Grain Boundaries, Interfaces, and Surfaces: Fundamental Structure-Property-Performance Relationships: Segregation
Sponsored by: ACerS Basic Science Division
Program Organizers: Shen Dillon, University of California, Irvine; Wolfgang Rheinheimer, University of Stuttgart; Catherine Bishop, University of Canterbury; Ming Tang, Rice University; John Blendell, Purdue University; Wayne Kaplan, Technion - Israel Institute Of Technology; Melissa Santala, Oregon State University

Tuesday 8:00 AM
October 11, 2022
Room: 323
Location: David L. Lawrence Convention Center

Session Chair: Shen Dillon, University of California, Irvine; Ming Tang, Rice University


8:00 AM  
Computational Modeling of Surface Segregation Dynamics in Cu-Au Alloys: Guofeng Wang1; Siming Zhang1; 1University of Pittsburgh
    Surface segregation in multicomponent materials results in a surface layer with its own set of composition and structure different from the bulk ones, which serves as an important model system to advance understanding of interface dynamics in nanoscale systems for future materials design. In this study, we applied the computational methods to predict the surface segregation profiles in Cu-Au alloys. For Cu80Au20 solid solution, our computation reveals that it is energetically favorable for Au segregation to the surface and form a sequence of ordered Cu-Au phases, and surface step can lead to the formation of antiphase boundary in subsurface region if the terrace width is larger than 3 nm. For Cu3Au L12 ordered (100) surface, we predict that is the Au surface segregation is attributed to Au anti-site migration, rather than direct exchange of Au atom at bulk with Cu atom at the outermost surface.

8:20 AM  Invited
Predicting Grain Boundary States in Ferroelectrics: K.S.N. Vikrant1; R. Edwin Garcia2; Catherine Bishop3; 1IIT Delhi; 2Purdue University; 3University of Canterbury
    Polycrystalline (ceramic) ferroelectrics have properties that depend on grain size and texture. Most models for grain boundaries in ferroelectrics treat them as sharp interfaces and neglect the structural degrees of freedom at the interface; whereas, grain boundary models for non-polar materials routinely account for this structural effect. Here, variational methods have been employed to predict equilibrium and metastable grain boundary configurations in polar materials containing point defects. Grain boundary energetics are derived in a self-consistent framework for ferroelectric bi-crystals and ceramics. There are two kinds of grain boundary: one with a paraelectric core and the other with a finite polarisation at the grain boundary core. We determine the energetics and conditions for transitions in grain boundary state using barium titanate as a model material.

8:50 AM  
Surface Thermochemistry of TiO2 Doped with Alkaline Earth Metal Ions and Its Relationship with Nanostructure: Andre Da Silva1; Bruno Ramos1; Jefferson Bettini2; Ricardo Castro3; Douglas Gouvêa1; 1University of São Paulo; 2Brazilian Nanotechnology National Laboratory; 3University of California, Davis
    This work investigates the relationship between the surface thermochemistry of TiO2 doped with alkaline earth metal ions and the micro and nano-structural features. The polymeric precursor method enabled the synthesis of TiO2 nanoparticles containing Mg2+, Ca2+, Sr2+, or Ba2+. Dopants' spontaneous segregation to the nanoparticles' interfaces led to an incremental surface energy reduction directly measured by microcalorimetry of adsorption. The surface excess was directly measured using an innovative lixiviation method and then, confirmed by EELS and EDS combined with STEM. The phenomenon was a direct function of ionic radius and led to improved thermal stability against coarsening and, consequently, stabilizing the anatase polymorph and increasing the specific surface area.

9:10 AM  
Atomic Structure Analysis of Inversion Domain Boundary in MgO-doped AlN: Daiki Kato1; Bin Feng2; Yasunobu Noritake1; Tomoko Hishida1; Naoya Shibata2; Yuichi Ikuhara2; 1NGK SPARK PLUG CO.,LTD.; 2The University of Tokyo
    Aluminum nitride (AlN) has been widely used as an insulating and heat-dissipating substrate material because of its various properties, such as high thermal conductivity, high insulation, and high strength. The volume resistivity of MgO-doped AlN was found to increase by about 4 orders of magnitude compared to pristine AlN. However, the detailed mechanism of this increase is still unknown. In this study, in order to understand the structural origin of the enhanced volume resistivity, the microstructure and local composition of MgO-doped AlN were analyzed in detail using state of the art scanning transmission electron microscopy (STEM). It was found that Mg and O segregate into intragranular defects inside AlN grains. Atomic resolution observations confirmed that the defects were Inversion Domain Boundaries (IDBs), which invert the polarity of the bulk. The IDBs were found to have a similar structure to the MgO octahedron, with Mg and O segregated in these layers.

