Computational Thermodynamics and Kinetics: Microstructure Evolution II, Thermodynamics and Alloys II
Sponsored by: TMS: Chemistry and Physics of Materials Committee, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Niaz Abdolrahim, University of Rochester; Stephen Foiles, Sandia National Laboratories; James Morris, Oak Ridge National Laboratory; Raymundo Arroyave, Texas A & M University

Wednesday 2:00 PM
March 1, 2017
Room: 11B
Location: San Diego Convention Ctr

Session Chair: Thien Duong, Texas A&M University; Mark Asta, UC Berkeley

2:00 PM  Invited
First-Principles Calculations of Coherent Phase Equilibria and Short-Range-Order Hardening in the Alpha-Ti-O System: David Olmsted1; Maarten de Jong1; Mark Asta1; 1University of California, Berkeley
    Oxygen interstitial solutes are known to have pronounced effects on the mechanical behavior of alpha-Ti alloys. In this work we investigate coherent phase equilibria, and short-range-order hardening in alpha Ti-O solid solutions employing a first-principles computational framework combining a microscopic elasticity model for strain-induced oxygen interactions, with a cluster expansion of the configurational energetics. The approach is combined with Monte-Carlo simulations to quantify the effects of coherency strains on solubility limits for coherent precipitation. In addition, from the equilibrated solid-solution configurations we explore the effect of oxygen short-range ordering on the energetics underlying slip of <a> type screw dislocations on both prismatic and pyramidal planes. The results are discussed in the context of published experimental data relating to the effect of oxygen on dislocation deformation microstructures. This research was supported by the U.S. Office of Naval Research under grant N00014-12-1-0413.

2:30 PM  
Microstructural Pattern Formation during Eutectoid Transformation in Fe-Mn-C Steels: Phase-field Simulations: Leslie Mushongera1; Kumar Ankit2; Britta Nestler2; 1Karlsruhe University of Applied Sciences; 2Karlsruhe Institute of Technology
    A cursory glance at the available literature on the mechanisms of eutectoid transformation in ternary steels reveals that the subject remains fascinating, with many unresolved issues and disparate observations. Cooperative growth of pearlitc lamellae and the factors that engender transition to divorced eutectoid are the areas where stipulated bridging between theory and experiments is yet to established. We use a grand-chemical potential model that uses thermodynamic information from the CALPHAD database to explore the conditions that stimulate fascinating morphological transitions as the eutectoid transformation proceeds in Fe-Mn-C steel. To begin with, the numerically simulated growth kinetics are compared to 1-D DICTRA sharp-interface calculations, in the parameter space of interest. The validated model is used to investigate the influence of different processing and boundary conditions on the 3-D microstructural evolution. Meaningful insights on the mechanisms of eutectoid transformation are derived based on synergies established between computational and experimental micrographs.

2:50 PM  
Joint Formation and Microstructural Evolution in the Microbumps of Three Dimensional Integrated Circuits (3DICs): Vahid Attari1; Raymundo Arroyave1; 1Texas A&M University
    It is been a while that microelectronic industry has replaced Al based on-chip conductors with Cu based ones and Cu-Sn-Cu micro-joints are used widely in the current 3DIC architecture. While, miniaturization and microstructural effects are still source of reliability concerns, the electromigration induced failure treats the design of 3DICs. In this work, multi-phase field modeling is utilized to study the process of joint formation during isothermal solidification in these joints. Heterogeneous nucleation and evolution of Cu6Sn5 and Cu3Sn interfacial intermetallics are modeled by considering the thermodynamics and kinetics of Cu-Sn reacting system at 260, 300 and 340°C. Experimental observations are considered in the development of the computational model and the values of the grain boundary and interfacial diffusion regimes are optimized. This study paves the way for further investigation of the microstructural evolution due to simultaneous chemical and electromechanical interactions to optimize the desired microstructure for in-service conditions.

3:10 PM  Invited
First-Principles Evaluation of Ti2AlC-Cr2AlC Psuedo-binary Phase Diagram: Thien Duong1; Anjana Talapatra1; Woongrak Son1; Huili Gao1; Miladin Radovic1; Raymundo Arroyave1; 1Texas A&M University
    We report the first attempt to evaluate the finite-temperature pseudo-binary phase diagram of Ti2AlC-Cr2AlC through ab initio methods. Particularly, first-principles calculations were conducted within the framework of density-functional theory to estimate finite-temperature free energies of MAX and competing phases. The calculations take into account both vibrational and electronic contributions to the total energies of the systems. Resulting energies were attributed to a linear minimization process to derive the most competitive phases at different composition and temperature conditions. The phase diagram was constructed based on the results of the analysis of phase competition. It has been shown that the evaluated phase diagram is in reasonable agreement with previous experiments, albeit there still exists room for further refinements.

