Computational File Repository
http://hdl.handle.net/11256/2
2019-02-02T11:07:24ZImpact of solutes on the lattice parameters and elastic stiffness coefficients of hcp Fe from first-principles calculations
http://hdl.handle.net/11256/982
Impact of solutes on the lattice parameters and elastic stiffness coefficients of hcp Fe from first-principles calculations
Fellinger, Michael R.; Hector Jr., Louis G.; Trinkle, Dallas R.
The hexagonal close-packed (hcp) $\epsilon$-martensite phase in steels nucleates from the austenite parent phase during plastic straining and can be stabilized by solute additions. We compute the lattice parameters and elastic stiffness coefficients $C_{ij}$ of single-crystal hcp Fe as functions of solute concentration in the dilute limit for the substitutional solutes Al, B, Cu, Mn, and Si, and the octahedral interstitial solutes C and N. Solute strain misfit tensors determine the solute dependence of the lattice parameters, as well as the strain contributions to the solute-induced changes in the $C_{ij}$. We also compute chemical contributions to the changes in the $C_{ij}$ for each solute, and show that the sum of the strain and chemical contributions agrees with more computationally expensive direct calculations that simultaneously incorporate both effects. The computed data can be used to estimate solute-induced changes in polycrystalline elastic moduli and changes in mechanical properties such as strength and ductility, and can be directly incorporated into mesoscale simulations of multiphase steels to model solute effects on the $\epsilon$-martensite phase.
2018-12-16T00:00:00ZGeometries of edge and mixed dislocations in bcc Fe from first principles calculations
http://hdl.handle.net/11256/978
Geometries of edge and mixed dislocations in bcc Fe from first principles calculations
Fellinger, Michael R.; Tan, Anne Marie Z.; Hector Jr., Louis G.; Trinkle, Dallas R.
We use density functional theory (DFT) to compute the core structures of a_0[100](010) edge, a_0[100](011) edge, a_0/2[-1-11](1-10) edge, and a_0/2[111](1-10) 71 degree mixed dislocations in body-centered cubic (bcc) Fe. The calculations are performed using flexible boundary conditions (FBC), which effectively allow the dislocations to relax as isolated defects by coupling the DFT core to an infinite harmonic lattice through the lattice Green function (LGF). We use the LGFs of the dislocated geometries in contrast to most previous FBC-based dislocation calculations that use the LGF of the bulk crystal. The dislocation LGFs account for changes in the topology of the crystal in the core as well as local strain throughout the crystal lattice. The standard deviations of the dislocation Nye tensor distributions quantify the widths of the dislocation cores. The relaxed cores are compact, and the local magnetic moments on the Fe atoms closely follow the volumetric strain distributions in the cores. We also compute the core structures of these dislocations using eight different classical interatomic potentials, and quantify symmetry differences between the cores using the Fourier coefficients of their Nye tensor distributions. Most of the core structures computed using the classical potentials agree well with the DFT results. The DFT core geometries provide substitutional and interstitial sites for computing solute-dislocation interactions and can serve as inputs for mesoscale models of solute diffusion near dislocations.
Thermodynamic Assessments of Bi-Te Bi-Se Sb-Te
http://hdl.handle.net/11256/974
Thermodynamic Assessments of Bi-Te Bi-Se Sb-Te
Peters, Matthew
The Bi-Te, Bi-Se, and Sb-Te systems have been assessed. The compounds Bi2Te3, Bi2Se3, and Sb2Te3 have been assessed using a 3 sublattice model and the intrinsic carriers of each compound have been assessed. The homologous series between the end-members have been assessed using a stoichiometric mixture of the end-members and a metastability has been assumed between them.
Na-Doped Pb(S,Se,Te) CALPHAD Assessment
http://hdl.handle.net/11256/973
Na-Doped Pb(S,Se,Te) CALPHAD Assessment
Peters, Matthew; Peters, Matthew
The PbX (X=S,Se,Te) system has been thermodynamically assessed. The individual binaries of the PbX system have been assessed using a two-sublattice model to describe the intrinsic carriers of the system. The 2SL model has been used to model the pseudobinaries and pseudoternary in this system as well. Na doping in the individual PbX compounds has also been taken into account using experimental and DFT data.
2018-08-02T00:00:00Z