| We developed and exercised a first principles based multiscale approach to model plastic behaviors of high-purity Tantalum (Ta) single crystals. Our approach consists of three hierarchical parts. (1) Derive the atomistic interaction potential for Ta based on the data obtained from the accurate quantum mechanics (QM) calculation. (2) Predict the properties and behaviors of dislocations in the atomistic simulations using the derived first principles potential. (3) Describe the material plasticity in the kink pair mechanism based mesoscopic model with the input of the predicted atomistic level dislocation properties. In this thesis work, we accurately determined the core structure, core energy, Peierls energy barriers, Peierls stresses, kink formation energy, kink migration energy, and kink structures for 1/2a<111> screw dislocations in bcc Ta using molecular dynamics (MD) simulations. The major results are as follows. (1) The core energy is 1.400 eV/b for the asymmetric screw dislocation cores, which spread out along three <112> directions in the {lcub}110{rcub} planes. (2) The dislocation core is formed by the 12 atoms with higher strain energies around the dislocation center. (3) The twinning and anti-twinning asymmetry of shears is the main cause for the non-Schmid behavior of screw dislocations in bcc metals. (4) For 1/2a<111> screw dislocations in Ta, the Peierls energy barrier is 0.032 eV/b under twinning shears and 0.068 eV/b under anti-twinning shears. The Peierls stress is 790 MPa under twinning shears and 1430 MPa under anti-twinning shears. (5) The minimal energy cost to form a kink pair along the dislocation is 0.794 eV. (6) The effective kink pair nucleation length is 16 b. (7) There are two kinds of elementary kinks and six kinds of composite kinks. We further input these atomistic simulation results to a mesoscopic plasticity model [A. M. Cuitiño, L. Stainer and M. Ortiz, Journal of the Mechanics and Physics of Solids, 2001]. The resulting atomistically informed model is found to capture many salient features of the behavior of Ta single crystals. |
