Stability of APB-dissociated 〈111〉 screw superdislocations in B2-ordered structures

The stability of an infinitely long screw 〈111〉 superdislocation dissociated into APB-coupled superpartials on {110}, {112}, or a combination of both, has been analysed under the approximation of linear elasticity theory of dislocations. In the absence of an applied load, the variation of the configurational energy of the dislocation pair in equilibrium has been examined analytically as a function of two basic material parameters, i.e. the elastic anisotropic parameter along 〈111〉M and the ratio of {112} vs {110} APB energies λ = γ₁₁₂/γ₁₁₀. It is found that although there is no tor1ue force on the screw partials on both {110} and {112}, the torque force is present at intermediate angular positions and acts in the direction of stabilizing {112} dissociation and destabilizing {110} dissociation. In general dissociation on {112} is favoured energetically if λ > M^1/3. Since M > 1 in anisotropic elastic media, ranging from M = 1.09 for FeAl to M = 1.64 for AuCd, favourable {112} dissociation does not require γ₁₁₂ < γ₁₁₀. For compounds with $\text{M > 1.22(√}\text{3}\text{2}\text{)}$, the screw superdislocation may dissociate into stable non-planar configurations with the APB lying partly on {110} and partly on {112}, forming a locked structure.