Research Highlights

Energetics and Kinetics of Helium Clusters in Grain Boundaries in Iron

Helium bubble formation and grain boundary embrittlement is important for understanding the high temperature behavior of irradiated steels. Molecular dynamics simulations and interatomic potential development were used to understand the energetics associated with different types of helium defects and the complex interaction of these helium defects with grain boundaries. The present work probes He defect interactions in iron to better understand and model the physical behavior of He diffusion and trapping by grain boundaries in polycrystalline steels.

Tschopp, M.A., Gao, F., Solanki, K.N. "Binding of He-V Clusters to alpha-Fe Grain Boundaries," Journal of Applied Physics 115 (2014) 233501.

Tschopp, M.A., Gao, F., Yang, L., Solanki, K.N., "Binding Energetics of Substitutional and Interstitial Helium and Di-Helium Defects with Grain Boundary Structure in alpha-Fe," Journal of Applied Physics, 115 (2014) 033503.

Tschopp, M.A., Solanki, K.N., Baskes, M.I., Gao, F., Sun, X., Khaleel, M., Horstemeyer, M.F., "Generalized framework for interatomic potential design: Application to the Fe-He system," Journal of Nuclear Materials, 425 (2012) 22-32.

Nanocrystalline materials experiments and simulations

Nanocrystalline materials with grain sizes on the order of tens of nanometers allow materials scientists access to extraordinary properties and deformation mechanisms not encountered in conventional materials. This research focuses on experimental methods for generating nanocrystalline materials, thermodynamic approaches for stabilizing the grain structure, high temperature consolidation techniques, surface nanocrystallization techniques, and other mechanical alloying research (e.g., solid state metal foaming). The significance of the present work is that it may enable the production of bulk nanocrystalline materials with much higher properties and microstructure stability than previously obtained.

Tschopp, M.A., Murdoch, H.A., Kecskes, L.J., Darling, K.A., "“Bulk” Nanocrystalline Metals: Review of the Current State of the Art and Future Opportunities for Copper and Copper Alloys," JOM 66 (2014) 1000-1019.

Darling, K.A., Tschopp, M.A., Atwater, M.A., VanLeeuwen, B.K., Liu, Z.K., "Mitigating grain growth in binary nanocrystalline alloys through solute selection based on thermodynamic stability maps,'' Computational Materials Science, 84 (2014) 255-266.

Darling, K.A., Tschopp, M.A., Roberts, A.J., Armstrong, L., Kapoor, D., Mathaudhu, S.N., Kecskes, L., "Influence of Mn Solute Content on Grain Size Reduction and Improved Strength in Mechanically Alloyed Al-Mn Alloys," Materials Science and Engineering A 589 (2014) 57-65.

Darling, K.A., Tschopp, M.A., Roberts, A.J., Ligda, J.P., Kecskes, L.J., "Enhancing the grain refinement in polycrystalline materials using surface mechanical attrition treatment at cryogenic temperatures," Scripta Materialia, 69 (2013) 461-464.

Atwater, M.A., Darling, K.A., Tschopp, M.A., "Towards reaching the theoretical limit of porosity in conventional solid state metal foams: Intraparticle expansion as a primary and additive means to create porosity," Advanced Engineering Materials, accepted, Cover Image.

Quantifying structure-property relationships in single crystal Ni-base superalloys

Turbine blades in the hot section of the modern turbine engine utilize single crystal nickel-based superalloys. Understanding the properties and behavior of these superalloys requires understanding the connection between processing, the microstructure that ensues, and the resulting properties and performance. Several different methods for characterizing the superalloy microstructure have been studied to assess their ability to quantify the homogeneity of the underlying material microstructure. Additionally, high temperature creep experiments of bulk specimens and small scale indentation creep have been used to probe the high temperature properties and associated property uncertainties in these single crystal alloys.

Tschopp, M.A., Miller, J.D., Oppedal, A.L., Solanki, K.N., "Characterizing the local primary dendrite arm spacing in directionally-solidified dendritic microstructures," Metallurgical Transactions A 45(1) (2014) 426-437, Editor's Choice Article.

Shang, S., Wang, Y., Du, Y., Tschopp, M.A., Liu, Z.-K., "Integrating computational modeling and first-principles calculations to predict stacking fault energy of dilute multicomponent Ni-base alloys," Computational Materials Science, 91 (2014) 50-55.

