The structure of deformation twins in BCC transition metals during nucleation and growth

Abstract

Nucleation and growth of deformation twins in BCC transition metals have been investigated in many computational and experimental studies without conclusively describing the critical twin nuclei thickness and its subsequent growth. While most studies conclude that the thickness is three layers by assuming conservation of Burgers vector and nucleation from a screw dislocation, recent experimental studies have contradicted this, suggesting a minimum of six layers. Here we demonstrate, under nonzero finite pure shear stresses, that the minimum thickness during twin nucleation is two layers in Group VB and VIB metals whereas it is three layers in iron. The twinning dislocations that constitute the nuclei have been determined which are dependent on metal's electronic structure i.e, position in periodic table. Growth of twins occurs in a layer-by-fashion maintaining isosceles twin boundary structures in Group VB metals and Fe whereas the more commonly acknowledged reflection twin boundaries are favored in Group VIB.