Atomistic simulation of fracture in CoAl and FeAl

The behavior of mode I cracks in CoAl and FeAl is investigated using molecular statics computer simulation methods with embedded atom (EAM) potentials developed by Vailhe and Farkas (not yet published). A double ended crack of finite size embedded in a cylindrical simulation cell and fixed boundary conditions are prescribed along the periphery of the cell, whereas periodic boundary conditions are imposed parallel to the crack front. The displacement field of the finite crack is represented by that of an equivalent pileup of opening dislocations distributed in a manner consistent with the anisotropy of the crystal and traction free conditions of the crack faces. The crack lies on the {110} plane and the crack front is located either along [100], [110] or [111] directions. Cleavage in found to occur in both materials for most crack orientations. In one orientation, cleavage in FeAl is found to occur concurrently with dislocation emission. The crack tip response is rationalized in terms of the surface energy (gamma(s)) of the cleavage plane and the unstable stacking energies (gamma(us)) of the slip planes emanating from the crack front. (C) 1997 Elsevier Science Limited.