3:40 PM Break

4:00 PM  
Atomic Scale Modeling of Fe-Al-Mn-C Alloy Using Pair Models and Monte-Carlo Calculations: Jérôme Dequeker1; Alexandre Legris1; Rémy Besson1; Ludovic Thuinet1; 1Université Lille 1
    The Fe-Al-Mn-C system is widely studied for an automotive application due to its good mechanical properties and its relatively low density. To start with, we focused on the Fe-Al binary system and tested the capability to reproduce its phase diagram combining ab initio calculations and the cluster expansion method. Several models have been adjusted using different input atomic configurations as: pure iron, a substitutional aluminium atom diluted in iron, pairs of substitutional aluminium atoms located at different neighbour shells and eventually complementary structures (B2, B32 and D03). Long range order parameters (occupation of four sublattices) have been defined to analyse the equilibrium configurations generated by Monte-Carlo runs in the semi-grand canonical ensemble. Phase diagrams have been plotted for each model and compare well with experimental ones. The methodology used allows to explore the ternary (Fe-Al-Mn) system for which encouraging results were obtained.

4:20 PM  
Microstructure Evolution and Deformation Behavior of Powder Materials during Sintering: Sudipta Biswas1; Vikas Tomar1; 1Purdue University
    Sintering is an advanced manufacturing technique that compacts small powder particles into a solid polycrystalline structure by reducing the void fraction and surface area. Diffusion as well as plastic deformation facilitates the powder compaction process improving the density of the material. Current work focuses on capturing the microstructural changes during the sintering process and it’s impact on the deformation behavior of the material. Phase field modeling approach has been adopted for apprehending the microstructural evolution during the process in combination with the temperature and stress field. Additionally, Chaboche’s viscoplastic deformation model has been incorporated to observe the impact of plastic flow and creep behavior during the process. It has been observed that initially powder compaction is governed by surface diffusion; however as the applied stress exceeds yield strength of the material plastic flow accelerates the densification process. In addition, grain growth due to grain boundary diffusion also occurs during sintering.

4:40 PM  
Kinetics of Phase Transformations Using Quasi-Coarse-Grained Dynamics Simulations: Sumit Suresh1; Terrance O'Ragan2; Avinash Dongare1; 1University of Connecticut; 2US Army Research Laboratory
    A new method called quasi-coarse-grained dynamics (QCGD) is developed to expand the capabilities of classical molecular dynamics (MD) simulations to the mesoscales. The QCGD method is based on solving the equations of motion for a chosen set of representative atoms from an atomistic microstructure and retaining the energetics of these atoms as would be predicted in MD simulations using scaling relationships for the interatomic potentials. The success of the QCGD method is demonstrated by reproducing the thermodynamic behavior as well as defect evolution behavior of FCC, BCC, HCP and diamond cubic systems as observed using MD simulations using a reduced number of atoms and improved time-steps. The scaling relationships for QCGD simulations and a comparison of the the prediction of the pressure-temperature phase diagram, the kinetics of the melting and recrystallization behavior in Ge systems will be presented.

5:00 PM  
Kinetics Study of Thin Film Phase Transformation via Level-Set Method Simulation: Mahyar M. Moghadam1; Peter Voorhees1; 1Northwestern University
    In this work we address the effect of finite size on kinetics of thin film phase transformations by employing the level-set method simulation. Characteristic length and time scales of the system are determined in order to conduct a systematic kinetic study over a broad range of film thicknesses and different nucleation mechanisms. Interpreting the results via the classic framework of Johnson-Mehl-Avrami-Kolmogorov (JMAK) shows that at finite system the average Avrami exponent and rate constant become a function of film thickness. The analysis also reveals that in thin films the JMAK framework can yield a spurious thickness dependent activation energy for the transformation. As a remedy, we propose an analysis that allows determining all the kinetic parameters, including the nucleation rate and interface velocity from the experiment. We also extend this work to anisotropic growth, in order to examine the effects of grain shape on the kinetics of the transformation.