A Multiscale Approach for Modeling Crystalline Solids

In this paper we present a modeling approach to bridge the atomistic with macroscopic scales in crystalline materials. The methodology combines identification and modeling of the controlling unit processes at microscopic level with the direct atomistic determination of fundamental material properties. These properties are computed using a many body Force Field derived from ab initio quantum-mechanical calculations. This approach is exercised to describe the mechanical response of high-purity Tantalum single crystals, including the effect of temperature and strain-rate on the hardening rate. The resulting atomistically informed model is found to capture salient features of the behavior of these crystals such as: the dependence of the initial yield point on temperature and strain rate; the presence of a marked stage I of easy glide, specially at low temperatures and high strain rates; the sharp onset of stage II hardening and its tendency to shift towards lower strains, and eventually disappear, as the temperature increases or the strain rate decreases; the parabolic stage II hardening at low strain rates or high temperatures; the stage II softening at high strain rates or low temperatures; the trend towards saturation at high strains; the temperature and strain-rate dependence of the saturation stress; and the orientation dependence of the hardening rate.Comment: 25 pages, 15 figures, LaTe

The analysis of the stress corrosion effects for H atom in the symmetrical tilt Ni Σ 5 (012) grain boundary structure

We employ a first-principles total energy method based on density functional theory as implemented in the Vienna ab-initio simulation package (VASP) for a detailed analysis of the symmetrical tilt Ni Σ 5 (012) GB with H impurity atoms in the structure of Σ 5 (012) GB. The effects of H segregation at the Ni Σ 5 (012) GB are investigated in details. The main goal of this study is to perform the ab initio simulations for the Ni Σ 5 (012) GB including the various impurity atoms at GB level as well as pure grain boundary models of Ni Σ 5 (012) GB. The grains can either be pushed apart or pulled together depending on the size of the impurity and nature of the local relaxations. Fundamental understanding of stress-corrosion cracking in metals and alloys including various impurity atoms is important to develop a new-structural material. Our calculations are compatible with the other first principle calculations. © 2017 Elsevier Ltd. All rights reserved

Melting of tantalum at high pressure determined by angle dispersive x-ray diffraction in a double-sided laser-heated diamond-anvil cell

The high pressure and high temperature phase diagram of Ta has been studied in a laser-heated diamond-anvil cell (DAC) using x-ray diffraction measurements up to 52 GPa and 3800 K. The melting was observed at nine different pressures, being the melting temperature in good agreement with previous laser-heated DAC experiments, but in contradiction with several theoretical calculations and previous piston-cylinder apparatus experiments. A small slope for the melting curve of Ta is estimated (dTm/dP = 24 K/GPa at 1 bar) and a possible explanation for this behaviour is given. Finally, a P-V-T equation of states is obtained, being the temperature dependence of the thermal expansion coefficient and the bulk modulus estimated.Comment: 31 pages, 8 figures, to appear in J.Phys.:Cond.Matte