PLANAR FAULTS IN ORDERED TERNARY ALLOY A2BC HAVING AN ORTHORHOMBIC STRUCTURE-BASED ON TI2ALNB

Possible planar faults (obtained by shear operations) in an ordered te rnary A2BC(Cmcm) alloy with an orthorhombic structure have been studie d using a hardsphere model. Planar faults on various planes equivalent to D0(19) basal, prismatic and pyramidal (first- and second-order) pl anes are considered and the energies of 29 antiphase boundaries, two s uperlattice intrinsic stacking faults and two complex stacking faults have been formulated in terms of pairwise interactions up to the seven th-nearest neighbour. These results are compared with the h.c.p.-based D0(19) ordered structure. The crystallography of various faults are e xamined on the basis of symmetry criteria using Neumann's principle. P ossible dislocation dissociations on various slip planes are proposed.