Grain Boundaries, Interfaces, and Surfaces in Functional Materials: Fundamental Structure-Property-Performance Relationships: Kinetic Processes and Interface Transitions
Sponsored by: ACerS Basic Science Division
Program Organizers: Catherine Bishop, University of Canterbury; John Blendell, Purdue University; Shen Dillon, University of Illinois at Urbana-Champaign; Wolfgang Rheinheimer, Purdue University; Ming Tang, Rice University; Melissa Santala, Oregon State University
Wednesday 8:00 AM
November 4, 2020
Room: Virtual Meeting Room 34
Location: MS&T Virtual
Session Chair: John Blendell, Purdue University
8:00 AM
A Survey of Constrained Grain Boundary Migration Mechanisms: Ian Chesser1; Elizabeth Holm1; 1Carnegie Mellon University
Grain boundary motion accommodates a variety of constraints during polycrystalline grain growth including boundary curvature and local strains generated by a mobile grain boundary network. In this work, we categorize a wide range of constrained grain boundary migration mechanisms via direct analysis of atomic displacement fields generated during clamped molecular dynamics bicrystal simulations and polycrystalline simulations in FCC Ni and BCC Fe. Although our taxonomy of constrained migration mechanisms supports existing models for grain boundary migration in special cases, several interesting examples call for more flexible models. Anisotropic mobility distributions from molecular dynamics simulations are reconciled with experimental data.
8:20 AM
Equilibrium and Kinetic Shapes of Grains in Polycrystals: Wolfgang Rheinheimer1; John Blendell2; Carol Handwerker2; 1TU Darmstadt; 2Purdue University
We present a suite of measurements and combined analyses of grain growth of large, oriented single crystals into polycrystals. The growth distance, its standard deviation and the microstructure evolution along the single crystal-matrix interface are used to characterize the migration behavior as a function of temperature, time, and interface orientation. The relative grain boundary mobility was determined between 1250 °C and 1600 °C for the four most important orientations {100}, {110}, {111} and {310}. The conclusions are that the kinetic shapes observed in the microstructures are dominated by the growing side of the interface and not by the dissolving side. The implications for grain growth underscore the applicability of crystal growth models to grain growth in polycrystals. In particular, in strontium titanate, the anisotropy of the grain boundary mobility is reduced from five macroscopic parameters to two easing the incorporation of growth rate anisotropy in simulations of microstructure evolution.
8:40 AM
Electromigration-induced Defects' Evolution in Polycrystalline Interconnects: Insights from Phase-field Simulations: William Farmer1; Sree Vemulapalli1; Kumar Ankit1; 1Arizona State University
Miniaturization of microdevices comes at the cost of increased circuit complexity and operating current densities. At large current densities electromigration leads to degradation of interconnects and solder, ultimately resulting in circuit failure. Although electromigration-induced defects in electronic materials can manifest in several forms, the formation of voids and channel-like slits can be commonly observed. This research aims at understanding the morphological evolution of voids and slits under electromigration by formulating a phase-field model that accounts for anisotropic mobility in the metallic interconnect. On the basis of an extensive parametric study, we report the conditions under which 'pancaking' of voids or the novel void 'swimming' regimes are observed. The simulated morphological evolution of slits propagating along grain boundaries is found to be strongly dependent on the grain size, atomic mobility and operating current density. Finally, inferences are drawn to formulate strategies using which the reliability of interconnects can be improved.
9:00 AM
Relating Grain Size Distributions and Grain Boundary Excess Coverages to Complexion Transitions in Eu-doped MgAl2O4: Christopher Marvel1; Caroline Riedel1; Amanda Krause2; Martin Harmer1; 1Lehigh University; 2University of Florida
A gap in understanding grain boundary complexion transition kinetics is correlating the role of the grain size (i.e. sites for segregation) to the rate of complexion transitions. In this work, Eu-doped MgAl2O4 was synthesized, annealed for multiple temperatures and times, and abnormal grain growth was monitored to construct a complexion time-temperature-transformation (TTT) diagram. Thermally grooved surfaces were characterized to obtain statistically significant grain size distributions, and aberration-corrected electron microscopy was applied to verify differences in grain boundary structure and/or composition in different regions of the TTT diagram. Overall, using atomic-resolution imaging and ζ-factor microanalysis, it was confirmed that increases in grain size led to increases of excess Eu grain boundary coverage. Asymmetric grain boundary complexions were also identified on the abnormal grain boundaries (i.e. ordered on one grain surface but disordered on the abutting grain surface), thereby pinpointing an atomistic mechanism for the vast differences in grain boundary mobility.
9:20 AM
Grain Boundary Engineering ZnAl2O4 via Rare Earth (RE) Doping with Varying Ionic Radii: Luis Sotelo Martin1; Ricardo Castro1; 1University of California, Davis
Nanocrystalline ZnAl2O4 powder was synthesized with 0.5 mol% (RE)2O3 (RE=Nd, Y, Sc, In) using reverse-strike coprecipitation. RE dopants were chosen to span a range of crystal ionic radii (88.5 to 112.3 ppm) in order to study segregation behavior in ZnAl2O4. Resulting powders were analyzed with x-ray diffraction and electron microscopy where Nd exhibited the highest degree of grain boundary segregation. Microcalorimetry measurements were used to analyze the powders’ grain boundary and surface energies. The data showed a correlation between dopant characteristics and interfacial energies, with consequences to stability against coarsening for doped ZnAl2O4. Nanoindentation experiments on pellets sintered with high-pressure spark plasma sintering (HP-SPS) revealed Vickers hardness is dependent on doping chemistry which may be explained by the effects of dopants on grain boundaries. These results have implications for the future of grain boundary engineering as we continue to understand mechanical properties of nanocrystalline ceramics.
9:40 AM Cancelled
Roughening and Screening Transitions in Grain Boundaries and the Implications on Grain-Boundary Properties: Jian Han1; Kongtao Chen2; David Srolovitz1; 1City University of Hong Kong; 2University of Pennsylvania
A grain boundary (GB) migrates via propagation of line defects, i.e., disconnections, along the boundary. The translational symmetry of bicrystallography dictates both step and dislocation characters of disconnections. The step character may lead to GB roughening transition (GB roughness diverges). A GB may also undergo a transition associated with the dislocation character, i.e., (Kosterlitz-Thouless type) screening transition where the long-range interactions amongst disconnections is screened above a critical temperature. We develop a novel Monte Carlo approach to reveal these two types of transitions in GBs. The same approach is applicable to interfaces in functional materials, e.g., polarization domain walls, which migrate via motion of line defects characterized by step height and charge; the charge replaces the Burgers vector in screening transition. Phase transitions have deep implications on GB/interface kinetic properties. We will show that a possible source for the anomalous temperature dependence of the GB/interface mobility is the screening transition.