CAVS Press Release, "CAVS Studies High Temperature Aerospace Materials in Modern Turbine Engines," December 6, 2013.

Grain boundary segregation of impurities and substitutional atoms in Iron

Grain boundaries serve as traps and sinks for both impurity and substitutional atoms, which can ultimately lead to nucleation sites for precipitates, grain boundary pinning, or grain boundary embrittlement/strengthening. In this research, we have used molecular dynamics with empirical potentials to probe large databases of grain boundary structures, defect types, elements, and grain boundary sites with the ultimate goal of obtaining a universal framework for grain boundary segregation.

Rajagopalan, M., Bhatia, M.A., Solanki, K.N., Tschopp, M.A., Srolovitz, D., "Role of atomistic-scale energetics on liquid-metal embrittlement of aluminum due to gallium," Acta Materialia 73 (2014) 312-325.

Rajagopalan, M., Tschopp, M.A., Solanki, K.N., "Grain boundary segregation of interstitial and substitutional impurity atoms in alpha-iron," JOM (Journal of Materials) 66 (2014) 129-138.

Rhodes, N.R., Tschopp, M.A., Solanki, K.N., "Quantifying the Energetics of Carbon Segregation to Fe Symmetric Tilt Grain Boundaries Using Atomistic Simulations," Modeling and Simulation in Materials Science and Engineering, 21(3) (2013) 035009, Cover image.

Solanki, K.N., Tschopp, M.A., Bhattia, M.A., Rhodes, N.R., "Nanoscale Investigation of Role of Grain Boundary Character on Hydrogen Segregation and Embrittlement in alpha-Fe," Metallurgical and Materials Transactions A, 44 (2013) 1365-1375.

Tschopp, M.A., Solanki, K.N., Gao, F., Sun, X., Khaleel, M., Horstemeyer, M.F., "Probing grain boundary sink strength at the nanoscale: Energetics and length scales of vacancy and interstitial absorption by grain boundaries in alpha-Fe," Physical Review B, 85 (2012) 064108.

Tschopp, M.A., Horstemeyer, M.F., Gao, F., Sun, X., Khaleel, M., "Energetic driving force for preferential binding of self-interstitial atoms to Fe grain boundaries over vacancies," Scripta Materialia, 64 (2011) 908-911.

Crystallography of shear and shuffles in twinning in HCP metals

El Kadiri, H., Barrett, C.D., Tschopp, M.A., "The candidacy of shuffle and shear during compound twinning in hexagonal close-packed structures," Acta Materialia 61 (2013) 7646-7659.

Barrett, C.D., Tschopp, M.A., El Kadiri, H., "Automated analysis of twins in hexagonal close-packed metals using molecular dynamics," Scripta Materialia, 66 (2012) 666-669, 'compute basal/atom' implemented into LAMMPS.

Design of Experiments and Analysis

Tschopp, M.A., Solanki, K.N., Baskes, M.I., Gao, F., Sun, X., Khaleel, M., Horstemeyer, M.F., "Generalized framework for interatomic potential design: Application to the Fe-He system," Journal of Nuclear Materials, 425 (2012) 22-32.

Eshraghi, M., Tschopp, M.A., Zaaem, M.A., Felicelli, S.D., "Effect of resistance spot welding parameters on weld pool properties in a DP600 dual-phase steel: A parametric study using thermomechanically-coupled finite element analysis," Materials and Design, 56 (2014) 387-397.

Deng, X., Potula, S., Grewal, H., Solanki, K.N., Tschopp, M.A., Horstemeyer, M.F., "Finite Element Analysis Head Injury Study: Parametric Effects on the Side curtain airbag deployment interaction with a dummy head in a side impact crash," Accident Analysis & Prevention 55 (2013) 232-241.

Potula, S., Solanki, K.N., Oglesby, D.L., Tschopp, M.A., Bhattia, M.A., "Investigating occupant injuries and safety through simulating the interaction between side curtain airbag deployment and an out-of-position occupant," Accident Analysis and Prevention, 49 (2012) 392-403.

Tschopp, M.A., "Fluidity of Aluminum A356 in the Lost Foam Casting Process," Transactions of the American Foundry Society, 110 (2002) 1387-1397.

