Atomistic modeling of interfaces and their impact on microstructure and properties

Material properties emerge from phenomena on scales ranging from Angstroms to millimeters, and only a multiscale treatment can provide a complete understanding. Materials researchers must therefore understand fundamental concepts and techniques from different fields, and these are presented in a comprehensive and integrated fashion for the first time in this book. Incorporating continuum mechanics, quantum mechanics, statistical mechanics, atomistic simulations and multiscale techniques, the book explains many of the key theoretical ideas behind multiscale modeling. Classical topics are blended with new techniques to demonstrate the connections between different fields and highlight current research trends. Example applications drawn from modern research on the thermo-mechanical properties of crystalline solids are used as a unifying focus throughout the text. Together with its companion book, Continuum Mechanics and Thermodynamics (Cambridge University Press, 2011), this work presents the complete fundamentals of materials modeling for graduate students and researchers in physics, materials science, chemistry and engineering.

Modeling Materials: Continuum, Atomistic and Multiscale Techniques

We present atomistic simulations of the tensile and compressive loading of single crystal face-centered cubic (FCC) nanowires with 〈 1 0 0 〉 and 〈 1 1 0 〉 orientations to study the propensity of the nanowires to deform via twinning or slip. By studying the deformation characteristics of three FCC materials with disparate stacking fault energies (gold, copper and nickel), we find that the deformation mechanisms in the nanowires are a function of the intrinsic material properties, applied stress state, axial crystallographic orientation and exposed transverse surfaces. The key finding of this work is the first order effect that side surface orientation has on the operant mode of inelastic deformation in both 〈 1 0 0 〉 and 〈 1 1 0 〉 nanowires. Comparisons to expected deformation modes, as calculated using crystallographic Schmid factors for tension and compression, are provided to illustrate how transverse surface orientations can directly alter the deformation mechanisms in materials with nanometer scale dimensions.

https://imechanica.org/files/parkJMPS2006.pdf

Deformation of FCC nanowires by twinning and slip

Atomistic calculations for the 112 -generalized stacking fault (GSF) energy curve are performed for various embedded atom models of FCC metals. Models include those by Voter and Chen; Angelo, Moody and Baskes; Oh and Johnson; Mishin and Farkas; and Ercolessi and Adams. The resulting curves show similar characteristics but vary in their agreement with the experimental estimates of the intrinsic stacking fault energy, sf , and with density functional theory (DFT) calculations of the GSF curve. These curves are used to obtain estimates of the unstable stacking fault energy, us , a quantity used in a criterion for dislocation nucleation. Curves for nickel and copper models show the theoretically expected skewed sinusoidal shape; however, several of the aluminium models produce an irregularly shaped GSF curve. Copper and aluminium values for us are underestimates of calculations from DFT, although some of the nickel models produce a value matching one of the available DFT results. Values for sf are either fitted to, or underestimate, the measured results. For use in simulations, the authors recommend using the Voter and Chen potential for copper, and either the Angelo, Moody and Baskes potential or the Voter and Chen potential for nickel. None of the potentials model aluminium well, indicating the need for a more-advanced empirical potential.

https://iopscience.iop.org/article/10.1088/0965-0393/8/2/302/pdf

Generalized stacking fault energies for embedded atom FCC metals

https://www.cavs.msstate.edu/publications/docs/2001/12/693Length%20scale.pdf

Length scale and time scale effects on the plastic flow of fcc metals

This paper addresses the energy associated with the trapping of hydrogen to defects in a nickel lattice. Several dislocations and grain boundaries which occur in nickel are studied. The dislocations include an edge, a screw, and a Lomer dislocation in the locked configuration, i.e. a Lomer-Cottrell lock (LCL). For both the edge and screw dislocations, the maximum trap site energy is approximately 0.1 eV occurring in the region where the lattice is in tension approximately 3-4 angstroms from the dislocation core. For the Lomer-Cottrell lock, the maximum binding energy is 0.33 eV and is located at the core of the a/6(110) dislocation. Several low-index coincident site lattice grain boundaries are investigated, specifically the Sigma 3(112), Sigma 9(221) and Sigma 11(113) tilt boundaries. The boundaries all show a maximum binding energy of approximately 0.25 eV at the tilt boundary. Relaxation of the boundary structures produces an asymmetric atomic structure for both the Sigma 3 and Sigma 9 boundaries and a symmetric structure for the Sigma 11 tilt boundary. The results of this study can be compared to recent experimental studies showing that the activation energy for hydrogen-initiated failure is approximately 0.3-0.4 eV in the Fe-based superalloy IN903. From the results of this comparison it can be concluded that the embrittlement process is likely associated with the trapping of hydrogen to grain boundaries and Lomer-Cottrell locks.

http://iopscience.iop.org/article/10.1088/0965-0393/3/3/001/pdf

J E Angelo

Papers

Trapping of hydrogen to lattice defects in nickel