Energies of conservative and non-conservative antiphase boundaries in Ti3Al: a first principles study

Abstract

The energies of conservative and non-conservative antiphase boundaries (APBs) on and (0001) planes of stoichiometric Ti3Al are calculated ab initio in order to shed light on the reason for the enormous strengthening by antiphase domains (APDs). The energy of the non-conservative APB, which has never before been estimated either experimentally or theoretically, is found to be between those of the two types of conservative APBs, and therefore, the great strengthening cannot be attributed to the energy of the non-conservative APB. On the other hand, large differences are found between the calculated energies of conservative energies and those estimated from dissociation distances of superdislocations. This is similar to the differences seen in the case of the APB energies of TiAl, which are probably due to the equilibration of APBs by rearrangements of atoms in the vicinity of APBs. The calculated APB energies in Ti3Al are significantly larger than those estimated experimentally, and the APD size dependences of the critical resolved shear stress (CRSS) estimated by substituting these calculated values into the previously proposed equations are in better agreement with the actual dependence than those obtained using the experimental values. This implies that the enormous strengthening by APDs may be attributed to the quite large energy of the APBs created by shearing of APD boundaries.