9:30 AM  Invited
Understanding Grain Boundary Properties and Transitions in Multiple Dimensions: Jian Luo1; 1University of California, San Diego
    Understanding and controlling grain boundaries (GBs) in 8+ dimensions – including 5 GB macroscopic degrees of freedom (DOFs), temperature, composition, and external fields – represent great opportunities and challenges. Here, deep learning was combined with atomistic simulations to predict GB properties as functions of five DOFs plus temperature and composition in a 7D space [Materials Today 2020]. Applied electric fields provide yet another dimension to alter the GB structure. We combined AC STEM, DFT calculations, and ab initio molecular dynamics to reveal an electrochemically induced GB transition that can cause enhanced or abnormal grain growth [Nature Communications 2021 & unpublished results]. Data driven prediction the GB properties as functions of four independent compositional degrees of freedoms and temperature in a 5D space for high-entropy alloys (HEAs) have been realized [Materials Horizon 2022]. More recent ongoing investigation of GBs in refractory HEAs and compositionally complex oxides will also be discussed.

10:00 AM Break

10:20 AM  Invited
Vacancies and Other Grain-boundary Surfactants and Their Effect on Grain Growth: W Craig Carter1; Arun Baskaran2; Daniel Lewis3; Catherine Bishop3; 1Massachussetts Institute of Technology; 2Argonne National Laboratory; 3Rensselaer Polytechnic Institute
     A grain boundary's excess quantities (e.g., entropy, volume, and chemical species content) are determined by system's equilibrium phase(s). Even if a--possibly multiphase--polycrystal is closed with respect to exchange of chemical species (i.e., fixed composition), the grain boundary is an open system with respect to the equilibrium phases whether they abut the grain boundary or not. Thus--in the artificial case where the total grain boundary area can be treated as fixed--the excess grain boundary concentrations and the bulk compositions depend on the total grain boundary area in a fixed-composition system. Similar considerations apply to the grain boundary's excess volume and entropy. For a fixed-volume system, the vacancy concentrations also depend on total grain boundary area, as will the relationship between all concentrations to compositions.One implication is that the equilibrium phase concentrations and grain boundary excesses must change during grain growth. We examine this behavior's effects by simulation.

10:50 AM  
Atomistic and Gaussian Process Modeling of Solute Segregation in Metastable Grain Boundaries: Yasir Mahmood1; Maher Alghalayini1; Enrique Martinez1; Christiaan Paredis1; Fadi Abdeljawad1; 1Clemson University
    The interaction of solutes with grain boundaries (GBs) influences many interfacial phenomena. While GB solute segregation has been the subject of active research, most work focuses on ground-state, i.e., lowest energy, GB structures. However, in a polycrystal, GBs can access other metastable states. Solute segregation in metastable GBs has not been examined systematically. Herein, using atomistic simulations, we generate metastable structures for a series of [001] and [110] symmetric tilt GBs in a model Al-Mg system and quantify Mg segregation to these boundaries. Our results show large variations in the Voronoi volume distribution due to GB metastability, which influences the segregation energy. The atomistic data is used to train a Gaussian Process machine learning model, which provides a probabilistic description of the segregation energy in terms of the local atomic environment. Our treatment extends existing models by accounting for variability introduced by GB metastability.

11:10 AM  
Effects of Interdiffusion on Cu/Ni Semi-coherent Interface Properties: Alex Selimov1; Kevin Chu1; David McDowell1; 1Georgia Institute of Technology
    Nanolaminate materials exhibit improved properties relative to their constituent materials due to a high density of interfaces. Accurate representation of interface structure is critical for accurately predicting nanolaminate properties and response to loading. Existing computational models generally assume atomically sharp interfaces and neglect the reality of interdiffusion which occurs as a result of manufacturing processes. The effects of intermixing of chemical species on the interface structure and properties must be characterized for improved predictions of real-world nanolaminate properties. This work will investigate the effects of increasing solute concentration and decreasing misfit dislocation density, as a result of interdiffusion, on the Cu/Ni system using atomistic simulation techniques. Interface energetics and distribution of solutes at the interface will be presented alongside the material response to tensile and shear loading. This work will show the range of material response obtained from diffuse interfaces, highlighting the importance of considering interdiffusion in reduced-order models.