Integration between Modeling and Experiments for Crystalline Metals: From Atomistic to Macroscopic Scales IV: Session V
Sponsored by: TMS Advanced Characterization, Testing, and Simulation Committee, TMS Materials Characterization Committee, TMS: Nanomaterials Committee
Program Organizers: Arul Kumar Mariyappan, Los Alamos National Laboratory; Irene Beyerlein, University of California, Santa Barbara; Levente Balogh, Queen's University; Caizhi Zhou, University of South Carolina; Lei Cao, University of Nevada; Josh Kacher, Georgia Institute of Technology
Wednesday 8:00 AM
October 12, 2022
Room: 401
Location: David L. Lawrence Convention Center
Session Chair: Janelle Wharry, Purdue University; Ill Ryu, University of Texas at Dallas
8:00 AM Invited
Multi-scale and Multi-physical Model of Defect-driven Plasticity in Nanostructural Metals: Ill Ryu1; 1University of Texas at Dallas
A multiscale and multi-physical model which could couple dislocation dynamics and finite element method was developed to simulate the mechanical response of nanostructural metals. The multiscale model can capture detailed dynamics evolution of dislocation structures and can predict macroscopic constitutive response. In addition, the developed model could account for complex multi-physical phenomena, which would play an important role in obtaining a fundamental understanding of deformation mechanism in nanostructural metals. Applications of developed concurrent coupled model includes Taylor impact test, nanoindentation, and hydrogen embrittlement at submicron length scale. The developed model will shed light on fundamental investigation of “defect-controlled” mechanical behaviors in nanostructural metals.
8:30 AM
Influence of the Cross Slip Based Dynamic Recovery during Plane Strain Compression of Aluminium: Chaitali Patil1; Supriyo Chakraborty1; Stephen Niezgoda1; 1Ohio State University
Cross slip of the screw dislocations is one of the important mechanisms during deformation of the medium to high stacking fault energy fcc metals. In the recent literature, it has been proposed that activation energy for the cross slip depends on the applied stress state. As a result, cross slip mediated dynamic recovery of the screw dislocations will also be governed by the applied stress state. Hence, we incorporated the stress dependent dynamic recovery of the screw dislocations in the dislocation density based constitutive law. We analyzed influence of the dynamic recovery on the evolution of the field variables during the plane strain compression of polycrystalline aluminium. Results indicate that cross-slip based dynamic recovery enhances nucleation propensity of the cube orientations. As the cube texture is commonly observed after static recrystallization of fcc materials, our results highlight importance of dynamic recovery of the screw dislocations during deformation.
8:50 AM
Atomistic Modeling of a Nano-precipitate Strengthened Alloy: Edwin Antillon1; Colin Stewart1; Noam Bernstein1; Michelle Johannes1; Richard Fonda1; Keith Knipling1; Patrick Callaham1; 1Naval Research Laboratory
We present a series of atomistic level calculations for properties relevant to phase stability and strengthening mechanisms of a nano-precipitate strengthened austenitic steel alloy. Density functional theory is used to calculate bulk energies, point defects, and elastic properties of disordered and ordered phases observed in a novel nano-precipitate strengthened austenitic steel Fe–17.7Mn–10.0Ni–5.0Al–4.7Cr–4.0Cu–0.48C (wt.%). To capture short-range and long-range interactions between the precipitates and the matrix, we make use of a surrogate interatomic potentials to model interfacial properties and deformation mechanisms between the matrix and the precipitate. Our atomistic results are validated against experiment by comparing precipitate shape-morphology and quantifying the contribution of solute-solution and precipitate strengthening to the overall yield strength of the alloy.
9:10 AM Cancelled
Atomistic Simulation of the Effect of Grains Misorientation on the Fatigue Nano-crack Growth in NiTi: Saeed Ataollahi1; Mohammad J. Mahtabi1; 1University of Tennessee at Chattanooga
Effect of grain misorientation on the fatigue crack growth of austenitic NiTi has been studied using atomistic simulations of bicrystals. Molecular Dynamics simulations were employed to apply cyclic loads to bicrystal NiTi models containing a middle crack. The crack was modeled in one of the grains having [11-2] crystallographic orientation. The adjacent grain had different orientations in different models (i.e. [100], [110] and [111]), while the grain boundary was perpendicular to the crack. In addition, the effect of the grain boundary angle was investigated on the fatigue crack growth. The results showed that the grain boundary acts as a barrier against the crack propagation. Moreover, the propagation of crack was faster in the grain with [111] crystal orientation compared to the other cases. This is because {110}<111> is favorable slip system for B2 NiTi. In addition, it was observed that the crack growth is influenced by the grain boundary angle.
