Mechanical Propertieshttps://hdl.handle.net/11256/6672022-05-21T02:41:55Z2022-05-21T02:41:55ZImpact of solutes on the lattice parameters and elastic stiffness coefficients of hcp Fe from first-principles calculationsFellinger, Michael R.Hector Jr., Louis G.Trinkle, Dallas R.https://hdl.handle.net/11256/9822018-12-16T20:59:06Z2018-12-16T00:00:00ZImpact 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 calculationsFellinger, Michael R.Tan, Anne Marie Z.Hector Jr., Louis G.Trinkle, Dallas R.https://hdl.handle.net/11256/9782018-11-28T23:51:04ZGeometries 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.
Effect of solutes on the lattice parameters and elastic stiffness coefficients of body-centered tetragonal FeFellinger, Michael R.Hector, Louis G. Jr.Trinkle, Dallas R.https://hdl.handle.net/11256/9592018-07-05T18:26:33Z2018-03-03T00:00:00ZEffect of solutes on the lattice parameters and elastic stiffness coefficients of body-centered tetragonal Fe
Fellinger, Michael R.; Hector, Louis G. Jr.; Trinkle, Dallas R.
We compute changes in the lattice parameters and elastic stiffness coefficients Cij of body-centered tetragonal (bct) Fe due to Al, B, C, Cu, Mn, Si, and N solutes. Solute strain misfit tensors determine changes in the lattice parameters as well as strain contributions to the changes in the Cij. We also compute chemical contributions to the changes in the Cij, and show that the sum of the strain and chemical contributions agree with more computationally expensive direct calculations that simultaneously incorporate both contributions. Octahedral interstitial solutes, with C being the most important addition in steels, must be present to stabilize the bct phase over the body-centered cubic phase. We therefore compute the effects of interactions between interstitial C solutes and substitutional solutes on the bct lattice parameters and Cij for all possible solute configurations in the dilute limit, and thermally average the results to obtain effective changes in properties due to each solute. The computed data
can be used to estimate solute-induced 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 bct martensite phase.
2018-03-03T00:00:00ZAb initio calculations of the lattice parameter and elastic stiffness coefficients of bcc Fe with solutesFellinger, Michael R.Trinkle, Dallas R.Hector Jr., Louis G.https://hdl.handle.net/11256/6712017-03-06T02:54:08Z2016-04-20T00:00:00ZAb initio calculations of the lattice parameter and elastic stiffness coefficients of bcc Fe with solutes
Fellinger, Michael R.; Trinkle, Dallas R.; Hector Jr., Louis G.
Density functional theory calculates the effects of substitutional Al, B, Cu, Mn, Si solutes, and octahedral interstitial C and N solutes on the lattice parameter and elastic stiffness coefficients of bcc Fe at 0 K. We introduce a solute strain misfit tensor that quantifies how solutes change the lattice parameter. Solutes modify the elastic stiffness coefficients through these volumetric changes and by altering chemical bonds. We compute each of these contributions to the elastic stiffness coefficients separately, and verify that their sum closely agrees with changes in the elastic stiffness coefficients computed directly using fully optimized supercells with solutes. Computing the two elastic stiffness contributions separately is more computationally efficient and provides more information on solute
effects than the direct calculations. Comparison with experimental data indicates that our approach accurately predicts solute-induced changes in the structural and elastic properties. The computed data can be used to quantify solute-induced changes in mechanical properties such as strength and ductility, and can be incorporated into higher length-scale models to improve their predictive capabilities.
2016-04-20T00:00:00Z