Phase Transformations and Microstructural Evolution: Modeling and Simulations
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Rongpei Shi, Harbin Institute of Technology; Yipeng Gao, Jilin University; Fadi Abdeljawad, Lehigh University; Bharat Gwalani, North Carolina State Universtiy; Qi An, Iowa State University; Eric Lass, University of Tennessee-Knoxville; Huajing Song, Los Alamos National Laboratory
Monday 8:30 AM
March 15, 2021
Room: RM 57
Location: TMS2021 Virtual
Session Chair: Fadi Abdeljawad, Clemson University
8:30 AM
Burgers Circuit Analysis of Grain Boundary Junctions: Ian Winter1; Robert Rudd1; Tomas Oppelstrup1; Timofey Frolov1; 1Lawrence Livermore National Laboratory
Line defects at grain boundaries are recognized to be important in understanding grain growth, phase transformations and deformation in polycrystals. These defects interact with each other through their elastic fields. To describe these interactions, it is important to quantify the possible dislocation content of these defects. We propose a general method to calculate the Burgers content of line defects at grain boundary junctions. We apply this method to three different line defects in grain boundaries: grain boundary phase junctions, facet junctions, and triple junctions. We show that all of these junctions can possess Burgers content, which has contributions from excess grain boundary properties, meaning that crystallography alone does not determine possible Burgers vectors. The quantification of these line defects has potentially significant implications for how interface dynamics are modeled. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
8:50 AM
Electron-hole Carriers Induced Microstructure Evolution in Inorganic Semiconductors: Yidi Shen1; Qi An1; 1University of Nevada, Reno
Photomechanical effects have been known for decades, while the underlying mechanism remains not fully understood. Here, we employed advanced quantum mechanics (QM) simulations to investigate how the excited e-h pairs affect the deformation and failures in several typical semiconductors: ionic crystal ZnS, covalent crystal GaP and superhard boron carbide (B4C). We found that in ZnS the dislocation dominated deformation mode transforms to a twin dominated deformation mode when the electron-hole pair are excited, leading to a brittle failure. While the dislocation dominated mechanism leads to a ductile mechanical behavior under the ground state. For covalent GaP, we found that the energy barrier for deformation slip in GaP is significantly reduced by generating high-concentration EHPs, exhibiting metal-like ductility. For superstrong B4C, the excited e-h pairs affect the deformation mechanism leading to amorphous band formation. Our results provide the theoretical basis to investigate the photon-mechanical behaviors of semiconductors.
9:10 AM
Image-driven Discriminative and Generative Machine Learning Algorithms for Establishing Microstructure-processing Relationships: Wufei Ma1; Elizabeth Kautz2; Arun Baskaran3; Aritra Chowdhury4; Vineet Joshi2; Bulent Yener3; Daniel Lewis3; 1Purdue University; 2Pacific Northwest National Laboratory; 3Rensselaer Polytechnic Institute; 4GE Research Center
Methods of microstructure representation for the purpose of predicting processing conditions from image data were investigated via discriminative and generative machine learning methods. A U-10Mo (wt%) metallic nuclear fuel was studied for building predictive models to link microstructure to processing conditions through image processing, object recognition and characterization. This study includes testing different microstructure representations and evaluating model performance based on the F1 score. A F1 score of 95.1% was achieved, indicating that our microstructure representation describes image data well, and the traditional approach of utilizing area fractions of different phases is insufficient for distinguishing between multiple classes using a small, imbalanced original data set of 272 images. To explore applicability of generative methods for supplementing limited data sets, generative adversarial networks were trained to produce artificial microstructure images. Challenges and best practices associated with applying machine learning to limited image data sets will be discussed.
9:30 AM
Structure and Local Environment of Intermetallic Precipitate Phase
Nucleus: Deep Choudhuri1; 1New Mexico Institute of Mining and Technology
A physics-based model was developed for the formation of intermetallic phase nucleus, whose structure, symmetry and lattice parameter differ substantially from the parent phase. Towards that end, we have examined the nucleus structure and local environment of an intermetallic β1 strengthening precipitate phase within hcp-Mg of creep-resistant Mg-Nd alloys. First principles computations were conducted, which allowed the calculation of an energy-structure parameter landscape, and determination of the minimum energy nucleus structure. DFT analysis yielded two critical insights. First, the nucleus contains only the template or imprint of the equilibrium intermetallic structure, while nominally maintaining the symmetry and stoichiometry of the equilibrium phase. Such template-mediated nucleation allows the intermetallic phase to accommodate itself within the parent phase of different symmetry. Second, the template-nucleus is stabilized by being immersed within pockets of covalent-bonded environment in the metallic parent matrix.