9:30 AM
Leveraging Electron Microscopy to Inform Ab Initio Calculation: Deducing Surface Chemistry and Annealing Conditions from Equilibrium Tungsten Nanoparticle Shapes in Scandate Cathodes: Mujan Seif1; Xiaotao Liu1; John Balk1; Matthew Beck1; 1University of Kentucky
Scandate cathodes (“scandates”) are a high-performing subset of thermionic cathodes composed of a porous Sc-doped W nanocrystalline pellet impregnated with BaO, Al2O3, and CaO. Extensive characterization of scandate cathode microstructure motivates a hypothesis that all high-performance scandates contain W nanoparticles of a characteristic Wulff shape. Here, we evaluate the relationship between Sc and this shape. We utilize density functional [perturbation] theory to compute the finite-temperature excess free energies of several Sc-containing and Sc-omitted surface configurations. With these results, we quantify the relative stability of the configurations as a function of temperature and O2 availability. We then search this T, O2 phase space to find a window wherein the relative surface excess free energies yield the characteristic W nanoparticle shape present in high-performing scandate cathodes. We find that the presence of Sc in certain surface arrangements further stabilizes W configurations and creates multiple regions where the characteristic Wulff shape appears.
9:50 AM Break
10:10 AM Invited
Unexpected Deformation-Induced Martensitic Transformations in Ni-Cr Alloy 625: Janelle Wharry1; Caleb Clement1; Chao Yang2; 1Purdue University; 2MSE Supplies
The objective of this talk is to demonstrate unexpected deformation-induced martensitic transformations in Ni-Cr superalloys. In fcc crystals, deformation-induced bcc and/or hcp martensites form through diffusionless, solid-state phase transformations. Martensitic transformations are not believed to be active in high-stacking fault energy (SFE) materials such as Ni-Cr superalloys. Here, we present novel nanoscale martensitic transformations under high strain rate deformation in Alloy 625 (nominally Ni-20Cr-8Mo). Nanoindentations are dissected using focused ion beam milling to extract transmission electron microscopy (TEM) lamellae. High resolution scanning TEM (HR-STEM) reveals nanoscale deformation twinning and martensites, often only a few atomic layers thick. Inverse fast Fourier transformations (FFT) suggest that both hcp and bcc martensites form. Molecular dynamics simulations of Ni-20Cr concur that martensitic transformations occur following stacking fault formation. These results have significant implications for the mechanical behavior of Ni-Cr superalloys, and more fundamentally, challenge our understanding of SFE as a criterion for martensitic transformations.
10:40 AM
Interactions between Defects and Omega Phase in Ti via Molecular Dynamics and Phase Field Simulations: Khanh Dang1; Darshan Bamney1; Carlos Tomé1; Laurent Capolungo1; 1Los Alamos National Laboratory
Under extreme conditions, alpha-Ti becomes unstable and transforms into beta-Ti (at high temperature) or omega-Ti (at high pressure). For the alpha to omega phase transformation, there has been a wide range of experimentally reported transition pressures from approximately 2 to 15 GPa at room temperature. Defects are often considered as the cause for this variation. In this study, we investigate the interactions between {101'2}! twins anddislocations and an omega phase nucleus to understand the effect of these interactions on the alpha to omega phase transformation in Ti. This is done via a combined approach of continuum mechanics, molecular dynamics, and phase field simulations, which allows us to gain a comprehensive understanding of the interactions across different length scales. Overall, we found that these interactions reduce the critical size of the w nucleus required to promote the alpha to omega phase transformation in Ti.
11:00 AM
Hybrid Ab Initio-machine Learning Simulation of Dislocation-defect Interactions: Petr Grigorev1; Alexandra Goryaeva2; James Kermode3; Mihai-Cosmin Marinica2; Thomas Swinburne4; 1Aix-Marseille Université / CNRS; 2CEA; 3University of Warwick; 4CNRS
Calculations of dislocation-defect interactions require system sizes at or beyond ab initio limits. Current estimates thus have extrapolation or finite size errors that are very challenging to quantify. Hybrid methods offer a solution, embedding small ab initio simulations in an empirical medium. However, current implementations can only match mild elastic deformations at the ab initio boundary. We describe a robust method to employ linear-in-descriptor machine learning potentials as a highly flexible embedding medium, precisely matching core properties to allow dislocations to cross the ab initio boundary in fully three dimensional defect geometries. Investigating helium and vacancy segregation to edge and screw dislocations in tungsten, we find long-range relaxations qualitatively change impurity-induced core reconstructions compared to those in short periodic supercells. Our approach opens a vast range of mechanisms to ab initio investigation and provides new reference data for interatomic potentials. preprint: arXiv:2111.11262code: https://github.com/marseille-matmol/LML-retrain/
11:20 AM Invited
Extended Core Structure of Planar Defects and Localized Phase Transformation in Crystalline Solids: Longsheng Feng1; Shakthipriya Baskar Kannan1; Ashton Egan1; Maryam Ghazisaeidi1; Mike Mills1; Yunzhi Wang1; 1Ohio State University
Extended defects in crystalline solids such as dislocations, stacking faults, homo-phase and hetero-phase interfaces may cause atomic structure rearrangement and solute re-distribution, creating new phase equilibria and phase transformations not seen in the bulk. For stacking faults and twin boundaries, because of the change in stacking sequences, structurally new phases already exist at these defects, which could be stable, metastable, or unstable in the bulk forms. If unstable, the new phases will be confined at the cores of these defects, a phenomenon called localized phase transformation (LPT). In this presentation, we show that by using a combination of experimental characterization, crystallographic analysis, ab initio calculations, thermodynamic modeling, and phase field simulations, one can predict (a) the structures of, (b) solute segregation and segregation transition at, (c) phase transformation and LPT at these extended defects, and (d) impact of LPTs on deformation pathway and mechanical properties.