DEFORMATION, TWINNING AND THERMOMECHANICAL STRENGTHENING OF TI50NI47FE3

The dislocation Burgers vectors for the B2 intermetallic compound, Ti50Ni47Fe3, are shown to be the < 010 > type, which provide this alloy with only three independent slip systems. However, concurrent dislocation slip and mechanical twinning on {114} planes affords the polycrystalline material with greater than 50% room temperature ductility. Individual twins do not grow greater than 50-150 nm in width, and the twinning density increases with the extent of cold working. Annealing a cold worked structure, comprised of mechanical twins and dislocations, results in the formation of subgrains with a size limited by the width of the twins. Greater cold working produces a finer twin spacing and, subsequently after annealing, a refined subgrain size which in turn brings about an improved combination of yield strength and ductility.