Abstract
Density functional theory (DFT), molecular dynamics (MD) with referential modified embedded-atom method (MEAM) potential, and in-house built DFT-genetic algorithm (DFT-GA) have been used to derive the influence of N interstitials in alpha-Ti and N vacancies in 8-TiN on structural and mechanical properties. A DFT-GA was applied to find the low energy distributions of N interstitials/vacancies within their experimentally observed concentration ranges, and for each distribution the lattice parameters and bulk modulus were determined by DFT and MD. For 8-TiN phase, we observed increasing lattice parameters and bulk modulus with decreasing number of N vacancies by DFT and MD in agreement with experimental references. For alpha-Ti phase, DFT lattice parameters a and c were increasing with increasing number of N interstitials in correspondence with experimental data, but the lattice parameter c by MD was decreasing. This indicated that the used referential parametrization of MEAM may not be suitable for this type of calculation. Bulk modulus of alpha-Ti was observed to be increasing with increasing concentration of N interstitials by both methods, which agreed with experimental references. In addition, to illustrate how the obtained dependencies may provide expected values across the depth of the alpha-Ti target modified by N ion implantation, we extrapolated them on the N depth concentration distribution computed by MD.
NSTL
Elsevier