9:50 AM
The Origin and Stability of Nanostructural Hierarchy in Nickel-base Superalloys: Subhashish Meher1; Larry Aagesen1; Tresa Pollock2; 1Idaho National Laboratory; 2University of California Santa Barbara
A combined experimental and phase-field modeling approach has been used to explore a hierarchical structure at nanoscale for enhanced coarsening resistance of ordered γ′ precipitates in a multicomponent, high-refractory nickel-base superalloy. The hierarchical microstructure formed in this alloy is composed of a γ matrix with γ′ precipitates that contain embedded, spherical γ precipitates, which do not directionally coarsen during high-temperature annealing but do delay coarsening of the larger γ′ precipitates. Atom probe tomography suggests that the supersaturation of Co, Ru, and Re in the γ′ phase is the driving force for the phase separation, leading to the formation of this hierarchical microstructure. Representative phase-field modeling highlights the importance of larger γ′ precipitates to promote stability of the embedded γ phase and to delay coarsening of the encompassing γ′ precipitates. These results suggest that the hierarchical material design has the potential to influence the high-temperature stability of precipitate strengthened metallic materials.
10:10 AM
The Role of Grain Boundaries in Nanoscale Sintering: An Atomistic Simulation Study: Omar Hussein1; Maher Alghalayini1; Fadi Abdeljawad1; 1Clemson University
Sintering is an integral processing step used to fabricate many nanostructured or nanograined materials. The ability to control densification and coarsening processes remains one of the most formidable challenges facing nanoscale sintering. Classical sintering treatments have several inherent assumptions, such as zero grain boundary (GB) energy and linearized chemical potential, that make it challenging to integrate GB anisotropy effects and defect-GB mediated processes. To probe such effects, molecular dynamics are leveraged in this study to examine the role of GB character in GB formation, particle neck growth, and densification rates during nanoscale sintering. GBs with various microstates are used to investigate the effect of GB metastable structures on sintering kinetics. In such studies, several key thermodynamic and kinetic properties and topological attributes are used to relate sintering rates to GB type. Our results provide future avenues to enrich existing mesoscale sintering models with interface-driven processes.
10:30 AM
A Phase Field Modeling Study on Coupling of Compositional Patterning with Evolution of Grain Boundaries in Irradiated Binary Immiscible Alloys: Qun Li1; Pascal Bellon1; Robert Averback1; 1University Of Illinois Urbana-Champain
Prior experimental and simulation results have shown that finite-range ballistic mixing by ion irradiation can induce compositional patterning in immiscible alloys, resulting in finite and stable nanoprecipitate sizes. Some experimental results suggest that patterning can simultaneously take place along grain boundaries (GBs) and within grain interiors. Here we use phase field modeling to investigate the conditions required for these two types of patterning to coexist. We introduce a new real-space expansion of a Gaussian mixing model to study the effect of the characteristic ballistic mixing range R and apply this mixing model to a bicrystal using the “Abdeljawad-Foiles” approach. For small R, close to the onset of patterning, GB patterning is found to suppress patterning at the grain interior. For large values of R, however, both patterns can be present, but with larger precipitates at GBs. An extended steady-state phase diagram is proposed to rationalize these results.
10:50 AM
Characterizing Evolution of Grain Boundary Network Structure during Anisotropic Grain Growth.: Jose Nino1; Oliver Johnson1; 1Brigham Young University
The evolution of the microstructure of polycrystalline materials during grain growth affects many mechanical properties of the material. Historical modeling efforts considered isotropic interface properties. However, it has been shown that anisotropic boundary properties also affect grain growth. We present the results of anisotropic grain growth simulations (based on level set methods) in three dimensions. Full grain boundary (GB) energy anisotropy is achieved by using a recently developed GB energy model that considers all five GB crystallographic degrees of freedom. Initial microstructures with a diverse set of textures are used to perform the simulations. We characterize the global structure of the GB network using a recent spectral decomposition technique where the GB network is represented as a GB energy weighted graph. The present work shows how anisotropic interface energies influence the evolution of the spectrum of the GB network during grain growth.
11:10 AM
Investigating the Microstructural Evolution of Cylindrical Interfaces: Anqi Qiu1; Ian Chesser1; Elizabeth Holm1; 1Carnegie Mellon University
A materials interface is a planar defect that occurs at the intersection of materials with different structural parameters, such as different crystal orientations or phases. The free energy and mobility of interfaces are key parameters in determining microstructural evolution, including grain growth in solids and melting and solidification processes at solid-liquid interfaces. The free energy and mobility of a flat solid-liquid interface have been determined by applying the synthetic driving force (SDF) molecular dynamics method. In this work, we extend the SDF scheme to determine the free energy and mobility of cylindrical grain boundaries and solid-liquid interfaces, in order to investigate the thermodynamics and kinetics of the interfaces in stable and metastable structures. The defect formation process and the rotation of the cylindrical interfaces are also investigated.