Transmission electron microscopy of room temperature deformed polytwinned L10-ordered FePd

The defect structure present in polycrystalline polytwinned FePd (PT-FePd) intermetallics with the L10-ordered crystal structure after room temperature tensile testing to failure has been studied in detail by transmission electron microscopy (TEM). The active deformation modes responsible for accommodation of plastic strain include octahedral glide of ordinary dislocations (ODs) with Burgers vector, b=1/2<1 1 0>, and mechanical twinning on octahedral planes, i.e., the ordered twinning systems 1/6<1 1 2>{1 1 1}. The details of shear transfer processes across the PT-interfaces that are required for macroscopic plasticity have been identified from experimental TEM observations. Superdislocations (SDs) with b=<0 1 1> have been observed infrequently and have been identified as by-products of the transfer of mechanical twins across the PT-interfaces which produces glissile ODs. The OD glide and the mechanical twinning represent complementary deformation modes, which must operate in a synergistic interplay in alternating twin-related lamellae of the PT-grains in order to achieve general plasticity in polycrystalline PT-FePd. Mechanisms based on the interactions of the active deformation systems with the PT-interfaces have been discussed that are suitable to rationalize the plastic flow behavior characteristic of PT-FePd