Abstract

The ordering tendency in binary f -Ti solid solution containing 3sp or 4sp simple-metal or 3d transition-metal solute is investigated systematically by the linear muffin-tin orbital method within the atomic sphere approximation . We demonstrated that the effective pairwise interaction energy in a solid solution is equal to half the solute-solute interaction energies and can be evaluated by a supercell total energy approach. The calculations of EPI energy both with and without volume relaxation of the supercells and local density of states show that the EPI energies of Ti-SM and Ti-TM solutions are dominated by different factors. For Ti-SM solutions, the EPI energies are of large absolute values with a negative sign, indicating strong ordering tendency in these solutions. The volume relaxation does not alter the EPI energy substantially. The calculated LDOS shows that the ordering tendency in Ti-SM solutions may be related to the hybridization between the electrons of the SM atoms when they are close to each other. For most Ti-TM solutions, if calculated without relaxation, the absolute EPI energies are very small; however, if calculated with relaxation, they are of relatively large positive values, indicating a clustering tendency in these solutions. By combining the calculated EPI energy and Flinn's model for short-range order strengthening, the increase in critical shear stress ‰ sro due to SRO is estimated for Ti-SM alloys, and the results qualitatively agree with experiment