Design and uncertainty in the interatomic potential development process

Liyanage, L., Houze, J., Kim, S., Tschopp, M.A., Kim, S-G., Baskes, M.I., Horstemeyer, M.F., "Structural, elastic and thermal properties of cementite (Fe3C) calculated using Modified Embedded Atom Method," Physical Review B, 89 (2014) 094102.

Nouranian, S., Tschopp, M.A., Gwaltney, S., Baskes, M.I., Horstemeyer, M.F., ``An interatomic potential for saturated hydrocarbons based on the modified embedded-atom method ,'' Physical Chemistry Chemical Physics, 16 (2014) 6233-6249.

Asadi, E., Zaeem, M.A., Moitra, A., Tschopp, M.A., ``Effects of Vacancy Defects on Generalized Stacking Fault Energy of FCC metals,'' Journal of Physics: Condensed Matter, 26 (2014) 115404.

Tschopp, M.A., Solanki, K.N., Baskes, M.I., Gao, F., Sun, X., Khaleel, M., Horstemeyer, M.F., "Generalized framework for interatomic potential design: Application to the Fe-He system," Journal of Nuclear Materials, 425 (2012) 22-32.

Point defect sinks at grain boundaries in iron

Tschopp, M.A., Solanki, K.N., Gao, F., Sun, X., Khaleel, M., Horstemeyer, M.F., "Probing grain boundary sink strength at the nanoscale: Energetics and length scales of vacancy and interstitial absorption by grain boundaries in alpha-Fe," Physical Review B, 85 (2012) 064108.

Tschopp, M.A., Horstemeyer, M.F., Gao, F., Sun, X., Khaleel, M., "Energetic driving force for preferential binding of self-interstitial atoms to Fe grain boundaries over vacancies," Scripta Materialia, 64 (2011) 908-911.

MSU Press Release, "CAVS studies radiation effects on nuclear reactor materials," March 09, 2012.

Understanding dislocation and twin nucleation in HCP metals

Barrett, C.D., Tschopp, M.A., El Kadiri, H., "Breakdown of the Schmid Law in Homogeneous and Heterogeneous Nucleation Events of Slip and Twinning in Magnesium," Journal of the Mechanics and Physics of Solids, 60 (2012) 2084-2099.

Barrett, C.D., Tschopp, M.A., El Kadiri, H., "Automated analysis of twins in hexagonal close-packed metals using molecular dynamics," Scripta Materialia, 66 (2012) 666-669, 'compute basal/atom' implemented into LAMMPS.

Molecular Deformation in Amorphous Thermoplastic Polymers

Nouranian, S., Tschopp, M.A., Gwaltney, S., Baskes, M.I., Horstemeyer, M.F., ``An interatomic potential for saturated hydrocarbons based on the modified embedded-atom method ,'' Physical Chemistry Chemical Physics, 16 (2014) 6233-6249.

Hossain, D., Tschopp, M.A., Ward, D.K., Bouvard, J.L., Wang, P., Horstemeyer, M.F., "Molecular dynamics simulations of deformation mechanisms of amorphous polyethylene," Polymer, 51 (2010) 6071-6083.

Tschopp, M.A., Bouvard, J.L., Ward, D.K., Bammann, D.J., Horstemeyer, M.F., "Influence of ensemble boundary conditions (thermostat and barostat) on the deformation of amorphous polyethylene by molecular dynamics," arXiv:1310.0728 [cond-mat.mtrl-sci].

Bouvard, J.L., Francis, D.K., Tschopp, M.A., Marin, E.B., Bammann, D.J., Horstemeyer, M.F., "An internal state variable material model for predicting the time, thermomechanical, and stress state dependence of amorphous glassy polymers under large deformation," International Journal of Plasticity, 42 (2013) 168-193.

Microstructure evolution using in situ experiments

Tschopp, M.A., Bartha, B.B., Porter, W.J., Murray, T., Fairchild, S., "Microstructure-dependent local strain behavior in polycrystals through in situ scanning electron microscope tensile experiments," Metallurgical Transactions A, 40 (2009) 2363-2368.

Lugo, M., Tschopp, M.A., Jordan, J.B., Horstemeyer, M.F., "Microstructure and Damage Evolution during Tensile Loading of AZ61 Magnesium Alloy," Scripta Materialia, 64 (2011) 912-915.

Lugo, M., Jordan, J.B., Horstemeyer, M.F., Tschopp, M.A., Harris, J., Gokhale, A., "Quantification of Damage Evolution in a 7075 Aluminum Alloy using an Acoustic Emission Technique," Materials Science and Engineering A, 528 (2011) 6708-6714.

