljawad1; 1Clemson University
Recently, several solid-state additive manufacturing (AM) techniques have demonstrated the ability to fabricate complex 3D objects with a nanometric feature size. While such techniques differ in their operating principles, sintering of nanoscale particles is a key aspect of the AM process. Herein, atomistic studies, employing hybrid Monte Carlo-Molecular Dynamics schemes, are used to examine the role of alloying and grain boundaries (GBs) in densification rates. A recently developed mesoscale phase field model is used to examine sintering kinetics of nanoscale powder compacts over diffusive scales. Several statistical and topological metrics are employed to quantify microstructural evolution and pore shrinkage rates. In broad terms, our modeling approach provides future avenues to explore evolving morphologies and interfacial phenomena in AM.
4:25 PM Invited
Structure and Properties of Ni-doped MoS2: Phase Diagrams, Raman Spectra, and Solid Lubrication: David Strubbe1; 1University of California, Merced
MoS2 can be used as a solid lubricant for space. Preliminary studies suggest doping with Ni can reduce friction and wear, but the structure and mechanisms remain unclear [MR Vazirisereshk, A Martini, DA Strubbe, and MZ Baykara, Lubricants 7, 57 (2019)]. We use density functional theory (DFT) to study bulk and monolayer Ni-doped MoS2, in various polytypes and doping levels. We consider formation energies for Mo or S substitution, intercalation, or adsorption, to build up a phase diagram, and predict stable phases or phase segregation. We compute corresponding Raman spectra to enable experimental identification. We additionally calculate elastic properties and potential energy for sliding to connect to atomic-force microscopy friction experiments, and use our data to parametrize classical force fields for molecular dynamics that can directly address friction and wear on larger length and time scales, and reveal mechanisms of tribological performance.
4:55 PM
A Phase-field Method for Modeling Solute Segregation at Interphase Boundary in Binary and Ternary Alloys: Sourabh Kadambi1; Srikanth Patala1; 1North Carolina State University
Precipitate coarsening limits the operating temperatures of age-hardened structural alloys. Experimental and theoretical findings suggest that solute segregation at the interphase boundary (IB) can reduce the IB energy and stabilize the precipitation microstructure against coarsening. In this talk, I present a phase-field model that describes solute segregation to the interphase boundary in binary and ternary component systems. The proposed modeling framework can incorporate bulk thermodynamics and interfacial free energies. Analytical equilibrium solutions for the flat boundary case can be derived and excess IB quantities can be evaluated independent of the Gibbs dividing surface convention. Under the regular solution approximation, computational studies elucidating the dependence of the IB energy and segregation on temperature, composition and free-energy model-parameters will be presented. The model is consistent with the Gibbs adsorption equation, and hence, it will be possible to compare the predicted segregation behavior with experiments and atomistic simulations.
5:15 PM
Revisiting the Early Stages of Precipitation in Al-Cu Alloys: Kang Wang1; William Soffa1; Bi-Cheng Zhou1; 1University of Virginia
The early stages of precipitation in Al-Cu alloys, an epitome of the ubiquitous precipitation phenomenon responsible for improved strength of alloys, is fascinating due to the complex interplay between chemical and strain energies. Much of the studies on this topic focused on the transitions from Guinier-Preston (G.P.) zones to θ' (Al2Cu). The very nature for the formation of G.P. zones, esp. their relations with the ordering / clustering tendencies under chemical and elastic interactions, remains unclear. In the current study, the structure, stability and formation of G.P. zones are examined by the combined first-principles calculations, mixed-space cluster expansion and Monte Carlo simulations. The thermodynamics for nucleation of G.P. zones are analyzed and the metastable phase diagram with the G.P. zones and θ' is constructed.