Twinning stress prediction in bcc metals and alloys

The development of a twin stress relationship for bcc metals and alloys in agreement with experiments has been both scientifically challenging and technologically vital. A modified approach to Peierls-Nabarro model is formulated that predicts the twinning stress in excellent agreement with experiments. We utilize the first principles energy calculations to extract the energy landscape associated with twinning and obtain the disregistry function to account for the interaction of multiple dislocations comprising the twin. The metals and alloys considered include Fe, V, Nb, Ta, Mo, W, Fe-3at.%V, Fe-35at.%Ni and Fe-3at.%Si. The variation of twinning stress within metals is substantial (90-800 MPa) and depends primarily on the twin boundary migration energy, the shear moduli, the interplanar spacing and the geometrical positions of the fractional dislocations constituting the twin.