Techniques for Assessing Microstructure Length Scales

Tschopp, M.A., Wilks, G.B., Spowart, J.E., "Multi-Scale Characterization of Orthotropic Microstructures," Modelling and Simulation in Materials Science and Engineering, 16 (2008) 065009.

Wilks, G.B., Tschopp, M.A., Spowart, J.E., "Multi-Scale Characterization of Inhomogeneous Morphologically Textured Microstructures," Materials Science & Engineering A, 527 (2010) 883-889.

Tschopp, M.A., Wilks, G.B., Spowart, J.E., "Multiscale Characterization of Chemically Reactive Multiphase Composite Microstructures," Journal of Engineering Materials and Technology (special issue on Recent Advances on Composites and Heterogeneous Materials), 133 (2011) 011004.

Li, D.S., Tschopp, M.A., Khaleel, M., Sun, X., "Comparison of reconstructed spatial microstructure images using different statistical descriptors," Computational Materials Science, 51 (2012) 437-444.

Digital image processing for materials characterization and stereology

Li, D.S., Tschopp, M.A., Khaleel, M., Sun, X., "Comparison of reconstructed spatial microstructure images using different statistical descriptors," Computational Materials Science, 51 (2012) 437-444.

Lugo, M., Jordan, J.B., Horstemeyer, M.F., Tschopp, M.A., Harris, J., Gokhale, A., "Quantification of Damage Evolution in a 7075 Aluminum Alloy using an Acoustic Emission Technique," Materials Science and Engineering A, 528 (2011) 6708-6714.

Lugo, M., Tschopp, M.A., Jordan, J.B., Horstemeyer, M.F., "Microstructure and Damage Evolution during Tensile Loading of AZ61 Magnesium Alloy," Scripta Materialia, 64 (2011) 912-915.

Tschopp, M.A., Wilks, G.B., Spowart, J.E., "Multiscale Characterization of Chemically Reactive Multiphase Composite Microstructures," Journal of Engineering Materials and Technology (special issue on Recent Advances on Composites and Heterogeneous Materials), 133 (2011) 011004.

Tschopp, M.A., Groeber, M.A., Simmons, J., Rosenberger, A.H., Woodward, C., "Automated Extraction of Symmetric Microstructure Features in Serial Sectioning Images," Materials Characterization, 61 (2010) 1406-1417.

Tschopp, M.A., Tiley, J.S., Viswanathan, G.B., "Automated Identification and Characterization of Secondary & Tertiary gamma prime Precipitates in Nickel-based Superalloys," Materials Science & Technology, 26(12) (2010) 1414-1422.

Tschopp, M.A., Groeber, M.A., Fahringer, R., Simmons, J., Rosenberger, A.H., Woodward, C., "Symmetry-Based Automated Extraction of Microstructural Features: Application to Dendritic Cores in Single Crystal Ni-Based Superalloys," Scripta Materialia, 62 (2010) 357-360.

Tschopp, M.A., Groeber, M.A., Fahringer, R., Simmons, J., Rosenberger, A.H., Woodward, C., "Automated Detection and 3D Characterization of Microstructural Features: Application to Eutectic Particles in Single Crystal Ni-Based Superalloys," Modelling and Simulation in Materials Science \& Engineering, 18 (2010) 025014, Featured Article.

Tiley, J.S., Rajagopolan, S., Viswanathan, G.B., Shiveley, A., Tschopp, M.A., Banerjee, R., Fraser, H.L., "Measurement of gamma prime Precipitates in a Nickel-based Superalloy using Energy-Filtered Transmission Electron Microscopy coupled with Automated Segmenting Techniques," Micron, 41(6) (2010) 641-647.

Grain boundary structure and energy in FCC metals

Tschopp, M.A., McDowell, D.L., "Structures and energies of Sigma3 asymmetric tilt grain boundaries in Cu and Al," Philosophical Magazine, 87 (2007) 3147-3173.

Tschopp, M.A., McDowell, D.L., "Asymmetric tilt grain boundary structure and energy in copper and aluminum," Philosophical Magazine, 87(25) (2007) 3871-3892.

Tschopp, M.A., McDowell, D.L., "Structural unit and faceting description of Sigma3 asymmetric tilt grain boundaries," Journal of Materials Science, 42(18) (2007) 7806-7811.

