Atomistics simulations of structures and properties of 1/2 <110> dislocations using three different embedded-atom method potentials fit to gamma-TiAl

摘要

Molecular statics simulations were made of dislocations in L1(0) structures, using three different embedded-atom method (EAM) potentials that were fitted to the bulk properties of gamma-TiAl. The three EAM potentials were fitted to produce complex stacking-fault energies of 120, 320 and 580 mJ m(-2) so that the effects of variations in fault energies could be investigated parametrically. Core structures were determined for each of the potentials for the following orientations: screw, 30 degrees mixed, 60 degrees mixed and edge. These cores were all planar except the screw orientations calculated with the 320 and 580 mJ m(-2) potentials. These showed substantial amounts of non-planar spreading. The 60 degrees orientations for these two potentials had a tendency for the screw component of the displacement to spread out of plane and the edge component to spread in the glide plane. The screw orientation of the 320 mJ m(-2) potential was found to have two possible states: planar and non-planar. The friction stresses were determined for all orientations of the 320 mJ m(-2) potential, since this appeared to represent gamma-TiAl most closely. The friction stresses for the other potentials were determined only for the orientations producing the highest friction stress for the 320 mJ m(-2) potential. It was also found that the close-packed directions, screw and 60 degrees, had the highest friction stress and the more sparsely packed directions having a considerably lower value. The friction stress for the 320 mJ m(-2) potential was found to be 250 MPa, in good agreement with published experimental values of critical resolved shear stress for gamma-TiAl. Comparing line orientations with the same atomic directions, the effects of ordering on the friction stress predicted by Greenberg et al (1991, Acta metall. mater., 39, 233) in 1991 were observed. These variations had a considerably smaller effect than did the atomic density along the line orientation.