Quantitative Characterization of Planar Faults with Dissociated <111> Screw Super-Dislocations in B2 Alloys

Abstract

It has been long hypothesized that planar faults are well-defined defects with constant displacements and energy, corresponding to the local minima of γ-surfaces in super-dislocation dissociations in intermetallic compounds. In this work, planar faults associated with [111] screw super-dislocations on (1-10) planes are quantitatively characterized in different B2 systems by atomistic modeling. A striking phenomenon is found that the associated planar faults are not restricted to the local minima of the (1-10) γ-surfaces, but varying from metastable to unstable. To understand why these distinct planar faults occur in different compounds, a general approach has been developed with a pioneering assumption that the planar fault could adjust its displacement and energy to minimize the system energy. Besides, it is found that the planar fault state of screw super-dislocations could change gradually at finite temperatures, which provides a novel cross-slip mechanism. Furthermore, the energy increment of state transition of planar faults could cause different responses of super-dislocations to external loading. Therefore, in addition to non-planar core effects, more attentions should be paid to the role of variable planar faults in slip and cross-slip behaviors of [111] screw super-dislocations.