Tschopp, M.A., Tucker, G.J., McDowell, D.L., "Structure and free volume of <110> symmetric tilt grain boundaries with the E structural unit," Acta Materialia, 55 (2007) 3959-3969.

Tucker, G.J., Tschopp, M.A., McDowell, D.L., "Evolution of Structure and Free Volume in Symmetric Tilt Boundaries during Deformation using Atomistic Simulations," Acta Materialia, 58 (2010) 6464-6473.

Grain boundary dislocation nucleation mechanisms in FCC metals

Tschopp, M.A., McDowell, D.L., "Dislocation nucleation in Sigma3 asymmetric tilt grain boundaries," International Journal of Plasticity, 24 (2008) 191-217.

Tschopp, M.A., McDowell, D.L., "Grain boundary dislocation sources in nanocrystalline copper," Scripta Materialia, 58 (2008) 299-302.

Tschopp, M.A., Tucker, G.J., McDowell, D.L., "Atomistic simulations oftension-compression asymmetry in dislocation nucleation for copper grain boundaries," Computational Materials Science, 44 (2008) 351-362.

Spearot, D.E., Tschopp, M.A., Jacob, K.I., McDowell, D.L., "Tensile strength of <100> and <110> tilt bicrystal copper interfaces," Acta Materialia, 55 (2007) p. 705-714.

Spearot, D.E., Tschopp, M.A., McDowell, D.L., "Orientation and Rate Dependence of Dislocation Nucleation Stresses computed using Molecular Dynamics," Scripta Materialia, 60 (2009) 675-678.

Tucker, G.J., Tschopp, M.A., McDowell, D.L., "Evolution of Structure and Free Volume in Symmetric Tilt Boundaries during Deformation using Atomistic Simulations," Acta Materialia, 58 (2010) 6464-6473.

Homogeneous dislocation nucleation in FCC metals

Tschopp, M.A., McDowell, D.L., "Influence of single crystal orientation on homogeneous dislocation nucleation under uniaxial loading," Journal of Mechanics and Physics of Solids, 56 (2008) 1806-1830.

Tschopp, M.A., McDowell, D.L., "Tension-compression asymmetry in homogeneous dislocation nucleation in single crystal copper," Applied Physics Letters, 90 (2007) 121916:1-3.

Tschopp, M.A., Spearot, D.E., McDowell, D.L., "Atomistic simulations of homogeneous dislocation nucleation in single crystal copper," Modelling and Simulation in Materials Science and Engineering, 15 (2007) 693-709.

Spearot, D.E., Tschopp, M.A., McDowell, D.L., "Orientation and Rate Dependence of Dislocation Nucleation Stresses computed using Molecular Dynamics," Scripta Materialia, 60 (2009) 675-678.

Bhattia, M.A., Solanki, K.N., Moitra, A., Tschopp, M.A., "Investigating damage evolution at the nanoscale: Molecular dynamics simulations of nanovoid growth in single crystal aluminum," Metallurgical and Materials Transactions A, 44 (2013) 617-626.

Understanding casting defect mechanisms in the lost foam process

Tschopp, M.A., Wang, Q.G., DeWyse, M.J., "Mechanisms of Misrun Formation in Aluminum Lost Foam Castings," Transactions of the American Foundry Society, 110 (2002) 1371-1386.

Tschopp, M.A., "Fluidity of Aluminum A356 in the Lost Foam Casting Process," Transactions of the American Foundry Society, 110 (2002) 1387-1397.

Bennett, S., Tschopp, M.A., Vrieze, A., Zelkovich, E., Ramsay, C.W., Askeland, D.R., "Observations on the Effect of Gating Design on Metal Flow and Defect Formation in Aluminum Lost Foam Castings: Part I," Transactions of the American Foundry Society, 109 (2001) 1473-1487.

Tschopp, M.A., Ramsay, C.W., Askeland, D.R., "Mechanisms of Formation of Pyrolysis Defects in Aluminum Lost Foam Castings," Transactions of the American Foundry Society, 108 (2000) 609-614, Best paper.

Tschopp, M.A., Ramsay, C.W., Askeland, D.R., "Processing Variable Significance on Metal Flow and Defect Formation in Thick Section LFCs - Full Factorial Experiment," Transactions of the American Foundry Society, 108 (2000) 267-274.