1991 Volume 31 Issue 10 Pages 1049-1062
The mechanistic understanding of yield and flow strengths and brittle fracture behavior of ordered transition-metal aluminides has been critically assessed on the basis of quantum mechanical total-energy calculations, atomistic simulation modeling, and anisotropic elasticity theory of dislocations and cracks. The bonding mechanism is described by the combination of charge transfer and strong p-d hybridization effects. The ground state elastic constants, various shear fault energies, and cleavage energies are calculated for aluminides of cubic (L12 and B2) and tetragonal (L10 and D022) structures. The orientation dependence of Peierls stress at low temperatures is estimated based on the anisotropic coupling effect of non-glide stresses on the dislocation core. The anomalous yield behavior is analyzed by means of symmetry considerations and the interaction torque effect on the mobility of superdisloations subjected to a generalized applied stress. The ideal cleavage strength is determined by the surface electronic structure calculation, and the critical stress-intensity factor for Model-I crack is obtained using the calculated cleavage energy and elastic constants. In tetragonal aluminides, the twin-slip conjugate relationship makes an important contribution to the strain compatibility for localized plasticity at a crack tip. The boron ductilizing effect in Ni3Al and the hydrogen embrittlement effect in FeAl are briefly discussed in terms of the present results.
